Almost finished my first pinhole camera

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Originally Posted by RalphLambrecht

Let's think about this!

I agree with your f/stop calculation, but I think f/360, which is 9 stops from f/16 is close enough. Now to the exposure time:

You said you measured 4s at f/16 (are you sure, it wasn't 1/4 s at f/16). Assuming it was 4 s and the 9 stops above, this calculates to:

1st stop > 8s at f/22
2nd stop > 16s at f/32
3rd stop > 32s at f/45
4th stop > 1m at f/64
5th stop > 2m at f/90
6th stop > 4m at f/128
7th stop > 8m at f/180
8th stop > 16m at f/256
9th stop > 32m at f/360

and this doesn't even include reciprocity, which would take it to:

> 2h at f/360 (I don't think so)

It must have been 1/4 s, wasn't it? In which case:

1st stop > 1/2s at f/22
2nd stop > 1s at f/32
3rd stop > 2s at f/45
4th stop > 4s at f/64
5th stop > 8s at f/90
6th stop > 16s at f/128
7th stop > 32s at f/180
8th stop > 1m at f/256
9th stop > 2m at f/360

and with reciprocity failure:

6-12 minutes, depending on the film.

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For the shot in my living room, the exposure was actually 4 seconds @f/16. It was hard for me to believe, too. You have me doubting myself now, so I'll check again tonight. I cant check right now because I took the picture of my couch at night, so there was no (or very little) light coming in through the windows.

I didnt adjust for reciprocity at all on the first one, and I kinda just guessed at reciprocity adjustment on the second shot I did outside.

I noticed that you adjusted for reciprocity by adding about two stops overexposure. Is that a rule of thumb kind of thing or is there an actual equation for adjusting for reciprocity? I've read the data sheet for hp5+ and found the recirpocity chart, but I dont think it covers exposures longer than 75 seconds. I dont have it printed out, but I'll look it up again and make sure about that

You will find a lot of info at http://www.mrpinhole.com/index.php

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Originally Posted by Existing Light

For the shot in my living room, the exposure was actually 4 seconds @f/16. It was hard for me to believe, too. You have me doubting myself now, so I'll check again tonight. I cant check right now because I took the picture of my couch at night, so there was no (or very little) light coming in through the windows.

I didnt adjust for reciprocity at all on the first one, and I kinda just guessed at reciprocity adjustment on the second shot I did outside.

I noticed that you adjusted for reciprocity by adding about two stops overexposure. Is that a rule of thumb kind of thing or is there an actual equation for adjusting for reciprocity? I've read the data sheet for hp5+ and found the recirpocity chart, but I dont think it covers exposures longer than 75 seconds. I dont have it printed out, but I'll look it up again and make sure about that

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Reciprocity differs with emulsions, but the attached chart may serve as a guide. This is the reciprocity chart from Way Beyond Monochrome'. It is constructed from data, I received from Howard Bond, John Sexton and my own experiments. It has served me well so far.

Thanks for the chart, Ralph.

I wish I could upload scans of the negs, but it seems like i'm going to have to wait till I have some prints. My flatbed scanner doesnt like stuff that isnt opaque or nearly opaque :D

Fuji Acros 100 has virtually no reciprocity failure at typical pinhole exposure times. So it ends up being faster than more traditional 400-speed films.

~Joe

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Originally Posted by Joe VanCleave

Fuji Acros 100 has virtually no reciprocity failure at typical pinhole exposure times. So it ends up being faster than more traditional 400-speed films.

~Joe

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Joe

virtual, typical? You've got some data?

Acros needs no change in exposure for anything up to 2 minutes according to Fuji. Beyond that, and it does apply, but I've not done any formal
testing beyond 2 minutes.

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Originally Posted by Andrew Moxom

Acros needs no change in exposure for anything up to 2 minutes according to Fuji. Beyond that, and it does apply, but I've not done any formal
testing beyond 2 minutes.

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Thanks.

Has anybody tried this an can share an experience?

Well, I've shot and developed a few more shots with my pinhole camera, and i'm suprised at the sharpness of the negs. While it's obviously not up to par with my Canon L lenses, I am suprised at the sharpness and detail.

I do have one dumb question (well, one more dumb question :D ).

I did some contact prints on Arista edu glossy and Slavic double weight FB paper, and noticed what I first thought was the dreaded newton rings. but before I went out and bought some anti newton ring glass, I decided to look at my negs. I noticed they had the little bands in the sky areas just like my contact prints did. They're not perfectly circular; they look more like really thing faint tree rings or the ridges of a fingerprint. Unfortunatly, they dont show up in the scan of the prints. I'm assuming that's a development problem, but could the pinhole cause that kind of problem?

The pictures are shot outside on an overcast day, so there's no direct sun. The 5x7 negs are HP5+ developed for 10 minutes in Rodinal 1:50 @ 20C in a 6x9 flat-bottom tray I found at Target. I did an intermittent agitation scheme like I do my 3mm negs: Agitation for first 30 seconds, then 10 seconds every minute. I also picked the negs up out of the developer and let the developer drip off the corner at the end of every agitation. The total time for agitation and picking the negs out of the developer and putting them back in took like 20 seconds.

If it's development related, could someone tell me a better tray developing method or give me a link? I'm really not finding much, but perhaps i'm just overlooking something very obvious.

BTW, the rings show up more in the glossy Arista paper than the matte Slavic paper