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02-05-2013, 03:49 AM   #1
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K-7 autofocus issues

So..

After I've "cleaned" my focusing screen with isopropanol it's all blurry now and I'm under the impression that since this very occasion my AF is kinda off. However, I know these two don't really related so what might the problem be? LV focuses fine, btw.

Here's an example of what I'm talking about (focused on the nibble between 0.5 and 0.7): http://i.imgur.com/J0DhuLj.jpg

Lens: Sigma 30/1.4 - Mode: Av, f/1.4, 1/60, Iso 100

Any hints?

Thanks in advance.

02-05-2013, 04:27 AM   #2
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Oh dear! This is too late for you, but I'll say it in the hope that it saves someone else:
Never touch the focusing screen with anything. NOTHING is soft enough to avoid damaging the screen. Not cotton buds, not special lens tissue etc...
Iso-propyl will have melted it for sure.

The good news is that you can buy a new focusing screen, but they're about $45.
The one standard with the camera is the:
Pentax MF-60 Focusing Screen (Standard with K-7)
(search your favourite stores)

I recommend using the:
Pentax ML-60 AF Cross-lined Matte Focusing Screen
as it has grids on it to help composition and ensuring that horizons are straight.

They come with special tweezers and instructions to carry out the job properly. Beware! It's fiddly, so be sure not to do more damage, such as scratching your mirror...
02-05-2013, 04:31 AM   #3
crs
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While I appreciate your effort and your reply it doesn't have anything to do with the focusing screen per se. One could even add a metal plate and the camera would focus just fine.

I'm after a solution for my focus being off.

Edit:
This picture (http://i.imgur.com/lBQyodG.jpg) I have just shot with a micro adjustment of +10. In my book it's still off. Is there any way to go further than +10?

Mode: Av, f/1.4, 1/125, Iso 100

Edit2:
This one I have just taken without any micro adjustment at all. Focused on the "b". What the *#~" is happening right now? -> http://i.imgur.com/iIja9CA.jpg

Mode: Av, f/1.4, 1/160, Iso 800

And again, the very same motive with +10: http://i.imgur.com/Skh4jIe.jpg

Last edited by crs; 02-05-2013 at 04:59 AM.
02-05-2013, 05:38 AM   #4
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I would not trust AF at all in those conditions.

Assuming a distance from focal plane to subject of 10", using a 30 mm lens at f1.4 would give you a depth of field of about 0.14 of an inch which is not a heck of a lot to play with.

Is camera on tripod? The slightest forward or backward camera movement would throw out the focus. I am not too bad at holding a camera pretty still for long distance shots but no way can I keep it still enough for closeups. The inbuilt shake reduction does not compensate for forward or backward movement. If using a tripod SR should be turned off.
What focus pattern are you using, Auto, Select or Centre? If "Auto" the camera has no idea of your desired point of focus and will do the best it can according to it's own algorithms. If "Select" make sure the camera does not move after focus is achieved. I have no idea how selective the "Centre" function is. It may not be enough to ensure the camera selects the same point of focus you wish. Again ensure the camera does not move after focus is achieved
Are you using AF.S or C? I really do not know what the limitations of the auto focusing system are but I suspect you are trying to operate outside of it's envelope.

In short try to eliminate all possible variables.
Put camera on a tripod for all close up work.
Turn off SR
Use manual focus

02-05-2013, 07:42 AM   #5
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QuoteOriginally posted by Bruce Clark Quote
I would not trust AF at all in those conditions.

Assuming a distance from focal plane to subject of 10", using a 30 mm lens at f1.4 would give you a depth of field of about 0.14 of an inch which is not a heck of a lot to play with.

Is camera on tripod? The slightest forward or backward camera movement would throw out the focus. I am not too bad at holding a camera pretty still for long distance shots but no way can I keep it still enough for closeups. The inbuilt shake reduction does not compensate for forward or backward movement. If using a tripod SR should be turned off.
What focus pattern are you using, Auto, Select or Centre? If "Auto" the camera has no idea of your desired point of focus and will do the best it can according to it's own algorithms. If "Select" make sure the camera does not move after focus is achieved. I have no idea how selective the "Centre" function is. It may not be enough to ensure the camera selects the same point of focus you wish. Again ensure the camera does not move after focus is achieved
Are you using AF.S or C? I really do not know what the limitations of the auto focusing system are but I suspect you are trying to operate outside of it's envelope.

In short try to eliminate all possible variables.
Put camera on a tripod for all close up work.
Turn off SR
Use manual focus
Hi,
I don't think it's true. According to DOFMaster the dof is about 1.9" (K-7 with 30mm lens at f/1.4, subject 10ft away)
02-05-2013, 09:03 AM   #6
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QuoteOriginally posted by sinus007 Quote
According to DOFMaster the dof is about 1.9" (K-7 with 30mm lens at f/1.4, subject 10ft away)
So what happens with the focus if you try that lens shot from 10 feet away...

edit: it is actually 0.14" at 10".

Last edited by Ex Finn.; 11-11-2014 at 05:46 PM.
02-05-2013, 09:22 AM   #7
crs
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I'ma just sum this up real quick.

- No tripod
- Focus center and SEL (center as well), tried both
- AF-S

I've shot yet another picture with a micro adjustment of +7 which led to a somewhat decent result, imho.

-> http://i.imgur.com/MSJdQxs.jpg
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