DIY slide projector

[Crysist]

I'm interested in making slide projector from a camera and some other light source. I've seen similar things made and sold, most recently a demo of replacing a 4x5 camera back with a light source to make a 4x5 projector. But I'm trying to make a general solution that I can pop behind any camera, where I can sandwich film between the rails and a bright light source acting in place of the pressure plate. Not only does it seem like it'd fit my desire to quickly set up and project my un-mounted film strips, but also because I could do other fun things like do "projection testing" of my lenses, use it with different cameras at a moment's notice, etc. I've done something like this when I try to magnify my phone's flashlight with a lens and observe the image it throws on a wall, but haven't had much success using its relatively weak light for projecting slides. And trying to hold them together.

Furthermore, considering how efficient modern lights are, generating little heat too, would something like a strong flashlight work well? I don't know much else about how slide projectors have to be designed, whether the light needs to be collated or diffuse. Or whether a video light, like the Cinestill lightpad basically is, would work well or better and just needs some kind of condenser. Then just 3D print something that'd hold what I need and a strip of film together and I can press it to the film plane of any camera.

Also, should I aim for a warmer light (closer to halogens color temp) for projection always or is a more neutral light fine?

Has anyone tried something like this or has any suggestions?

 

[koraks]

Furthermore, considering how efficient modern lights are, generating little heat too, would something like a strong flashlight work well?

That's all quite relative. To get in the ballpark of a regular slide projector in terms of illumination, you're still looking at 50W (at the very least) of LED power. The vast majority of that power is going to be dissipated in the light source itself and the optics and housing right in front of it (i.e. your camera). Dumping that amount of power into, let's say, a regular SLR camera (35mm or MF) will likely create problems with melting lubricants, warping of parts etc.

Then just 3D print something that'd hold what I need and a strip of film together and I can press it to the film plane of any camera.

In terms of thermal management regular 3D printed parts (from filament printers) will be a liability as they tend to conform to Dali's watches in close proximity to a high-power LED source.

With a large format camera, you have a fighting chance because of their relatively simple and voluminous/open construction.

 

[Crysist]

That's all quite relative. To get in the ballpark of a regular slide projector in terms of illumination, you're still looking at 50W (at the very least) of LED power. The vast majority of that power is going to be dissipated in the light source itself and the optics and housing right in front of it (i.e. your camera). Dumping that amount of power into, let's say, a regular SLR camera (35mm or MF) will likely create problems with melting lubricants, warping of parts etc.

Damn. Asking experienced people does really show a lot of "fun" project ideas I might have aren't well thought out...

However, don't slide projectors already have a glass layer between the light and the film that blocks a lot of the heat from reaching it? Because, wouldn't the same heat of the light melt/warp the film the exact same way?

 

[koraks]

Asking experienced people does really show a lot of "fun" project ideas I might have aren't well thought out...

So the proper way ahead is to not ask questions and get started! All joking aside, that's what I sometimes do, and it's often a really good way to learn.

However, don't slide projectors already have a glass layer between the light and the film that blocks a lot of the heat from reaching it? Because, wouldn't the same heat of the light melt/warp the film the exact same way?

Yes, but:
1: Slide projectors have a thermal design/layout (including a beefy fan) for this reason. A picture-taking camera doesn't, so you have to take measures to avoid thermal problems in a system not inherently designed to deal with them.
2: The materials and components used in slide projectors are comparatively crude and robust compared to the parts of a typical camera. There's no/less sensitive mechanics involving shutters, optics (mirrors, pentaprisms etc.)
3: Slide 'pop' is indeed a problem with projectors; you generally have to wait 2-3 seconds and then refocus the projector.

So the concerns aren't so much about the film - it's also that, but my main concern is that you'll end up damaging the camera.

 

[Mr Bill]

Hi, actually this whole thing is more complicated than you mighg think. I've done something related... different but using similar optical principles.

Essentially you would have two overlapping optical systems. The first one would "collect" the light from your source (whatever lamp, etc., you are using) and then attempt to funnel this light into your projection lens. Whatever light you cannot get into the projection lens aperture is obviously no use to you, right?

The second system is the one you seem familiar with; the one that focuses an image of your film/slide onto the wall, or whatever. It interacts with the first system in that the film/slide must be in an appropriate place in the first system such that 1) it can be fully illuminated and 2) that all of this illumination will ideally be directed into the aperture of the projection lens. (The projection lens will be at different distances depending on its focal length, etc.)

If you consider something like a condenser enlarger you can see the two systems at work. First you have a lamp that emits light, typically in nearly all directions. A largish condenser lens collects as much light as it can, and then directs this light into the enlarger lens, which will be in different places depending on its focal length and size of the enlargement. (This is the reason why enlargers have things like different condenser configurations for different size negatives.) And obviously (?) an enlarger's condenser(s) must be larger in diameter than the film being used.

Something else worth pointing out is that some enlargers might have a large diffuse light source behind the negative, and that these seem to work ok. Well, that's true, BUT... enlargers are used in the dark, and the exposure times can be increased to whatever might be needed. If they had to be used in some sort of room light, even dim, they would have a hard time overcoming the ambient light.

Regarding your idea to use a "strong flashlight" (aka "torch), this will likely work to some extent. But probably only in a small area near the center of the film/slide. Cuz the light beam has a fairly small diameter.

I'm glad to elaborate more, so feel free to ask questions.

 

[Harry Callahan]

...
but also because I could do other fun things like do "projection testing" of my lenses, use it with different cameras at a moment's notice, etc. ...

. Then just 3D print something that'd hold what I need and a strip of film together and I can press it to the film plane of any camera.

Also, should I aim for a warmer light (closer to halogens color temp) for projection always or is a more neutral light fine?

I don`t know if this "projection testing" would work at all. For whatever reason a projection lens seems not to need that high quality than a taking lens - maybe because the contrast of the slide is high, because of the bright light source inside the projector. Single-coated projection lenses can be pretty sharp and contrasty, when used for projection wide open , while they wouldn`t perform that good as a taking lens - wide open.
So even if your idea would work, you probably couldn`t really test your camera lenses regarding taking quality.

Film inside of a projector should be flat - and film should be parallel to the lens, i doubt you could achieve this with something 3D printed - and again you couldn`t judge the quality of the lens.

Projectors have been using bulbs or halogen lamps for decades, because there wasn`t any better (maybe some high pressure lamps, but these are big and get very warm etc...) regarding color temperature. If there was a classical bulb that could produce daylight temperature, they had taken it decades ago. That`s an advantage of LEDs today - on the other hand the human eye does get used to small color shifts pretty fast, that`s why classical bulbs work too though they produce even warmer light than halogen bulbs.

So even if you could solve the light-source-problem, other problems still were there.

 

[Crysist]

So the proper way ahead is to not ask questions and get started! All joking aside, that's what I sometimes do, and it's often a really good way to learn

Oh, I won't be stopping it for a moment, haha! I just feel silly that there were such big oversights in the way of what I thought would be quite simple! I greatly appreciate yours and everyone else's responses!

Yes, but:
1: Slide projectors have a thermal design/layout (including a beefy fan) for this reason. A picture-taking camera doesn't, so you have to take measures to avoid thermal problems in a system not inherently designed to deal with them.
2: The materials and components used in slide projectors are comparatively crude and robust compared to the parts of a typical camera. There's no/less sensitive mechanics involving shutters, optics (mirrors, pentaprisms etc.)
3: Slide 'pop' is indeed a problem with projectors; you generally have to wait 2-3 seconds and then refocus the projector.

So the concerns aren't so much about the film - it's also that, but my main concern is that you'll end up damaging the camera.

Well then, is it worthwhile if I get a total junk rangefinder and dedicate it to being an impromptu "projector"? Because a projector minus the film advance mechanism would be very useful. My slides are uncut and differing sizes, it'd be nice if there were projectors where you could just slide the film through instead of having them mounted.

Hi, actually this whole thing is more complicated than you mighg think. I've done something related... different but using similar optical principles.

Essentially you would have two overlapping optical systems. The first one would "collect" the light from your source (whatever lamp, etc., you are using) and then attempt to funnel this light into your projection lens. Whatever light you cannot get into the projection lens aperture is obviously no use to you, right?

Yes, that's also what the parabolic mirrors behind the bulbs are for, right? So you're not losing out of the "back half" of light emitted?

The second system is the one you seem familiar with; the one that focuses an image of your film/slide onto the wall, or whatever. It interacts with the first system in that the film/slide must be in an appropriate place in the first system such that 1) it can be fully illuminated and 2) that all of this illumination will ideally be directed into the aperture of the projection lens. (The projection lens will be at different distances depending on its focal length, etc.)

If you consider something like a condenser enlarger you can see the two systems at work. First you have a lamp that emits light, typically in nearly all directions. A largish condenser lens collects as much light as it can, and then directs this light into the enlarger lens, which will be in different places depending on its focal length and size of the enlargement. (This is the reason why enlargers have things like different condenser configurations for different size negatives.) And obviously (?) an enlarger's condenser(s) must be larger in diameter than the film being used.

Something else worth pointing out is that some enlargers might have a large diffuse light source behind the negative, and that these seem to work ok. Well, that's true, BUT... enlargers are used in the dark, and the exposure times can be increased to whatever might be needed. If they had to be used in some sort of room light, even dim, they would have a hard time overcoming the ambient light.

Regarding your idea to use a "strong flashlight" (aka "torch), this will likely work to some extent. But probably only in a small area near the center of the film/slide. Cuz the light beam has a fairly small diameter.

I'm glad to elaborate more, so feel free to ask questions.

Hmm, well then I have two opposite questions. My lightpad (basically a strong video light CS sells rebranded) is very bright and larger than my film, can I condense the light from the larger area into smaller film? Would that be a good light source?

Also, can I flip a condenser around to use against a smaller light source like a flash light? I know that's losing the benefit of the former case, instead of focusing more light into a smaller area, this would spread it out and you'd need quite a strong flashlight.

I don`t know if this "projection testing" would work at all. For whatever reason a projection lens seems not to need that high quality than a taking lens - maybe because the contrast of the slide is high, because of the bright light source inside the projector. Single-coated projection lenses can be pretty sharp and contrasty, when used for projection wide open , while they wouldn`t perform that good as a taking lens - wide open.
So even if your idea would work, you probably couldn`t really test your camera lenses regarding taking quality.

I might not have said this in the clearest way. What I mean by projection testing is assessing a lens, any lens, by projecting a very very fine pattern from the film plane out to the focus plane on the object-side. This seems to be a very common form of rough metrology of lenses. I envisioned I could carry some little flashlight-like device around and test any camera lens by pressing it to the film plane and observing how the projected image looks.

And while projector lenses may not need to be the highest quality to get a great image, there's still a lot you can scrutinize. The corners, certainly. Distortion.

Film inside of a projector should be flat - and film should be parallel to the lens, i doubt you could achieve this with something 3D printed - and again you couldn`t judge the quality of the lens.

Projectors have been using bulbs or halogen lamps for decades, because there wasn`t any better (maybe some high pressure lamps, but these are big and get very warm etc...) regarding color temperature. If there was a classical bulb that could produce daylight temperature, they had taken it decades ago. That`s an advantage of LEDs today - on the other hand the human eye does get used to small color shifts pretty fast, that`s why classical bulbs work too though they produce even warmer light than halogen bulbs.

So even if you could solve the light-source-problem, other problems still were there.

I could get something sent out to be machined, I suppose. All-in-all, the larger goal is merely some more simple slide projector for my own use. To just work off film strips, which I could probably just press against etched glass for both diffusion and ANR. No slide mounts, no transport, just a strong light, a film support, and some way to hold a lens. I could just get a 2ndhand projector lens. Does that sound like a better concept?

The projection testing idea was just a similar idea that I figured would naturally be possible with something like this.

Thank you all for the help!

 

[wiltw]

Is this merely a project, or do you need a slide projector and want one on the cheap? Lots of slide projectors available via trhift stores for not much money.

 

[koraks]

Well then, is it worthwhile if I get a total junk rangefinder and dedicate it to being an impromptu "projector"?

You could definitely give it a go. I expect there will be challenges, but it can be a fun project and I can see how it might end up sort of working.
If you want to limit light falloff in the corners, I think you'll have to tackle the challenge of collimation of the light as @Mr Bill also mentioned.

 

[Harry Callahan]

...

Well then, is it worthwhile if I get a total junk rangefinder and dedicate it to being an impromptu "projector"? Because a projector minus the film advance mechanism would be very useful. My slides are uncut and differing sizes, it'd be nice if there were projectors where you could just slide the film through instead of having them mounted.


...


I might not have said this in the clearest way. What I mean by projection testing is assessing a lens, any lens, by projecting a very very fine pattern from the film plane out to the focus plane on the object-side. This seems to be a very common form of rough metrology of lenses. I envisioned I could carry some little flashlight-like device around and test any camera lens by pressing it to the film plane and observing how the projected image looks.

And while projector lenses may not need to be the highest quality to get a great image, there's still a lot you can scrutinize. The corners, certainly. Distortion.


I could get something sent out to be machined, I suppose. All-in-all, the larger goal is merely some more simple slide projector for my own use. To just work off film strips, which I could probably just press against etched glass for both diffusion and ANR. No slide mounts, no transport, just a strong light, a film support, and some way to hold a lens. I could just get a 2ndhand projector lens. Does that sound like a better concept?

The projection testing idea was just a similar idea that I figured would naturally be possible with something like this.

Thank you all for the help!

There were film-strip slide projectors... in the 50s i think. There also were multiformat slide projectors, being for 6x6 but having an exchangable holder for 35mm slides - some even having an exchangable film-strip holder for 35mm. Havn`t seen a film-strip projector for uncut medium format film though.
Otherwise get an enlarger for whatever your biggest slide format is. Turn it to a wall - and viola you can project any slide strips you have. The enlarger should have glass holder and masks for different slide sizes, a swing head, and rather fast lenses matching format by focal length - but then you had an all-in-one multiformat-film-strip slide projector.

I get what you mean. You want a small device you can test the lens of a camera with by turning the camera into a projector - so you can judge lens quality on a flea market for example.

Also if you have something machined, it may have the required precision, but it also should not scratch the film rails in the camera you press it against. There are problems and problems.
I don`t think that`ll work, due to the reasons mentioned. Even if, you needed a high quality testing slide inside the camera. Some film can resolve up to 150ll/mm and your test slide had to have this sharpness - up into the edges. Your light source had to be very even in illumination so you can check brightness fall off of the camera lens into the edges.
You needed a very dark room with a white, unstructured wall to project the image on. If the lens can resolve 100ll/mm, you`d have to enlarge by x100 to have one line on the film to be 1mm on the screen. If you enlarge a 35mm neg by x100 you end up with a picture being 3,6m or about 12feet wide. Then you can judge whether the lens does 100ll/mm or not. You needed a strong light source to project 35mm to 12feet, a dark room and a big wall or screen. Also the camera had to be on a tripod, as you cannot hold the camera still enough to enlarge by x100 and see 1mm on the screen sharp. Also, when enlarging 35mm by x100 the distance between camera and screen is (usually, for wide angle lenses it was less) so big that you cannot judge sharpness of the projected image when holding the camera. You had to move closer to the screen, while the camera had to remain distant to the screen. The camera body had to be parallel to the screen or the image would get unsharp edges - though the lens may be excellent.
...

And even if you'd get all this right - imagine you going to a flea market or camera store, asking the seller to open the camera so you can press a home-built apparatus into the back of the camera... into a camera you *might* buy.

I get your idea, it was great if it worked (easily), but i`m afraid it wouldn`t work (easily) - if it did such devices were around for decades or even a century.
Get a film-strip projector or turn an enlarger into a multiformat projector. Lens test on the fly...

EDIT:
Ok, you needed an enlarger with some sort of "double-swing-head" so you can switch between horizontal and vertical format. That would be a problem. On the other hand i don`t know if these film-strip slide projectors did have a swing head... maybe these were fixed too...

 

[koraks]

and viola

A viola is a type of violin, slightly larger, with a C string on the low end instead of the violin's E-string on the high end. "Voila" is a French exclamation that translates as "see there".

 

[Crysist]

Is this merely a project, or do you need a slide projector and want one on the cheap? Lots of slide projectors available via trhift stores for not much money.

You could definitely give it a go. I expect there will be challenges, but it can be a fun project and I can see how it might end up sort of working.

Right, it's not just to get a slide projector, but rather something more useful for my situation. I have multiple formats I'm interested in projecting (35mm, half-frame, submini) and want to avoid needing to do any mounting. And I'm feeling the weight of getting more and more photography stuff and am trying to be a bit more wary of large items lol

If you want to limit light falloff in the corners, I think you'll have to tackle the challenge of collimation of the light as @Mr Bill also mentioned.

Could a simple Fresnel lens work for that purpose, or are proper condensers more elaborate and I should use an existing one?

There were film-strip slide projectors... in the 50s i think. There also were multiformat slide projectors, being for 6x6 but having an exchangable holder for 35mm slides - some even having an exchangable film-strip holder for 35mm. Havn`t seen a film-strip projector for uncut medium format film though.
Otherwise get an enlarger for whatever your biggest slide format is. Turn it to a wall - and viola you can project any slide strips you have. The enlarger should have glass holder and masks for different slide sizes, a swing head, and rather fast lenses matching format by focal length - but then you had an all-in-one multiformat-film-strip slide projector.

That actually sounds like a very great idea! Heck, I could even get a color head and do live color correction as well, lol

I've shot rather little MF though, so I probably won't have a big need to project it. Additionally, what I last shot on 6x6 had some bad focus errors cause I used a Super Ikonta whose lens wasn't parallel with the film plane. It's been relegated to a shelf for now.

Does the output of the bulbs in an enlarger differ from a slide projector? I'd imagine that it'd be less powerful because you have the benefit of time when printing, while when projecting you want to be able to output through higher density positives and project them over a larger area. Maybe changing the bulb would help in that case.

I get what you mean. You want a small device you can test the lens of a camera with by turning the camera into a projector - so you can judge lens quality on a flea market for example.

Right, exactly, just making sure! Or even testing my own stuff. It merely seems easier to judge than the opposite case, if you had some gate-focuser like device that you'd pop on the film plane and instead analyze the aerial image formed by the lens. I do that in a very casual sense sometimes by holding a loupe at the backside of a lens (if it can be unmounted from a camera), but again those are differences that are not visible at that scale.

Also if you have something machined, it may have the required precision, but it also should not scratch the film rails in the camera you press it against. There are problems and problems.
I don`t think that`ll work, due to the reasons mentioned. Even if, you needed a high quality testing slide inside the camera. Some film can resolve up to 150ll/mm and your test slide had to have this sharpness - up into the edges. Your light source had to be very even in illumination so you can check brightness fall off of the camera lens into the edges.
You needed a very dark room with a white, unstructured wall to project the image on. If the lens can resolve 100ll/mm, you`d have to enlarge by x100 to have one line on the film to be 1mm on the screen. If you enlarge a 35mm neg by x100 you end up with a picture being 3,6m or about 12feet wide. Then you can judge whether the lens does 100ll/mm or not. You needed a strong light source to project 35mm to 12feet, a dark room and a big wall or screen. Also the camera had to be on a tripod, as you cannot hold the camera still enough to enlarge by x100 and see 1mm on the screen sharp. Also, when enlarging 35mm by x100 the distance between camera and screen is (usually, for wide angle lenses it was less) so big that you cannot judge sharpness of the projected image when holding the camera. You had to move closer to the screen, while the camera had to remain distant to the screen. The camera body had to be parallel to the screen or the image would get unsharp edges - though the lens may be excellent.
...

Those are very good points, but some of it isn't quite impractical. When I project the image of my phone's flashlight against a wall, just handholding a lens, I am able to hold it on okay focus just with my hands. I can blow up the light shining through the Fresnel like surface with lines 0.1-0.2mm apart to be nearly 1 cm apart at a very close range. I can tell the differences in stopping down on spherical aberration and contrast quite well. But you're very correct, I needed to do this in my room with the lights out. Also since I used my phone I can't share a pic of the fun projection trick with my friends lol

Another idea I thought of was to find some kind of transparent "test target". First I was just trying some film itself but I couldn't hold them all aligned with my hands, and the light was far too weak. Instead, noticing test targets are pretty expensive, I bought a glass microscope scale reference slide. It just shows some 1/100 mm divisions in the middle. Holding this together is hard too, but I've made good use of it taping it to the film place of a camera and checking infinity focus on it by pointing another camera focused on infinity at the lens and seeing if the scale was sharp behind the lens.

I had also thought about using a laser in some way, much smaller area but far stronger. Something like those little laser projector pens that shoot a tiny image on the wall. Haven't tried that yet.

So your main points about struggles to overcome are right, but I see some value possible with a setup like that.

And even if you'd get all this right - imagine you going to a flea market or camera store, asking the seller to open the camera so you can press a home-built apparatus into the back of the camera... into a camera you *might* buy.

I get your idea, it was great if it worked (easily), but i`m afraid it wouldn`t work (easily) - if it did such devices were around for decades or even a century.

Hey - I have bothered my local camera shop guy successfully quite a lot thankyouverymuch!

Most of what I check out are free to pick up and look through, test, etc. Of course, with the shop owner knowing. So, perhaps I'm more focused on the lenses I own, lets say.

And projection testers do exist of course. Just not tiny!

Get a film-strip projector or turn an enlarger into a multiformat projector. Lens test on the fly...

EDIT:
Ok, you needed an enlarger with some sort of "double-swing-head" so you can switch between horizontal and vertical format. That would be a problem. On the other hand i don`t know if these film-strip slide projectors did have a swing head... maybe these were fixed too...

You mean whether the part you slot the film into being able to be rotated by 90 degrees? So as to right an image that was taken in a different orientation? Is that required for enlargers if you can just rotate the paper instead? I last used an enlarger 15 years ago, I forget if the negative holder could be turned on the ones I used.

Right, normal slide projectors do have the advantage that the slide mounts are square, you can just turn each to make the image upright, so that wasn't needed.

A viola is a type of violin, slightly larger, with a C string on the low end instead of the violin's E-string on the high end. "Voila" is a French exclamation that translates as "see there".

You're even helpful on such minor things, haha! Sometimes I think "oh, I hope someone like one of the mods or someone very experienced replies to my post/thread with the answer" but end up surprised at how active you all actually are! C:

 

[koraks]

Could a simple Fresnel lens work for that purpose, or are proper condensers more elaborate and I should use an existing one?

I expect you could construct a good enough condenser using a pair of fresnels.

You're even helpful on such minor things, haha!

Ah, it was pedantry really, but as an ex/recovering violinist (not a violist!), the 'viola' mistake constitutes an itch that I find difficult not to scratch. I also find it somewhat hilarious as it brings up the image of an old-fashioned waiter with a white napkin over one arm held to his body while with the other hand triumphantly thrusting a viola in someone's face, screaming "VIOLA!!"

 

[Harry Callahan]

A viola is a type of violin, slightly larger, with a C string on the low end instead of the violin's E-string on the high end. "Voila" is a French exclamation that translates as "see there".

Ah, ok. I meant the French exclamation.

...

That actually sounds like a very great idea! Heck, I could even get a color head and do live color correction as well, lol

I've shot rather little MF though, so I probably won't have a big need to project it. Additionally, what I last shot on 6x6 had some bad focus errors cause I used a Super Ikonta whose lens wasn't parallel with the film plane. It's been relegated to a shelf for now.

Does the output of the bulbs in an enlarger differ from a slide projector? I'd imagine that it'd be less powerful because you have the benefit of time when printing, while when projecting you want to be able to output through higher density positives and project them over a larger area. Maybe changing the bulb would help in that case.

...

Enlargers usually have weaker bulbs and slower lenses, so it does depend on how big you want to project. Depending on what enlarger you have/get you could put in a stronger bulb (LED also should be possible) and adapt a faster projection lens to it.

...

Right, exactly, just making sure! Or even testing my own stuff. It merely seems easier to judge than the opposite case, if you had some gate-focuser like device that you'd pop on the film plane and instead analyze the aerial image formed by the lens. I do that in a very casual sense sometimes by holding a loupe at the backside of a lens (if it can be unmounted from a camera), but again those are differences that are not visible at that scale.


Those are very good points, but some of it isn't quite impractical. When I project the image of my phone's flashlight against a wall, just handholding a lens, I am able to hold it on okay focus just with my hands. I can blow up the light shining through the Fresnel like surface with lines 0.1-0.2mm apart to be nearly 1 cm apart at a very close range. I can tell the differences in stopping down on spherical aberration and contrast quite well. But you're very correct, I needed to do this in my room with the lights out. Also since I used my phone I can't share a pic of the fun projection trick with my friends lol

...

I don`t know if the aerial image would help you ahead. There are movie cameras, S8 cameras, which have an aerial reflex finder, but looking through it won`t tell you how good or bad the camera lens will perform. You could put a ground glass on the film plane, but apart from scratching the film plane of the camera, a ground glass has grain and this grain will prevent you from judging sharpness of the lens (unless its a really bad lens).

Ok, then you have really steady hands - but if you enlarge 0.1mm to 1cm you have an enlargement factor of 100, what focal length did the lens have? You say Fresnel surface, do you mean the light of your phone having a Fresnel like surface? If so, does the light have some sort of lens in front?

...

Another idea I thought of was to find some kind of transparent "test target". First I was just trying some film itself but I couldn't hold them all aligned with my hands, and the light was far too weak. Instead, noticing test targets are pretty expensive, I bought a glass microscope scale reference slide. It just shows some 1/100 mm divisions in the middle. Holding this together is hard too, but I've made good use of it taping it to the film place of a camera and checking infinity focus on it by pointing another camera focused on infinity at the lens and seeing if the scale was sharp behind the lens.

I had also thought about using a laser in some way, much smaller area but far stronger. Something like those little laser projector pens that shoot a tiny image on the wall. Haven't tried that yet.

So your main points about struggles to overcome are right, but I see some value possible with a setup like that.

...

Did you try to project this microscope scale? This would show how good or bad it works. Lasers could be problematic again as they concentrate a lot of energy on a small area. Projector pens probably not, but if you find these to be too weak you again run into danger of damaging the camera.

...

You mean whether the part you slot the film into being able to be rotated by 90 degrees? So as to right an image that was taken in a different orientation? Is that required for enlargers if you can just rotate the paper instead? I last used an enlarger 15 years ago, I forget if the negative holder could be turned on the ones I used.

Right, normal slide projectors do have the advantage that the slide mounts are square, you can just turn each to make the image upright, so that wasn't needed.

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Yes. I`m not into these film-strip projectors, maybe there were some where you could rotate the film holder - but if you decide to get one check this before you buy.
Some enlargers can rotate their head, so they don`t project the image down on the easel but to the wall, but enlargers cannot rotate the negative holder - and that`s what you needed to project different orientations on a film-strip.

Slides mean some work as you have to mount them, but then you`re good. You can change orientation, order, blown shots and even format. If you have a 6x6 projector you also can adapt 35mm slides into the mount - or even smaller formats.

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I also find it somewhat hilarious as it brings up the image of an old-fashioned waiter with a white napkin over one arm held to his body while with the other hand triumphantly thrusting a viola in someone's face, screaming "VIOLA!!"

Sometimes i`m exactly in this mood... but i am not sure if i was when i made this typo...

 

[Crysist]

I expect you could construct a good enough condenser using a pair of fresnels.

A pair of lenses are needed? I mean, I know that single elements are very limited in terms of quality, but wouldn't putting a light source at the focal point of a lens be enough to collimate it?

I suppose that's good in my case, as when I went to buy a fresnel lens on ebay, a seller sold them in pairs so I have two.

Ah, it was pedantry really, but as an ex/recovering violinist (not a violist!), the 'viola' mistake constitutes an itch that I find difficult not to scratch. I also find it somewhat hilarious as it brings up the image of an old-fashioned waiter with a white napkin over one arm held to his body while with the other hand triumphantly thrusting a viola in someone's face, screaming "VIOLA!!"

ELEGANT!!!

Enlargers usually have weaker bulbs and slower lenses, so it does depend on how big you want to project. Depending on what enlarger you have/get you could put in a stronger bulb (LED also should be possible) and adapt a faster projection lens to it.

Right, I figured. But if it is easy to swap that might be okay! Also, besides the shape being perhaps odd and needing to swap out a the bulb/lens, are there any other main things to look out for? Or do you suppose that's a good enough setup?

I don`t know if the aerial image would help you ahead. There are movie cameras, S8 cameras, which have an aerial reflex finder, but looking through it won`t tell you how good or bad the camera lens will perform. You could put a ground glass on the film plane, but apart from scratching the film plane of the camera, a ground glass has grain and this grain will prevent you from judging sharpness of the lens (unless its a really bad lens).

I thought that's the point and thus the advantage, no? Avoiding ground glass just as you can avoid using film to assess a lens in isolation. GG is definitely important for finding and assessing the plane of focus in particular, but I don't mean to do that for judging the quality that much.

Oh, and I never knew some cameras had such reflex finders! That's very interesting! I figure it's much easier because, from such tiny lenses, you can capture more of the light from the exit pupil to show the operator. Meanwhile, for larger lenses you only see a smaller exit pupil, and to get the entire field of view of the lens you have to look back along the axis the light came from. To get the light that strikes the far edge of the film, you need to be focused at the film plane at that point and point towards the exit pupil.

I've seen old documentary shorts from Kodak and others on making cameras and lenses, and when they get to showing how they assess the quality of them, among other techniques like projection out the test lens, one is where they mount the lens on a special microscope. The focal point of the microscope objective seems to be at the film plane and the operator can swivel the microscope about the back half of the lens. I think one use of this and similar tests was for centering and setting focus (besides using a collimator).

Ok, then you have really steady hands - but if you enlarge 0.1mm to 1cm you have an enlargement factor of 100, what focal length did the lens have? You say Fresnel surface, do you mean the light of your phone having a Fresnel like surface? If so, does the light have some sort of lens in front?

I redid it just to verify. I can cup a 50mm lens (specifically a Contax 50/1.5 Sonnar) in my hand, put it in front of my phone's flashlight, usually resting my cupped hand against my phone, and project and image on the wall 5-10ft away in a dark room. At that distance they're enlarged closer to 5mm, but I am able to point it out the door to another room's wall that's around 20ft away. Then the details are around 1cm in diameter.

I have a Samsung Galaxy Note 20, there's an image on the Samsung website which shows it just close enough to start to see the surface texture. There doesn't seem to be an actual lens, just a layer of glass over what you see.

For reference, the flash is 4mm across. I used a measuring microscope with 1/2000'' divisions and counted the width of each "ring", the upward or downward slope of the surface, to be 5 divisions in width to correlate to what shows up as a solid ring on the wall. That's around 0.06mm.

Unfortunately, the light is so close to the cameras that I can't take a picture of the image I project. And my old phone's battery died, so this is the only digital camera I have with me currently :/

Did you try to project this microscope scale? This would show how good or bad it works. Lasers could be problematic again as they concentrate a lot of energy on a small area. Projector pens probably not, but if you find these to be too weak you again run into danger of damaging the camera.

I did! I was able to make the scale project through the lens far more easily.

Also, aren't lasers and lenses more dangerous if they create a smaller point of focus than the laser? I think most examples where people's sensors get fried at laser light shows, they magnification ratio is probably so low that the already bright lasers get squeezed onto a far far tighter area and thus become dangerous. How can this be a problem inside the lens though? Or coming from the rear of the lens, where it will be magnified?

Yes. I`m not into these film-strip projectors, maybe there were some where you could rotate the film holder - but if you decide to get one check this before you buy.
Some enlargers can rotate their head, so they don`t project the image down on the easel but to the wall, but enlargers cannot rotate the negative holder - and that`s what you needed to project different orientations on a film-strip.

You don't like them? They seem to also do a good job at fitting my needs. I just don't know if they were a lesser-quality option and might offer less options for upgrading. But in terms of being the rather simple layout I was thinking about, something that would also just accept smaller formats, they look like a good option. And aren't too expensive.

I suppose the remaining question is which would likely be better, a filmstrip projector or an enlarger head? Hmm. I suppose I can just try both.

Slides mean some work as you have to mount them, but then you`re good. You can change orientation, order, blown shots and even format. If you have a 6x6 projector you also can adapt 35mm slides into the mount - or even smaller formats.

The destructive aspect never sat well with me. Especially as I've massacred a cut between frames a handful of times when cutting strips to put in sleeves. Even after getting a film slicer to use instead of a scissor, I still occasionally get one that the slicer doesn't cut through and damages the emulsion at the end of the cut.

Sometimes i`m exactly in this mood... but i am not sure if i was when i made this typo...

Consider yourself lucky that you weren't part of the group who had no clue how to spell it and thought it began with a W!