Pentax P30 focus problem.

Cluster

Cluster

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Dave
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I have a new to me Pentax P30 with a 50mm f2 lens. It has been working quite well for me but for a couple of rogue images on the last roll.
The two images were focused in lower light levels and each was the first shot of the day. The focus point is way off,
not just a little but of the order of 15ft vs 50ft, or in the case of the tree trunk in the image attached, about 5ft vs 15ft.

I can't find anything loose in the camera (screen/mirror etc), so am now thinking it must be me, or the way I used the split image of the
screen to find my focus point.. It's putting me off using it.
Is there a way to find a good focus that I am missing? Maybe just using the split image is not the most reliable.

Image tree trunk, focused on the bunch of dead leaves at the centre.

ooftrunk.jpg
 
I have a P30T, and the focusing is ok with the split-image. The one thing that is slightly awkward is that it's split diagonally rather than horizontally. While this should increase ability to focus against various contrasty surfaces, I sometimes find it easier to tilt the camera by 45 degrees one way or the other so that I'm effectively getting a pure horizontal or vertical split, For some reason, I find it easier to focus this way.

If the majority of your photos with the camera are correctly focused, then my first thought would be operator error in the ones that weren't, e.g. the focus ring was knocked when changing aperture or something like that.
 
If it was only the first shots of the day and the rest were alright, it cannot be the camera. While the split image facility is useful, I would not rely on it. Do you have a circle of microprisms around the split image part? In poor light or with low contrast images, these are usually better than the split image, which is why they are there (but not on all cameras which is why I asked). It is always possible to completely ignore all the focus aids and just focus by eye on the focus screen and I always check the image is as I want it even when using focus aids.
 
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The split prism is in the middle of an oblong of fine prism-like points.. Perhaps I shouldn't rely on the main prism entirely..

Both images seem to have areas nearer the camera that are in (better) focus, but camera shake might have made it all worse...they go off with a good clunk.

I bought an MZ-30 which will work with the "A" lens in aperture priority. Surprisingly it works (or at least at the moment), so I can run the lens in a body that gives focus confirmation, but I will go back to the P30 for another roll and be more careful focusing in lower light levels.
 
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Dunno what aperture you used, but the closer you get the more critical focus becomes. I wouldn't panic about it, just stay alert. For what it's worth I never rated focus aids, & relied on what I saw on a plain screen. That way you aren't reliant on the central area for focus so don't need to recompose by moving the camera ...
 
droj said:
Dunno what aperture you used, but the closer you get the more critical focus becomes. I wouldn't panic about it, just stay alert. For what it's worth I never rated focus aids, & relied on what I saw on a plain screen. That way you aren't reliant on the central area for focus so don't need to recompose by moving the camera ...
Click to expand...
I have been shooting test shots to get an idea of how/if it works before I try to shoot images that I want.
One of the tests was to shoot some objects at around 3ft away with background ranging away from that (I also wanted to see what the OOF areas looked like as that's what i want to explore). In those at 2.8 and 2, there seems to be a small issue in that whilst the objects are in focus, the wheely bin on which my plank that has the objects arranged upon it has super good focus on the parts a few inches nearer to the camera. I suspect that really is down to my use of the split prism focus... there is a little "dead band" when focusing.
Maybe I'm seeing things......

Note, no beer was spilled in the making of this image.

test2.jpg
 
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Cluster said:
I have been shooting test shots to get an idea of how/if it works before I try to shoot images that I want.
One of the tests was to shoot some objects at around 3ft away with background ranging away from that (I also wanted to see what the OOF areas looked like as that's what i want to explore). In those at 2.8 and 2, there seems to be a small issue in that whilst the objects are in focus, the wheely bin on which my plank that has the objects arranged upon it has super good focus on the parts a few inches nearer to the camera. I suspect that really is down to my use of the split prism focus... there is a little "dead band" when focusing.
Maybe I'm seeing things......

Note, no beer was spilled in the making of this image.

View attachment 326172
Click to expand...

It could be the angle the image was taken from. If you were pointing the camer down then that would tilt the plane of focus so that the front of the wheelie bin and the upper parts of the Pot-Noodles and IPA box are the same distance from the camera. Wide apertures of f/2 & f/2.8 on subjects quite close to the camera would also reduce the depth of field considerably as well, which would further emphasise differences in focus.
 
Neither of my two main cameras has a split-prism screen, both have just smooth areas in the centre. I usually rack in and out of focus a few times to be sure. The ME has split-prism, and I usually quite like it when I use it, but it doesn't work well in all situations...
 
Looking at the images again, for the focus to be that far off, it really does look as if I've set up the focus, then set the aperture and got a good twist on the focus ring at the same time, as FishyFish suggests.

EDIT: I've been playing with the lens on my P30. The focus ring is very close to the aperture ring. I can't adjust the aperture without my thumb also being on the focus. I believe that my problem is down to the way that I have used it. For the lower light shots, the focus was set then the aperture (which would have been left somewhere around 5.6) would have to be opened, so giving a significant turn in the nearer focus direction. I guess that close inspection of some of my other shots will show a smaller focus shift. All my own fault.
Thanks All for your input.
 
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