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Schneider 72mm Apo Digitar Focus Shift when stitching??

Viewmaster

New member
Hi all,

Quick update. I believe Audii might be correct. The front and rear standards are out of alignment. I put some engineering calipers on the camera and did some measurements and it appears to be out. Not by much, but enough so that when you are shifted to one side, it could amplify the problem. I also redid my tests with a second longer lens, and did a side by side comparing with the 72 in the same scene, and sure enough, it goes out in exactly the same way. It was just harder to see since due to the image magnification in the longer lens I didn’t picking up on it when I first got the camera. The wider 72 makes it a lot easier to see there’s a problem.

Not sure what a good fix is as it appears to be in the manufacture/assembly of the camera itself, but am looking into it.
 

vjbelle

Well-known member
I have used my Cambo Actus for quite awhile and have two front standards neither of which can claim 'true zero' by etched numbers. However I find the Cambo approach to this much better than having a 'Detent' which Arca Swiss uses which could also be off and would be very difficult to bring to the true 'zero' position. Cambo chose to use a 'play mechanism' which allows for a very fine tuning to find true 'zero'. I have also found that the fastest and most accurate method is to use machinists levels such as Starrett No. 98 levels which fit/work perfectly along the front and rear standards. There is sufficient room on the front standard lens plate for placement of the level for accurate readings. This can all be accomplished way ahead of time and as long as the front standard isn't moved you should remain in alignment for some time - although I always check alignment the night before going out on a shoot. Its amazing how little off the swing can be to cause some focus anomalies.

Victor
 
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Audii-Dudii

Active member
Not sure what a good fix is as it appears to be in the manufacture/assembly of the camera itself, but am looking into it.
What I did that helped, but did not solve, the problem was to tighten both the friction of the tilt and swing mechanisms so they didn't move as easily.

Unfortunately, this also has the effect of making them more difficult to use precisely, because with the increased effort required to rotate the adjusting knobs, it's easy to overshoot the amount of movement that you apply.

I had assumed that I was mostly the cause of this problem, because I carried the camera on a tripod over my shoulder while walking several miles on each outing and it was bouncing around a lot as a result.

But given that you're experiencing similar issues, now I wonder about that...

Fortunately, it's now moot for me, because I'm using a modified Cambo WDS instead. But there are times when I'd like to have tilt-and-swing movements available again... <sigh>

Do post back with your solution, if/when you find one, so others will benefit from it. :D
 

tjv

Active member
It's interesting, I've never noticed any parallelism issues with my Linhof Techno. I guess as it only has rise / fall on the rear it's a little easier to keep plum?

I will say that when I handled an Actus in a shop a while back, I wasn't impressed by its rigidity and precision. Not to say it's a bad setup–I quite liked it overall–but I thought for the money it should have been more solid.
 

PhiloFarmer

Member
Help me out here...

Why would anyone want to "stitch" images that were out-of-perspective?..... (front-standard movements...shift or otherwise...)

Or..similarly...why would anyone want to "stitch" images that were out-of-geometric-congruence?.... (rear-standard movements...shift or otherwise...)

If one wants to stitch "equivalent" images in either perspective or geometry...using a "sliding-back" accomplishes this nicely, without any distortion. You're using the full IC available...and choosing where to limit your "overlap."

Educate me......why use distorting "camera-movements" instead of a "sliding-back?"
 

Gerd

Active member
Help me out here...

Why would anyone want to "stitch" images that were out-of-perspective?..... (front-standard movements...shift or otherwise...)

Or..similarly...why would anyone want to "stitch" images that were out-of-geometric-congruence?.... (rear-standard movements...shift or otherwise...)

If one wants to stitch "equivalent" images in either perspective or geometry...using a "sliding-back" accomplishes this nicely, without any distortion. You're using the full IC available...and choosing where to limit your "overlap."

Educate me......why use distorting "camera-movements" instead of a "sliding-back?"

Viewmaster has the Actus Mini (as it turned out in the course of the post). The Actus Mini can not shift at the front standard. The Actus Mini can only be used on the back standard for shift and it can not be mounted a sliding-back.

When shift with the Back Standard, there are no perspective error. This is exactly the same as using a sliding-back.

You could now only discuss whether a sliding-back is more precise.

As it looks like, Viewmaster has zero point alignment problem. At the Actus, the zero point grid all have a slight movement (that's the same with my Actus XL/DB).

Greeting Gerd
 

PhiloFarmer

Member
Ah..."precision"...there's the "rub!"

Technically one could "shift" the rear-standard, and then "refocus"...and hope to regain a similar "appearance"...but in real-life...shifting the rear-standard always results in a differing geometry (not perspective...that's front-standard shift).

The distance between the rear-optic of the lens and the sensor-plane evidently changes enough to require "refocusing" to correct. With my Sinar P-2 I can move the sliding-back and not experience optical interference with the bellows.Shifting with the rear-standards, I sense that the bellows creates an optical distortion before I reach the limits of the IC. Silvestri similar...although not as much overlap within the body of the bellows...so the distorting effect is greater there.

I've failed at this many-many times......!!...15mm shift with rear-standard = distortion...15mm shift with sliding-back = no (or very limited) distortion.

Cheers.......
 

Audii-Dudii

Active member
Technically one could "shift" the rear-standard, and then "refocus"...and hope to regain a similar "appearance"...but in real-life...shifting the rear-standard always results in a differing geometry (not perspective...that's front-standard shift).
I confess to not understanding the point(s) you've been trying to make in this thread.

I'm no expert, to be sure, but I do have a degree in Mechanical Engineering (although I've never worked a day in my life as an engineer) and so far as I'm aware, the camera or digital back doesn't know or care how it was shifted, whether by shifting the rear standard or via a sliding back.

In fact, in my experience with view cameras large and small, new and old, both methods are pretty much equally likely to cause issues with alignment relative to the front standard, especially considering the precision that's required to get the best results from today's high-res digital sensors, however they are packaged.

Although I do wish I still had tilt and swing movements available on those occasions when I would use them, this is the reason why I switched from using an Actus with my A7R to using a modified Cambo technical camera and haven't looked back.

What am I overlooking or missing here???
 

PhiloFarmer

Member
I think we're just "talking-past" each other. We both have "scientifc" backgrounds...your is engineering...mine is physics. But...together, we're both photo-folks.

Technically (optically...) you are correct...the geometrical "shift" at the rear standard should not be different from the sliding-back.

But...in my experience...it is. Whether it's mis-alignment between front-rear standards...interference by the bellows...or Gremlims. The "explanation" doesn't seem to change the "facts," as I experience them.

That's all I'm saying.....

We can debate the "technicalities" till the cows come home.

In the end...it's the image that counts. If there is any deviation....it shows....

The curiosity in my original reply involved asking the question why anyone would use the "standards" to "shift"...rather than using a "sliding-back." For some systems (like the Actus...) there is no sliding-back available. I know this. That's one of the reasons I do not use that system. I have sliding backs for my Sinar as well as my Silvestri....I get better results.
 

TimoK

Active member
I think we're just "talking-past" each other. We both have "scientifc" backgrounds...your is engineering...mine is physics. But...together, we're both photo-folks.

Technically (optically...) you are correct...the geometrical "shift" at the rear standard should not be different from the sliding-back.

But...in my experience...it is. Whether it's mis-alignment between front-rear standards...interference by the bellows...or Gremlims. The "explanation" doesn't seem to change the "facts," as I experience them.
The curiosity in my original reply involved asking the question why anyone would use the "standards" to "shift"...rather than using a "sliding-back." For some systems (like the Actus...) there is no sliding-back available. I know this. That's one of the reasons I do not use that system. I have sliding backs for my Sinar as well as my Silvestri....I get better results.
If I put me into this, I'm not "scientic" any way, nor engineer or physician. I'm only a photographer with some kind of "artistic" orientation.
But I use Cambo Actus mini with Canon 6d body for my "artistic" goals, most often for landscape photography. And what I have not seen is any distortion from shifting the rear standard. There is possibly some shadowing, from bellows, at the center side of a 20mm shifted shot, but I did not call it distortion.
It is possible that rear and front standards of Actus are misaligned when shooting, but I see it more an "user error" than a camera error.
I wonder if shifting Actus's rear makes misalignment or focus shift or other that kind of issues, theres some part loose in Actus or something wrong in your workflow. I don't disagree with Audii-Dudii, because he has experianced both systems: Actus and sliding back, but my experience is that Actus is very much useful a camera in sthiching shifted shots.
 

TimoK

Active member
My workflow when shooting with Actus:
First I put all settings to zero: tilt, swing: shifts. Then I try to composite the final photo with moving the camera, shifting the rear from side to side. When I think i've found the shooting point and direction, I focus, then look if I need the front movements, tilt or swing or both. If so, I try set those in the best way, usually looking the center shot, but sometimes I have to shift the rear to look the sharpness at the whole (becaming) picture
When shooting I always start from center shot. I set the rear standard to center, lock it, check the focus, take a shot. Then I move the rear, most often 10mm into some direction, lock it gently, took the shot and so on. Always I lock the rear standard before shooting.
Here is my example: 5 vertical shots, Actus, Canon 6d, Hbl Distagon 50mm cf fle, around 1 degree tilt (if my memory serves)

No, I can not insert my image, but I have done it before, I'll look ...
Edit: It's easier to give a link: Fun with 35mm Camera images
 
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Gerd

Active member
Hello PhiloFarmers,

Enclosed a test picture with my Sinar P2, Sironar-N 210mm F5.6 MC, a 645Z as digiback and a sliding back. The sliding back was in zero position and was not used. Instead, the rear standard was used for horizontal and vertical shifts.

The picture consists of 16 shots



Under the following link you can zoom in on the picture and have a close look at it. LINK:

Shifting the back standard changes the perspective. But the perspective of the pictures among each other remains in the right proportion. There is no perspective error.
It makes no difference if a horizontal row in this picture was taken with the sliding back.
But what you always see that the edge performance of the lens is worse.

The picture was taken with the Actus XL, a Schneider & Kreuz after Apo Symmar 5,6 / 120 mm and the Fuji GFX 50s, Acros RAW Profil.
The picture consists of 12 shots.

Only the rear standard was used horizontally and vertically to shift.




Greeting Gerd
 

Gerd

Active member
Hello PhiloFarmers,

Enclosed a test picture with my Sinar P2, Sironar-N 210mm F5.6 MC, a 645Z as digiback and a sliding back. The sliding back was in zero position and was not used. Instead, the rear standard was used for horizontal and vertical shifts.

The picture consists of 16 shots



Under the following link you can zoom in on the picture and have a close look at it. LINK:

Shifting the rear standard changes the perspective. But the perspective of the pictures among each other remains in the right proportion. There is no perspective error.
It makes no difference if a horizontal row in this picture was taken with the sliding back.
But what you always see that the edge performance of the lens is worse.

The picture was taken with the Actus XL, a Schneider & Kreuznach Apo Symmar 5,6 / 120 mm and the Fuji GFX 50s, Acros RAW Profile.
The picture consists of 12 shots.



Only the rear standard was used horizontally and vertically to shift.


Greeting Gerd
 
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PhiloFarmer

Member
Hello Gerd,

Obviously you are a better photographer than I am!

Keep up the good work.....

Art is an adventure...without borders....
 
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