8X10 pinhole build -

edcculus · Mar 27, 2013

Sounds good. I have a Print File "custom proofer" that I use to make contact prints off of regular negs. No troubles with that so far, so hopefully it will work with paper negs too.

edcculus · Jul 8, 2013

I ended up getting some cheap 4X5 holders, so I'm changing this build to the smaller format.

With the film holders in hand, I'm basically going to follow this tutorial. http://www.stanford.edu/~cpatton/foamcore.html

Couple questions:
-what is a good focal length to start with on 4X5?
-on this build, what is the purpose of the foam core back? Also pictures of it at the end of this link http://www.stanford.edu/~cpatton/dai.htm. If I'm using a film holder, do I need it?

Once I get these questions answered, I'll hopefully draw this out in my CAD program and cut it at work at the end of the week. Then all I have to do is assemble the pieces and make the pinhole.

NedL · Jul 8, 2013

That back is like a "window frame" for the film holder to rest against. It provides 1/2" of support on all four sides of the film holder. Does that make sense? The first page also mentions that you can make a second one to press against the film holder from behind... that would be for applying some pressure to hold the filmholder tightly in place. I haven't done this myself so can't offer any other comment...

I really like the wide angle field of view on my 8x10 camera with a 5" "focal length". The equivalent on a 4x5 would be 2.5 inches. Others might have a different idea what a nice focal length would be.

In re-reading this thread I realized I might mention something for future readers. My 5x7 camera has a mat board "window" that holds the paper in place on 3 sides. That seemed to work pretty well. But when I did the same thing on the 8x10 camera, the paper fell out inside the camera. Now it is is held in place on all 4 sides by strips of mat board about 3/8" wide. Even this is not ideal.... I've noticed that the center of the paper still has a tendency to warp out and I don't get nice straight border lines, but slightly curved ones. I don't own any 8x10 film holders, so I don't know how they manage to keep the film flat, but I think Joe's suggestion of a couple pieces of two-sided tape, not too sticky, is a good one and I will try it soon myself.

Have fun!

edcculus · Jul 8, 2013

Thanks Ned, that makes sense about the film back.

I plugged in a 2.5" focal length to the pinhole calcuator, and it looks like it won't give me enough coverage. I increased it to 3.5" and here is what I got:

Focal lenght: 3.5"
pinhole diameter: .016" (.4mm)
fstop 224
film dimension 6.4
angle of view 84.9
coverage 6.72

Does all of that look good? I basically tried to get the coverage larger than the film dimension.

NedL · Jul 8, 2013

I'm not sure how the program computes coverage. On my calculator I just verified all the other numbers... if I assume a "daylight" wavelength of 550nm and a "user constant" of 1.8 it's very close to a 0.4mm pinhole.

That angle of view will be similar to a 24mm lens on 35mm film. Which is pretty nice, I think. ( I'm biased... 24mm is my favorite lens )

Since I use paper negatives, I usually use 500nm or even 475nm for the wavelength, because paper is so sensitive to blue light. And I tend to use a smaller "user constant" of 1.56. If I was making that camera for paper, I'd start with a 0.33mm pinhole. But I think your 0.4mm will probably work well for film. If you will be mostly using paper, I think you could get away with a smaller pinhole.

DWThomas · Jul 8, 2013

My 4x5 pinhole parameters:

Pinhole to film distance ( "focal length"): 2.44 inches (62 mm)
Exposure Mask Area: 3.9 x 4.75 inches (100 x 120 mm) Diagonal: 6.15 inches (156 mm)
Diagonal Field of View: 103º
Pinhole diameter: 0.012 inches (0.30 mm); about f/210
Pinhole Constant: 1.65
f/22 Exp Multiplier: 88
Weight: 550g (~1.22 lb) with filmholder

If the "coverage" dimension you state is coming from Mr Pinhole, I think it's rather pessimistic but he doesn't actually describe the criteria. I recall it told me the numbers above were good for 4+ inches, vs the 6.15 I'm using. Yes, there is some fall-off away from the center but it's not that awful!

(Backing up from that link will get you to all my pinhole stuff to date, such as it is. )

NedL · Jul 9, 2013

If you want to go crazy with the math, here is a thread to read all the way through:
http://www.f295.org/main/showthread.php?15473-Exposure-mapping

Some months ago I started to use these formulae to try to find the shape of a surface that would have constant illumination ( instead of a flat film surface ). The shape accounts for the off-axis squint, the "tunnel" caused by the thickness of the pinhole material, and the distance to the film. I'm not convinced it really takes into account the shape of the diffraction blurring all that well. I haven't gotten back to it but the shape is somewhat vase-like, at first bulging outward and then diving inward toward the pinhole itself. It makes sense: as you move away from the center of the image, at first the distance is the dominant effect, requiring you to move upward closer to the pinhole to compensate, but as you move upward, the squint becomes more pronounced causing the radius to decrease.

( My undergrad degree was mathematics, and I've been a member of the Mathematical Association of America for almost 30 years now... so this sort of thing is a great temptation for me... )

But. Recently I've had to catch myself making things too technical and complicated. So I pulled back from all of this. I don't want to mess up the simple joy of finding the picture, placing my pinhole coffee can or cardboard box, and then watching the magic of the image coming up in the developer. To me the idea that the light from the scene landed directly onto the paper to make a permanent captured image is just wonderful. So these days I'm trying to keep things more about "play" and less about the technical part. Not that the technical part can't be fun, but there is a balance to reach!

So my advice: build the camera and have lots of fun making wonderful pinhole pictures with it!

DWThomas · Jul 9, 2013

NedL said:
[ ... snip ...]
But. Recently I've had to catch myself making things too technical and complicated. So I pulled back from all of this. I don't want to mess up the simple joy of finding the picture, placing my pinhole coffee can or cardboard box, and then watching the magic of the image coming up in the developer. To me the idea that the light from the scene landed directly onto the paper to make a permanent captured image is just wonderful. So these days I'm trying to keep things more about "play" and less about the technical part. Not that the technical part can't be fun, but there is a balance to reach!

So my advice: build the camera and have lots of fun making wonderful pinhole pictures with it!

Yes, especially so with pinhole stuff; I take the view that it's all pretty much a compromise and you'll get something interesting from almost anything! That said, most of my pinhole shooting has been one day a year, the WPPD festivities. I do, as a compulsive tinkerer, manage to suddenly decide I need a new camera for it every couple of years. I sold my sheet metal equipment a while back, but I still have woodworking stuff, so these cameras can get quite "involved." It's like one of the approaches to model railroading where the energy goes into designing and building layouts, not running the trains!

(And last B&H order I picked up a Canon EOS body cap that might put a pinhole on my bit-zapper SLR. Most of what I've seen from that on the pinhole day galleries has been lackluster and I'm curious to learn if it's an inherent limitation or weak craftsmanship. )

edcculus · Jul 9, 2013

DWT - yes I was using Mr. Pinhole as the calculator. I'm not really opposed to falloff thogh. I mean, I'm using paper negatives in a pinhole. I'm not going to get a tack sharp image anyways. Thats what the RB67 is for!

Ned - I tend to over think things too, especially in the conceptual phase (hence the size of this thread, and no pinhole built yet).

I might just go with DWThomas's numbers and go from there. Just 2 more questions though.

1- If I'm shooting for a .30mm pinhole, what is the best method, and how should I (somewhat) accurately measure?
2- what is the f/22 exposure multiplier?

DWThomas · Jul 9, 2013

edcculus said:
1- If I'm shooting for a .30mm pinhole, what is the best method, and how should I (somewhat) accurately measure?
2- what is the f/22 exposure multiplier?

1) I use the dimple and sand method, generally in one or two mil brass shim stock. I use a sewing needle and work against a scrap of mat board to produce the dimple, then #400, or even #600, wet-or-dry sandpaper, wet, and try to "sneak up on the size." First rule: it is much easier to make the hole a little bigger than a little smaller!
Thanks to some quasi-professional activities four decades ago, I have a little 50x hand-held microscope with a direct measuring reticle to check small dimensions, so I use that along the way. I believe others use a scanner or enlarger to try to measure.

2) That f/22 multiplier is a handy output from Pinhole Designer. You take the light meter reading of shutter speed at f/22 and multiply it by that factor. P.D. saves doing the math to get the multiplier, which is necessary because few meters go to f/275 or whatever. I usually generate a pocket-sized table for the multiplied shutter speeds to avoid calculators in the field. P.D. can even output such a table with or without reciprocity compensation for a number of films. Unfortunately it hasn't been updated in a long time, so some newer films are not in it. But all that stuff can be generated with generic tools (or pencil and paper!!!)

edcculus · Jul 9, 2013

Awesome Dave, thanks for the quick reply!

I work in the Graphics Arts industry, so i MAY have a loupe at work that has measurements on the base. It probably won't be powerful enough or measure small enought though. I'll probably have to do the scan and measure method.

NedL · Jul 9, 2013

I make mine just like Dave.

Until recently, mine were all measured with just a hand magnifying glass and a ruler with mm markings on it. You can estimate the size to within about .1mm that way. Sometimes lately I've used my enlarger to project a circle.

Another trick is to hold the pinhole up really close to your eye and look through it toward something bright. You will be able to tell if the hole is round and if there are any largish burrs. ( You might also see "floaters"... cells floating around in your eye's vitreous humour. )

pdeeh · Jul 9, 2013

rbeech said:
You should be able to find a 8x10 film holder on ebay for around $20.

oh wow I wish I could find an 8x10 for that price over here on eBay UK.
You can at least triple and usually quadruple it for the odd one that comes up

DWThomas · Jul 9, 2013

Hmm yes, I followed ePrey auctions for a while last spring and the average was about $32 for wooden ones and $52 for the newer more modern ones. The ones that went for less typically had missing latches or some dubious looking wear on frame or dark slides. Those could still be usable but I like to at least start with "nice" stuff!

edcculus · Jul 9, 2013

Thats kind of why I went for 4x5 right now

I got 2 wooden holders from a member in the classifieds for $10 including shipping.

edcculus · Oct 29, 2013

After a few months of inactivity, i've finally made some way on the project. Its now become a 4X5 instead of 8X10.

All I have left to do now is make the actual pinhole and tape up the joints!

NedL · Oct 29, 2013

Yay! Looks great to me. Have fun with it!

DWThomas · Oct 29, 2013

Cool! Looking good.

Yesterday I was in an art and craft store (A.C. Moore) and happened to notice they had what appeared to be 1/2 inch thick black foamcore, black skin, black foam. Might be handy stuff for a large pinhole machina fotografica if one doesn't want to go with wood. Alas, I did not check the price.

NedL · Oct 29, 2013

My 8x10 is made from black double weight mat board, and it is starting to wear out. The top is warping a little and I suspect it will develop a light leak around the lid eventually. It's been a lot of fun and I'm really glad I made it but next time I'm going to make something sturdier, probably from wood. I could imagine 1/2" thick foam core might be pretty good too!

edcculus · Oct 30, 2013

Ok, one more question re the actual pinhole. If I use an enlarger to measure the hole...how exactly do I calculate or figure out the enlargement? Sorry if that is such a stupid question.

TheToadMen · Oct 30, 2013

Howto: measure a pinhole

edcculus said:
Ok, one more question re the actual pinhole. If I use an enlarger to measure the hole...how exactly do I calculate or figure out the enlargement? Sorry if that is such a stupid question.

1) Take a piece of clear film and make a mark of 1 cm on it with a pen like this |----|.
2) Put it in your enlarger and project the line. Now measure the line on the base board (lets say 8 cm).
3) Calculate the enlarging factor for this line: 1 cm/8 cm = 1/8 or (0.125).
4) Put the pinhole in your enlarger and measure the diameter of the projected circle (lets say 1.2 cm).
5) Multiply this factor with the measured diameter: 1/8 x 1.2 cm = 0.15 cm.

Now you know your pinhole diameter is 0.15 cm.

Note:
* it doesn't matter how high you turn your enlarger: but use the same hight for both measurements!
* it also works with inches ;-)

edcculus · Oct 30, 2013

oh awesome. I knew it would be something simple. I'll stick to metric. its easier!

Thanks!

NormanV · Oct 30, 2013

Put a plastic ruler in the negative stage of your enlarger and use another ruler to measure the degree of enlargement.

NedL · Oct 31, 2013

NormanV said:
Put a plastic ruler in the negative stage of your enlarger and use another ruler to measure the degree of enlargement.

Yep, this is what I do. But then I just measure how many mm in 2cm, and do just what Bert said.
And if you are aiming at a particular diameter, you need to make it slightly too small and then slowly expand the pinhole until it's just right.

Honestly, I've only done this a few times. Usually I just make several pinholes and hold them next to a ruler with mm markings, look through a hand lens, and pick one that's close and looks clean. You might find different pinholes do have different character. Occasionally there will be one that makes particularly nice pictures, and it's not always just about sharpness... sometimes there is just a "certain something" and it is hard to say what it is.

I've swapped out the pinhole in my instant film camera several times. The first few looked perfectly round and clean and the right size, but were unsatisfying. The one that is in it right now was a little too small and close but not perfectly round, but it's my favorite so far. I used paper negatives in it to test the different pinholes quickly without wasting film. You could try that if you want. Quick and easy.

( Okay, actually now that I think about it, that's not totally true. I did use paper negatives and picked the best, and it looked really good, but ended up swapping it again after that... the color instant film pictures were not as good as the b/w paper. That could have been because the paper is not sensitive to the same range of wavelengths, or just something subjective about instant color film, I don't know. So I'm not sure the paper negative advice is good after all. )

edcculus · Oct 31, 2013

Thanks guys!

One more thing. For the actual pinhole material. I have access to aluminum offset printing plates. The thinnest we have is .2mm. I guess I'm assuming its mm because the other dimension on the label are in mm as well (340 X505 x.2). Will that be thin enough?

8X10 pinhole build -

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