Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Quote:
Originally Posted by
brucetaylor
I was unsure about the plane of focus on an 8x10 camera. I wanted to confirm the gg position. I took an old holder and a hole saw, I drilled 5, 1" holes in a pattern, 4 corners and the center. I put a developed sheet of film in the holder. I removed the gg and put the holder in place. Wide open, I focused on a focus chart and with a loupe confirmed the targets were in focus. I then removed the holder and replaced the gg. Again with the the loupe I confirmed focus. In my case no adjustment was needed, but I think it would have been relatively easy to make gg shim adjustments to match my true plane of focus as determined by the film at the actual film plane.
This is a great method that I hadn't though of and should give accurate enough results! It's worth sacrificing a holder for IMO.
Doremus
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Quote:
Originally Posted by
brucetaylor
I was unsure about the plane of focus on an 8x10 camera. I wanted to confirm the gg position. I took an old holder and a hole saw, I drilled 5, 1" holes in a pattern, 4 corners and the center. I put a developed sheet of film in the holder. I removed the gg and put the holder in place. Wide open, I focused on a focus chart and with a loupe confirmed the targets were in focus. I then removed the holder and replaced the gg. Again with the the loupe I confirmed focus. In my case no adjustment was needed, but I think it would have been relatively easy to make gg shim adjustments to match my true plane of focus as determined by the film at the actual film plane.
Just trying to understand. A negative was unexposed, but developed, resulting in a transparent film, correct? If the film was fully exposed and developed, it would be totally black. You then used the film in the holder to act as a groundglass, and focused on it through the holes. Were you able to focus on it?
Kumar
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
The b&w negative was exposed to a gray field and processed normally, so the film emulsion acted as a focusing surface. It was very easy to see and focus accurately.
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Okay, got it.
Thanks,
Kumar
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Quote:
Originally Posted by
brucetaylor
I took an old holder and a hole saw, I drilled 5, 1" holes in a pattern, 4 corners and the center. I put a developed sheet of film in the holder. I removed the gg and put the holder in place. Wide open, I focused on a focus chart and with a loupe confirmed the targets were in focus. I then removed the holder and replaced the gg.
That’s a great technique! I have some old holders that I can sacrifice and drill through and then use a sheet of tuff-frost diffusion material as the “film” to check focus. I love this forum, so much great advice for the asking.
-Schaf
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Quote:
Originally Posted by
schafphoto
That’s a great technique! I have some old holders that I can sacrifice and drill through and then use a sheet of tuff-frost diffusion material as the “film” to check focus. I love this forum, so much great advice for the asking.
-Schaf
The advantage to using film instead of some other diffusing material is that film is exactly the thickness of - well - Film! If you use something else, make sure it is the same thickness as your film. Kodak films are 7 mil thick, others are similar (.175-.18mm).
Have fun,
Doremus
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
I put one of my fresnel screens in front of the BOSSCREEN and the focus is now perfect. I also tried a number of other screens and even flipping the BOSSCREEN backward. The answer was fresnel in front smooth side to front of BOSSCREEN, fresnel grooves toward lens. This still seems odd because the nice little tabs on the sides of the BOSSCREEN with the factory tape shims are now about .6mm away from the side of the frame... but who am I to argue (the BOSS seats on ledges on the side of the frame while the fresnel sits closer to the lens on the top/bottom ledges). I have three Cambo/Calumet spring back frames and they seem to all have the same dimensions when it comes to GG placement/distance. I now need to buy a second plain fresnel to get my second Cambowide + BOSSCREEN in order and Ebay seems to only have gridded fresnels.
I tried a standard Cambo matte glass grid screen without a fresnel and it was a lot closer than my flawed setup before but not as spot-on as the BOSS+Fresnel combo. Thanks again for all the help.
How far should the focusing surface of the GG be from the frame front? (In other words, how deep is film in a 1980s era all-plastic Fidelity/Lisco 4x5 film holder?)
-Schaf
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Schaf,
If placing a Fresnel screen between gg and lens has solved you problem, then the camera was likely designed that way and the original gg/Fresnel sandwich lost somewhere along the way.
About measuring: you can compare the depth from the inside surface of the camera back to the ground glass with camera back to film (in a loaded filmholder) and see if they match. Different cameras have different distances; the main thing is that the film and gg should end up in the same place. Tolerance here is very small and unless you are a trained machinist and have the tools and experience to do this kind of measuring, it is usually better to do the exposure tests mentioned above.
Just FYI, here are the American Standards specs for 4x5 filmholders: For 4 by 5 holders the depth is 0.197" and the tolerance is +/- 0.007". When considering the GG depth, the nominal film thickness of .007" must be subtracted from the above figure.
Best,
Doremus
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Quote:
Originally Posted by
Doremus Scudder
American Standards specs for 4x5 filmholders: For 4 by 5 holders the depth is 0.197" and the tolerance is +/- 0.007".
Any Idea what that is in milimeters?
Re: Wide angle focus questions - front focusing -Schneider vs. Nikon
Quote:
Originally Posted by
schafphoto
Any Idea what that is in milimeters?
0.197 x 25.4 = 5.0038
0.19 x 25.4 = 4.826
:)