Alpa shimming process - tips?

[tylerallenmohr]

Tyler,
We are talking about shimming the camera (actually the adapter between the camera and the DB), not the DB itself. All this is much less important on a back that has live view.

Dave

Thanks for pointing that out Dave. I bought the IQ250 second hand and haven't had much chance to use it yet. Sadly, this Minnesota winter is continuing well into April. Do you think since it has the CMOS/Live view I even need to be concerned with shimming the camera? I plan to use live view most of the time.


~ Tyler

 

[narikin]

Thanks for pointing that out Dave. I bought the IQ250 second hand and haven't had much chance to use it yet. Sadly, this Minnesota winter is continuing well into April. Do you think since it has the CMOS/Live view I even need to be concerned with shimming the camera? I plan to use live view most of the time.


~ Tyler

Just to point out the obvious here: this is a shimming process for matching digital backs to *ALPA* cameras. If you are not using Alpa, this does not apply!

 

[tylerallenmohr]

Just to point out the obvious here: this is a shimming process for matching digital backs to *ALPA* cameras. If you are not using Alpa, this does not apply!

• Alpa TC
• IQ250 back
• Rodenstock 23 HR

Bought the various components over the winter individually and have just been postponing any calibrations. Test images look good, but haven't really gotten a sense of how things look at infinity and if I should worry about shimming or other things. That part is all new to me.

Thanks to everyone for all the info in this thread.

 

[narikin]

• Alpa TC
• IQ250 back
• Rodenstock 23 HR

Bought the various components over the winter individually and have just been postponing any calibrations. Test images look good, but haven't really gotten a sense of how things look at infinity and if I should worry about shimming or other things. That part is all new to me.

Thanks to everyone for all the info in this thread.

Wow, with a 23mm, it's barely required - that lens has so much d-o-f, critical accuracy is really not required.
Just saying, YMMV.

 

[dchew]

Do you think since it has the CMOS/Live view I even need to be concerned with shimming the camera? I plan to use live view most of the time.


~ Tyler

I agree with Narikin; That lens has a very wide DoF. Even with other lenses shimming will rarely, if ever, make a difference if you have live view. Most of us are on a tripod at f-stops in the 8-16 range making it even less necessary.

As I mentioned earlier, I do it because there are times I am shooting when it is pretty dark out, like the blue hour. Live view in those situations can be a bit frustrating for me. I like to know infinity is infinity on all my lenses. Maybe it is my Linus Blanket...?

Dave

 

[algrove]

Yes, indeed!

I suppose it is worth mentioning the quick way to ensure no lenses are front focused on the Alpa: just go into the adapter and remove about 0.10mm of shims.

Abracadabra, all your lenses will now focus beyond infinity.
:thumbup:

Dave

So do I need a beer to remove 0.10 of shims? (BTW is it actually that simple?) Or better yet, should I have a beer for each corner screw removed on the adpater? And then celebrate with 4 more once each corner screw has been replaced. Now I first need to make a beer run before starting this delicate procedure.

 

[dchew]

So do I need a beer to remove 0.10 of shims? (BTW is it actually that simple?) Or better yet, should I have a beer for each corner screw removed on the adpater? And then celebrate with 4 more once each corner screw has been replaced. Now I first need to make a beer run before starting this delicate procedure.

Yes, yes, yes and yes.


If I was going to do that, I would shoot a target first and see where it focuses. Remove the back, remove the 0.10 shims and reassemble. Mount the back again and see the difference just to be sure you are happy with the difference before going out to shoot something.

Theoretically you will have to rotate the helical to focus closer about 3 degrees after removing the shims. That should be enough for almost every situation.

Removing shims is indeed pretty easy. The hardest part is judging which shim is what size, but even that is pretty obvious except for the really thin ones, like < 0.03mm. Also, make sure they are all oriented squarely in place before you button it back up. Damaging a shim isn't the end of the world, but you would rather not have to deal with that.

Dave