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A300 and 50mm prime

paulbed4d

Established Member
Hi
This seems strange.
Ive got a Sony A300 with 50mm prime lens.
When the camera locks on focus, the image in the view finder/live view screen seems slightly out of focus, but the resulting photograph is in focus.
If i manual focus, so the image on the viewfinder/screen is in focus the resulting image is out of focus.
I've tried adjusting the dial by the side of the viewfinder but this still cant bring the viewfinder image into focus.
Any ideas?
 

eduk

Distinguished Member
Is this your first dSLR? Have you just bought it? Have you any other lenses?

To clarify terminology:

The optical view finder is what you look through. There is a diopter adjustment wheel that can be used to adjust for your eyesight, but it has its limits. The diopter doesn't affect auto-focus, but can give problems for manual focus.

To set it, remove the lens and look through the optical view finder at a blank wall so that you can clearly see the focus points. Turn the diopter wheel until the focus points are sharp. This will remove any doubt about the lens and your eyesight.

The rear LCD on the A300 (and many other models) does not show what the main sensor records. There is a second smaller sensor that gives the live-view feed to the rear LCD. This is how Sony dSLRs have faster live-view than their competitors (the later SLTs has changed this).

Start with setting the diopter up properly and then come back with how the auto-focus is performing. It shouldn't make a difference to auto-focus, but you may be chasing red-herrings by confusing the viewfinders and their expected results. :smashin:
 

paulbed4d

Established Member
Hi. Thanks for the reply.
Yeah the diopter is set up properly.
I've had the camera for a few years now. I have a few other lenses and don't seems to have this problem with any of them.
When using the 50mm, the autofocus locks, it beeps and focus lock is confirmed by the red square, but the image i see in the optical view finder is OOF. However, when i look at the photograph either on the screen or on my pc the picture is properly in focus.
I'm seeing a different image through the OVF to what is actually being recorded on the main sensor.
Does that make sense?
Ta
 

eduk

Distinguished Member
Hi. Thanks for the reply.
Yeah the diopter is set up properly.
I've had the camera for a few years now. I have a few other lenses and don't seems to have this problem with any of them.
When using the 50mm, the autofocus locks, it beeps and focus lock is confirmed by the red square, but the image i see in the optical view finder is OOF. However, when i look at the photograph either on the screen or on my pc the picture is properly in focus.
I'm seeing a different image through the OVF to what is actually being recorded on the main sensor.
Does that make sense?
Ta

It doesn't make sense that your other lenses are fine.

If the mirror (not the main mirror) that reflects light onto the live-view sensor was out of alignment you'd see it with all your lenses. Same with the live-view sensor, you'd have the problem with your other lenses.

It points of course to the lens, but I am puzzled how this can be so. Does it happen when shooting wide open at f1.7 then at f8 and then say f11?
 

paulbed4d

Established Member
After doing some more tests I've found that it does the same with both lenses, its just more noticeable with the 50mm prime.
Anyway i think I've sorted it now.
I removed the focus screen a few weeks ago as a bug had somehow become trapped behind it. Looks like i fitted back the wrong way around and it wasn't sitting flush.
I've flipped it over and all seems fine now.
Problem solved!
 

eduk

Distinguished Member
After doing some more tests I've found that it does the same with both lenses, its just more noticeable with the 50mm prime.
Anyway i think I've sorted it now.
I removed the focus screen a few weeks ago as a bug had somehow become trapped behind it. Looks like i fitted back the wrong way around and it wasn't sitting flush.
I've flipped it over and all seems fine now.
Problem solved!

I wish you'd have said that in the first place. :facepalm:
 

paulbed4d

Established Member
Yes, although i can now see a couple of specs of dust/fine fibres through the ovf!!
I've tried taking it out again to clean it but just can't get rid of them all!!
 

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