testing film plane alignment, and flattnessgreenspun.com : LUSENET : Large format photography : One Thread
I'm about to get a crown graphic. I'll be using the fuji quickload film holder, and the quickload film.Is it possible for the film plane to be out of alignment (not perpendicular to the central axis of the lense). If so, then how can I test for this, and how can I fix it? Even if the film plane is properly aligned then is it possible for the film plane to not be flat causing the film to pucker out in certain spots. How can I test for this, and how can I fix it? Finaly how do I test the sharpness of a lense?
-- jon miller (email@example.com), November 20, 1999
Jon, The answer to both your questions is yes. There are ANSI specifications for the position of the film in the film holder as well as tolerances from the ideal. These are very difficult to measure without machining a set of precision tools. If you read my article in ViewCamera magazine (Nov./Dec. 1996) you will find instructions for conducting a very revealing test and building the necessary test target for doing same. As far a fixing any problem that uncover, feel free to email me with your results and what you suspect might be wrong and I'll do my best to suggest some fixes. Good luck.
-- Robert A. Zeichner (firstname.lastname@example.org), November 21, 1999.
This endeavor is very much more difficult to carry out then to explain. A good shop can use equipment cost tens of thousands of dollard to have the accuracy to properly check this. I have tried this several times with some sophisticated measuring equipment and had less than satisfactory results. Having milled steel bars is imperative, I was amazed how we think something is flat to our eyes, but in reality it is no where near flat. I came up with a much simplier method to test film / gg alignment, because in the end you are looking for the entire camera system to be aligned. Check down on the bottom of page for past threads and see a thread that I started about film alignment, then go to the end, I explain the process there, it is full proof and creates much more confidence in the analysis, because seeing properly focussed film is the ultimate goal... good luck
-- Bill Glickman (Bglick@pclv.com), November 23, 1999.
I think Bill is referring to this thread.
-- Alan Gibson (Alan.Gibson@technologist.com), November 23, 1999.