DOF and Infinity focus on Cambo Wide RS Camera

Questions, comments and suggestions regarding Phase One IQ4, IQ3, IQ2 and IQ1 series digital camera backs.

DOF and Infinity focus on Cambo Wide RS Camera

Postby Rudgey » Tue May 08, 2018 2:57 pm

I wonder if anyone has experienced this?

I have just purchased a Combo Wide RS camera with a Schneider App-Digitar 47mm XL lens using it with a Phaseone IQ150 50mp back.

The problem I am having is with the depth of field scale on the helicoid mount. Normally I would set the infinity to the f stop on the right of the scale to get the maximum DOF, however when I set this to the mark, say f11, I cannot achieve infinity focus. In fact the only way to get infinity focus is to set the infinity mark to focus point? Reducing the hyperfocal distance.

Is this this the case with digital backs on this camera? if so, why are the DOF f stops marked out f5.6- f32 in both directions on the helicoid focus mount?

I phoned my dealer in the UK who told me digital backs tend to work best between f8- f11 but was not sure about the DOF issue, hopefully someone can help me before my next shoot?
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Re: DOF and Infinity focus on Cambo Wide RS Camera

Postby mkphotomedia » Tue May 15, 2018 6:32 am

Seems to be common to have the DOF scales on the Cambo lenses be slightly (to thoroughly) miscalibrated as to where the infinity point is. My Sch35 is bang on (but it's been factory-serviced recently); my Sch43's mark is off by about a stop; and my Sch72's mark is off by about 2 stops (and I should really get it serviced, but I tend never to use it at HFD anyhow, so...).

Since you're in Europe, you could probably have Cambo recalibrate your helical. Not sure how long/expensive that is, since mine was done as part of a general servicing awhile back.

You can figure this out empirically by setting the camera up on the end of a long table or railing with a series of marked targets (or several meter sticks), and a reasonable view of some fairly contrasty object in the far distance. Set yourself up for tethered capture so you can zoom in to 100%, and then figure out where the point of hyperfocal distance at each marked aperture is for each of your lenses. Mark that offset on your barrel with a bit of white paint or a label. You *should* find that the offset is constant across all your apertures, once you find it for one.

Your dealer is correct that your best overall diffraction-limited sharpness will be in the f/8-f/11 range.
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Re: DOF and Infinity focus on Cambo Wide RS Camera

Postby Rudgey » Tue May 15, 2018 10:48 am

Thanks for the advice, I would like to get the max DoF of this lens at F8-F11, but can only get the nearest DoF range, not distant, if that makes sense.
If I place infinity on anything but the focus mark, Infinity is out of focus a bit, even if I stop down to f22. In other words, I cannot place infinity along the DoF range, Its like a fixed lens.

I like your idea of a test, Cambo said the DoF scale may not be calibrated to the latest Phaseone backs which have much smaller pixels than the older backs when this lens came out. However, my understanding of photography the DoF should have nothing to do with what the image is projected onto, film, sensor... whatever??

They also said the lens and H mount come complete from Schneider, maybe I should contact them, anyone have a contact?
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Re: DOF and Infinity focus on Cambo Wide RS Camera

Postby ben_US » Tue May 15, 2018 2:30 pm

Rudgey wrote:I like your idea of a test, Cambo said the DoF scale may not be calibrated to the latest Phaseone backs which have much smaller pixels than the older backs when this lens came out. However, my understanding of photography the DoF should have nothing to do with what the image is projected onto, film, sensor... whatever??


The DoF will be relatively shallower with an increase of resolution or decrease of pixel size. If you can see more detail, you can see where the apparent sharpness begins to fall off; clearer boundaries for the edges of the DoF.
Please make a support case for Technical Support with Capture One software:
http://support.phaseone.com and click on Contact Support, then select Technical Support.
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Re: DOF and Infinity focus on Cambo Wide RS Camera

Postby Rudgey » Tue May 15, 2018 2:56 pm

ben_US wrote:The DoF will be relatively shallower with an increase of resolution or decrease of pixel size


That's interesting never experienced this but it makes sense. I wonder how Sch & Rodenstock deal with this? It would mean lens DoF would change as new back come out with more MP?. What do most people do ? not use the scale and preview each setup.
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Re: DOF and Infinity focus on Cambo Wide RS Camera

Postby NN635295556271985100UL » Wed May 16, 2018 9:42 am

According to the Lumariver DOF calculator the hyperfocal distance of your lens and DB combination at f11 is 13.3m - giving a range of 6.69m to infinity.
If you can't achieve this DOF at the above settings it sounds possible that the camera body needs re-shimming to ensure that the lens DB distance is correct.
It sounds like you can't focus on infinity so shims need to removed (at least I think it is that way round) to shorten your lens to back distance. It's a trial and error process taking photos at max aperture with the lens set on infinity and checking the sharpness of objects a (very) long way off.
I only have experience with an Alpa STC and IQ3100 so can't be sure this will all work on The Cambo but hope that it helps.
As others have said, the DB will be far more critical of focusing errors but it's well worth the effort to get it right!
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