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09-24-2010, 09:30 AM   #1
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Mirror vs. Prism, I only use MF glass

I know this question has been answered time and time again, but this is a very specific one.

I would like to know how much of a difference the the pentaprism makes in manual-focus. I almost solely use the A 28 2.8, A 50 1.7, and K55 1.8, because I like the image quality over the kit, and those 3 lenses cost significantly less than a new high quality zoom.

I have the opportunity to sell my k20d, and for the same price, pick up a k-x with the 55 - 300 lens bundled! Very cool. I would also appreciate the increase in ISO image quality... but I understand those improvements come at a price.

However, the long end of the zoom is less important to me than high quality at the wide end. I find I already have some troubles nailing focus with the k20d (no split prism), and I was wondering if swapping to the KX will cause me to pull my hair out.

09-24-2010, 09:35 AM   #2
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You can easily buy and change the focus screen yourself. I bought an excellent one from Taiwan for ca, $50 and it's been flawless. You can select from many different types to get the one that will suit you best. It's a definite improvement over the standard focusing screen.
09-24-2010, 09:55 AM   #3
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Some people find the difference between the prism-based cameras and the mirror-based cameras significant. I don't. I made a similar switch - from *istDS to K200D - and have to say, while comparing side by side I can see the difference, it's not really that significant. It's more noticeable with the kit lens or other slower lenses, as the difference in brightness is more noticeable than with faster lenses. But the size difference isn't that great either way. I did eventually outfit my K200D with an O-ME53 viewfinder magnifier, and really have no complaints. But the 28 remains hardest to focus, just as it was on the DS, simply because neither viewfinder is very big compared to a FF camera. 28mm is more or less a "normal" FOV on APS-C, and it would sure be nice if that also meant 100% magnification in the viewfinder as it did with 35mm film cameras, but that's just not the case with APS-C.
09-24-2010, 10:08 AM   #4
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From my own experience, the mirror/prism difference is subjective.

However, if you put in a katzeye with optibright, the difference between the two will be over 1 entire stop of light. I don't quite know why it does this, but the optibright responds much more to the prism than the mirror.

09-24-2010, 10:09 AM   #5
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QuoteOriginally posted by Marc Sabatella Quote
Some people find the difference between the prism-based cameras and the mirror-based cameras significant. I don't. I made a similar switch - from *istDS to K200D - and have to say, while comparing side by side I can see the difference, it's not really that significant. It's more noticeable with the kit lens or other slower lenses, as the difference in brightness is more noticeable than with faster lenses. But the size difference isn't that great either way. I did eventually outfit my K200D with an O-ME53 viewfinder magnifier, and really have no complaints. But the 28 remains hardest to focus, just as it was on the DS, simply because neither viewfinder is very big compared to a FF camera. 28mm is more or less a "normal" FOV on APS-C, and it would sure be nice if that also meant 100% magnification in the viewfinder as it did with 35mm film cameras, but that's just not the case with APS-C.
Thanks marc. I expect a challenge either way (I completely agree w.r.t. the 28mm lens), but if it's not really going to make much difference in the final picture, I think I would be happy to try out the K-X for the upgrade in image quality and portability.

I'm not really that happy with the K20d between 1600 and 3200, and if it does not seem to make much a difference in your "in focus" and "out of focus" pictures, then I think it would be worth the swap.

With the k20d, I tend to focus by running along the DOF and shooting right as the image "pops". Is this a feature of the ground-glass focusing screen, and will I miss that feature with the KX?
09-24-2010, 11:03 AM   #6
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Of the eight lenses I use only two are from the DA series or equivalent: the rest are SMCP-M.
As I have poor eyesight, both pentaprism and pentamirror (GX20 & K200D) are equally unhelpful. On this score, I didn't think much of the film MX either. For non-action shots, some kind of viewfinder eyepiece should help.

As an aside I should mention the awestruck look of a shop assistant who had had his first look through the viewfinder of a Nikon F2AS which I had just handed back to him. He had only peered through the viewfinder of DSLRs before this revelation.
09-24-2010, 01:50 PM - 1 Like   #7
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The physical appearance of the K-x and K20D screens should be identical. So the exact same focusing techniques work.
09-24-2010, 04:55 PM   #8
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QuoteOriginally posted by Marc Sabatella Quote
The physical appearance of the K-x and K20D screens should be identical. So the exact same focusing techniques work.
Great, I'm going to seriously consider the switch. Take care.

09-24-2010, 10:20 PM   #9
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The K-x viewfinder is both physically smaller and offers less magnification. I found it harder to manually focus on it.

Info from dpreview:

K-x:

• Eye-level penta-mirror
• 96% frame coverage
• Magnification: 0.85x (with 50 mm F1.4 lens at infinity,-1m-1)
• Dioptre adjustment: -2.5 to +1.5 dioptre
• Natural Bright Matte II focusing screen

K20D:

• Eye-level pentaprism
• 95% frame coverage
• Magnification: 0.95x (with 50 mm F1.4 lens at infinity)
• Dioptre adjustment: -2.5 to +1.5 dioptre
• Natural Bright Matte II focusing screen

See if you can try a K-x before buying it. If you get one, get the O-ME53 as well.
09-25-2010, 12:02 AM   #10
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QuoteOriginally posted by Laurentiu Cristofor Quote

See if you can try a K-x before buying it. If you get one, get the O-ME53 as well.
Would this O-ME53 help with manual focus on the k20d?

I kind of like that idea... losing some of the periphery, and more precise focus...
09-25-2010, 01:17 AM   #11
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I think the O-ME53 is the most useful Pentax accessory you can get if you like manual focusing - it's compatible with all camera models, so it will work great on K20D (I use it on K10D and K-7). It will always help and you're not really losing the edges of the viewfinder - you'll just have to roll the eyeball more to check them out - I can still read the digital display by looking down, so it doesn't affect any functionality. And unlike a focusing screen, it's easier to setup and it helps with slow lenses too (i.e. it doesn't darken the viewfinder). Oh, and one more advantage is that it keeps your nose further away from the LCD.
09-25-2010, 03:15 AM   #12
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I've read that the Nikon (DK M-21) x 1.17 and the Olympus (x1.5 and x2) both fit as well. Nikon is cheaper, Oly - don't know.

I bought a RA finder for macro, hardly ever use it because it's disorientating - useful only on a tripod IMO.
09-25-2010, 04:57 AM   #13
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Gosh, O-ME53 viewfinder magnifier cost less than 30 USD, if it works then I want one too.
- Thanks for sharing discussion, I hope they let me try it out in the shop
09-25-2010, 06:30 AM   #14
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QuoteOriginally posted by JoepLX3 Quote
Gosh, O-ME53 viewfinder magnifier cost less than 30 USD, if it works then I want one too.
- Thanks for sharing discussion, I hope they let me try it out in the shop
Just ordered one today - US$22. I looked on the official site and it said $50 !!
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