| T O P I C R E V I E W |
| Dick Danis |
Posted - 14/07/2009 : 01:47:26
Hi, I am getting a 6x18 pinhole camera (custom made) with a focal length of 85mm. I am not clear with my understanding of it's focal length in relationship to 35mm or it's fstop. Help.
Thanks Dick
One frame at a time |
| 5 L A T E S T R E P L I E S (Newest First) |
| peter k |
Posted - 26/08/2009 : 15:34:21
quote:
I tried to find a list of fstops, but the lists I found only go up to f32.
The international aperture-scale, f-stop, is increased by a factor of V2, square root,(rounded). So 1.414 gives the scale:
0.7 - 1.0 - 1.4 - 2.0 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 45 - 64 - 90 - 128 - 180 - 250 - 350 - 500 - 700 - 1000
Peter
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| Dick Danis |
Posted - 26/08/2009 : 02:41:40
Ralph thanks, that should get me a good exposure. I've got four exposures to shoot on a roll, meter-shoot, bracket, bracket, bracket. I am glad I asked about the fstop after f128. I didn't realize that f180 was next. I know starting with f1 you multiply by 1.4 up to f16 then it doubles. However if you multiply f128 by 1.4 you get f179.2 (f180). I tried to find a list of fstops, but the lists I found only go up to f32. Have you got a website I can check out on fstops? I use a better understanding. Once again thanks.
One frame at a time |
| rbarker |
Posted - 25/08/2009 : 05:41:54
Almost, but there's an intermediate stop of 180.
Depending how high (small) your meter goes, you could also set the meter to that f-stop, and then adjust the film speed a corresponding number of stops (downward), and then read the time directly. Your f/213 would be close to a half stop down from f/180.
Ralph Barker
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| Dick Danis |
Posted - 25/08/2009 : 02:30:34
OK the focal length is about 8mm (35mm equiv) and the fstop is 213. Do the fstop's go from f32,f64,f128 then f256? If so I can figure my EV once I get a light reading. That would put me about 2/3 stops above f128. How does that sound. Thanks Dick
One frame at a time |
| rbarker |
Posted - 14/07/2009 : 06:15:04
A "normal" lens for 6x6 film is 80mm, so 85mm on a 6x18 panoramic would be wide.
The manufacturer should specify an f-stop for the hole drilled. Use that in the normal manner for determining exposure time. Most pinhole manufacturers will also provide a sheet showing approximate exposure times for various lighting conditions.
The approximate nature of the whole process is part of the pinhole "charm".
Ralph Barker
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