Focusing Problem with 50mm Lens, not with zoom lens

timdoyle91 · 05-19-2012, 05:57 AM

Hi there. This is a bit of a beginners problem to be honest, but I'm having trouble tracking down what the problem is here.

I recently bought a Pentax ME Super with a 50mm1.7 Lens, and a Petri 80-200mm zoom lens. I got my first set of shots back (a lot of which were mainly to test out various configurations e.g. different lenses, different flash settings etc.). However there was a problem with my shots: all the shots that I had taken on the 50mm lens were badly out of focus. A couple had areas that were almost in focus, but most were completely out. However, all the shots I took with the zoom lens came out relatively sharp and definitely in focus.

The majority of shots on the 50mm lens were indoors without a flash and so I had the aperture almost or completely wide open for most of them. Is this where I am going wrong? I'm assuming the problem isn't the camera if the shots on the zoom lens are OK? I'm thinking that the problem is most likely me but i thought in a batch of 20 shots I would've at least got one close?

Any help would be greatly appreciated!

Thanks

Tim

Mareket · 05-19-2012, 06:01 AM

It's probably because the viewfinder can only show a DoF around an aperture of f/2.8, and the 50mm will be faster than that, so you can't truly see if it's properly in focus.

vladimiroltean · 05-19-2012, 06:58 AM

Can you post some examples of what you call "badly out of focus"?

timdoyle91 · 05-19-2012, 07:58 AM

Focus Problems - a set on Flickr <--- This photo set has the whole roll in it, the last four (filenames zoom1-4) are the ones taken with the zoom lens. I know some are unsuccessful for other reasons but most of them show the focusing problem.

Thanks Mareket. What would you suggest to avoid the problem?

JohnX · 05-19-2012, 09:22 AM

Are you saying it looked ok when you focussed, but ended up oof?

Sorry if I'm insulting you here, but it looks like you haven't focussed them at all, and anything that is vaguely in focus is due to dof.

timdoyle91 · 05-19-2012, 09:33 AM

Yeah pretty much. I focused a lot with the prism but I wouldn't have ignored the image as a whole. The shots look nothing like what I saw in the viewfinder. What I can't understand is why only this lens seems to do it.

JohnX · 05-19-2012, 09:57 AM

One thing that comes to mind is that the focus screen isn't seated properly. When you look through the viewfinder you're looking at an image on the focus screen. If the screen's moved, the focus on the screen may look correct but it will be out at the film plane, hence your oof shots.

Send me a pm with your email address, and I'll send you copies of a ME Super service manual and a ME Super user manual I've got.

timdoyle91 · 05-19-2012, 11:54 AM

Would that not affect the zoom lens as well though?

Thanks, will message it now.

vladimiroltean · 05-19-2012, 12:04 PM

OK they are badly out of focus. I can't explain why, though. You are right in assuming that focusing errors should be constant regardless of lens used, but it's possible that the smaller aperture of that tele zoom (and consequently, larger DOF) masks focusing inaccuracies to an extent. It would be easier for us to tell you the exact reason if you uploaded some pictures taken with the Petri zoom as well. Otherwise, the focusing screen or the mirror are the only things that can bust your focusing precision.
You seem to have a case of back-focus (image is focused behind the point where you intended it to be). Can you tell if the camera has been previously taken apart?

timdoyle91 · 05-19-2012, 12:29 PM

The last 4 images in that set are the ones taken with the zoom. I was told by the previous owner that it was serviced in 2007 and not used much since.

vladimiroltean · 05-19-2012, 01:10 PM

I can't judge from those. You may want to spend another film shooting a focus test chart, and if your problem is consistent with both lenses, send your camera to a repair shop.

stevebrot · 05-21-2012, 08:13 AM

Originally posted by Mareket

It's probably because the viewfinder can only show a DoF around an aperture of f/2.8, and the 50mm will be faster than that, so you can't truly see if it's properly in focus.

...This is a 35mm film camera with an old style focus screen. The DOF in the viewfinder will be the same as at the film plane for 1:1 image size (i.e. contact print).

I looked at the series on Flickr and to be honest, all look to be pretty soft with most being grossly OOF though there is a tendency to back focus (background in focus) on all examples. Here are my suggestions:

Do your focus test on a flat subject having fine detail and high contrast, newsprint taped to the wall is a good target.
Do your focus test in good light with camera on tripod (if possible)
Use the focus aides in the viewfinder
If you wear eyeglasses, have them on when focusing
If possible, evaluate the negative using a loupe rather than a scanned image

Possible explanations:

Bad scans. Focus is critical when scanning and the negative carriers for most consumer scanners do a poor job of properly positioning the negative
Missing or damaged film pressure plate in body
Body has been "serviced" and the focus screen installed upside-down or without its shims

To be very specific...it is highly unlikely that the lens is the cause of your problem. If you can attain focus and a sharp image in the viewfinder, the same should be true with the final image. That is why we use an SLR.

Steve

timdoyle91 · 05-21-2012, 01:20 PM

I compared my camera with a friend's fully functional ME Super, and my viewfinder seems cloudy and unclear compared to his. Even though in mine I can seem to get the image into what looks like focus, there is still a general cloudiness over the whole picture in the viewfinder.

vladimiroltean · 05-21-2012, 01:27 PM

Did you try swapping the lenses, so you could isolate the problem to the camera or the lens?

stevebrot · 05-21-2012, 03:36 PM

Originally posted by timdoyle91

I compared my camera with a friend's fully functional ME Super, and my viewfinder seems cloudy and unclear compared to his. Even though in mine I can seem to get the image into what looks like focus, there is still a general cloudiness over the whole picture in the viewfinder.

Your viewfinder should be crystal clear and bright...like looking through a window. The ME Super was known for its excellent viewfinder (one of the best ever made) and images should snap into focus.

Possible causes:

Focus screen installed upside down
Crazed or fogged focus screen due to exposure to solvents or superglue vapors
Wrong ocular (highly unlikely)
Focus screen and/or prism surfaces badly fouled by fungus

Steve

05-19-2012, 05:57 AM	#1
timdoyle91 New Member Join Date: May 2012 Posts: 7	Focusing Problem with 50mm Lens, not with zoom lens Hi there. This is a bit of a beginners problem to be honest, but I'm having trouble tracking down what the problem is here. I recently bought a Pentax ME Super with a 50mm1.7 Lens, and a Petri 80-200mm zoom lens. I got my first set of shots back (a lot of which were mainly to test out various configurations e.g. different lenses, different flash settings etc.). However there was a problem with my shots: all the shots that I had taken on the 50mm lens were badly out of focus. A couple had areas that were almost in focus, but most were completely out. However, all the shots I took with the zoom lens came out relatively sharp and definitely in focus. The majority of shots on the 50mm lens were indoors without a flash and so I had the aperture almost or completely wide open for most of them. Is this where I am going wrong? I'm assuming the problem isn't the camera if the shots on the zoom lens are OK? I'm thinking that the problem is most likely me but i thought in a batch of 20 shots I would've at least got one close? Any help would be greatly appreciated! Thanks Tim

05-21-2012, 08:13 AM	#12
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Mareket It's probably because the viewfinder can only show a DoF around an aperture of f/2.8, and the 50mm will be faster than that, so you can't truly see if it's properly in focus. ...This is a 35mm film camera with an old style focus screen. The DOF in the viewfinder will be the same as at the film plane for 1:1 image size (i.e. contact print). I looked at the series on Flickr and to be honest, all look to be pretty soft with most being grossly OOF though there is a tendency to back focus (background in focus) on all examples. Here are my suggestions: Do your focus test on a flat subject having fine detail and high contrast, newsprint taped to the wall is a good target. Do your focus test in good light with camera on tripod (if possible) Use the focus aides in the viewfinder If you wear eyeglasses, have them on when focusing If possible, evaluate the negative using a loupe rather than a scanned image Possible explanations: Bad scans. Focus is critical when scanning and the negative carriers for most consumer scanners do a poor job of properly positioning the negative Missing or damaged film pressure plate in body Body has been "serviced" and the focus screen installed upside-down or without its shims To be very specific...it is highly unlikely that the lens is the cause of your problem. If you can attain focus and a sharp image in the viewfinder, the same should be true with the final image. That is why we use an SLR. Steve Last edited by stevebrot; 05-21-2012 at 08:24 AM.

05-21-2012, 03:36 PM	#15
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by timdoyle91 I compared my camera with a friend's fully functional ME Super, and my viewfinder seems cloudy and unclear compared to his. Even though in mine I can seem to get the image into what looks like focus, there is still a general cloudiness over the whole picture in the viewfinder. Your viewfinder should be crystal clear and bright...like looking through a window. The ME Super was known for its excellent viewfinder (one of the best ever made) and images should snap into focus. Possible causes: Focus screen installed upside down Crazed or fogged focus screen due to exposure to solvents or superglue vapors Wrong ocular (highly unlikely) Focus screen and/or prism surfaces badly fouled by fungus Steve

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05-19-2012, 06:01 AM	#2
Mareket Veteran Member Join Date: Jun 2011 Location: Chester Photos: Gallery \| Albums Posts: 719	It's probably because the viewfinder can only show a DoF around an aperture of f/2.8, and the 50mm will be faster than that, so you can't truly see if it's properly in focus.

05-19-2012, 06:58 AM	#3
vladimiroltean Veteran Member Join Date: Dec 2010 Location: Bucharest, Romania Photos: Gallery Posts: 1,465	Can you post some examples of what you call "badly out of focus"?

05-19-2012, 07:58 AM	#4
timdoyle91 New Member Join Date: May 2012 Posts: 7 Original Poster	Focus Problems - a set on Flickr <--- This photo set has the whole roll in it, the last four (filenames zoom1-4) are the ones taken with the zoom lens. I know some are unsuccessful for other reasons but most of them show the focusing problem. Thanks Mareket. What would you suggest to avoid the problem?

05-19-2012, 09:22 AM	#5
JohnX Pentaxian Join Date: Jul 2009 Location: London Posts: 1,116	Are you saying it looked ok when you focussed, but ended up oof? Sorry if I'm insulting you here, but it looks like you haven't focussed them at all, and anything that is vaguely in focus is due to dof.

05-19-2012, 09:33 AM	#6
timdoyle91 New Member Join Date: May 2012 Posts: 7 Original Poster	Yeah pretty much. I focused a lot with the prism but I wouldn't have ignored the image as a whole. The shots look nothing like what I saw in the viewfinder. What I can't understand is why only this lens seems to do it.

05-19-2012, 09:57 AM	#7
JohnX Pentaxian Join Date: Jul 2009 Location: London Posts: 1,116	One thing that comes to mind is that the focus screen isn't seated properly. When you look through the viewfinder you're looking at an image on the focus screen. If the screen's moved, the focus on the screen may look correct but it will be out at the film plane, hence your oof shots. Send me a pm with your email address, and I'll send you copies of a ME Super service manual and a ME Super user manual I've got.

05-19-2012, 11:54 AM	#8
timdoyle91 New Member Join Date: May 2012 Posts: 7 Original Poster	Would that not affect the zoom lens as well though? Thanks, will message it now.

05-19-2012, 12:04 PM	#9
vladimiroltean Veteran Member Join Date: Dec 2010 Location: Bucharest, Romania Photos: Gallery Posts: 1,465	OK they are badly out of focus. I can't explain why, though. You are right in assuming that focusing errors should be constant regardless of lens used, but it's possible that the smaller aperture of that tele zoom (and consequently, larger DOF) masks focusing inaccuracies to an extent. It would be easier for us to tell you the exact reason if you uploaded some pictures taken with the Petri zoom as well. Otherwise, the focusing screen or the mirror are the only things that can bust your focusing precision. You seem to have a case of back-focus (image is focused behind the point where you intended it to be). Can you tell if the camera has been previously taken apart?

05-19-2012, 12:29 PM	#10
timdoyle91 New Member Join Date: May 2012 Posts: 7 Original Poster	The last 4 images in that set are the ones taken with the zoom. I was told by the previous owner that it was serviced in 2007 and not used much since.

05-19-2012, 01:10 PM	#11
vladimiroltean Veteran Member Join Date: Dec 2010 Location: Bucharest, Romania Photos: Gallery Posts: 1,465	I can't judge from those. You may want to spend another film shooting a focus test chart, and if your problem is consistent with both lenses, send your camera to a repair shop.

05-21-2012, 01:20 PM	#13
timdoyle91 New Member Join Date: May 2012 Posts: 7 Original Poster	I compared my camera with a friend's fully functional ME Super, and my viewfinder seems cloudy and unclear compared to his. Even though in mine I can seem to get the image into what looks like focus, there is still a general cloudiness over the whole picture in the viewfinder.

05-21-2012, 01:27 PM	#14
vladimiroltean Veteran Member Join Date: Dec 2010 Location: Bucharest, Romania Photos: Gallery Posts: 1,465	Did you try swapping the lenses, so you could isolate the problem to the camera or the lens?