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Fine focus adjusted but still back focuses!!!


JAK

Link Posted 08/02/2019 - 00:42
The image exif with the Sigma is
Quote:
Date 2019-02-02 14:12:59 +0000
Make PENTAX
Model PENTAX K-5
Software Adobe Photoshop Camera Raw 9.10.1 (Windows)
Exposure Time 0.0010s (1/1000)
Aperture /2.8
Exposure Manual
ISO equivalent 100
Exposure Bias none
Metering Mode Matrix
Flash Fired No (enforced)
Focal Length 70.0mm 105mm=35mm equivalent
Exposure Mode Manual
White Balance Auto
Focal Length (35mm) 105
LensModel Sigma Lens
Lens Sigma Lens

And the 50mm Pentax:
Quote:
Date 2019-02-02 14:43:26 +0000
Make PENTAX
Model PENTAX K-5
Software Adobe Photoshop Camera Raw 9.10.1 (Windows)
Exposure Time 0.0005s (1/2000)
Aperture /2.8
Exposure Manual
ISO equivalent 100
Exposure Bias none
Metering Mode Matrix
Flash Fired No (enforced)
Focal Length 50.0mm 75mm=35mm equivalent
Exposure Mode Manual
White Balance Auto
Focal Length (35mm) 75
LensModel smc PENTAX-FA 50mm F1.4
Lens smc PENTAX-FA 50mm F1.4

That should show the problem.
Some readers may have a sense of deja vue!
https://www.pentaxuser.com/forum/topic/k-5-af-problems-29648
I note the problem was also with a Sigma lens.
Pentax have worked on improving low light AF in cameras since the K-5 so it would be a good idea to try the lens on another body (didn't I suggest that earlier??) The whole issue could be just that particular camera and lens combination.
John K
Last Edited by JAK on 08/02/2019 - 01:10

richandfleur

Link Posted 08/02/2019 - 02:40
JAK wrote:
(didn't I suggest that earlier??)

Stay with us man, your input is much appreciated.

michaelblue

Link Posted 08/02/2019 - 08:12
I have a Sigma 70-200mm f2.8 which my K5 does not like, I had a lot of out of focus problems with it and I got all kinds of weird camera shake (even using a tripod), all other lenses are fine with the K5 (including a Sigma 10-20mm) I now have a KP and it works perfect with the Sigma 70-200mm (as it does with all the other lenses)
Regards,
Michael
My new website:link

reso

Link Posted 08/02/2019 - 16:33
i had a sigma 70-200 f2.8 and would not work with my k5iis again focus problems now have a Tam 70-200 f2.8 and works as it should
k5iis tamron 10-24 tamron 17-50 2.8 pentax Da 18-55 wr sigma 24-70 2.8 ex dg macro pentax f 35-135 tamron 70-200 sp 2.8 sigma 120-400 apo dg hsm
kenko pz af 1.5 dg converter and a flash
Last Edited by reso on 08/02/2019 - 16:47

johnducguz

Link Posted 08/02/2019 - 18:02
Jak, I think you make the most relevant point. Independents have always been cheaper than body brand lenses & maybe this has proved the adage 'you get what you pay for'. Much as I appreciate the helpful comments, at the end of the day I want to point the camera, have it focus accurately & do so in a timely manner. I'll try Live view just to understand it a bit but I'm struggling to see why I should. I've fine focused the combo already, if I then have to change it 'cause live view doesn't agree what's the point of having fine focus? Just everyone use live view to adjust. I'll try the zoom on another body this weekend to see what happens.

JAK

Link Posted 08/02/2019 - 22:20
Nothing wrong with fine focus on Pentax's own lenses... as far as I know all of them that support automatic focus can be fine tuned (up to 20 lens types.) As that doesn't always work for Sigma lenses given their use of generic lens type codes they instead market a dock which allows lens adjustments to be made directly to the lens for some of their offerings:
https://www.sigma-imaging-uk.com/accessories/sigma-usb-docks/
I don't think it will help with your lens though so don't rush and order one before checking for compatibility (there's a list of supported lenses on that link to Sigma.)

Should you or someone reading the thread decide a dock would be useful in any event, there's a source for them here (Wex).
John K
Last Edited by JAK on 08/02/2019 - 22:28

davidstorm

Link Posted 08/02/2019 - 22:32
I fully take JAK's point and I agree with him regarding the difficulty in applying fine focus settings, however, I have a slightly different point to make about Sigma lenses vs. Pentax lenses. I've owned (and still own) a fair few Sigmas, 50-500, 150-500, 50mm Macro, 105mm Macro, 70-300, 17-70 f2.8-4 HSM DC Macro and my son has the latest 17-70 f2.8-4. All of these lenses have been superbly accurate at focusing, apart from the 50-500, from which I couldn't get a sharp image with any camera body, so I suspect the lens had some sort of issue. By contrast, I've had poor focus issues with some Pentax lenses, notably the 17-70 f4, the 55-300 (focus hunting) and the 100mm macro. My experience with the Sigma lenses is that they are generally excellent and don't require much adjustment, but there are always exceptions to the rule.

Also, my experience with the K-5 body and AF focus accuracy has been poor. I used to own 2 of these bodies and both were variable at best in the focus department. I've had no such issues with the K-5iis or the K-3, both of which continue to be excellent.

Regards
David
My Website http://imagesbydavidstorm.foliopic.com

Flickr

Some cameras, some lenses, some bits 'n' bobs

JAK

Link Posted 08/02/2019 - 23:19
I've never suggested there's a major issue with Sigma lenses, just that Pentax's AF fine tuning system often doesn't support them (for reasons already stated.) I own several including their 8-16mm rectilinear which has nothing comparable elsewhere and does what it does well (apart from having the ability to write some of the the focal lengths to the exif as Sigma were too mean to request Pentax include it in their cameras and the detail wasn't present anywhere in other lenses to extract it from.)
As to the K-5 and later cameras, if the K-5 had been the ultimate Pentax camera and offered all we required we'd never have purchased their newer offerings as they'd have been no point. I presume we purchased the newer ones as they offered improvements to features such as AF. With regards to video on Pentax cameras however it may well be true that the K-5 was the ultimate release but that's a different discussion!
By the way Sigma's reverse engineering isn't just with Pentax mounts, it seems they are reluctant to licence protocols from most if not all camera manufacturers. It's quite common for Sigma lenses in mounts other than Pentax to require re-chipping when a new camera body comes along. If the lens is under warranty they re-chip it under warranty but that isn't always possible.
This makes an interesting short read: https://www.lensrentals.com/blog/2011/02/things-you-should-know-about-your-lense...
John K
Last Edited by JAK on 08/02/2019 - 23:40

johnducguz

Link Posted 10/02/2019 - 09:48

So here's a shot with the 24-70 Sigma on my K10 body. As it's raining I shot from indoors focusing on the end of the bench. Hopefully you can see the berries, 1-2ft behind the focus point, are sharper, those not moving anyway. The bench end definitely aint sharp. So conclusion is.....duff lens!! Kinda makes my mind up that a K3ii wont accept this Sigma lens either as 2 bodies didn't, so my wonga will probably go to a prime from Pentax. Quite fancied a K3ii as well, shame. Thanks to all particularly Jak. P.S. Anyone want a nearly new, barely used Sigma 24-70 zoom, cracking results, read the reviews, why use primes when one lens will do it all for you!!

redbusa99

Link Posted 10/02/2019 - 10:25
disable the focus from the shutter release and set up the AF back button to perform it , can't remember how to do it on K5 but there will be someone on here or a youtube video that will show you. that will eliminate any chance of the camera trying to refocus as you press the shutter release also are you allowing time for the stability sysstem to settle or if on a tripod have you turned it off to stop it creating sensor movement by trying to stabilise
K3 II and the odd lens or 2

Flickr
ppg
Last Edited by redbusa99 on 10/02/2019 - 10:29

pschlute

Link Posted 10/02/2019 - 10:31
johnducguz wrote:
So here's a shot with the 24-70 Sigma on my K10 body.

Using single point AF for this ?
Peter



My Flickr page

JAK

Link Posted 10/02/2019 - 12:08
The camera looks to have focussed on the bush behind the intended target. As redbusa9 suggests turn off AF on shutter release and move it to the back button. Then focus first with the back button, recompose the shot and it doesn't matter where that point of focus ends up in the frame, the camera won't refocus when you press the shutter release.
The camera doesn't actually know what you want in focus, you have to make sure it does what you want! Leaving it to the camera to sort out when you take the photo often ends up with it focussed on something other than the intended target. Some might be right (eg your 50mm prime shot) others not; it's a very hit or miss way of taking photos to simply rely on the camera to get it right, every time. If you want to get it right, take charge of the process and don't rely on the camera to do it for you at the moment of exposure. You'll guarantee many failures if you do whatever the camera/lens combination.
John K

pschlute

Link Posted 10/02/2019 - 12:35
To add to what JAK (John) said, and the reason I asked if you used single point, is that if you use one of the auto focus point settings you are allowing the camera to choose out of a number of points where it will focus. If it thinks it finds more contrast in the branches/berries, that is where it will focus.

You will see which focus points it is using when AF lock is attained, they flash red in the viewfinder. When focus is critical as in short camera to subject distance it is vital that you observe this as you take your shots.
Peter



My Flickr page
Last Edited by pschlute on 10/02/2019 - 12:35

JAK

Link Posted 10/02/2019 - 14:16
.. and to add to that, sometimes one has to press the AF button several times before it focusses where one wants it to. People often blame focussing issues on the camera when the reality is the camera has no idea what the person taking the photo wants in focus and what they want out of focus. The camera just does its own thing if the photographer doesn't take charge!
John K
Last Edited by JAK on 10/02/2019 - 14:17

johnducguz

Link Posted 10/02/2019 - 15:20
This was one shot from a few, all focused more on the berries. I focused more than once on the bench end also to try & ensure a focus was grabbed. I thought it was standard practice to focus, keep the shutter button half depressed recompose then take the shot. That's why a lot of folk focus on the eye of the subject then recompose to include more of the torso before completing the shot. I've not heard of it being standard practise to use the back button. I have set both bodies to centre point focus. The manual says that a half pressed release locks the focus in. Focus is indicated by the indicator appearing a hearing a beep, these things happen.
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