Diagnosis please?

I finally managed to get a few images from my 145mm f272 645 pinhole camera and I have some questions.

The farther away the object is, the less sharp the edges are. But the closeup images are right about where I want them to be. Here are 4 images, an overall of each frame and a full resolution crop. All are unsharp masked in Photoshop to the same amount, and scanned with the same settings. Contrast on the first shots could be a little better too.

Distance from hole:40 feet to infinity



Distance from hole about 4 inches to a few feet:



You need to click on the images to see them at the real full size, they should then open in a new window so that you can view them at full size.


I think the pinhole was made with a number 75 drill in 0.001 stainless and it has clean edges. Film is XP2 developed by Main Photo and shows good dynamic range, better than the kodak I used for previous testing. As I said I'm happy with the close up performance, but would like to get the far performance a little better on the large edges and contrast.

Forgot to mention that is was mounted on a good sturdy tripod, and metered with a handheld light meter and opened with a cable release. Timed with the same meter if needed.

Now that you bring it up, some of my shots show a bit of that too. I'm inclined to think the issue is that as distance increases, the little area details that make up the image approach the pinhole size and can no longer be differentiated; e.g., it's a sort of relative effect. (But I may be all wrong!)

I know when I [whisper] scanned [/whisper] some 4x5 pinhole negatives, I found that relatively large decreases in scan resolution showed no effect on file size until I got down to a fairly low resolution threshhold. That says to me there just isn't a whole lot of information in those negatives. If the finest "dot" (I'm avoiding the P-word) resolved is some small unit of arc, that dot will represent a larger and larger percentage of more and more distant objects.

I may not be describing this too well. But I have this intuitive feeling it's a normal result involving proportions. Maybe it's this: we are not really talking focus - we're talking projection of a small spot. Each time you double the distance from pinhole to object, the effective resolution is reduced by half.

(Enh - I better shut up now! )

Interesting - is that a pinhole mod scale on your Digisix?

DaveT

Yes the digisix was modded for the smaller apertures in pinhole. It does not compensate for reciprocity, but it does make a nice quick reference. My camera seems to be about one dot past the f256.

And yes as the (apparent) size of the object approaches the pinhole size you lose details, but the larger objects should still hold more detail between the edges from light to dark. I was surprised at how well the Dandelion came out. It was a little windy that day, no tripod just propped up in the grass, and I counted the exposure as about 2 seconds (no timer).

I guess I need to make a couple of smaller pinholes and see what happens. I also need to make a 210mm assembly, I'm not that happy with the angle of view with this 145mm. It's fine for 35mm films, but too wide for 645 for my tastes.

I agree with DWThomas about the things further away having smaller details, more affected by the low resolution of pinhole (roughly 3 lp/mm on a good setup, I think Matt Young article was source of that numeric figure).

Another possibility is if the pinhole is toward the small side of optimal it will favor distances closer to macro (Paul Prober's PinPlus site macro math article).

Murray

Optimum pinhole diameter has been debated for over a hundred years. Many people still rely on the Lord Rayleigh formula. He was apparently more of a physisist than photographer. I usually use http://www.pinhole.cz/en/pinholedesigner/ with a user constant of 1.5. This provides optimum on-axis sharpness on panchromatic film with some fall-off towards the edges, especially in wide angle pinhole photography. Since shorter focal lengths require smaller pinholes, and image blur is proportional to pinhole diameter, wide angle pinhole cameras have an advantage in sharpness over normal or longer focal lengths. A slightly smaller pinhole should improve sharpness somewhat in your camera. For close-up pinhole photography, the diameter should be reduced even more.

The hole is pretty close to the 1.9 constant that pinhole designer uses as the default.

The 1.9 constant is probably a good compromise between center sharpness and edge sharpness. It certainly is popular in several pinhole calculators. Considerable testing supports a 1.5 constant as better for on-axis sharpness of distant subjects, though.

I'll have to find the other pinholes that came with the shutter and give them a try again. It came with .4, .3, and .2mm holes And the one from these images is somewhere around .5mm

I'm not a scientist, just a simple pinhole user, but my understanding is that the angular resolution of the subject is what gets limited by the pinhole's optical abberations, not merely the object's absolute size as compared to the pinhole size. Meaning that if, for instance, the pinhole 'blurr' was around a half a degree (a totally made-up number), then objects much larger than the pinhole could still be blurred if they were far enough away to subtend an angular view of a half a degree or smaller. That is what I believe is happening in your first image, as illustrated in the subsequent enlargement.

Regarding the overall 'quality' of a "photograph" (i.e. a silver print) made using a pinhole camera, it's much less objective and more subjective; much has to do with the film format size and degree of enlargement used. In your posted images, I am more much put off by the enlarged film emulsion granularity than I am by the degree of edge softness to the objects. And the rather soft contrast bothers me, too.

But I do not mean to critique your image, rather to use its attributes as a point of discussion around what influences the viewer's subjective sense of image quality. I've found that soft images, combined with emulsion granularity, is a show stopper, at least for me. You can do one OR the other - large format pinhole negatives contact printed to produce very nice images with no emulsion grain visible, OR very small formats, enlarged extremely high to accentuate the granularity effect to an almost pointellistic style. But mixing them both rarely works, in my opinion.

Another thing common to photography in general, that seems to also be true with pinhole, is the subject matter verses the final print size. Your landscape image posted here deserves a larger print size, but the small (medium format) negative won't handle extreme enlargement without the telltale emulsion granularity interfering with the edge-softness of the pinhole image.

Landscape subject: large film format, contact printed.
Intimate closeup subject: small film format, contact printed.

if, for instance, the pinhole 'blurr' was around a half a degree (a totally made-up number), then objects much larger than the pinhole could still be blurred if they were far enough away to subtend an angular view of a half a degree or smaller.

Click to expand...

Yes! An even more eloquent way of expressing what I think I was trying to say.

DaveT

Actually, if I took a little more time in the scanning, I could enlarge these images to a truly huge size without the film grain. Because these have soft edges you don't see the typical effects of enlarging, at least not with my workflow. However that work flow has no place in this forum.