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Ask any commercial photographer who shot tabletop, jewelry, etc. regarding tape and film bowing. Remember that sometimes you'd leave the loaded holder in the camera for several minutes while doing multiple pops and you don't want the film moving. Perhaps some other crusty half-dead geezer could rise from the depths and give me a confirmatory slap across the nether area of my body that used to be functional before the maggots ate it away.Quote:
Originally Posted by Ben Syverson
Hmmm I might well be one of those commercial photographers who did indeed use multi flash and many other things of that nature including double exposures on separate cameras, and not once did I or anybody else I knew used a vacuum back, what we did do was put a strip of double sided tape in the centre of the slide and de tacked it, the film was stuck and peeled off with out any problems, it is also a lot more cost effective and more portable than a vacuum back
If you focus with dollar store spectacles and use a wobbly tripod, you are correct - film flatness will never be an issue.Quote:
Originally Posted by Ben Syverson
Admit it, Frank. This has nothing to do with film flatness. You just want someone to slap you across your nether regions. ;)Quote:
Originally Posted by Frank Petronio
A colleague of mine has a saying when he wants to remind people that you don't need experimental evidence of what is self evidence: nobody ever felt the need to do a study demonstrating the effectiveness of the parachute. I just figured that if Contax went to the trouble to put a vacuum back in the RTS III (which, like all 35mm cameras, already has a pressure plate), then there must be objective value in a LF vacuum back. I guess film flatness in LF is not as cut and dry as I thought.
I've seen this discussion before, and I think I know why some people never need to use sticky tape and others do. The nice folks at Zeiss put out this article, Schrfentiefe und Bokeh, and included this formula;
image-side depth of focus = twice z times k,
where z = circle of confusion size
and k = aperture number
People shooting at wide apertures (small k), and making big enlargements (tiny z) are going to see focus errors that their peers aren't. This is going to be particularly bad for short focal lengths* (wide angles) and I believe (but can't reference) infinity focus.** If your shooting doesn't meet those conditions, you aren't going to notice, and don't need to care.
So, who do we know uses vacuum backs? Some people who do aerial photography. I don't know if astronomers did, but I do know they used glass plates until really recently.
Adam, the OP, I would encourage you to do a little math with the typical apertures, focal distances, and the CoC you use for your biggest prints. I'll point out that the IQ180 vs. 8x10 test seemed to suggest that f/16, an almost unworkable shallow f-stop, allowed the best resolution on a particular lens. You might want to make a similar test, or hire someone to do so for you. (I really recommend the second; you'll only ever need to do it once, so it should be money well spent.)
Will
*the article explains that with longer focal lengths you usually get *something* in focus, so errors are less apparent.
**for some purposes, you can assume that infinity is, ah, infinitely flat.
The idea behind all these view camera movements is that you should be able to shoot tack sharp 8x10 at f/16 if you do the right moves (if your subject matter works). Unfortunately, unless you do the classic Ansel Adams rocks in the foreground of the mountains shot over and over, very few subjects comply!
Yes astronomers did.For example well known astrophotographer Tony Hallas used a Pentax 67II with a modification that pumped gas into the body to keep the film flatQuote:
Originally Posted by Will Frostmill
Astronomers use glass plates because they are flat and can be accurately positioned.
Thanks Will, I will do some math, thanks for the article and formulas. I don't shoot wide, and try to keep my F stop at 22 or 32 when shooting 8x10. I also never point the camera down. So I might not be overly impacted by film bowing, however I think I will still try the double sided tape just to see.
Frank, I may seem anxious, but I would call it curious, and I do prefer to have top notch camera gear....but within reason. The way I look at it, I'm spending around $20 per color negative, so I might as well do the best I can. I have been pleased with my Caltar, but am just curious whether I would get better results with a different lens.
(PS...Frank, I don't lust after fancy cars or houses, as long as they get me around and keep me warm respectively I'm happy. I'm not itching to go out and drop a pile of cash for a lens...but if it would make sharper negs than my current setup I might consider it.)
Adam, I understand your desire to get the best results possible. To show a real difference between the 300mm lens you have, and a newer Apo-type, EVERYTHING else will have to be impeccable. And even then, the difference won't be large, and may well not exist due to sample (of lens) variations.