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Guest
02-06-2006, 09:11 AM
Hello,
Im thinking about building a 20x24 wide camera based on a exhibition of 20x24 pinhole poleriods I recently saw. Any one else experimented with this crazy size?
Any way of calcuating the resolution of such a camera? I know the resolution increases with the film size and these 20x24's were amazingly sharp looking!
Thanks
Pete

luscher
02-06-2006, 10:50 AM
youmight want to read Tom Vanderbuilt's article ( ''Sharpest Image'' in Pop Sci 11 2005 ) about an analog gigapixel camera.

Graham Flint's camera makes 9x18'' images and uses Kodak roll film which he states cost him something like 1200 $US / roll. the film magazine comes from a Fairchild Aviation corp. K38 aerial camera, courtesy US Military/Industrial Cold War surplus.

be sure to keep us posted !

JoeVanCleave
02-06-2006, 11:31 AM
Focal length alone determines your choice of aperture size around the optimal pinhole size. So, you'd have to determine your desired angle of view, first. That then dictates the required focal length, which then determines optimal pinhole size.

I have a falling plate camera with a focal length of 11 inches, which could be a workable size for a wide-angle 24 inch negative, and it is really sharp, even on contact printed paper negatives. See my "Tent Rocks" image on the November page of the calendar. Its around f458. Getting good exposure on paper requires bright daylight only; at its working focal ratio, even in cloudy weather the exposure times get unwieldy.

You could use sheet film, but at that size, paper would be much more economical. If you do paper at that size, I would recommend preflashing the paper as a method for increasing, somewhat, its working speed, and getting some shadow detail within reasonable exposure times.

Ralph Y.
02-06-2006, 01:23 PM
Welcome to the forum. A few years ago I built a 10x24 camera. This is a link to an image from the camera.

http://f295.tompersinger.com/cgi-bin/Blah/Blah.pl?b-cc/m-1117939769/

As Joe indicated, exposure times with paper are quite long. Good luck.

Guest
02-06-2006, 02:33 PM
Ralph, very very nice camera design and an amazingly sharp photograph.
couple of questions; why the curved film back? how did you make it? what kind of pinhole did you use? what are the problems and solutions in building a 20x24 scaled up version of your camera? did you use RC paper for the photograph you posted? Do you find that the lack of tones in RC paper negs. to be a problem? many thanks for your advice

Ralph Y.
02-06-2006, 08:53 PM
The curved film back is made from countertop laminate and is held in place by vertical stops on each side of the case. The curved back eliminates distortion and minimizes light falloff by maintaining a constant distance between the pinhole and the film plane. The pinhole is made from brass shim stock (.001 inch thickness) and the pinhole size of .029 was determined using this formula: Pinhole size in inches = SQRT(Focal length) * .0073

I've only used RC matte paper in this camera and in the 10x16 camera that I built at the same time. Yes, lack of tones can be an issue with paper negatives, but JoeVanCleave has posted some very good advice about pre-flashing paper to decrease contrast. Check back on some of his posts concerning paper negatives - he does some great things with paper.

The problems you'll encounter in building an ultra-large format pinhole camera are similar to those of builiding smaller cameras - the main one being keeping the box light-tight. Some things to consider are: how to process the negative and how to make a contact print from the negative. I process negatives in a Unicolor 20x24 processing drum. For contact prints, I built a contact frame that uses a 12x26 inch piece of safety glass.

You might want to consider building a scaled-down version of the 20x24 (perhaps 8x10) just to get a feel for what's involved.

Good luck. Send me a private message if you run into any problems.

murrayatuptowngallery
02-06-2006, 11:03 PM
I >think< the only article I have seen that quantitatively discsusses pinhole resolution was a physics article by first-initial-forgotten Young...maybe M. Young.

If I find it I'll let you know. I'm on a quest for mathematical origins of pinhole optimization and oddly none of the papers I've recently found approach it quantitatively, just visually.

Murray

dvoracek
02-07-2006, 10:52 AM
Funny how two references to things I have in my old articles collection came up on the same day.

For the original research on optimization of a pinhole, by the Lord Rayleigh himself, see
http://idea.uwosh.edu/nick/rayleigh.pdf

The index is at http://idea.uwosh.edu/nick/oldarticles.htm

Nick

dvoracek
02-07-2006, 12:39 PM
Just incidentally, Here are two images I made with 16 x 20 inch paper cameras in a workshop about 10 years ago. I've never made positives of these before. (These were done with a digital camera on a copystand)

The first was 16 inches long, (meant to match the proportions of the 5 inch long 4 x 5 cameras workshop participants were using). The pinhole was about .8 mm. I guess that makes it f507. The exposure was about 15 minutes. It was actually raining. Funny how many people walked by and looked at this huge black box sitting on a trash receptacle, and didn't notice me sitting there opposite it.

The second was 5 inches long (to match the actual length of the cameras workshop participants were using) It had the same .5 mm pinhole as the paricipants' cameras for f250. There's a faint ghost image of me between the left and center doors, but that was the motor driven handicapped door and a guy in wheelchair came by and I had to move. Exposure was about 3 minutes.

I did exposures from the same spots with the participant cameras but I've misplaced those negatives. The idea was to show that the image was the same if the focal length to film size was the same with the first, and if you cropped a 4x5 section out of the second, it would be exactly the same as with the participant camera.

My original thought was to do a group portrait with the giant camera, but the weather was just about as dark as it could be for a pinhole workshop.

Nick Attached files http://f295.f295.org/uploads/16inchcamera_5262.jpg (http://f295.f295.org/uploads/16inchcamera_5262.jpg) http://f295.f295.org/uploads/5inchcamera_7482.jpg (http://f295.f295.org/uploads/5inchcamera_7482.jpg)

EMolczan
02-07-2006, 01:58 PM
I >think< the only article I have seen that quantitatively discsusses pinhole resolution was a physics article by first-initial-forgotten Young...maybe M. Young.

If I find it I'll let you know. I'm on a quest for mathematical origins of pinhole optimization and oddly none of the papers I've recently found approach it quantitatively, just visually.

Murray

Matt Young.
http://www.pinhole.com/archive/371

Tom Miller
02-07-2006, 03:04 PM
In the 20x24 build-or-buy discussion, here's the "buy" side:
http://www.wisner.com/Page13.html
At these prices... maybe a little out of my range.

I saw this camera demonstrated two or three years ago at the Minneapolis College of Art and Design. Rich Silha, who took the photos on the web page, had this camera set up in one of MCAD's studios, with Polaroid providing film, processor and two or three technicians. The advanced color students got a chance to make portraits with the setup, and local photographers were able to rent time to make portrais of their clients. The results are simply stunning. The detail and beauty in the images is hard to believe. On the other hand, there is no enlarging. What surprised me was the color pallete, which somehow seemed "truer" than any other Polaroids I've ever seen.

Guest
02-07-2006, 04:12 PM
gods... what a monster! I was thinking of maybe $200 to convert an aluminum flightcase...

Guest
02-07-2006, 04:20 PM
"Since the optimum pinhole diameter increases as the square root of the focal length, you can improve the detail in the image by scaling everything up. For example, if you quadruple both the focal length and the size of the film, you will retain the same field of view while only doubling the pinhole diameter. Resolution is thereby improved by a factor of 2, since the ratio of the film size to the resolution limit has been doubled. In the jargon of modern optics, we would say that there are more pixels (picture elements) in the larger format. In rough numbers, a 35-mm format with 50-mm focal length is about 180 pixels wide, whereas a 100 x 127-mm (4 x 5-in) format with 150-mm focal length is about 340 pixels wide, or about the same as a TV image. Since the picture is two-dimensional, the larger format carries about four times the information. Nothing is free, however; the larger format also has a higher F-number, or lower light-gathering ability, so the exposure time is longer. "

So, a 20x24 camera would have more then twice the optimum resolution of a 4x5 camera!

Guest
02-07-2006, 06:08 PM
It is said that the lowest resolution needed for a super sharp image print is 7 lines per mm. It would seem that a 20x24 camera could come close to this...?

murrayatuptowngallery
02-07-2006, 08:12 PM
Thanks for the links. I missed but had been looking for the Rayleigh article.

I actually found an article by a retired researcher at NIST on limits of resolution of pinhole photography. It's pretty tough reading.

I don't have first hand experience with anything that large, lens or pinhole, other than having hoarded materials to build both someday.

I would still think that a 20x24 lens image would be sharper than a 20x24 pinhole image, but the 20x24 pinhole image would still look pretty impressive, and if viewed from whatever the 'proper' viewing distance is (much further away than your average 'print sniffer' attemtps), the low res to satisfy human vision does apply.

Guest
02-08-2006, 06:32 AM
Hi,
I know that the old camera obscura's used a simple lens as well as a pinhole. Why dont pinhole photographers also use a simple positive meniscus lens with their pinhole camera? Can you imagine what the effect of this would be? Do you think it would be useful especially for a 20x24 camera?
Thanks!

ImageMaker
02-08-2006, 03:38 PM
Why dont pinhole photographers also use a simple positive meniscus lens with their pinhole camera? Can you imagine what the effect of this would be?

This would give an effect almost identical to the larger format "consumer" cameras of the pre-WWI and immediately post-WWI era -- when a box camera took 3x4 inch negatives, for instance. Those cameras used simply meniscus or meniscus achromat lenses, and the images they produce, when contact printed (as almost all photographs were before 127 and smaller formats took over the market), are almost indistinguishable from those made with much more expensive optics. They have no similarity to pinhole images; they're sharp (though they tend to soften at the edges), even with ISO 12 equivalent films they stop motion, mostly (exposure would have been, say, f/11 at 1/25 in bright sun), and they have limited DOF (most of the box cameras are set up as hyperfocal -- DOF for a contact print to barely include infinity, so they're "in focus" for everything from 6-10 feet out to the horizon).

To me, that's an entirely different aspect of photography (and one I engage in -- I've got, at least count, ten simple-lens cameras in the house, 8 of them immediately usable), not really closely related to pinhole.

Daryl
02-08-2006, 09:25 PM
The fundamental difference:
Pinhole is diffractive imaging.
Lenses are refractive imaging.

There is no bending of the light ray attributed to glass in the pinhole set up.
The pinhole is the objective piece responsible for the image.

Filters are okay since they are optically flat - 0.0 diopters - are not responsible for the imaging
and only conditions the spectra landing on the senitized surface.

Guest
02-10-2006, 05:15 AM
Murry,

What would be the optimum distance for viewing a 20x24 print so it looks "sharp"? How do you work out these things. I like math!

Pete

Guest
02-22-2006, 05:31 AM
i'm just started making a 20x24 camers and film holder out of black foam core - trouble is... how do i scan & post 20x24 photographs? lol

earlj
02-22-2006, 08:36 AM
You scan it by taking a digital photo with your trusty lens camera.

Guest
02-22-2006, 08:51 AM
of course.. thanks earlj

i dont have one but i could borrow my brothers