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Cambo owners - shimming the back

torger

Active member
My Linhof Techno review goes into depth of ground-glass precision and focusing.

Focusing a 3D landscape scene is quite different from focusing say indoor architecture, or focusing straight onto a wall or similar.

Landscape shooting f/11 can surely be done successfully with ground glass, but it is still not for everyone. I have got the sense that Joe Cornish does not really have the pixel-peep sickness like the rest of us :). I use a 20x loupe to focus my Techno and then mistakes is very rare when working with an f/11 DoF.

The largest and most damaging myth concerning modern ground glass focusing is that you should not use high magnification loupes because you then only see grain. Quite the opposite, I'd say if you don't use a proper 20x you're not maximizing the potential. With a 20x you do see some grain structure, but that does not mean that you don't see more detail. It's just like looking closely at film -- resolution is considerably higher than the largest grains.

I'd say that the 10x like Joe Cornish uses is too low magnification for safe results, I have the exact same loupe so I have tried it. If you have very good eyes it may work well though, and for scenes when you do tilting (quite frequent in landscape) it is hard to fail.

Ground glass focusing just like manual focusing with MF SLRs is something that requires training and skill, and to some extent good eyes.

It also is a bit dependent on how you look upon focus accuracy. The DoF is generally always too short to have perfect sharpness over the whole frame. Does it really matter exactly where the peak focus is? Focusing on a brick wall it surely does, but in landscape I find that in 90% of the scenes there is a quite big tolerance on focus placement, i e if you happen to miss a bit you're not really making a worse picture.

All this makes us see statements about ground glass ranging from "it is totally impossible" to "it works perfectly every time". There's no absolute truth, it's a personal thing.
 
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etrump

Well-known member
1. Cambo specifically states that shimming the back is not advised for end users. The shims are simply different thickness of washers on four contact points in combination with screw adjustments on the same contact points so they calibrate a perfectly flat plane of focus. It would be extremely difficult to achieve acceptable results outside of a lab environment. Each lens is then calibrated for infinity focus on top of that. It creates a very specific system for assuring focus calibration at infinity only. It could be me but I have found their distance markings totally useless.

2. I for one could never get accurate results using a ground glass. I wish I had the eyesight to determine real focus accuracy down to 5um. With live view, I am able to achieve 100% focus accuracy in moments without taking an exposure but rarely need to in 90% of my shots. Full frame focus is never any sharper than when you are at infinity and most of the shots posted on this site could be focused at infinity. I'm not saying 100% of the time but using mathematical focusing based on extensive testing I know for most scenes what the optimal focus will be even without checking it and which shots will be tricky enough to require focus confirmation using live view or a test exposure even prior to the fantastic workflow of the IQ series. I am sure that it would be slightly more critical for indoor architecture and even more so for product/still life photography but nothing will be more accurate than view actual pixels in the critical focus area of the frame.
 

alan_w_george

New member
Above seem tedious as compared to using GG focusing.
You've obviously never done this before...

For focus, taking the picture and viewing (100%+) it is the only "accurate" way of insuring you are on target and it's easy. When you start taking things off or sliding things around, you are never going to be as accurate as looking at the picture, I don't care how "matched" things are. A simple variable such as heat (or lack of it) can take out all that painstaking machining/shimming work.

If you shoot no faster that f8 and shorter that 90mm, a Disto D5 is more than enough. Quit obsessing and take some pictures already:)
 

Don Libby

Well-known member
Tedious...

That was part of the allure that working with a tech camera brings to me. Nothing is easy. Nothing is fast. Nothing is automatic nor automated.

I stop. See something I think I'd like to capture; a place or moment in time, a feeling. Set the tripod up still looking at what I'm about to capture - redefining it in my head as I go along. Place the camera on the tripod - still thinking. By now I've got the image in my head and all I need to do is set the camera up.

Focus the lens, cock the shutter, remember to turn the back on and remove the lens cap. Capture the image. Review it on the screen (now using the IQ160). Think about it and either move on or capture another either using a different f/stop or shutter speed or decide to do a shift movement.

Thinking all the time. Almost Zen. Tedious? Wouldn't have it any other way; but that's me.

Don
 

Guy Mancuso

Administrator, Instructor
It's a process for sure and a fun one at that. I shot with 2 Cambos and a Arca in Zion with the guys and I do miss it sometimes. That's a dangerous comment. Lol
 

danlindberg

Well-known member
Tedious...

That was part of the allure that working with a tech camera brings to me. Nothing is easy. Nothing is fast. Nothing is automatic nor automated.

I stop. See something I think I'd like to capture; a place or moment in time, a feeling. Set the tripod up still looking at what I'm about to capture - redefining it in my head as I go along. Place the camera on the tripod - still thinking. By now I've got the image in my head and all I need to do is set the camera up.

Focus the lens, cock the shutter, remember to turn the back on and remove the lens cap. Capture the image. Review it on the screen (now using the IQ160). Think about it and either move on or capture another either using a different f/stop or shutter speed or decide to do a shift movement.

Thinking all the time. Almost Zen. Tedious? Wouldn't have it any other way; but that's me.

Don
+1
Very much the same feel and workflow that I am used to. And I can definitely copy your last sentence - wouldn't have it any other way....
 

Anders_HK

Member
You've obviously never done this before...
Have not done what??? What I have done is shot on a Shen-Hao 4x5 view camera and achieved focus for a 28MP Leaf back. How good focus? Looked sharp even on SK SA 72XL and Rod 150 Sironar-N. Obvious it did not have fine adjustments for tilt and swing but I actually found the focus mechanism suffice... though obvious more crude than a helical! Yup, have done that using a 6x lupe. I also designed the custom made sliding adapter I used and it was fabricated for me by Shen-Hao. I used a Maxwell GG on it and did not end up using the adapter much because I found sliding adapter too tedious compared to 4x5 film. The gent I sold that adapter to replaced his late Mamiya adapter and said mine was better quality... go figure.

I also attempted designing tech cameras with another Chinese company but they simply would not want to understand tolerances required for digital back... thus still looking for that tech camera for my personal use. Above was mere "fun" side opportunities outside my daily job in a complete different field of engineering... :toocool:


My Linhof Techno review goes into depth of ground-glass precision and focusing.

Focusing a 3D landscape scene is quite different from focusing say indoor architecture, or focusing straight onto a wall or similar.

Landscape shooting f/11 can surely be done successfully with ground glass, but it is still not for everyone. I have got the sense that Joe Cornish does not really have the pixel-peep sickness like the rest of us :). I use a 20x loupe to focus my Techno and then mistakes is very rare when working with an f/11 DoF.

The largest and most damaging myth concerning modern ground glass focusing is that you should not use high magnification loupes because you then only see grain. Quite the opposite, I'd say if you don't use a proper 20x you're not maximizing the potential. With a 20x you do see some grain structure, but that does not mean that you don't see more detail. It's just like looking closely at film -- resolution is considerably higher than the largest grains.

I'd say that the 10x like Joe Cornish uses is too low magnification for safe results, I have the exact same loupe so I have tried it. If you have very good eyes it may work well though, and for scenes when you do tilting (quite frequent in landscape) it is hard to fail.

Ground glass focusing just like manual focusing with MF SLRs is something that requires training and skill, and to some extent good eyes.

It also is a bit dependent on how you look upon focus accuracy. The DoF is generally always too short to have perfect sharpness over the whole frame. Does it really matter exactly where the peak focus is? Focusing on a brick wall it surely does, but in landscape I find that in 90% of the scenes there is a quite big tolerance on focus placement, i e if you happen to miss a bit you're not really making a worse picture.

All this makes us see statements about ground glass ranging from "it is totally impossible" to "it works perfectly every time". There's no absolute truth, it's a personal thing.
Based on my own brief experience I much share Torger's view. However, I believe that rather than using such high magnification for focus, a better GG will substantially help. The Maxwell one I used enabled a very bright view to point of even seeing the image on a bright sunny day as long as sun rays were not direct shining onto the GG. If I understand correct Maxwell can provide brighter GG than is offered by Cambo, Alpa, Arca and Linhof, but please correct me if someone have different information. Thus seems that for tech cam it can be advisable to similar for 4x5 to upgrade to a better GG. :D


Tedious...

That was part of the allure that working with a tech camera brings to me.
Same can be said of 4x5 :D + :thumbs:


1. Cambo specifically states that shimming the back is not advised for end users.
That makes sense. This one seems like taking camera apart and attempting a fix where should not be made;

Notably the three screws on a Cambo "lens" is on the helical, provided by Schneider and should be same also on an Alpa. Those are for adjustment of the lens to the camera. Notably Cambo thus appear to adjust the camera to their tolerances per four screws at the mount for the back interface. Notably, there is no other means than the helical to adjust to the back. That seem as a weakness in the Cambo system, though it may work to adjust for also off tolerance in back and interface to the camera.

That leads to the other weakness of the Cambo system, namely there appear to be no way for user to adapt the GG to the place of the sensor in the back. Then... there seems an obvious reason it will not be very good to use such GG for focus. :facesmack:

Please do not get me wrong, no bashing, mere pointing out what I see. Any system have weaknesses, also Alpa (e.g. that they do not provide a scale for the new type of tilt adapters...).

The Cambo should work, but the above weakness makes me tad ask questions of how prices the Cambo actually is. Take the RS5000 and similar camera that have two sliding planes. How perfect are those planes to the plane of the lens (image from lens) and the plane of sensor? What about a tilt lens and its indent? How perfect parallel does that ident permit the lens to the body? Does anyone know if there are any stated tolerances by Cambo? Perhaps it works, but... how perfect? Does it work as sharp and precise as a well adjusted Alpa?

With Alpa, they permit using very thin shims to shim the back to the Alpa system. The Alpa system should (assumably) in itself be to very tight tolerances. Thus it should be possible to better (more assuringly) arrive at focus using a GG in the Alpa system. Are there indents on the Alpa tilt adapters and how perfect do they make the lens plane to the sensor plane?

For sliding, Cambo uses rails and Alpa uses roller bearing. Per my understanding roller bearings are more precise.

How precise do we need? Well, I will want to make the most from the sharp lenses...

For me, Alpa STC is very interesting indeed, and very well thought out and smart cam. However, the Cambo RS400 is lower priced, smaller and permit slight more shift. :thumbs: Also the RS5000 is very interesting because it will allow essentially digital version of 8x10!!! :thumbs:

Accordingly, I will much appreciate more info from those who have looked at accuracy of their systems for high resolving digital back. I use Leaf AFi-II 12 (80MP) and have no plan to upgrade to the iphone interface. I prefer to optically visualize an image:
1. For normal work using an optical viewfinder.
2. For tilt work:
a) maximizing DOF can be per presets on tilt scale
b) for e.g. three trees lined up 45 degree to camera using GG (this one use is similar to a Techno, the others are not)

Notably for all 1~2a&b the precise tolerances and adjustment for back and sensor plane are very important.

Anyone?

Thanks!!! :thumbs:

Best regards,
Anders
 

Anders_HK

Member
Reply from Schneider to my email questions on adjustment of tolerances;

1. On Alpa permitting 1/100mm back shim adjustments vs. Cambo adjustment of screws on Scheider helical

"Basically all remaining camera manufacturers work with the same precise tooling machinery and modern 3-d cad systems. That lead to accuracy down to less than 2/100 of a mm. At the end of the day the quality of a camera system is as good as the number of connections from lens to CCD plane because you cannot make any interface with zero tolerance."

2. Alpa vs. Schneider preciseness

"All manufacturers use shims, if they cannot readjust the tolerance by setting up the flange focal distance with the helical mount."

3. To what tolerance can the Schneider helical be adjusted?

"Less than 2/100 of a mm"

4. On Alpa sending lenses to Schneider for adjustment but Cambo making adjustments in house

"The adjustment of Schneider lenses combines a optical adjustment for the best lens performance as also an mechanical alignment for the infinity position with all the parts, tube, helical mount, shutter and lens in combination. Cambo has the equipment to to the mechanical alignment in their own factory because they have collimatiors and the tools for this alignment."



Thus, seems Alpa sending lenses to Schneider adds an optical adjustment, over Cambos adjustment. Otherwise --- assuming that a sensor is in perfect parallel plane to the image plane from a camera/lens --- then it appears that it should be possible to adjust a Cambo system using the screws on the helical to same "perfect" tolerance as an Alpa system. In fact, that seems would require the Alpa system with its joints to be no less out of tolerance than the adjustment that is made on the Cambo using the screws on the Schneider helical (which of course is also used to adjust lenses on Alpa products). The bottom line however appear to be that infinity adjustment should be at least to within 2/100mm.

A difference is also that Alpa uses sliding bearings, while Cambo uses sliding on rails. Per my understanding sliding bearings is more precise, but a question is if both in fact are are suffice and reliably such??


Regarding GG; for Alpa it is adjusted in the factory to be assumably "perfect" in tolerance with the Alpa system, thus when the back interface is adjusted using shims both the lenses and GG will be within tolerance. The weakness of the Cambo system thus appear to be if one wants to be able to focus precise also using the GG, since there appear to be no way for a user to shim it!!! Or...

-----> Does anyone know if it is possible and easy to add and subtract shims for the Cambo GG?


On another note, the new Alpa 17mm tilt/swing adapter does not appear to have a scale for the amount of tilt applied [per Alpa website product photos].

------> Does anyone know if in fact there is a scale to readout the degrees tilt/shift applied?


Thanks! :)

Best regards,
Anders
 
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