Sigma 17-70 2.8-4.5 lens out of focus on my K7

[bdparker]

Hi all

this is why i have not posted for a (long) while

to me, most of my photos look out of focus, using my Sigms 17-70mm F2.8-4.5 DC Macro on my K7

As in the image attached, the focus is on the student, but he looks blured and everthing else behind him is sharp?

F/L 53, 1/500, f4.0, ISO 125, manual mode, Multi-Seg metering, Autofocus , Auto W/B, Fine Sharpness2 +1, Shake Reduction On, JPG 14m ****

Any ideas, any Pentaxian live near me that could take a look at my gear to see what they think?

[ricktas]

Could be several issues

1. You or your camera are focusing on the wrong point in the scene (check your focus modes and make sure you have it set correctly). I don't use Pentax but assume when looking through the viewfinder you have a red circle or square that you point at the subject you want in focus.

2. You are using a continuous focus mode that is constantly adjusting for what the camera thinks you want to focus on, thus the background. Use your manual to choose a single focus mode.

3. There is something wrong with your lens, or the Auto-Focus system in your camera body.

My guess is that you have the camera in some multi-point focus mode and it is not picking what you want it to as the subject.

[I @ M]

Barry, assuming that you used the centre focus point to take this image it is clearly focussed on the wall rather than the student.

If you are sure that you are doing everything correctly to ensure that focus is on and remains on the subject in an image like this then I would suggest a trip to CR Kennedy in South Yarra for them to measure and rectify any problems with the lens / camera combination seeing as they are the importers / distributors of both Pentax & Sigma products.
They are quick, helpful and pretty close to you.

[Kym]

The K-7 has micro adjustment to correct possible front/back focus.

But more likely its your technique. Use the centre focus only for now and practice.

[bdparker]

Thanks for the feedback so far.

This issue has been going on for several months and I am acutely aware of what the camera (and I) am suppose to be focusing on, and I can gaurrante that the [red] focus square IS selecting the correct point in single-point AF mode. Also the camera is set to fire only when in focus, for those who may question this setting.

[KevPride]

Then with the latter post it is back focussing - if this photo is typical - as Kym has said it is easy to fix in the K7 with a micro adjustment, found within Custom Settings - "AF Fine Settings" however make sure you select "apply one" as all will adjust all of your lenses. Hope this helps.

Having reread your post it appears you have added some + fine adjustment, I would keep adjusting until problem gone. If this does not help then off to CRK.

[ricktas]

Whilst this is for a D70 (no idea why they called it that as its just a focus chart for a DSLR), you can use this (http://focustestchart.com/chart.html) to check focus accuracy and use micro-adjust. If this doesn't fix it, then your lens may need a recalibration and taking it to CR Kennedy's is the go

[Ozzi Paul]

I have the same lens but on a K20D & don't have any focus issues with it, I only use centre spot focus. My Sigma 70-200 f2.8 does back focus at apertures larger than f4.5 & longer focal lengths though on the same camera body. From what I have read, its just a lens to camera body compatability thing, you could put same lens on another K-7 & it could work fine. Something to do with manufacturers tolerances. Might have to send it in to CRK & have lens calibrated or something to suit your camera.

[bdparker]

Thanks Ozzi Paul

I have read about the lens to camera body compatibilityty thing elsewherere. people where noticing when they moved away from their kit lens('s) to good lens('s) and finding supposablely poor quality images in their good lens('s), not realising that the kit lens('s) were calibrated to the camera body in the first place.

both my K7 & lens are still under warranty (separater purchases) so i will take them over to CRK (when I find time).

[Lance B]

Thanks Ozzi Paul

I have read about the lens to camera body compatibilityty thing elsewherere. people where noticing when they moved away from their kit lens('s) to good lens('s) and finding supposablely poor quality images in their good lens('s), not realising that the kit lens('s) were calibrated to the camera body in the first place.

both my K7 & lens are still under warranty (separater purchases) so i will take them over to CRK (when I find time).

I would definitely try to use the AF focus adjustment feature before giving up and sending it back. As for the kit lens being 'calibrated' to the camera in the first place, I am reasonably sure this isn't actually the case. Your after market 17-70 f2.8/4.5 is a good lens and should work perfectly well with your K-7, even if it needs some focus adjustment. Even some of Pentax's lenses need AF adjustment, I know as I had 3 that required adjustment and once done, they were perfect.

Try focusing on a paling fence at a 45 degree angle. First make a cross mark on the fence with a texta, maybe 25mm x 25mm, and then zoom to the 70mm focal length open the lens up to max aperture of f4.5, stand back about 2-3mts and then focus on the mark. Make sure it look sharp in the VF and then take the photo. Have a look at the result on the computer screen and see whether the focus is in front (front focus) or behind (back focus) of the mark on the fence. If the camera has front or backfocused, you then need to go into the custom menu (one of the last menu items) and use the adjustment feature, see page 121 of the manual. It's no real big deal and is relatively easily done. It only adjusts the focus for that particular lens and asves it into the memory so that it keeps that adjustment for ever, unless you alter it. It can save the AF adjustment for up to 20 different lenses and they can all be adjusted differently. If I lived nearby I would love to assist you in getting it right, but alas, I am in Sydney.

[bdparker]

Thanks Lance

I did as you suggested but on a brick wall. I took two photo the first time, one in autofocus and one in manual (just to check)
The autofocus showd backfocus and I have ended up moving the focual point +5

I will see how i go over the next couple days.

Br Barry