Focus check with SMC Tak 50/1.4 ?

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Archive 2008 · Focus check with SMC Tak 50/1.4 ?

Mike Ganz
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p.1 #1 · Focus check with SMC Tak 50/1.4 ?

Been having some focus issues with a Rokkor 58/1.2 and an SMC Tak 50/1.4, so I tried an unscientific test early this morning using a ruler. The aperture was set to wide-open. Not sure if I need to shim my Ee-S focusing screen or pay a visit to the eye doctor. Basically, I took three shots each using naked eye focus and the adapter's AF-confirm and picked what I thought was the sharpest of each set. Images were converted and re-sized in ACR, no sharpening was applied, 100% crops. The numeral "6" was centered in the center focus point. The naked eye shot looks a bit back-focused, and the AF focus looks a bit front-focused, or am I seeing things? Any ideas?

Focused with naked eye ("6" appeared sharp in the VF):

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Focused with adapter AF-confirm ("6" appeared OOF in the VF):

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Nov 02, 2008 at 01:33 PM

W9SIX
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p.1 #2 · Focus check with SMC Tak 50/1.4 ?

I'm struggling with these same issues. I'm good by eye on the close stuff, but struggle with medium to distant objects. I think I'm still doing better by eye than either of my cameras, a 1Ds and rebel xt. Sorry for having nothing more to offer than moral support

Nov 02, 2008 at 01:41 PM

cherubino
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p.1 #3 · Focus check with SMC Tak 50/1.4 ?

Not an uncommon problem. I have trouble getting the focus correct even with focus confirmation adapters. A lot of photographers use Katz eye and other screens, but I don't want to deal with that right now. I just stop down a couple of stops.

Nov 02, 2008 at 01:46 PM

Steve Spencer
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p.1 #4 · Focus check with SMC Tak 50/1.4 ?

Hi Mike,

My eyes see what your do. I would recommend shimming (or deshimming) your focus screen just a little. I think the AF would be considered within tolerances by Canon, so there is no sense in sending in the camera. AF just can't get the precision at such wide apertures, IMO, and even manual focus at these apertures is difficult. I wish I could be more helpful.

Best wishes,

Steve

Nov 02, 2008 at 02:00 PM

Mike Ganz
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p.1 #5 · Focus check with SMC Tak 50/1.4 ?

Steve Spencer wrote:
Hi Mike,

My eyes see what your do. I would recommend shimming (or deshimming) your focus screen just a little. I think the AF would be considered within tolerances by Canon, so there is no sense in sending in the camera. AF just can't get the precision at such wide apertures, IMO, and even manual focus at these apertures is difficult. I wish I could be more helpful.

Best wishes,

Steve

The problem seems to improve slightly when I stop down the lens to 2.8 (see below pics), but it does appear to have the same front/back focusing effects as above (as evidenced by the numeral "7").

Naked eye at 2.8, focus on "6":

This image is copyrighted by the owner

AF-confirm at 2.8, focus on "6":

This image is copyrighted by the owner

I understand about adding shim thickness to correct back-focusing issues (as shown in the first set at 1.4), but wouldn't that correction throw off focusing at smaller apertures? Or am I missing something? Maybe its best to leave things as-is and just use focus bracketing at very wide apertures? Maybe its just much ado about nothing on my part?

Nov 02, 2008 at 02:27 PM

Steve Spencer
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p.1 #6 · Focus check with SMC Tak 50/1.4 ?

Hi Mike,

At the narrower aperture I see the same tendency as in the above shots for manual focus, but the problem (which is not too severe) at the wide aperture is covered by the greater depth of field at the narrower aperture. Notice even in the f/2.8 shot for the manual focus the 5 is much sharper than the 7 (i.e., it is back focussed a bit just like the f/1.4 shot). For the autofocus, however, the front focus seen at f/1.4 is not evident any longer. I would chalk this up to the greater variability in autofocus. I think shimming your focus screen should help with both f/1.4 and f/2.8 shots. I hope this helps.

Nov 02, 2008 at 02:36 PM

cogitech
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p.1 #7 · Focus check with SMC Tak 50/1.4 ?

I agree with Steve. Shimming your focus screen should help with both f/1.4 and f/2.8 shots.

Nov 02, 2008 at 02:50 PM

Mike Ganz
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p.1 #8 · Focus check with SMC Tak 50/1.4 ?

cogitech wrote:
I agree with Steve. Shimming your focus screen should help with both f/1.4 and f/2.8 shots.

What's the recommended course...do I shim for the back-focusing in the naked eye test? Is there an actual shim kit sold by Canon (couldn't locate one on the B&H site), or is this a scotch tape kind of thing? TBH, I'd like to avoid the scotch tape approach if at all possible. Thanks for any expert advice.

Nov 02, 2008 at 03:34 PM

cogitech
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p.1 #9 · Focus check with SMC Tak 50/1.4 ?

I would shim for the naked eye test.

Canon apparently sells a stack of 14 (or so) progressively thicker shims.

I think it costs something like $20.

I've never needed to purchase them, but I would if I did need to.

Nov 02, 2008 at 03:54 PM

Mike Ganz
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p.1 #10 · Focus check with SMC Tak 50/1.4 ?

Thanks Paul, Thanks Steve.

I'll give Canon a call this coming week. From the looks of things, it appears that the shims in a 5D are located above the screen. I may try the tape approach just to have something to do until the Packers game

Looking at the 1.4 shots, my guess is that the backfocus is pretty close to about 0.5 cm. I assume that when using tape it gets applied to the top side of the left and right edges?

Nov 02, 2008 at 05:02 PM

PhotoMaximum
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p.1 #11 · Focus check with SMC Tak 50/1.4 ?

Mike, I posted a comment on the other thread on this. I am in the same boat and will look for any news you get from Canon on getting some shims. I did call Canon on Friday and we chatted about checking the stock screen again and making sure that the screens were inserted correctly. He did not mention any available shims to aid this process, but I failed to ask the guy about them.

If anyone has some more detailed experience with adjusting the screen or adding/removing shims I am all ears as the saying goes.

Thanks!

Max

Nov 02, 2008 at 05:10 PM

Mike Ganz
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p.1 #12 · Focus check with SMC Tak 50/1.4 ?

PhotoMaximum wrote:
Mike, I posted a comment on the other thread on this. I am in the same boat and will look for any news you get from Canon on getting some shims. I did call Canon on Friday and we chatted about checking the stock screen again and making sure that the screens were inserted correctly. He did not mention any available shims to aid this process, but I failed to ask the guy about them.

If anyone has some more detailed experience with adjusting the screen or adding/removing shims I am all ears as the saying goes.

Thanks!

Max

Max:

I'm not sure that sending the body to Canon would accomplish much...they'd probably adjust the focus screen to suit the AF system specs and not for MF (of course, I could be wrong about this).

I removed the Ee-S screen and re-inserted just as a precautionary measure. My guess is that if it were not inserted properly, the tray would not close and latch as easily as it should. I dug up the following number for Canon parts: 732-521-7230...I'll most likely call them tomorrow and see about a shim set.

Just gotta love the quirkiness of the 5D, huh?

Nov 02, 2008 at 05:31 PM

PhotoMaximum
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p.1 #13 · Focus check with SMC Tak 50/1.4 ?

Thanks for the part number Mike. I will also call them on Monday. Have a good book ready as the 1-800-ok-canon number will render your ears into cauliflower while you listen to the "please hold" elevator music...

Nov 02, 2008 at 05:54 PM

Mike Ganz
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p.1 #14 · Focus check with SMC Tak 50/1.4 ?

PhotoMaximum wrote:
Thanks for the part number Mike. I will also call them on Monday. Have a good book ready as the 1-800-ok-canon number will render your ears into cauliflower while you listen to the "please hold" elevator music...

Max: That's the *telephone* number for the Canon parts department, not a *part* number. Sorry for any confusion.

Nov 02, 2008 at 05:59 PM

PhotoMaximum
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p.1 #15 · Focus check with SMC Tak 50/1.4 ?

Got it... Thanks!

I had dinner at a friend's house last night and shot this handheld (with Rokkor 58/1.2) at f/2.0 at 1/30th at ISO 400, while focusing on the "S" on the label. Shot turned out well, but I still know my focus accuracy is not 100%.

Max

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Nov 02, 2008 at 06:08 PM

PhotoMaximum
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p.1 #16 · Focus check with SMC Tak 50/1.4 ?

PS: that was one hell of a bottle of wine... (note the vintage)

Nov 02, 2008 at 06:09 PM

PhotoMaximum
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p.1 #17 · Focus check with SMC Tak 50/1.4 ?

I tried calling Canon twice today and got bounced around from department to department without any joy in finding someone who could find a part number for these shims...

Nov 03, 2008 at 09:37 PM

Mike Ganz
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p.1 #18 · Focus check with SMC Tak 50/1.4 ?

PhotoMaximum wrote:
I tried calling Canon twice today and got bounced around from department to department without any joy in finding someone who could find a part number for these shims...

Max: I called Canon this morning...only had about a 5 minute wait with that horrid elevator music. Anyway, I did learn something (which is why I couldn't find anything when googling for "focus screen shims"). In Canon lingo, the shims are actually referred to as "washers". They also do not come in a set (at least for the 5D). There are about 12 or so washers in varying thicknesses, and they must be purchased individually. Good news is that they are very inexpensive. Since this will be a trial and error situation, I bought one of each washer. Including 2-day Fedex shipping, the total price was about $25 USD or so.

EDIT: I jotted down the individual part numbers on the desk blotter at my office. If you can wait until tomorrow (Tuesday), I can post them here.

Nov 03, 2008 at 11:08 PM

PhotoMaximum
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p.1 #19 · Focus check with SMC Tak 50/1.4 ?

Mike, that would be great! I am sure these numbers will be useful to have in the forum archive as well.

I bet Canon might suddenly get a surge of calls calling about these washers/shims...

Max

Nov 04, 2008 at 05:19 AM

Mike Ganz
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p.1 #20 · Focus check with SMC Tak 50/1.4 ?

These are the washer (aka focus screen shim) part numbers as obtained from the Canon parts department. I asked for washers that pertained specifically to the 5D. I neglected to ask if these part numbers were applicable to any other camera body. My guess is that the last set of three numbers are associated with the washer thickness (possibly in mils/thousandths of an inch?). Anyway, here they are:

CB3-2850-000-003
CB3-2850-000-005
CB3-2850-000-008
CB3-2850-000-010
CB3-2850-000-012
CB3-2850-000-015
CB3-2850-000-018
CB3-2850-000-020
CB3-2850-000-025
CB3-2850-000-028
CB3-2850-000-030

Again, I was told that they do not come in a set...you'd need to order each washer individually. One of each will total somewhere in the neighborhood of $22 USD, give or take. Mine are due in tomorrow (Wednesday), so I'll have more info then. If anything changes, I'll be sure to post some info.

I'll probably post these in a separate topic...others that may need the info may not realize that its buried in this thread.

Nov 04, 2008 at 09:58 PM

cogitech
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p.1 #21 · Focus check with SMC Tak 50/1.4 ?

Great info and good idea to create a separate thread.

(I'd guess the measurement is probably microns, or maybe thousandths of an inch, as you say)

Nov 04, 2008 at 10:00 PM

mrladewig
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p.1 #22 · Focus check with SMC Tak 50/1.4 ?

Mike,

I have the same issue with my XT. The XT does AF fine with f1.4 lenses, but the screen is off bad enough that I cannot use my M42 lenses wide open. Its off bad enough that not even the f3.5 lenses are in focus wide open.

I'll probably replace the XT sometime soon, so I'll just deal with it later.

Nov 05, 2008 at 04:48 PM


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