Alpa shim system, plus more questions

[Michael H. Cothran]

When employing the back shims Alpa supplies, does the pursuing back alignment only work for the lens used in the initial calibration, or will back accuracy remain true if one changes lenses? Seems to me that it would only be good with the initial lens, which , in turn, would relegate the system into a one-lens camera. Just curious.

With the 12 STC model, can you rotate the DB vertically, and still pan laterally?

Thanks.

[D Semick]

Hello Michael,

Once you shim the back, you're good to go.

For optimum results you should use a lens in the range of 70mm. Schneider and Rodenstock are mounting and properly calibrating the lenses. The precision employed at these factories are quite impressive. The calibration of the back is what ties the whole system together cleaning up any variances within the already precise tolerances used by ALPA and the digital back manufacturer.

Denny

[rljones]

I agree with Denny's comments. You want to shim with a longer lens and once done, all other Alpa mount lenses with work fine. The precision of each lens is why each one cost so much.

I use a Rodenstock 35, 60 and 100. I start with the 60 and verify with the 100. The other important aspect of shimming is to made certain your target is far away to ensure true infinity focus. Anything closer than about 5 miles is difficult for the 100mm, so I go to a hilltop and use targets 7 to 10 miles distance. (I learned this through the very patient tutelage of Jeff Hirsch at FotoCare in NYC.)

[dchew]

Regarding your second question, you can indeed rotate the back 90 degrees either way and shift laterally.  So you can shift the back in either the landscape or portrait orientation.  You can of course also mount the camera 90 degrees clockwise (from the back of the camera) which gives you rise and fall, also either in the landscape or portrait orientation.

Dave

With the 12 STC model, can you rotate the DB vertically, and still pan laterally?

[TH_Alpa]

Michael,

I would add to the comments already made, that IF it happens that after shimming your back you do not get precise focus with another lens, I suggest you to let this lens be calibrated by the manufaturer: It will certainly be out of tolerances.

Best regards
Thierry

[theguywitha645d]

Michael,

I would add to the comments already made, that IF it happens that after shimming your back you do not get precise focus with another lens, I suggest you to let this lens be calibrated by the manufaturer: It will certainly be out of tolerances.

Best regards
Thierry

By "manufacturer," I assume you mean Alpa. Do you send the body and shim in with the lens to be collimated? How does this work? I am just interested...

[TH_Alpa]

No, to the manufacturer of the lens, respectively where you bought the lens: they are the ones responsible for after-sales services, repairs and support.
Well, I guess each lens manufacturer has his own procedure to calibrate their lenses to infinity and in general. It doesn't need the camera for that.

Again, it's with a calibrated lens that the shimming is done, and this shimming will be valid for any calibrated lens. The shimming is done not to compensate on an un-calibrated lens but to compensate a misalignment of the sensor.

Thierry

By "manufacturer," I assume you mean Alpa. Do you send the body and shim in with the lens to be collimated? How does this work? I am just interested...

[henrikfoto]

Hi Thierry!

Is there any difference between the different backs when it comes to misalignments?
Does any brand have more of this problem than others?

Henrik

[TH_Alpa]

Not that I would know. It can happen with any, and for different reasons: out of factory, misalignment due to a shock, ....
All I know is that it is a fact, more than what one would expect.

Thierry

Hi Thierry!

Is there any difference between the different backs when it comes to misalignments?
Does any brand have more of this problem than others?

Henrik

[rljones]

Henrik,

I had a few Sinar eMotion backs (loaner during repairs, etc) along with a couple of Phase P65+ backs and now an IQ180. Each one was unique in shimming requirements on the Alpa. The Alpa was consistent within the various lenses, but the backs each varied. The difference within Phase backs was around 0.1mm (one was re-calibrated by Phase and when returned, required re-shimming by 0.1mm); the Sinar to Phase was over 0.2mm and Sinar to Sinar over 0.2mm as well. So in my limited samples, Sinar seemed to have more variation than Phase.

So, anytime a back is changed, the Alpa will need re-shimming for optimum infinity focus.

[Smoothjazz]

If you have the IQ back, doesn't that reduce or eliminate the need to shim, since you are viewing a live focus image? I am very curious about this, as I am about to but an IQ back prescisely for this reason; my hope is to avoid the whole need to shim.

[john milich]

with the IQ, you can use focus mask to check what parts of what you just shot were in focus and adjust for your next shot. 
If for some reason your back/sensor bit too far away from ideal you will not ever know it, except when you bump up on the inf stop and find inf is not in focus

[dchew]

For me it does not. I am not a live view expert yet.  But from what I've tried so far, the most reliable procedure is to measure distance with the Leica Disto, then set the distance with the HPF rings.  Live view is pretty finicky still.  If it was live view like a dslr, you would be essentially correct except for infinity.

Others have reported good results using live view for focus. For me the disto/HPF process is quicker and more reliable.

Dave

Edit:  I agree with John; I think focus mask is at least as valuable as live-view for focusing.

If you have the IQ back, doesn't that reduce or eliminate the need to shim, since you are viewing a live focus image? I am very curious about this, as I am about to but an IQ back prescisely for this reason; my hope is to avoid the whole need to shim.

[TH_Alpa]

"rljones", thanks to confirm with more practical and in-situ experiences than necessary what I am trying to explain here and on other places and what Alpa has said since years now.

At that time, years back, Alpa was often criticized as being introducing "shimming" for marketing purposes or that they were going much too far concerning the needed precision, still today. Some even laughed at it, including camera manufacturers, including the company I worked for and including myself. In fact it was already important and relevant for pixel sizes of 12 micros (with the 22 MPx sensors), and it becomes obviously even more dramatic and necessary now, when using sensors with pixels around 5 micros.

I think everybody wishing maximum precision with his tools should understand that it is not only a digital back from time to time which is out of the required tolerances, but it happens with almost each DB that there is such an out of alignment of the sensor. It is not to put the gun on DB manufacturers, nevertheless it is a fact which came as a conclusion when Alpa tested their cameras with the different DBs available.

It actually doesn't happen that often that one changes a back, or that one has 2 or more: in this case one can take a second adapter correctly shimmed for the corresponding back. It will cost a bit more, but gives convenience and maximum possible precision. Beside, shimming a back is done in less than an hour and needs to be done once only.

What is sure is that only a correct shimming will give the maximum possible precision, and that it is not the Alpa cameras which need to be shimmed, nor the lenses in Alpa-mount, but the digital backs themselves. Alpa simply allows to get the precision such sensors and lenses can give when calibrated correctly. And that is possible only with shimming.

And here again the way the shimming is done and how easy it is, have a look at the videos:

Alpa Adjustable Back Adapter

Thierry

Henrik,

I had a few Sinar eMotion backs (loaner during repairs, etc) along with a couple of Phase P65+ backs and now an IQ180. Each one was unique in shimming requirements on the Alpa. The Alpa was consistent within the various lenses, but the backs each varied. The difference within Phase backs was around 0.1mm (one was re-calibrated by Phase and when returned, required re-shimming by 0.1mm); the Sinar to Phase was over 0.2mm and Sinar to Sinar over 0.2mm as well. So in my limited samples, Sinar seemed to have more variation than Phase.

So, anytime a back is changed, the Alpa will need re-shimming for optimum infinity focus.

[henrikfoto]

If shimming is vital to get the absolute perfect focus, why is it that cambo, linhof, arca etc. are not offering this?

It shouldn't be hard and the shimmengrings are easy to find.

Anybody have an idea?

Henrik

[dchew]

I don't know about Linhof, but Cambo offers to adjust their camera, you just need to send it in to do it.  There are some descriptions on the web about how to do it yourself.  I've never done it, but I think Cambo uses set-screws.

Arca has a different approach, essentially calibrating the helical instead of shimming the back.  The Arca advantage is that it calibrates each lens.  Disadvantages are I am not sure how it adjusts for infinity, and some feel focusing is a more cumbersome process (I suspect you get used to whatever process you adopt...).

Dave

[rljones]

There are comments about live view and histo measuring, etc. but these have noting to do with shimming. The only purpose of shimming is to obtain optimum infinity focus. Specifically, if your back is 'over-shimmed', then you cannot focus at infinity: it is as if you have a small extension tube on your lens. You can certainly focus close (and use your histo or live view to do so) but you cannot physically focus at infinity, no matter what aids you employ. You must reduce the distance by reducing the shims, effectively removing the 'extension tube'. (Admittedly, if the over-shimmering were small, and you stopped down sufficiently, you could get better focus by using what amounts to hyper-focal focusing.)

On the other hand, if you are under-shimmed, then you can focus 'past' infinity and here, your favorite focus aid, will help.

I typically found that most backs were 'over-shimmed' from the factory, and required re-shimming to get sharp infinity focus. And in the case where your back was not parallel (and this must truly be rare), you could differentially shim the corners or edges to create a flat (planar) focus. I've never seen a need for this in my backs.