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Thread: OOF film with new ground glass

  1. #1

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    May 2006
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    OOF film with new ground glass

    I just got back around 12 rolls of film shot in 6x12 format that are 95% out of focus, and i've also developed my 4x5 BW from the same trip and they are also out of focus. All film was shot on a homemade field camera (6x12 with a roll back).

    The back on my homemade camera is actually a Toyo monorail international back that has been mounted onto a wooden frame.

    I'd been using this homemade camera for 8 months or so successfully until I recently broke the ground glass. I replaced it with ground glass from a old speed graphic and shot a coulple of rolls of film and the odd 4x5 and had no problems, though I found the speed graphic's ground glass significantly darker than the previous Toyo one. I recently bought a Sinar back off ebay (same as this one: http://cgi.ebay.com/Sinar-P-4x5-Film...QQcmdZViewItem )
    This is for another project, but in the meantime I took the ground glass out of this back and installed it in my current camera to replace the speed graphic glass. I didn't test this new setup before my last trip, but didn't see any reason why the camera would perform differently with this new ground glass (other than hopeing for a brighter image)

    The only other thing I changed in my shooting technique was I used a Toyo GG magnifier which I recently bought instead of a cheap loupe that I'd been using previously (the cheap loupe was higher magnification, and cost around $8). I found the Toyo much better to use - I could see closer to the edge of the frame as have a smaller diameter than my older loupe, and the whole circle was in focus, where as my old loupe only the centre was in focus, so it was hard to check the edges of the frame.)

    I'm pretty sure it's not user error as although I still get shots that aren't always sharp from time to time with focusing errors, I never get 95% of out of focus - especially with the roll film stuff as a lot of my 6x12 stuff is often just infinity focused anyway. Most stuff I get that is out of focus is when I've used tilts or swings and haven't got the focal plane quite right.

    Some of the shots have in focus areas - mostly the ones I'd set up with tilts. I'm sure that these infocus areas did not match what I was seeing on the ground glass when I set the shots ups (for example in focus foregrounds but out of focus infinity which I was sure was sharp on the ground glass).

    I'm at a bit of a loss to what may have happened here - the alignment between the ground side of the glass and the film plane should not have changed as there are no shims to be adjusted on the toyo back, just two clips that hold the glass onto the frame that are tightened be screws. The glass is installed with the ground side facing the lens.

    I'm going to do some test shots with some polariods when I get the time (in the next week or so) but I'd be interested if anyone can spot what the problem may be.

    Tim

  2. #2
    Donald Qualls's Avatar
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    Re: OOF film with new ground glass

    Did the original Toyo glass have an incorporated Fresnel? If so, you'd need to shim any plain ground glass, or possibly install it backward, to have it match the focus of the original. However, if the Speed Graphic was a plain glass (probable, since you mention it was dim), and the Sinar glass is as well, one ought to be as good as the other unless you had the Speed glass in backward without realizing it...
    If a contact print at arm's length is too small to see, you need a bigger camera. :D

  3. #3
    Robert A. Zeichner's Avatar
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    Re: OOF film with new ground glass

    It sounds as though you are using a back that was designed to have a Fresnel brightening screen installed between the gg and the lens. This is not an uncommon problem. Fresnels shift focus rearward by approximately 1/3 of the thickness of the screen. When you remove it, the position of the gg will not coincide with the film plane. A similar problem occurs when a user installs a Fresnel in front of a gg on a back that was not designed for such a configuration. You need to find out how your back was designed to work and replace the missing piece or remove the exta piece.

  4. #4
    Dave Karp
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    Re: OOF film with new ground glass

    My Crown has a Fresnel between the groundglass and the lens and the image on the glass is quite bright. My guess is that the Speed was supposed to be the same, so Robert is probably right.

  5. #5

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    Re: OOF film with new ground glass

    Thanks for the responses -

    When the original Toyo ground glass was in the back (before it shattered) everything was fine. There was no frensel ever installed, it least I don't think so - I've never used one, but it is a separate entity from the ground glass yes? When the original ground glass shattered there was no separate peices that I could see, and as I mentioned I installed another ground glass from my Speed Graphic and the images using that were fine. I'm pretty sure that I had installed the Speed's GG the correct way up as I have drawn some guide lines on the smooth side of the glass, and that was facing outwards. It has only played up since I installed the Sinar ground glass and been using the Toyo Loupe.

    Tim

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