ULTRA WIDE: Pinhole Calculators don't Jive?

I have built and used several pinhole cameras and I am now in the process of building an Ultra wide pinhole camera using a Polaroid MP4 carcass. By ultra wide I mean making the focal length as wide as possible that will just cover the 4x5 film format.

I thought that 25mm would be possible noting that the Zero Image 25B uses a 0.2mm pinhole with an effective aperture of f/138. It is difficult to see for sure but it appears to me that the example image in their gallery covers about 110mm (greater than 4 inches but less than 5 inches).

However, when I plug the numbers (25mm FL and 0.2 Dia.) into the various online calculators I get image diameters from 32.5 mm to 48mm. Obviously not enough. The online calculators seem to infer that a 50mm focal length would be the widest practical giving approximately a 100mm image circle.

Can anyone explain this discrepancy to me? What is the definition of image diameter for pinholes? is there a point where the image continues but is not counted as good enough perhaps?

I am about order the pinhole from Lenox Laser (thought I'd give them a try for comparison purposes) and do not want to end up with the wrong one so your input would be greatly appreciated.

The copal #1 shutter that I am fitting will be mounted in a "lens cone" so that the focal length can be varied in the future but for now I am only interested in as wide as possible with the 4x5 format.

Thanks to all, Terrance

I have had responses from Eric Renner (Mrpinhole.com) and Doug Jansen (Lennox Laser) and they both agree that it is matter of acceptable light falloff. My understanding is that the pinhole calculators give an image circle with acceptable lightfall off, the image circle continues someway beyond that but the light fall off is extreme. Extreme light fall of may be effective in some images but not for general purpose photography.

I wonder what the acceptable limit is perceived to be as a percentage of the light transmission at centre?

Any one ever build a graduated neutral density centre filter for a ultra wide pinhole camera? ;{D

Isn't the usual way of reducing falloff with a pinhole to curve the film plane?

In any case, it's hardly "general purpose photography."

Terrance Hounsell said:

Any one ever build a graduated neutral density centre filter for a ultra wide pinhole camera? ;{D

Click to expand...

Maybe this is a crazy idea, but couldn't a centre grad 4x5 ND be placed in front of the film plane to counter the light falloff?

Don't bother with a center grad. I've got a couple pinhole cameras made from Altoids gum tins; they use a 60 mm strip of 35 mm film, with a 16 mm projection distance. That's about 115 degrees corner to corner, and though the light falloff is visible, it's not really objectionable as long as I use film with good latitude and a development process that doesn't accentuate the contrast. Tri-X fills one half of that; HC-110 at high dilution with greatly reduced agitation (every 3rd minute) gives the other half. See attached...

Donald Qualls said:

That's about 115 degrees corner to corner, and though the light falloff is visible, it's not really objectionable as long as I use film with good latitude and a development process that doesn't accentuate the contrast. Tri-X fills one half of that; HC-110 at high dilution with greatly reduced agitation (every 3rd minute) gives the other half. See attached...

Click to expand...

How high of a dillution and for how long, Donald?
Thanks

The rule of thumb I have seen is pi (3.14...) times the 'focal' or 'projection' distance, what ever you prefer to call it, and at this amount of coverage there will be noticeable light falloff. That's the problem with pushing the limit of wide angle coverage. Using the approximate diagonal of 4x5 film as 162 mm (actually a bit shorter), dividing by pi gives about 52 mm

A 'normal' to 'long' f.l. reduces the falloff considerably. My first camera was a 35mm conversion with the pinhole at 46.5 mm spacing. This camera had no obvious falloff.

Murray

Oops, not done. If you wanted to reduce the falloff without unusual shaped film back, which introduces other distortion, I would aim for 'normal' angle of coverage...50-some degrees, pinhole spacing = diagonal of film. You could experiment and find out how wide (close spacing) you could use with your own esthetics...what you're willing to tolerate.

One thing I found disappointing with a 'normal' angle of view camera was composing images that didn't 'look' like lens composed images, because they were ypically disappointingly blurry 'ordinary' compositions. Taking advantage of the extreme depth of field gives perspectives that are out of the ordinary so the viewer appreciates the view before they criticize the blur.

One bad thing with very wide angle cameras is that you just can't seem to get CLOSE enough to fill the frame. It takes some getting used to.

I have a pinhole camera for 4x5 with a 35 mm distance hole to film. The film is flat, and there is of course considerable light fall-off in the corners, but I should add that I am still able to use a considerable rise and fall with the whole. What disturbes me more than the fall-off, at least with some motives, is the loss of sharpness at the periphery.

Jersey Vic said:

How high of a dillution and for how long, Donald?
Thanks

Click to expand...

My times are quite a bit shorter than many, so fair warning...

I use Dilution E (1:79) for full length 35 mm and 2x120 in my Paterson; Dilution G (1:119) for 120 on stainless and sheet film in my daylight fill tubes. For Dilution G, I give Tri-X 21 minutes at 68 F (20 C) with continuous agitation the first minute, then agitation every third minute; Dilution E, at 2/3 the dilution, gets 2/3 the time with the same agitation, or 14 minutes.

This development pushes up the shadows while keeping the highlights in check, which can produce a flat negative if the light is flat -- but it's a lot easier to add contrast (within reason) in printing or scanning and still get a good result than it is to remove it...