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10-17-2010, 10:11 AM   #1
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Split prism screen calibration

I've replaced my standard viewfinder screen in the K10D with a katzeye one and need to have it calibrated (shimmed).
I basically want to send the body with only one lens to the repair center for this.

What is the best lens for this calibration purpose?

31mm/1.8 (30cm)
55mm/1.8 (45 cm)
55mm/2.8 macro (25 cm)
85mm/1.8 (85 cm)
135mm/3.5 (150 cm)
200mm/4 (250 cm)
300mm/4 (550 cm)

Is it the lens that can give me the biggest projection of a subject at the minimum focusing distance? Or the lens with the shallowest DOF wide open? Are there other factors?

Or is it better to send the whole bunch?

PS first lens is the FA31Ltd, others are (M42) takumar flavors and a (M42) vivitar macro


Last edited by sterretje; 10-17-2010 at 10:56 AM.
10-17-2010, 12:46 PM   #2
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For calibrating focus screens:

(1) If Katz does the shim adjustment you don't need to send a lens, just the body.

(2) To accurately test focus screen calibration, you need shallow depth-of-focus, rather than shallow depth-of-field (check wikipedia for definitions).
(EDIT: text deleted)

Last edited by troyz; 01-12-2011 at 12:54 PM. Reason: brain failure
10-17-2010, 02:07 PM   #3
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QuoteOriginally posted by sterretje Quote
I've replaced my standard viewfinder screen in the K10D with a katzeye one and need to have it calibrated (shimmed).
I basically want to send the body with only one lens to the repair center for this.

What is the best lens for this calibration purpose?

31mm/1.8 (30cm)
55mm/1.8 (45 cm)
55mm/2.8 macro (25 cm)
85mm/1.8 (85 cm)
135mm/3.5 (150 cm)
200mm/4 (250 cm)
300mm/4 (550 cm)

Is it the lens that can give me the biggest projection of a subject at the minimum focusing distance? Or the lens with the shallowest DOF wide open? Are there other factors?

Or is it better to send the whole bunch?

PS first lens is the FA31Ltd, others are (M42) takumar flavors and a (M42) vivitar macro
are you sure there is a calibration issue?

I have a split image in my K10D and my *istD and never calibrated either. I always found them spot on.

I think it is the bodies with penta mirrors that need calibration more than prisms
10-17-2010, 03:06 PM   #4
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I used shims to calibrate my screen on K10D.
and the best lens for the purpose? The one that gives you the shallowest DOF.

Good luck

10-17-2010, 03:19 PM   #5
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I am not sure what troyz meant by depth-of-focus vs. depth-of-field (Wikipedia was no help), but having checked focus calibration on my K10D, I can give a few suggestions:For the last point, you don't need a camera with live-view. Just take a picture and use that. You can view using the camera LCD or your LCD computer monitor.

You will likely find that the camera does not need to be shimmed.


Steve
10-17-2010, 04:54 PM   #6
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QuoteOriginally posted by stevebrot Quote
I am not sure what troyz meant by depth-of-focus vs. depth-of-field (Wikipedia was no help)
Steve
The depth-of-focus is how far the film/sensor/focus screen can be from the plane of focus and still get an acceptably focused image.

(EDIT: text deleted)

Last edited by troyz; 01-12-2011 at 12:55 PM.
10-17-2010, 05:14 PM   #7
klh
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QuoteOriginally posted by sterretje Quote
I've replaced my standard viewfinder screen in the K10D with a katzeye one and need to have it calibrated (shimmed).
I basically want to send the body with only one lens to the repair center for this.

What is the best lens for this calibration purpose?

31mm/1.8 (30cm)
55mm/1.8 (45 cm)
55mm/2.8 macro (25 cm)
85mm/1.8 (85 cm)
135mm/3.5 (150 cm)
200mm/4 (250 cm)
300mm/4 (550 cm)

Is it the lens that can give me the biggest projection of a subject at the minimum focusing distance? Or the lens with the shallowest DOF wide open? Are there other factors?

Or is it better to send the whole bunch?

PS first lens is the FA31Ltd, others are (M42) takumar flavors and a (M42) vivitar macro
Just my 2 cents, but calibrating MF with shims is pretty easy to do yourself. I bought the complete set of shims for my K20D for about $15 (including shipping). It was a pretty simple matter to move down in shim sizes to find the one that gave the best focus results.
10-17-2010, 07:04 PM   #8
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QuoteOriginally posted by klh Quote
Just my 2 cents, but calibrating MF with shims is pretty easy to do yourself. I bought the complete set of shims for my K20D for about $15 (including shipping). It was a pretty simple matter to move down in shim sizes to find the one that gave the best focus results.
Assuming that additional distance will improve the focus. I am not sure, but I believe that shimmed K10Ds are relatively rare. (Mine had none and I don't remember any other forum members having shims in their cameras until I read @axl's comment above.)


Steve

10-17-2010, 07:37 PM   #9
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QuoteOriginally posted by troyz Quote
The depth-of-focus is how far the film/sensor/focus screen can be from the plane of focus and still get an acceptably focused image. For a given f-number and image distance (e.g. the length of your test bench) a longer lens will have a greater depth of focus, and could lead to less precise calibration.

So don't use a really long lens.

AFAIK this applies only to adjusting focusing screens, not to adjusting the camera's AF system.

Here's the wikipedia article
Depth of focus - Wikipedia, the free encyclopedia

and a link to a previous thread
https://www.pentaxforums.com/forums/pentax-camera-field-accessories/106874-wa...ow-select.html

Thanks for the explanation and link. I searched for depth-of-focus and got nothing except references to DOF.

Are you sure about the affect of focal length? From the general form of the equation t = 2Nc(v/f), t should decrease as f increases with all other terms held constant. Or am I missing something?

One thing to keep in mind is that there still is only one real focus point, regardless of the depth of focus since depth of focus like DOF is a subjective approximation of acceptable focus. In other words, viewfinder (or flange distance) calibration is less critical with shorter lenses than with longer but both should be calibrated to the same point.

Out of curiosity, does anyone know what shim thickness are included in the kit?


Steve
10-17-2010, 08:48 PM   #10
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QuoteOriginally posted by stevebrot Quote
Are you sure about the affect of focal length? From the general form of the equation t = 2Nc(v/f), t should decrease as f increases with all other terms held constant. Or am I missing something?
Oh crap. You are right -- a longer lens (with all other terms held constant) is better.

Will edit previous posts.


QuoteOriginally posted by stevebrot Quote
Out of curiosity, does anyone know what shim thickness are included in the kit?
According to https://www.pentaxforums.com/forums/907364-post4.html
they range from 0.15mm to 0.40mm in 0.05mm increments.

Last edited by troyz; 10-17-2010 at 09:12 PM. Reason: shim thickness info
10-18-2010, 08:10 AM   #11
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Original Poster
Thanks for the replies

The standard matte screen had a shim in my K10D. That same shim went in with the katzeye when I had the katzeye installed by the dealer.

Yep, I think it is necessary. The below were taken with the 135/3.5 at F/3.5 at a distance of around 30 meters. Photos taken with tripod, cable release and 2 sec delay.

Resized
Split prism

AF


Crops
Split prism

AF


Focus is on the left front edge of the box

And yes, I need a tripod with spirit level (or a K5)
10-18-2010, 09:30 AM   #12
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QuoteOriginally posted by sterretje Quote
Yep, I think it is necessary. The below were taken with the 135/3.5 at F/3.5 at a distance of around 30 meters. Photos taken with tripod, cable release and 2 sec delay.
I would say so! Anytime your AF does better than the split-image there is a problem. I would suggest doing your testing at a more moderate distance, say 20x the lens focal length. The helicoid on most lenses is too steep for fine focus past about 10'.


Steve
10-19-2010, 01:45 PM   #13
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QuoteOriginally posted by sterretje Quote
Thanks for the replies

The standard matte screen had a shim in my K10D. That same shim went in with the katzeye when I had the katzeye installed by the dealer.

Yep, I think it is necessary. The below were taken with the 135/3.5 at F/3.5 at a distance of around 30 meters. Photos taken with tripod, cable release and 2 sec delay.
Looks similar to what I was seeing. From the looks of it, I think your MF is backfocused, and you need a thinner shim. If you order from Pentax, you can get the shim set in about 5 days, and have your camera perfect minutes later.
10-19-2010, 07:50 PM   #14
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Have you double checked to make sure your view finder is set right?
10-19-2010, 10:05 PM   #15
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QuoteOriginally posted by klh Quote
Looks similar to what I was seeing. From the looks of it, I think your MF is backfocused, and you need a thinner shim. If you order from Pentax, you can get the shim set in about 5 days, and have your camera perfect minutes later.
Or perhaps try it without the shim?


Steve
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