RE: [pinhole-discussion] Bellows factor
Hello, On Sat, 1 Dec 2001, Andy Schmitt wrote: > (sorry Europe but there really is a use for inches) I doubt it ;-) Since the method you used was based on fractions, it does not matter at all which units you use. So no excuses for not using metric! ;-) Regards, Robert Sex discriminates against the shy and ugly. * Robert Kosara _ * * Institute of Software Technology/IFS /_)_ / __ __ 7 //_ _ __ __ __ * * Vienna University of Technology / \(_)/_)(- / / /\(_)_\(_// (_/ * * Favoritenstr. 9-11/E188 / A-1040 Vienna / Austria (Europe!) * * rkos...@asgaard.tuwien.ac.at * http://www.asgaard.tuwien.ac.at/~rkosara/ * * alternative mailto:rob...@kosara.net http://www.kosara.net/ *
RE: [pinhole-discussion] Bellows factor
Hey there How it was explained to me is use a Tape Measure.. Mark the tape measure off in fstop-inches... Say you start with a 4" lens and have a total bellows length of 9" 2.8" 4" 5.6" 8" 11" 16"...etc ^ ^ You have a 2+ a 1/3(?) fstop-inch extension and that is also your extension factor. ( +2 1/3 stops) (sorry Europe but there really is a use for inches) have a great Saturday andy -
Re: [pinhole-discussion] Bellows factor
> There is no "rule of thumb", just plain physics of light. > This case is in no way different than if you were using a glass lens. I guess you could say the rule of thumb is to add 2 stops every time you double the focal lenngth. You can think of it this way... If you have a 50mm lens at f/16, divide 50 by 16 and the opening would is 3.125mm. If you had that same opening on a 100mm lens, take 100 divided by 3.125, and you get f/32. Two stops from f/16. John
Re: [pinhole-discussion] Bellows factor
That was my instinct, Guillermo, and thanks for your answer. Funny thing is, I tried it yesterday at a minute and a half--my rough calculation, which was close to your suggested 84.5 seconds--and it completely overexposed the film. It was all white (using Polaroid Type 55). Then I tried it indoors in a setting that I know from experience needs about 45 minutes. I gave it about an hour--very little more than what I would normally—and the expoure was more or less correct. In other words, it was behaving very much like the extension had no effect at all. Wonder why? Colin > There is no "rule of thumb", just plain physics of > light. > This case is in no way different than if you were > using a glass lens. > > > If I would expect a 2-second exposure outside in > full > > sunlight with a 5.0CM "focal length", for example, > > what would be a theoretical equivalent at 32.5 CM? > > 84.5 seconds (uncorrected for reciprocity, time) > > Guillermo > > > > ___ > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??? > unsubscribe or change your account at > http://www.???/discussion/ __ Do You Yahoo!? Buy the perfect holiday gifts at Yahoo! Shopping. http://shopping.yahoo.com
Re: [pinhole-discussion] Bellows factor
- Original Message - From: "Colin Talcroft" > I have rigged up an "extension tube" for my Zero image > 4X5 camera that puts the pinhole 32.5CM from the film > plane. The pinhole is designed for use at about 5.0CM. > I'm not worried about the "optimal pinhole" thing. I'm > confident this will create an image, just wondering > how much this distance is likely to force me to > lengthen my exposure time. I will be experimenting, of > course, but in the hope of not wasting too much film, > does anyone have a rule of thumb? There is no "rule of thumb", just plain physics of light. This case is in no way different than if you were using a glass lens. > If I would expect a 2-second exposure outside in full > sunlight with a 5.0CM "focal length", for example, > what would be a theoretical equivalent at 32.5 CM? 84.5 seconds (uncorrected for reciprocity, time) Guillermo
[pinhole-discussion] Bellows factor
Hi everyone I have rigged up an "extension tube" for my Zero image 4X5 camera that puts the pinhole 32.5CM from the film plane. The pinhole is designed for use at about 5.0CM. I'm not worried about the "optimal pinhole" thing. I'm confident this will create an image, just wondering how much this distance is likely to force me to lengthen my exposure time. I will be experimenting, of course, but in the hope of not wasting too much film, does anyone have a rule of thumb? If I would expect a 2-second exposure outside in full sunlight with a 5.0CM "focal length", for example, what would be a theoretical equivalent at 32.5 CM? Thanks Colin __ Do You Yahoo!? Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month. http://geocities.yahoo.com/ps/info1
