Members: 76,307   Posts: 1,681,659   Online: 1029

# Thread: How wide is feasible?

1. ## How wide is feasible?

I'm making a 4x5 pinhole camera and I want to go as wide as possible. I'm looking for suggestions on what's the shortest focal length that will cover to the corners and also what size to make the pinhole to optimize sharpness out to the corners. At this point I think making the pinhole slightly bigger than the Rayleigh formula recommends might be a good start, but I'm unsure just how short of a focal length is practical. I think if I use Tmax and expose properly I will be able to burn in the center enough to conquer tonality from falloff, but I am more worried about sharpness.

2. Eventually it will be the differences in the distance from the pinhole to the film at the center vs the corners that will limit you. If it is twice the distance to the corners than to the center, that will be two stops (4x) less light hitting the corners. I have made 8x10 pinhole cameras using 250sht boxes of photopaper. Very wide angle, but the corners can go unexposed relative to the center. Size of the hole will make no difference -- more light will hit the corners, but totally overexpose the center. So you need to know how much dropoff of light in the corners you are willing to put up with. A "focal length" of 3 inches will give you about 1 stop of drop off in the extreme corners of a 4x5, if my math is anything close to right (no promises!LOL!).

I'll shut up and let someone who knows what they are talking about post.

3. How thin your pinhole material is is also a factor (yes that looks weird to me too). I made a pinhole out of a small coffee can, where the 5x7 photo paper was oriented horizontally and curved along the backside of the can, and was able to get coverage corner to corner. I used aluminum from a red bull can, and sanded it down really thin. The focal length of the camera was right at 100mm to the center of the paper, but obviously the sides were much closer.

4. You might consider making a pinhole aperture for a fisheye lens.

5. Is it cheating to bend the film plane? If you cut a piece of 6" PVC in half and put an 8x10 sheet against the curved side, you'd have a 3" focal length, and I think that's pretty wide for 8x10 - 75mm, I think that's the equivalent of 11mm on a 35mm. Pretty sure that'l get you close to 180 degrees coverage.

6. Originally Posted by totalamateur
Is it cheating to bend the film plane? If you cut a piece of 6" PVC in half and put an 8x10 sheet against the curved side, you'd have a 3" focal length, and I think that's pretty wide for 8x10 - 75mm, I think that's the equivalent of 11mm on a 35mm. Pretty sure that'l get you close to 180 degrees coverage.
That's basically what I did w/ the coffee can pinhole. It was made with the smaller cans, not the big Folger's type cans, but the smaller ones that only hold about 12-14 oz of beans.

7. Is it cheating to bend the film plane?
I don't know; I'm not sure how that would affect the image and how lines are drawn. I definitely do not want lines to bend, the way fisheyes do. I'm specifically building a wide-angle pinhole because I want a very wide angle but cannot tolerate bent lines, nor can I afford a very wide angle lens for 4x5 anyway.

8. Yea, bending the film plane does distort the image. I wish I had a good image to post, but I've only done 3 shots with it and they were just to see if I could get the right amount of coverage. The last one I took got messed up because it was a windy day and I didn't hold the can down well, so it's blurry.

9. Originally Posted by Vaughn
Eventually it will be the differences in the distance from the pinhole to the film at the center vs the corners that will limit you. If it is twice the distance to the corners than to the center, that will be two stops (4x) less light hitting the corners. I have made 8x10 pinhole cameras using 250sht boxes of photopaper. Very wide angle, but the corners can go unexposed relative to the center. Size of the hole will make no difference -- more light will hit the corners, but totally overexpose the center. So you need to know how much dropoff of light in the corners you are willing to put up with. A "focal length" of 3 inches will give you about 1 stop of drop off in the extreme corners of a 4x5, if my math is anything close to right (no promises!LOL!).

I'll shut up and let someone who knows what they are talking about post.
Another way to think about it is that the "ideal" pinhole size really only applies at the center of the image. If you curve the film plane along one axis to maintain a constant distance from the centerline of the film to the pinhole, then the pinhole can be the "ideal" size along the centerline. Making the hole bigger will just make it less sharp. If you really wanted the sharpest, most even exposure, then maybe a spherical film plane would be the answer......I'm not sure how that would work though! (or how you'd print it).

10. Hmmm? If the film was forced into a spherical shape rather than a semi-circular shape. The film would all be the same distance from the pinhole and you could make the focal length as short as was practical with the equipment you had. It would also give you a fisheye view, I think? I imagine the challenge is getting the film into this shape.
I agree with Vaughn: I have a Zero Image 4x5 camera and at the shortest "focal length" of approximately 25mm (from pinhole to film) the light drop off at the corners is significant. Vignetting on a B&W image is a nice effect but it doesn't look as good with colour film... IMHO...

Page 1 of 5 12345 Last

 APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:
Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin