Film Flatness - when does it matter?greenspun.com : LUSENET : Large format photography : One Thread
This has come up a few times recently, mainly in relation to using preloaded films in a non-dedicated holder. Elsewhere it was mentioned that 1/8 of an inch of bowing had been seen. I'm curious as to what effect this actually has. If the depth of field is very small then the centre of the film will be out of focus, so for product photography you should probably be using the film holder made specifically for the film you're using. For larger depths of field however, the only problems can be distortion effects caused by the shape of the film, and I wouldn't have thought that 1/8 of an inch would cause much of this type of distortion at all. Does anyone have any photographic examples of what actually happens? I know that seeing your film bow by 1/8 of an inch may look pretty damning, but perhaps this isn't a big deal at all; instead, it could just be something to be aware of and try to correct if the type of photography you're doing could be affected. For landscapes and architecture the convenience of only having one holder to carry may offset the problems caused by film flatness, given the nature of the work you're doing. There's an argument for saying "why compromise?", but from an purely engineering standpoint it would seem that flatness will have an acceptable range of tolerance based on lens length and depth of field, and I'm sure some mathematically endowed person could work out what it is...
-- Gavin Walker (firstname.lastname@example.org), October 17, 2001
The problem i noticed when testing Fuji Quickload and Kodak Readyload films in a Polaroid 545i holder was not the center being out of focus but the edges. The dedicated holders had a clear edge in terms of sharpness (I was testing with a 210mm lens and my target was a brick wall and both standards were carefully aligned to each other and the groundglass camera was very carefully checked to be parallel to the wall, camera was placed eight feet from the wall) from f/5.6 to f/22 once past f/22 the lack of sharpness at the edges on the long side of the film became acceptable to negliable by f/45. Using the dedicated holders film was crisp edge to edge and corners to center at f/5.6, though of course resolution got better as I stopped down, being optimum in the f/16 to f/22.5 range. My controls were a series of exposures on standard cut film in standard holders I'd already tested and okayed for film flatness and film plane alignment to groundglass position. So my conclusion is: If you like working at f/32 or smaller apertures with a normal lens at moderate to normal working distances go ahead and use the P'roid holder for all of your QL and RL film.
Probably at longer subject to camera distances the threshold of acceptable sharpness drops to f/16. likewise i'd expect the threshold to possible be lower for wide angle lenses and higher for longer focal lengths, But these possibles and probables are mere speculation on my part.
Now I don't know about you, but for the expense of shooting large format in both money and time led me to the conclusion that the particular dedicated Fuji holder was a good purchase, so I wrote the check. I was never able to make the old style of Kodak readyloads --the two sheets per packet version -- work without 25-30% ofthem failing because of light leaks, and I tried three iterations of the older design holder.
The purpose of my tests by the way was to prove that I didn't need the Fuji or Kodak holders and that the Polaroid 545i was fine for use with these films.
BTW: Alignment between film plane and groundglass placement for the Kodak and Fuji holders , and the Polaroid holder (when tested with the Type 55 negative was unformly excellent.
-- Ellis Vener Photography (email@example.com), October 17, 2001.
to answer the question in your header, film flatness only matters when you are exposing the film and when you are printing a negative :- ) i have put 1000s of negatives through my camera using the kodak readyload system, and for the past 2 years, i have had a zero failure rate, and have never noticed any type of film flatness problems. after understanding what the issues were, it was easy to find methods that ensure proper handling of the film packets to eliminate any potential light leaks or failures of the holder in gripping the inner film mount. i am now transitioning over to the new single sheet system, which seems definitely more secure in its operation. it is a wonderful system, as i am sure the fuji system is as well, and makes it possible for me to carry hundreds of negs on my shoots. there are days when i expose up to 200 negs - imagine trying to do that with regular film holders!
-- jnorman (firstname.lastname@example.org), October 18, 2001.
I have experienced film flatness problems with roll-film backs. I do not have samples posted on my site, but the thickness of 4 layers of gaffer tape was enough to to ruin some architectural jobs shot on 6x7cm format. Visit this link for film flatness with Calumet roll film backs. http://www.kinesisgear.com/opinion.html
-- Richard Stum (email@example.com), October 26, 2001.