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09-19-2016, 02:04 PM   #1
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Focusing Screen?

Well I have used my K-S2 into the 3rd week and I have used manual lenses exclusively (yes I have the kit lens, but it is on my shelf, serving as a backup). I have bought the magnifying eyepiece and focus confirmation works to an extent. However I notice that I focus slower when compared to using my Sears KSX-P which has a combined microprism/split prism rangefinder. The live view works but I do miss the red highlights of my Sony a5000 as the white highlight don't work very well. I am near sighted and I always wear glasses when shooting (otherwise I am half-blind) and I am seriously considering an alternative focusing screen.

I browsed FocusingScreen.com and they have a bunch of options. I personally like the EC-A and EC-L type screens (with grid) but I have heard that some screens can interfere with metering. Anyone has experience on this or have suggestions?

Sincerely

Edit: I read that the focusing screens are built from Canon or Nikon screens and are shipped from Taiwan, does anyone have experience with this site in general?

09-19-2016, 02:58 PM - 1 Like   #2
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QuoteOriginally posted by butangmucat Quote
Edit: I read that the focusing screens are built from Canon or Nikon screens and are shipped from Taiwan, does anyone have experience with this site in general?
Yes, they are cut-down screens from Nikon, Canon and other suppliers. The work (including laser etching) is done in Taiwan. Quality, workmanship, and packaging are excellent. Post-sales support is OK, though don't expect them to accept a return unless there is a defect. I had purchased the S-type screen with AF grid for my K-3, but encountered significant metering/exposure system issues (underexposure) at f/3.5 and narrower apertures. The problem was traceable to the bright laser etching and how it was evaluated by the RGB meter sensor on the K-3. I was unable to convince them to authorize a return and eventually sold the screen to a forum member at half price for use on a K-5.

To be fair, focusingscreen.com was unaware of the problem at the time and at present offer a disclaimer of sort on their grid line description page. At least I think that is what they are trying to say. They don't mention metering. Whether there might be a problem with grid lines and metering on the K-S2 is not known to me.


Steve
09-19-2016, 03:11 PM   #3
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QuoteOriginally posted by stevebrot Quote
Yes, they are cut-down screens from Nikon, Canon and other suppliers. The work (including laser etching) is done in Taiwan. Quality, workmanship, and packaging are excellent. Post-sales support is OK, though don't expect them to accept a return unless there is a defect. I had purchased the S-type screen with AF grid for my K-3, but encountered significant metering/exposure system issues (underexposure) at f/3.5 and narrower apertures. The problem was traceable to the bright laser etching and how it was evaluated by the RGB meter sensor on the K-3. I was unable to convince them to authorize a return and eventually sold the screen to a forum member at half price for use on a K-5.

To be fair, focusingscreen.com was unaware of the problem at the time and at present offer a disclaimer of sort on their grid line description page. At least I think that is what they are trying to say. They don't mention metering. Whether there might be a problem with grid lines and metering on the K-S2 is not known to me.


Steve
I was unable to find a disclaimer on the grid line page, but thanks.

So in theory a non-grid type focusing screen would not affect metering?
09-19-2016, 03:58 PM   #4
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QuoteOriginally posted by butangmucat Quote
So in theory a non-grid type focusing screen would not affect metering?
If there is a center focus aid, spot metering will be affected. As for other modes, I hesitate to say since I don't own a K-2S. KatzEye did metering studies for different cameras with their product, but those may not be applicable to your camera or another maker's screen.

Halfway down the page there is an additional information box with scroll bar. Scroll through to see metering information drawn from the K-7 model...

Pentax K-3 K-5, K-5II, K-7, K-30, K-50 & K-500 KatzEye Focusing Screen


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09-19-2016, 04:38 PM - 1 Like   #5
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Metering problems seem inherent but easy to compensate for.

---------- Post added 09-19-16 at 07:41 PM ----------

Don't forget you must calibrate the focusing screen. You also may need to use the af fine adjust to get away with focusing via focus confirmation. The downside is that each lens may need a different value but as the manual lenses lack any code identifier the setting is applied globally and then adjusted as you mount different lenses.
09-19-2016, 04:43 PM   #6
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QuoteOriginally posted by UncleVanya Quote
Metering problems seem inherent but easy to compensate for.

---------- Post added 09-19-16 at 07:41 PM ----------

Don't forget you must calibrate the focusing screen. You also may need to use the af fine adjust to get away with focusing via focus confirmation. The downside is that each lens may need a different value but as the manual lenses lack any code identifier the setting is applied globally and then adjusted as you mount different lenses.
Googled but did not find anything useful regarding calibration of focusing screen, any information on this?

Sincerely

Sent from my Android phone, please forgive any possible typos.
09-19-2016, 04:54 PM   #7
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QuoteOriginally posted by butangmucat Quote
Googled but did not find anything useful regarding calibration of focusing screen, any information on this?
You use the supplied shims to make sure distance L1 is equal to distance L2 as per the diagram on this page.
09-19-2016, 05:07 PM   #8
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QuoteOriginally posted by butangmucat Quote
Googled but did not find anything useful regarding calibration of focusing screen, any information on this?

Sincerely

Sent from my Android phone, please forgive any possible typos.
Katzeye had good tutorials. It basically means you get a lens that you have used liveview with and then used fine AF adjustment with to get the viewfinder focus confirmation to agree with the liveview cdaf and to be accurate. Then when you swap focusing screens you use shims to make sure that the focus point matches the optical split prism view. The PDAF focus system doesn't care if the viewfinder is in focus - and is in fact not affected by the focusing screen at all. The trick is to make sure that the actual in focus output of the lens matches both the PDAF and the optical split image viewfinder picture.

Here's a forum post about it:
https://www.pentaxforums.com/forums/115-pentax-k-5/142225-focus-adjustment-wa...nt-images.html

09-19-2016, 07:41 PM   #9
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QuoteOriginally posted by UncleVanya Quote
Don't forget you must calibrate the focusing screen.
This is not always required. It depends on the thickness of the cut-down screen. If the thickness is the same as a Pentax screen, no adjustment is needed.

QuoteOriginally posted by butangmucat Quote
Googled but did not find anything useful regarding calibration of focusing screen, any information on this?
You don't calibrate the screen, you shim the screen to the body such that the distance to the screen is the same as that to the sensor. The easiest way to do so on your camera is to use magnified live view against a high contrast, high detail flat target as the "gold standard". The screen is shimmed (forward/back) to match the live view result. All told, the process is not hard to visualize, though it may be hard to figure out whether to add or subtract shim thickness. I found it easiest to use the optical focus first and then note the focus ring direction to correct in live view. A slant target may be useful, but should not be used for final tuning.

Having appropriate shim thickness may a challenge. With any luck one of the flexible plastic shims provided by focusingscreen.com will be the correct thickness. My understanding is that they will provide a wider range of thickness if requested.

As noted above, there are instructions at focusingscreen.com, the archived (wayback machine) KatzEye site, and here at Pentax Forums. Note that the shim has its own retainer separate from that used by the focus screen. Note too that you will want to save both the stock screen and the shim that it was paired with it.

At this point, I will insert a shameless plug for my marketplace listing of genuine metal shims. I need to update how many I have of each size, but I do still have them.


Steve
09-19-2016, 08:49 PM - 1 Like   #10
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Steve, I disagree that the thickness is the only factor, my belief is that the accuracy of the original shimming is sloppy since the screen itself has a wide range of acceptable focus. This after all is what makes it difficult to use for manual focus to begin with.

However, while I have done this calibration/adjustment once, I wasn't ever satisfied since my screen was used and needed cleaning... you have more experience.
09-19-2016, 10:04 PM - 1 Like   #11
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QuoteOriginally posted by UncleVanya Quote
This after all is what makes it difficult to use for manual focus to begin with.
Hmmmm...yes, that is essentially correct, though it is a little more complicated than that. The stock screen has focus sensitivity of only about f/4. What that means is that the ability to detect an out-of-focus condition is never better than what can be attained at f/4. This can be visualized by mounting an f/2 manual aperture lens and carefully noting that the DOF is the same wide open as at f/4. This is a side-effect of brightness optimization to compensate for light lost to the PDAF system. As a result, fine focus using the stock screen is sort of a joke due to poor precision.

As a result, it is also difficult to determine whether the stock screen was properly shimmed at the factory or whether any effort was made to do so. I had discussions with Rachael Katz (KatzEye) about this and it was her opinion that manufacturing tolerances are sufficiently tight for both mirror box and screen stock that most bodies were fitted with the same thickness shims. When bodies were sent to KatzEye for shimming, a particular model would generally require a particular shim with very little variation. The nominal thickness difference would be the main reason to shim if you follow that line of reasoning.

FWIW, my K10D did not require calibration with the KatzEye screen (different stock screen than current models) back in 2008. I asked Rachael Katz about that at the time and she told me that most Pentax cameras did not require shims.


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09-20-2016, 06:42 AM   #12
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QuoteOriginally posted by stevebrot Quote
Hmmmm...yes, that is essentially correct, though it is a little more complicated than that. The stock screen has focus sensitivity of only about f/4. What that means is that the ability to detect an out-of-focus condition is never better than what can be attained at f/4. This can be visualized by mounting an f/2 manual aperture lens and carefully noting that the DOF is the same wide open as at f/4. This is a side-effect of brightness optimization to compensate for light lost to the PDAF system. As a result, fine focus using the stock screen is sort of a joke due to poor precision.

As a result, it is also difficult to determine whether the stock screen was properly shimmed at the factory or whether any effort was made to do so. I had discussions with Rachael Katz (KatzEye) about this and it was her opinion that manufacturing tolerances are sufficiently tight for both mirror box and screen stock that most bodies were fitted with the same thickness shims. When bodies were sent to KatzEye for shimming, a particular model would generally require a particular shim with very little variation. The nominal thickness difference would be the main reason to shim if you follow that line of reasoning.

FWIW, my K10D did not require calibration with the KatzEye screen (different stock screen than current models) back in 2008. I asked Rachael Katz about that at the time and she told me that most Pentax cameras did not require shims.


Steve
Very informative, thanks! I tried a katzeye in my k-3 but it was dirty (it was super cheap) and I haven't gotten around to cleaning it yet. I felt it was slightly off but my testing wasn't extensive.
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