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Gaoersi 617 infinity focus probs
Kind of a rookie with pano and large format lenses. Just bought a older Gaoersi body, installed my Fuji 90/8, and then discovered it won't focus at infinity. The focus mechanism is all the way in and it is beyond me how anything could be adjusted to get it closer. Hence, am I correct in that it has something to do with flange distance? The camera measures up at 102mm and I'm afraid my Fuji needs shorter than that. Any advice, including which lenses might work, would be greatly appreciated. (Seller wasn't sure what lens used to be on the camera, thought maybe a Super Angulon) Roger in Michigan
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Welcome to APUG.
The Gaoersi like other 617's with interchangeable lenses uses different lens cones for each focal length. So firts you need to make sure you have the correct cone. I have a first series Gaoersi and a cone set up for a 90mm Grandagon so can measure that for you. When I bought my camera they asked what lenses I was going to use and then set my cone specifically for them.
I will go get the cone, finding a ruler may be more difficult 
Ian
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Easier than I thought, the overall distance of the cone on its own when at Infinity is 6.5cm, and when fitted to the camera approx 10.3cm, so it sounds quite similar.
You should be able to find data sheets for the Fuji and Super Angulons and they will tell you the flange distance needed at Infinity, Gaoersi themselves can tell you how to adjust the cone if necessary I've always found them very helpful.
Ian
Last edited by Ian Grant; 06-02-2009 at 11:36 PM. Click to view previous post history.
Reason: typo
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Does it seem far off infinity when you get to the lock point?
In other words, is the furtherest point of focus far from the camera? Given the majority of shooting with this camera is with f16 and above (seeing you have the f8, not the f5.6 lens, I'm assuming that you're not after speed for hand held sooting), you may have a focus distance clode to the hyperfocal distance. If so, forget about infinity and shoot away!!
While you're looking for the data page that Ian suggested, also look for the page with hyperfocal distances for your lens as well. Even if you fix your issue, this information will be vital for any future shooting with this lens/camera combo. I have all of my lenses' HF and DOF data on a simple spreadsheet on my iPhone. I can't stress the importance of using HF over infinity!
Lachlan.
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Thanks for your comments so far. I am learning more about the importance of flange distance with fixed mounts, something my 4x5 never insisted upon. Anyway, via a test roll, it appears that acceptable sharpness arrives at f32; workable, but not convenient. The DoF charts along with using HF are things I'm familiar with, but I'd like to be a little closer to the ball park. At this point, I think the solution is a different lens as opposed to a new adapter for the camera. (easier to sell a lens than an adapter) I'll try to post again when things are working, or I hit another dead end. Thanks again!
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Two last thing (although I doubt either will be the case):
1) Check that the shutter is touching the helical mount (i.e. not sitting out a mm or two). There isn't a second retaining ring on the thread? You haven't cross-threaded the ring? It seems that you are very close with this lens (given the closer to infinity you focus, the less movement is required).
2) Have you got the right hole size for your shutter? Again, if the hole is too small, the lens cound be sitting off the mount.
Both seem too trivial to be right, but it's hard to tell without seeing the actual item.
Lachlan.
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102mm camera FFD
 Originally Posted by rvarland
Kind of a rookie with pano and large format lenses. Just bought a older Gaoersi body, installed my Fuji 90/8, and then discovered it won't focus at infinity. The focus mechanism is all the way in and it is beyond me how anything could be adjusted to get it closer. Hence, am I correct in that it has something to do with flange distance? The camera measures up at 102mm and I'm afraid my Fuji needs shorter than that. Any advice, including which lenses might work, would be greatly appreciated. (Seller wasn't sure what lens used to be on the camera, thought maybe a Super Angulon) Roger in Michigan
The camera's 102mm set up is appropriate for three different Schneider Super Angulons... the SA 5.6, SA 6.8 Classic, and SA 5.6 XL... all big and heavy lenses. All the other 90's, by an maker, have shorter FFD's, and will not achieve infinity focus.
Shooting @f32 will bring more into (better) focus, but the lens is probably diffraction limited at f16 (maybe f22)... so you are paying a big price in image quality.
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Originally Posted by Lachlan 617
Aren't these the same folks who's review of the Epson V700 have it running neck and neck with a drum scanner?
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Originally Posted by fotoman
Shooting @f32 will bring more into (better) focus, but the lens is probably diffraction limited at f16 (maybe f22)... so you are paying a big price in image quality.
Large format lenses are normally designed and optimised for use at f22, they are not diffraction limited to f16, and are still very usable at f32 and in many cases f45. You only need to read data from Zeiss, Schneider & Rodenstock etc and use lenses at these apertures and make large prints to see this statement isn't true.
This goes back to the Tessar design where edges and corners aren't sharp until f22, which is the recommended aperture given by Carl Zeiss & later Doctor Optic. Lenses like the late production f5.6 150mm Xenar stop down to f64 annd are excellent at f32. Sometimes the effects of diffraction are over-hyped and the very small decrease in image sharpness in the centre has to be traded off against an increase at the edges and also far greater DOF. In most cases it's the last marked aperture that begins to suffer diffraction, and you'd have difficulty seeing any drop in quality in a print, but of course it can be measured on an optical bench, or by examining negatives of test charts with a microscope.
Ian
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