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03-24-2012, 08:03 AM   #1
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K-7 and SMC-A 50mm 1.4 focus sharpness issues

Hey All,
I just purchased a Pentax SMC-A 50mm f1.4 lens for my K-7. When I take photos that are at a distance the photos are very unsharp. This isn't a result of my not focusing correctly because the ring is turned as far as it will go. I have better results at closer ranges in which I have to set the focus. My understanding is that calibration is for auto focus lenses. Is that correct? Is the lack of sharpness a lens or camera function? I've done multiple searches here and on the web, but have been unable to find any useful information

Thanks All
Theresa

03-24-2012, 08:06 AM   #2
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QuoteOriginally posted by tmharter Quote
Hey All,
I just purchased a Pentax SMC-A 50mm f1.4 lens for my K-7. When I take photos that are at a distance the photos are very unsharp. This isn't a result of my not focusing correctly because the ring is turned as far as it will go. I have better results at closer ranges in which I have to set the focus. My understanding is that calibration is for auto focus lenses. Is that correct? Is the lack of sharpness a lens or camera function? I've done multiple searches here and on the web, but have been unable to find any useful information

Thanks All
Theresa
Can you post the photos?
03-24-2012, 09:02 AM   #3
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http://smu.gs/GOnMX7

Here is a link. I will add more in a few because the variables are not entirely accurate between the two lenses. I trashed the photos last night with indoor shots which were taken at an indoor arena. you couldn't read the signs on the opposite side of the stadium.

Last edited by tmharter; 03-24-2012 at 09:14 AM.
03-24-2012, 09:12 AM   #4
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Can you re-add link? Doesn't seem to have made it into your post

03-24-2012, 09:14 AM   #5
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Try all resets. Like my K-7 have problem so I reset all. Better. I think K-7 have reset often.
03-24-2012, 09:16 AM   #6
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What do you mean by reset? Set everything to default? I sure wouldn't want to have to do that often!

T
03-24-2012, 09:36 AM   #7
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It could also be that you're shooting at F1.4- there, the DOF is really shallow and you'll have to nail the focus to get what you want to be sharp, at times even around infinity.

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03-24-2012, 09:43 AM   #8
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QuoteOriginally posted by tmharter Quote
This isn't a result of my not focusing correctly because the ring is turned as far as it will go.
My SMCA 50 1.7 will go past infinity if I turn the focus ring all the way to the stop. Set your camera on a tripod, go to 10X magnification in LV and see where it actually focuses best. There is also a chance that your lens can not achieve infinity focus. I do not see any reason for resetting the cam. to defaults, has nothing to do with manual focusing.

03-24-2012, 09:45 AM   #9
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If I set the ring at infinity, how would I get it any sharper, in focus? If something is 50 yards away, it should be at infinity. Actually, I did try adjusting the ring, but it just made it worse. If I have to set the 1.4 lens at f2 it defeats the purpose of having the f2, doesn't it? I will play more this week.

Theresa
03-24-2012, 09:54 AM   #10
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QuoteOriginally posted by tmharter Quote
If I set the ring at infinity, how would I get it any sharper, in focus? If something is 50 yards away, it should be at infinity. Actually, I did try adjusting the ring, but it just made it worse. If I have to set the 1.4 lens at f2 it defeats the purpose of having the f2, doesn't it? I will play more this week.

Theresa
The thing is one should never expect a lens to be sharp at wide open, unless you're buying a $2000 Leica lens, even so it's only "sharp" when shot close to the minimum focus distance, in this case for the A50/1.4 is at 0.5m. When you buy a fast lens (e.g. f1.2, f1.4, f1.8) it's to get a shallow DOF at wide open, if you want a sharp image from edge to edge, you need to stop down the lens close to f5.6 - f8

I got my k50/f1.2 because the previous owner complained that he couldn't get sharp images at f1.2, I was happy to get it for a very decent price
03-24-2012, 12:38 PM   #11
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This is not a problem with your K-7. If it works well with other lenses, it should work well with the A 50/1.4. Assuming, of course, that the lens is in proper working condition and in focus. A few things to check out:
  • Fungus and/or haze?
  • Evidence of being dropped or botched service?
  • Scratches to rear element?
To check for fungus, use a penlight in a dim room and shine the light at oblique angle into one end of the lens while looking into the other, preferably with a loupe. Fungus or haze will be readily evident. Ditto for scratches.

As for performance wide open...Very few lenses wider than f/1.7 are "acceptably" sharp wide open. At least as far as my definition of acceptable is concerned. As a result, I prefer the smaller and lighter f/1.7 and f/1.8 lenses. I do own a Auto-Rikenon 55/1.4 in M42 screw mount. It is a really nice lens, with a distinct purpose (looks incredible mounted on the Singlex TLS) and while very competent optically, it sees little use. Truth be told, I prefer the Helios 44M 58/2 or any other of my acceptably fast and much more light/compact 50s.


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03-25-2012, 01:49 AM   #12
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I think the main problem you're experiencing is that the A50/1.4 is notoriously soft when wide open (but I would definitely try more precise focusing using LV too). Just look at the test results here:

Nifty 50 Shootout : ERPhotoReview

You've asked the question "why bother with an f1.4 lens if you have to operate it at f2?". Well, if you look at the test results, you'll see that, at all apertures other than f1.4, it beats all the competition hands down. So, the point is that you have one of the sharpest lenses around - just don't shoot it wide open.

It's been pointed out to me on this forum that the 50/1.4 benefits greatly from the use of a lens hood, so you may like to try this.
03-29-2012, 12:26 PM   #13
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QuoteOriginally posted by tmharter Quote
If I set the ring at infinity, how would I get it any sharper, in focus? If something is 50 yards away, it should be at infinity.
Yes, but infinity is not achieved by turning the ring as far as it goes. Focus rings often go a little past infinity.


QuoteQuote:
Actually, I did try adjusting the ring, but it just made it worse
Nn one ever said manual focus was easy. It takes practice, and it doesn't help that the viewfinder shows too much DOF, fooling you into thinking more is in focus than really is.

QuoteQuote:
If I have to set the 1.4 lens at f2 it defeats the purpose of having the f2, doesn't it?
The lens is perfectly capable of taking sharp pictures at f/1.4. It's just that, as virtually with every single other lens ever made, it happens to get even sharper when you stop down a bit. But as has been noted, DOF is very shallow at f/1.4. Only a very thin slice of the picture will be in focus at that aperture. Most of the picture *will* be soft beause it is outside the very thin focus zone. And that is indeed the point of shooting f/1.4 - when you *want* most of your picture to be out of focus, except for the very thin slice you focused on. And then you have to be *extremely* careful when focusing to put that thin slice *exactly* where you want it.
03-31-2012, 06:22 AM   #14
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Your pictures look perfectly fine to me...
At 50mm 1.4 is a bit soft and low on contrast, so it might look like it is not in focus.
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