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02-25-2010, 08:33 AM   #1
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Can't shoot focused images through viewfinder at f/1.4

I have a Sears MC 50mm f/1.4 on a K-x. I'm shooting in manual mode using the viewfinder. I focus perfectly(sharp) using beep as a guideline, SR on/off and snap picture. Out of focus! Now, I use live view and do the same, Bam! in focus! Why do I only get focused shots through live view only??? If I drop back to f/2.0 or higher, shots come out focused through view finder. Any help appreciated.

02-25-2010, 08:38 AM   #2
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At f/1.4 your depth of field (portion of the scene that is in focus) is razor thin. The more you stop-up (like you observed when going from f/1.4 to f/2) the thicker your depth of field gets.

The K-x viewfinder isn't the easiest to focus with, especially at f/1.4. I just got a DA* 55 f/1.4 and am still getting the hang of focusing on the K-x viewfinder. The reason you get better results in live-view is probably because it's easier to see what's in focus with a bigger view.

This would be my guess. Do you have any examples with EXIF data you can post?
02-25-2010, 08:42 AM   #3
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Try using your eyes rather than the electronics to determine focus when using the viewfinder.
02-25-2010, 09:02 AM   #4
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I am using my eyes. I use the beep as a guide. I know because the beep is a little off. Thanks

02-25-2010, 09:05 AM   #5
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Have you tried adjusting the diopter?
02-25-2010, 09:20 AM   #6
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Thanks. The funny thing is with the viewfinder a get a beep and is pretty much in focus and same in live view. But, the shot in live view is focused and the view finder is way off. Its just the fact that how off the focusing thats giving me an issue. I just got this Sears MC 50mm f/1.4 for doing interesting dof pictures. I just want to use the viewfinder to shoot them. I tested shooting from 3ft away. I'll try different distances. Thanks for the help.
02-25-2010, 09:21 AM   #7
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Yes. I zeroed it in middle. Maybe I'll try with glasses of contacts and see if I get better results.
02-25-2010, 09:23 AM   #8
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QuoteOriginally posted by mrjamesabels Quote
I am using my eyes. I use the beep as a guide. I know because the beep is a little off. Thanks
The screens in these cameras are not really well designed for manual focus, and the viewfinders themselves are actually not very good either.
I suspect you are having an easier time with liveview simply because the screen you are looking at is bigger and shows minute differences in focus better in your situation.
A lot of people who are using manual focus lenses are installing aftermarket screens that have focusing aids to assist with accurate focus.

To adjust your diopter correctly, remove the lens and look through the viewfinder. The diopter is correct when the etched lines on the screen are sharpest.

I am sure you have taken into account the very shallow depth of field at f/1.4 and have eliminated the possibility that what you are perceiving as out of focus is not just shallow depth of field.

02-25-2010, 09:48 AM   #9
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50mm at 1.4, subject at 1 meter.
That would give you 20mm of DOF. Not much to work with. Very little would be in sharp focus on a subject.
02-25-2010, 10:32 AM   #10
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QuoteOriginally posted by wildlifephotog Quote
50mm at 1.4, subject at 1 meter.
That would give you 20mm of DOF. Not much to work with. Very little would be in sharp focus on a subject.

It's amazing how these details come out after the fact, isn't it?
02-25-2010, 10:38 AM   #11
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It's an easy thing to check. But then again, I do a lot of macro.
Online Depth of Field Calculator
02-25-2010, 11:05 AM   #12
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Do the same test with another lens. It might be that your sears lens doesn't quite fit the k-mount properly, or was badly serviced / wrongly put together (erm.. right?), but easy to check with another lens. If you only have the kit as a spare then try it at a close focussing distance, or borrow a faster modern / older pentax branded lens.

The live-view preview is what is actually hitting the sensor, so focus will be perfect with it. If live view is focussed and disagrees with the optical VF, then I would suspect something optically wrong. Probably the screen is not shimmed correctly (because as you say, its off from where LiveView says it should be.)

If the problem is the same on another lens (use manual focus for the test, and widest aperature!), then you need probably to adjust the shims on your focussing screen (easy, but a recursive PITA). If the problem is only that lens, then that sucks because you wouldnt want to adjust the whole camera for the one lens. At least you can depend on live view for sharp shots.
02-25-2010, 11:21 AM   #13
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QuoteOriginally posted by mrjamesabels Quote
Yes. I zeroed it in middle. Maybe I'll try with glasses of contacts and see if I get better results.
What do you mean you zeroed it in the middle?
Are you referring to the diopter?
If you are then, you have to focus the diopter until you see the data in the viewfinder as clear as possible.
The diopter should be adjusted to the user's eyes and not just to be zeroed in the middle.
02-25-2010, 12:32 PM   #14
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When you focus using Live View, you adjust focus directly on the sensor, so small wonder you are then in focus. If your camera does front/back focus a little bit, that would explain your problem. Try downloading PENTAX DSLRs: The AF Chart is acknowledged by PENTAX. this chart and verify the accuracy of your camera's AF.
02-25-2010, 01:28 PM   #15
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The viewfinder shows *too much* DOF at large apertures like f/1.4. There will always be more in focus in the viewfinder at f/1.4 than will be in the picture. So yes, *part of* what appears in focus in the viewfinder will not be in the picture. But part will. that's just a fact of life with the stock focus screen, which is optimzied to be as bright as practical with slower lenses, even at the expense of DOF accuracy with faster ones. Your task is to learn to anticipate which is which. I recommend practicing by shooting a printed page at an angle, paying close to attention to which lines appear in focus in the viewfinder, and which of those lines are still in focus in the picture and which aren't For my camera, if 10 lines appear in focus in the viewfinde,r maybe the *front* 4 will be in focus in the picture. So I try to be careful to make sure my subject is not only apparently in focus, but is also toward the *front* of the apparently-in-focus zone.
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