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01-30-2013, 07:02 PM   #1
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Pentax-M 200mm f4 focus correction?

A few weeks ago I won a Pentax-m 200mm f4 at ebay. It is in as new condition, with not a scratch anywhere. Came with original box, case, strap, and manual. Looks like it was never used. Glass is perfect.

Sadly, its not sharp. Or that's what I thought at first. I use this lens on an Olympus OM-D EM-5 in Manual Focus mode. I have other sharp lenses (Pentax-A 50mm 1.7, Pentax-M 100mm 2.8, and The Bokina). When you have a sharp lens in the viewfinder its no problem to lock on focus. The focus point is dramatically obvious. With the 200mm f4, it never looked sharp at infinity or even 20 feet away.

But then I decided to run some macro comparison tests. I put my Tokina at-x 90mm f2.5 up against my MF Pentax lenses + a Raynox DCR-150. The results were pretty even. Honestly there isn't a lot of difference in sharpness between the bunch of them. Each has a different focal view, and the faster lenses had better bokeh, but overall I could shoot flowers with the 50mm + the Raynox and I'd challenge anyone to see the difference with The Bokina.

And that's where the mystery began.... because when I put the Raynox on the 200mm f4 it was just as sharp for close focus as the 100mm f2.8. Is it possible that this 40 year old lens sat on a shelf all this time and lost focus calibration through disuse? Does anyone know how to calibrate focus on these lenses?

I'll say the lens looks beautiful, and I paid a very small amount for it. It is so light and the range is wonderful. Would love to know if there are some screws inside one can turn to correct long distance focus.

01-30-2013, 07:28 PM   #2
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Sample from my SMC PENTAX-M 1:4 200mm ( 2.4 MB camera jpg)
https://www.box.com/s/ztu4g2zkjy8s1xgd6d8d

See the spider's web
01-30-2013, 07:29 PM   #3
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It sounds like you saying it does not reach infinity? That is common -- it could have actually been intentionally adjusted that way to put on a Canon or something. It is fairly easy to tell especially if you have a body with live view -- just point at the moon or something very far away and rack the focus from close to infinity -- if it gets all the way there and never seemed to have snapped into focus then it needs adjustment. You need to check like this rather than just setting it at infinity because some lenses will go past infinity which is not sharp either, but you would have seen it snap into focus and then lose it again as you moved the ring.

Anyway, most old Pentax manual lenses can be fairly easily adjusted if you have the right screwdrivers and a friction tool to remove the faceplate ring. Only takes a few minutes and some trial and error, but is at your own risk naturally. I'm sure someone has posted instructions here before -- too lazy to type it myself right now...
01-30-2013, 07:34 PM   #4
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QuoteOriginally posted by wombat2go Quote
Sample from my SMC PENTAX-M 1:4 200mm ( 2.4 MB camera jpg)
https://www.box.com/s/ztu4g2zkjy8s1xgd6d8d

See the spider's web
That looks good and I guess I get about the same sharpness, which is fine without cropping. But when I crop it starts looking fuzzy. But maybe this is as good as this lens can give, and my copy is fine. Thanks for sharing that.

01-30-2013, 08:13 PM   #5
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This is one of the "unscrews in the middle" lenses, I think. It's been a long time since I had one. You should be able to focus to the minimum distance, grab the barrel above the focus ring, and unscrew it from the rest of the lens. That should give you easy access to the 3 screws that attach the focus ring to the rest of the lens, which is how the adjustment is made.
01-30-2013, 08:22 PM   #6
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Well I never had much success with anything above 50 mm hand held on the M43 and if I did, would not even try to crop down the shot!
However, I will try the -M 200/4 on the Oly M43 on the sturdy tripod tomorrow, stand clear and see what it looks like.
01-30-2013, 08:35 PM   #7
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QuoteOriginally posted by Just1MoreDave Quote
This is one of the "unscrews in the middle" lenses, I think. It's been a long time since I had one. You should be able to focus to the minimum distance, grab the barrel above the focus ring, and unscrew it from the rest of the lens. That should give you easy access to the 3 screws that attach the focus ring to the rest of the lens, which is how the adjustment is made.
Yes. That worked perfectly. Thank you. What an ingenious design. But what does one do with the three little screws? How do you make adjustments with that? Do you unscrew them and move the barrel a bit?
01-31-2013, 04:55 AM   #8
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IMO, the M200 is not overly sharp until F8 or even F11. Macro shooting, you are probably stopped down to get adequate DOF, and therefore more likely in its sweet spot. However, wouldn't discount infinity focus being misaligned. I suspect two of my M lenses are not correctly calibrated for infinity focus.

01-31-2013, 07:29 AM   #9
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The SMC Pentax-M1:4 200mm is not easy to use on M43, I don't think M43 is intended for such long lenses.
It a cold windy day here and I went out with the M43's little buttons hence no gloves!
After a few test shots I set the iso down to 100 as the Oly gets speckles above iso 400
Then set the lens down to f/16 for reasonable DOF after using the zoom focus at f/4 and set shutter down to 1/3 sec
Still not able to get a sharp shot using my old light duty Velbon tripod in the breeze with the self timer:
https://www.box.com/s/nv69t8qpeyutdtd4s2w3

So changed to the Heavy Duty Slik tripod I got for Large Format:
https://www.box.com/s/uaoahbqfr6l92l1jf8tx

What a difference the tripod made!

I think the register of my lens is correct, it was just off infinity focussed on the construction cones.

It is easy to blame the lens quality in a case like this but actually lens quality is a minor issue.

In my 1980 Pentax M catalog, the description of the SMC Pentax-M 1:2.5 200 mm says it is aimed at professional photography and refers to its excellence wide open,
whereas the description for the 1:4 200 mm only refers to its shallow DOF.
01-31-2013, 07:56 AM   #10
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QuoteOriginally posted by wombat2go Quote
The SMC Pentax-M1:4 200mm is not easy to use on M43, I don't think M43 is intended for such long lenses.
It a cold windy day here and I went out with the M43's little buttons hence no gloves!
After a few test shots I set the iso down to 100 as the Oly gets speckles above iso 400
Then set the lens down to f/16 for reasonable DOF after using the zoom focus at f/4 and set shutter down to 1/3 sec
Still not able to get a sharp shot using my old light duty Velbon tripod in the breeze with the self timer:
https://www.box.com/s/nv69t8qpeyutdtd4s2w3

So changed to the Heavy Duty Slik tripod I got for Large Format:
https://www.box.com/s/uaoahbqfr6l92l1jf8tx

What a difference the tripod made!

I think the register of my lens is correct, it was just off infinity focussed on the construction cones.

It is easy to blame the lens quality in a case like this but actually lens quality is a minor issue.

In my 1980 Pentax M catalog, the description of the SMC Pentax-M 1:2.5 200 mm says it is aimed at professional photography and refers to its excellence wide open,
whereas the description for the 1:4 200 mm only refers to its shallow DOF.
This information has really been helpful. I went out and tested the lens again and here is what I found.

1. On the OM-D you have to adjust the MF focal length above 200mm to get reasonable IS.
2. Shooting below 1/100 introduces camera shake even with IS on. So boost ISO
3. This lens seems optimized for f8 and f11. Shooting at f4 is very soft except close focus.
4. There is significant purple fringing at f4-7.1 even with the hood extended. It disappears at f8 and greater.
5. Image sharpness and contrast is fine at f8 and f11 for me.
6. It probably does not need calibration. Just needs a steady hand, the right IS focal length, a sunny day, and f8 or greater.

This lens is not in the same league as my M100 2.8 but it only cost me $62, it is super light, and I'll take it with me when I go to places with wildlife. The sharpest photos in the world it won't take, but it will bring the far away near and I can add some edge contrast in PP.

Will keep this one. Thanks to everyone for your valuable advice. Wonderful forum.
01-31-2013, 09:05 AM   #11
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My M200 gets sharp at the click between f/5.6 and f/8 - is that f/6.7? Very good at infinity, and edge-to-edge.
01-31-2013, 07:26 PM   #12
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QuoteOriginally posted by Datagov Quote
Yes. That worked perfectly. Thank you. What an ingenious design. But what does one do with the three little screws? How do you make adjustments with that? Do you unscrew them and move the barrel a bit?
Since you think your lens is not reaching infinity, I would loosen two of the screws, then put the camera on a tripod and find something really far away to focus on. Set the focus ring to infinity and take a shot. Then loosen the third screw enough so you can turn the focus ring without changing focus. (You'll only be able to turn it away from infinity.) Turn it back a few degrees, then tighten one of the screws. Screw on the front of the lens, being careful not to cross-thread. Then you can turn the focus ring a bit farther towards infinity. Take another shot and see if it's sharper.
02-01-2013, 12:04 PM   #13
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QuoteOriginally posted by Just1MoreDave Quote
Since you think your lens is not reaching infinity, I would loosen two of the screws, then put the camera on a tripod and find something really far away to focus on. Set the focus ring to infinity and take a shot. Then loosen the third screw enough so you can turn the focus ring without changing focus. (You'll only be able to turn it away from infinity.) Turn it back a few degrees, then tighten one of the screws. Screw on the front of the lens, being careful not to cross-thread. Then you can turn the focus ring a bit farther towards infinity. Take another shot and see if it's sharper.
The lens does reach infinity and actually goes beyond. That is, I can focus very far away and still not be at infinity. But even if I play with the screws on the barrel how does this effect the focus or sharpness for the rest of the range? Moving the barrel position doesn't change the distances between the glass elements. It just changes the measurement point of infinity along the barrel.
02-01-2013, 12:30 PM   #14
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QuoteOriginally posted by Datagov Quote
The lens does reach infinity and actually goes beyond. That is, I can focus very far away and still not be at infinity. But even if I play with the screws on the barrel how does this effect the focus or sharpness for the rest of the range? Moving the barrel position doesn't change the distances between the glass elements. It just changes the measurement point of infinity along the barrel.
When we say it "doesn't reach infinity", we don't mean the marks on the barrel, we mean the actual focus -- meaning when it set at infinity it is still not in focus at infinity. So by changing the position of the barrel and then locking it down again, it moves the hard stop at the end to a different position so that it can now be moved that little bit more that it needs to get to infinity. Usually what you have to do is:

-- set the focus at infinity
-- loosen the screws, so you can move the barrel without moving the focus
-- move the barrel so that what was infinity is now something less than that
-- lock it down again (lightly)
-- now move it back to infinity, and your new focus position at infinity is now farther out than it was before. Possibly too far, but it is not a bad idea to see what "past infinity" looks like. You should then be able to determine where actual infinity is. Loosen the barrel again, move the infinity mark to that spot, tighten again. Adjust as needed. Keep in mind temperature changes can slightly alter focus, so being just past infinity at the hard stop isn't the worst idea in the world as long as you don't mind dialing it in by eye when you focus. Or just find that exact spot where it is sharpest and lock it down there.

Did I get that right? It is confusing (for me) because I find it counter-intuitive -- you have to move the barrel the opposite way that my impulse tells me to at first, but it is an easy adjustment once you get the hang of it.
08-11-2013, 08:28 PM   #15
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I'm seeing the same sort of behavior with mine... it just isn't very sharp at f/5.6 or below, and sort of so-so below below f/8. I wonder if the A200/4 is any better? It sells for more than twice as much at KEH. Or for this focal length, maybe I should just hunt for an A*200/2.8 or K200/2.5?
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