Topic: Large Format Pinhole: Need Advice

[Ed Wenn]

Plan 'A' didn't work out on the Pinstant camera front so I decided instead to make a pinhole lensboard for my 5x4 Tachihara and use an instant film back instead of making a 'new' Pinstant camera from scratch. Technically it was alot easier to get off the starting blocks and actually take a picture that worked, but there is still an issue and I wanted to run it past the assembled sages here to double check I'm doing nothing too stupid (a certain level of stupidity is a given when I start messing about with cameras!).

I've included some visual aids by way of illustration. Please ignore subject matter, colours and composition. I forgot to take my tripod away with me for the weekend so these are all taken from a precarious postion on top of a cupboard in my parents' conservatory. All 3 shots were taken from roughly the same spot using Polacolor 125i film in a 405 film back..

The first attachment is a comparison of the normal 150mm lens that I use with the Tachihara and the new pinhole with the bellows extended to the "0" position on the focus track (if that means anything to anyone here....it's about 6 inches or 15cms from the film). As you can see, there's virtually no wide distortion from the pinhole at all.

The second attachment is from the pinhole only with the lens moved back so it's way closer to the film...an inch or two at most. The width has clearly increased, but the coverage has reduced.

Now, I'm happy to press on with this pinhole in the first position because I think it might give me some interesting results (moody, lo-fi black and whites for example) even without any additional width, but it would be nice to have both the lo-fi and the ultra-wide.

What are my options?

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[Ed Wenn]

Actually, I've just thought of one option already...I should try and find a sweet spot on the focus track where I get the best mix of film coverage + wide effect. The two examples shown here are from each extreme. Might not a shot taken somewhere in the middle of the focusing range work out better?

[Ed Wenn]

...and another thing: because I'm not using the full 5x4 available to me I guess this may have an effect too, right? I'm reluctant to waste any of my LF Fuji and Polaroid film until I know what I'm doing with this process, but would I see more wide distortion at the '0' position if I used larger film?

[DS]

Having a look at one of the numerous pinhole calculators out there might be helpful:
http://www.mrpinhole.com/calcpinh.php.

I'd say going for a focal length of 60-90mm ish would work better- wide but not silly wide and it should cover the film at that sort of distance. Not an expert though

[Ed Wenn]

Don't answer me with hard facts based on actual evidence...I need guesswork and magic.
 

OK, I'll try 60-90mm. Cheers!

[astrobeck]

I think you have answered your own question with the images presented.

I say just move the pinhole to a spot between the first and second position you used in your examples above. 

When I first began pinhole I read the tables, pinhole sizes, FOV's and did all the math to see which pinhole was the best for what focal length, etc. etc.
I even had different sized hand drilled pinholes for separate lens boards I had made for each scenario.
That bored me to tears and makes me nauseous now to think of it.

So toss away the tables, and the math and just adjust the distance  a bit to get the coverage you are happy with on the film.

You have seen in the above examples the last photo is past the sweet spot for coverage, so just eek it out a bit more and you've got it.

Good luck and show us more!  I'll set up my crown graphic later today and play and we can compare.   

[Francois]

Math is so much fun 

Actually, I would probably be tempted to adjust the "focus" to the minimum requirement to cover the entire groundglass.
That would give widest angle and shortest exposure time possible.

[Ed Wenn]

The planets have aligned...the sun is still out, I'm at home...alone. I'm heading outside with the Tachihara to get some Pinstant under my belt.

[astrobeck]

here's some fresh batches of wild daisies from the yard.

Progressively
the pinholes were 3, 4.5 and 5.5 inches from the film plane.
Ranging from 5 to 20 seconds per exposure more or less.
Pinhole in lensboard taped to the Crown Graphic.

And yes indeed the planets are aligned...but they always are in my world. 

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