How to calibrate split-prism focusing screen to DSLR?

[996gt2]

I recently purchased a cut Minolta split-prism focusing screen for my Canon 40D from Alex here at MFlenses, and it just arrived yesterday. However, after I installed it, I noticed that the Minolta screen was thinner than the standard Canon focusing screen. As a result, the split-prism screen rattles a bit in the camera and the calibration is also a bit off (meaning that when the split-prism indicates perfect focus, I'm actually slightly out of focus).

Would the best way to properly calibrate this new split-prism screen/get rid of the rattling be to use shims? Where can I get the shims?

Also, as far as shimming does, is there a proper procedure for doing it. For example, is there a specific side of the screen on which I should put the shims?

Thanks in advance

[poilu]

first check if it is inserted with mate side to viewfinder, shiny to mirror
download the chart http://focustestchart.com/chart.html to check how bad is the oof
you can order shim from Canon or cut them in paper or plastic
but with a 40D I would use a Canon screen, I would not like to redo the +100h I spent on the 400D
also don't forget that a split is not precise for under 2.8, use a EE-S screen

[996gt2]

[poilu]

from my experience split are not reliable under 2.8 but you can use the microprism part
putting shim on the shiny side doesn't help as the focus is made on the mate part
I found that split is not useful since when we have liveview
a EF-S allow to focus anywhere on the frame and free composition
focus need practice and lens play a important role, the better the lens, the more the focus snap

[ludoo]

The instructions at focusingscreen.com are pretty good

http://www.focusingscreen.com/work/test-fsen.htm

Make sure the camera is at 45 degrees to the ruler, or the out of focus areas in front and behind the point of focus won't match.

[996gt2]

Before I calibrate, should I put some shims on the glossy side (bottom) so that the screen has a snug fit? It seems to be a bit loose inside the 40D since it is thinner than the factory Canon screen.

Or does the 40D have a mechanism that compensates for the thinner screen by applying more clamping force to hold the screen in place?

[SkedAddled]

I have the same screen from Alex, and it looks identical to this one,
right down to the tape pieces on either side:


My only complaint is the specks on the center circle which can not be
removed with compressed air and gentle wiping with fresh cotton swabs,
but the screen fits my 40D perfectly. There is no play of the screen,
it required no shims, and the same can be said for my former XTi/400D
with one of Alex's screens installed. The other screen came clean, though.

I can actually focus with this screen up to around f/11, if I manage to
properly move my eye around the viewfinder.

Whatever you do, the matte/prism/circle side should face up towards
the pentaprism. Make any/all adjustments with the screen placed in
such a manner.

[visualopsins]

[SkedAddled]

Please explain: What is Eclipse?

[visualopsins]

Eclipse http://www.photosol.com/eclipseproduct.htm -- is reagent-grade methyl alcohol, obtainable in bulk at chemical supply houses for much lower cost.

[lulalake]

[peterqd]

The shims must go between the screen and the camera body, i.e. on the upper (viewfinder) side. This adjusts the distance between the screen and the mirror, shims on the underside would make no difference.

Adding shims corrects back focus and removing shims corrects front focus. If you need to add a shim, a tiny piece of 3M magic tape (the translucent kind) on each end of the shim works fine.