645N focusing screen with both splitscreen and microprism?

dag.bb · 01-24-2014, 01:52 PM

Hi all!

Just bought my first Pentax 645N (after having started out with a K1000 in 1999 or so, it seems I have come full circle!

).

I was happy to see that the owner had installed a manual focus-screen, as the AB-82 seems expensive to buy loose. I'm slightly confused however - the AB-82 screen is supposed to have only split-screen focusing. My screen has both split-screen and a microprism-"donut" around it. Is this a 645 screen fitted to 645n, or something else?

Dag

NotaxPen · 01-24-2014, 05:08 PM

Originally posted by dag.bb

Hi all!

Just bought my first Pentax 645N (after having started out with a K1000 in 1999 or so, it seems I have come full circle!

).

I was happy to see that the owner had installed a manual focus-screen, as the AB-82 seems expensive to buy loose. I'm slightly confused however - the AB-82 screen is supposed to have only split-screen focusing. My screen has both split-screen and a microprism-"donut" around it. Is this a 645 screen fitted to 645n, or something else?

Dag

If it has both split-image and microprism, it's an aftermarket screen.

dag.bb · 01-31-2014, 09:09 AM

I ordered an new AB-82 645N split-screen (without microprism) as a replacement, as the existing screen's microprism and splitscreen was never in complete agreement with the autofocus/beep. On replacing I found that the mounted screen was marked C21, e.g. a UC-21 screen for the 645. Not so happy with the seller, after all. So, buyer beware - if you find a 645N advertised as having a microprism and splitscreen - it's the 645-version, and manual focusing based on the screen will not be exact, even though the AF-system still works fine, and is correct.

**TDvN57** · 08-24-2018, 08:04 AM

Originally posted by dag.bb

I ordered an new AB-82 645N split-screen (without microprism) as a replacement, as the existing screen's microprism and splitscreen was never in complete agreement with the autofocus/beep. On replacing I found that the mounted screen was marked C21, e.g. a UC-21 screen for the 645. Not so happy with the seller, after all. So, buyer beware - if you find a 645N advertised as having a microprism and splitscreen - it's the 645-version, and manual focusing based on the screen will not be exact, even though the AF-system still works fine, and is correct.

Have you tried to flip the screen over?

**kaseki** · 08-24-2018, 09:57 AM

Originally posted by TDvN57

Have you tried to flip the screen over?

A very good observation. With the ground glass side 'up' the path length to focus will be about a third of the screen's thickness longer relative to the path length for the ground glass side 'down' (given a typical glass index of refraction).

On the 645N, I believe the Pentax supplied screens have a tab forcing the correct orientation. I haven't tried to change mine yet, do I could be mistaken in that regard. The aftermarket screen might not have such a tab.

01-24-2014, 01:52 PM	#1
dag.bb New Member Join Date: Jan 2014 Posts: 10	645N focusing screen with both splitscreen and microprism? Hi all! Just bought my first Pentax 645N (after having started out with a K1000 in 1999 or so, it seems I have come full circle! ). I was happy to see that the owner had installed a manual focus-screen, as the AB-82 seems expensive to buy loose. I'm slightly confused however - the AB-82 screen is supposed to have only split-screen focusing. My screen has both split-screen and a microprism-"donut" around it. Is this a 645 screen fitted to 645n, or something else? Dag

01-31-2014, 09:09 AM	#3
dag.bb New Member Join Date: Jan 2014 Posts: 10 Original Poster	Found a solution... I ordered an new AB-82 645N split-screen (without microprism) as a replacement, as the existing screen's microprism and splitscreen was never in complete agreement with the autofocus/beep. On replacing I found that the mounted screen was marked C21, e.g. a UC-21 screen for the 645. Not so happy with the seller, after all. So, buyer beware - if you find a 645N advertised as having a microprism and splitscreen - it's the 645-version, and manual focusing based on the screen will not be exact, even though the AF-system still works fine, and is correct. Last edited by dag.bb; 01-31-2014 at 09:18 AM.

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01-24-2014, 05:08 PM	#2
NotaxPen Senior Member Join Date: Feb 2011 Posts: 123	Originally posted by dag.bb Hi all! Just bought my first Pentax 645N (after having started out with a K1000 in 1999 or so, it seems I have come full circle! ). I was happy to see that the owner had installed a manual focus-screen, as the AB-82 seems expensive to buy loose. I'm slightly confused however - the AB-82 screen is supposed to have only split-screen focusing. My screen has both split-screen and a microprism-"donut" around it. Is this a 645 screen fitted to 645n, or something else? Dag If it has both split-image and microprism, it's an aftermarket screen.

08-24-2018, 08:04 AM	#4
TDvN57 Loyal Site Supporter Join Date: Jul 2011 Location: Berlin Photos: Gallery Posts: 1,149	Originally posted by dag.bb I ordered an new AB-82 645N split-screen (without microprism) as a replacement, as the existing screen's microprism and splitscreen was never in complete agreement with the autofocus/beep. On replacing I found that the mounted screen was marked C21, e.g. a UC-21 screen for the 645. Not so happy with the seller, after all. So, buyer beware - if you find a 645N advertised as having a microprism and splitscreen - it's the 645-version, and manual focusing based on the screen will not be exact, even though the AF-system still works fine, and is correct. Have you tried to flip the screen over?

08-24-2018, 09:57 AM	#5
kaseki Loyal Site Supporter Join Date: Dec 2017 Photos: Gallery \| Albums Posts: 1,138	Originally posted by TDvN57 Have you tried to flip the screen over? A very good observation. With the ground glass side 'up' the path length to focus will be about a third of the screen's thickness longer relative to the path length for the ground glass side 'down' (given a typical glass index of refraction). On the 645N, I believe the Pentax supplied screens have a tab forcing the correct orientation. I haven't tried to change mine yet, do I could be mistaken in that regard. The aftermarket screen might not have such a tab.