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!