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02-17-2013, 08:21 AM   #1
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50mm f1.7 older lens problem.

A friend let me have an older 50mm f1.7 lens. I can only focus in Live view, not in the viewfinder. When I get focused in the viewfinder the picture is way out of focus. Another issue is when I turn the camera of,f it will not turn back on when using this lens. I have to pull the battery and then turn it back on. Anyone else run into this or know what's going on? Thanks in advance for any help!!!

Eric

02-17-2013, 09:12 AM   #2
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What kind of lens is this? What does it say on there?
Make sure your camera mount and lens contacts are clean. And what material is the lens mount made of?
Do you have any other lenses that you can try using? Also, are you using a genuine battery or a knockoff?
02-17-2013, 09:41 AM   #3
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It's an Asahi Lens. Its an older manual prime so there are no contacts. Metal mount, I would assume aluminum. OEM battery. Yes I have other lenses and they work just fine. The focus difference is less troubling than the fact that the camera will not turn back on unless I pull the battery.
02-17-2013, 10:04 AM   #4
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QuoteOriginally posted by Elcogle3 Quote
It's an Asahi Lens.
That's pretty broad, lots of different lenses. I'm going to guess and say Pentax M 50mm? Unless it is M42 mount?

A picture of the lens mount might help to show anything out of alignment. But if it is the Pentax M there is no reason it should not work.

Regarding the focusing, do you use other manual focus lenses or are your other lenses all auto-focus? Have you adjusted the diopter on the camera?

02-17-2013, 10:11 AM   #5
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SMC Pentax-M 1:1.7 50mm 2815560 ASAHI OPT. CO. It's a K mount lens. My other lenses are Auto focus but I've used them a good deal in both Manual and Auto. I have not adjusted the diopter on the camera because my other lenses work both in viewfinder and live view so I don't want to adjust for one lens and be out of adjustment for my other lenses.
02-17-2013, 10:16 AM   #6
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Do you mean that when you shoot and focus, everything looks fine in the viewfinder but the final product (image) is out of focus?
02-17-2013, 10:30 AM   #7
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QuoteOriginally posted by Elcogle3 Quote
I have not adjusted the diopter on the camera because my other lenses work both in viewfinder and live view
And you shouldn't. I just wanted to see if you had ever set it. Or ever used fast glass. A lens at f/5.6 has a lot of leeway for focus when viewed through the viewfinder, one at f/1.7 does not and not everyone knows that. Apologizes if I'm pointing out the obvious but it is hard to tell someones level of experience on a forum and it is best to cover all the simple things first.

And just to check the lens does work and take good pictures? Especially can you change the aperture and does it work? Take a shot at f/1.7 and the same shot at f/22, are they exposed differently?
02-17-2013, 11:25 AM   #8
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In view finder things are in focus final image is way out of focus. Flipping between live view and viewfinder there is a huge difference between the two. Off camera the aperture moves normally but on camera when I take a picture at f1.7 and f22 the exposure does NOT change. Both images look the same and exposure is the same. Sorry I took so long to get back. I had to drive to work.

02-17-2013, 11:30 AM   #9
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Maybe the aperture pin is broken on the lens? Set your aperture below wide-open and take a 1 second exposure to just look into the lens from the front. The blades should close down. It sounds like they aren't in your situation. That would account for things being out-of-focus since it would be stuck on f/1.7 all the time (very shallow DOF)
02-17-2013, 11:31 AM   #10
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I'll do that Nitro. Thanks for the tip.
02-17-2013, 12:00 PM   #11
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I don't have the M but I do have a Pentax-A 50mm f/1.7 which in non-A mode should function the same.
So as a test:
Put the camera in M (Manual) mode
Aperture on the camera should show "F - -"
Set the aperture to f/1.7 on the lens
Adjust the shutter speed to take a reasonable exposure of something, chimp until you get a good exposure
Set the aperture to f/22 and take the same shot without changing anything except the aperture on the lens
At f/22 the image should be all black
If not there is something wrong with the aperture linkage, take a picture of the lens mount and attach it maybe we can see something wrong.

Another test, as NitroDC noted, would be to set a 1 second shutter opening
Set aperture at f/1.7 look down the lens and take an exposure, you should see the aperture blades move just very slightly
Set aperture to f/22 look down the lens and take an exposure, you should see the aperture blades close almost all the way
02-17-2013, 01:25 PM   #12
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Currently at work and won't be able to mess with it further until late tonight. Thanks for the suggestions!
03-06-2013, 10:19 AM   #13
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I have smc Pentax-M 1:1.7 50mm attached to K-30

The lens delivers amazing sharpness even wide open.

A couple of observations on focusing
1. focusing through viewfinder is slightly off. It becomes noticeable at f1.7, as the DOF is shallow. From 0.5 meter distance, the focus is maybe 0.5 cm closer than it appears in the viewfinder.
2. focusing through liveview is spot-on

ISO should be set to manual. When ISO is on Auto, aperture is always wide open - no matter where the aperture ring has been set.
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