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09-22-2014, 12:45 AM   #31
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QuoteOriginally posted by interested_observer Quote

The other thing I was going to say, is that the K5 can hold up to 20 separate (Pentax) lens corrections, but only 1 for a non Pentax lens. So, if you have 2 Sigma lenses, both of them get the same correction. When you have time, I would send the lens in to your local Sigma service for correction.

Is this correct? In all threats of residing threads on back/ front focus and adjusting this has never been mentioned before, If that's the case I have wasted hours setting individual 3rd part lenses and if that's the case which one is the non pentax one? The first one you set or which one?

09-22-2014, 03:28 AM   #32
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QuoteOriginally posted by adwb Quote
Is this correct? In all threats of residing threads on back/ front focus and adjusting this has never been mentioned before, If that's the case I have wasted hours setting individual 3rd part lenses and if that's the case which one is the non pentax one? The first one you set or which one?
I don't think it is true. But, at least a couple of Sigma zooms have the same number identifying them to the camera body (I think one of the 17-70s and one of the 70-200), meaning that the camera will apply the adjustment to both of them. Otherwise, I don't think it cares third party versus brand name.
09-22-2014, 08:24 AM   #33
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After shooting dogs in the park (boy does that sound bad) I can say the 18-135 range is most useful. Yes, some longer range once in a while is good but the dogs seem to want to play near the people a lot, so the wide side is more frequently used. Maybe if you're at an event and want to remain a discreet distance the 70mm minimum won't be a problem.

As usual, I'm using center focus, center-weighted metering or spot metering and stopped down for good DOF. I don't see why you'd shoot wide open if you have plenty of light, particularly if you're following motion. Using a multiple focus point mode I think you're giving too much control to the camera in that situation.

Maybe the camera is back focusing if all your shots are consistently displaying this behavior. It's definitely worth pursuing a profile for that lens.
09-22-2014, 02:05 PM   #34
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For all of you fine members advising the OP his lens is back focusing, can you explain how his lens is back focusing but has the sharp area of grass and dirt on the lower front left 1/3 of the photo? Take a look. One cant just look at the subject and what is in focus with it one needs to study the entire photo and make a determination based on the settings used for the distance and what the entire result is, then if it doesn't look right determine if more appropriate testing is needed and if the cameras fine tuning can be a fix or if servicing is required. Arbitrarily using the cameras fine tune adjustment can create more of a problem with ones photos.

When you set your K5 up for back button focusing did you shut off the half button press? If not then when your shutter button reaches half press then the camera would refocus. How much would depend on how quickly the shutter is fully depressed and where the focus point is aimed at the time. Also you need to consider what the depth of field is for your distance and aperture; such as if you were around 27-30 feet from your subject using a f2.8 your depth of field would be approx. 1.7ft using a long telephoto lens at 120mm. Most fully grown Great Danes I know are larger than that area so there will be areas of blurred focus dependent on the focus point.

What concerns I have with what I am seeing in your photo is the area to the lower left where the grass and dirt is in focus, given the presumed angle this photo was taken, the sharpness should run across and be as sharp in the right side at the same distance for which I am not seeing in the photo. The right side same distance is showing sharpness degradation Then coupled with the areas of the dog that are in and out of focus does indicate to me then lens may need some service adjustment and not be something the cameras fine adjustment could fix because I don't see this as just a front or back focus problem and certainly not a camera problem...


Last edited by Oldbayrunner; 09-22-2014 at 02:12 PM.
09-22-2014, 05:45 PM   #35
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QuoteOriginally posted by Digitalis Quote
...brand name lenses when used on the cameras they are designed for will have an inherent advantage.
No, they will not.

AF protocols have been fully reverse-engineered and there are no systemic problems with third-party lenses when it comes to AF.

QuoteOriginally posted by Digitalis Quote
The proprietary focusing protocols will be designed to work with the manufacturers cameras and lenses - but with third party makers things go pear shaped and protocols don't work as they are expected to.
Nonsense.

All my third-party lenses autofocus just as well as my Pentax lenses.

Many professionals use Sigma lenses on their high-end Canon bodies. Without a problem.
09-22-2014, 05:55 PM   #36
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QuoteOriginally posted by allie181 Quote
I will try and fix the back focus problem.
Good luck and let us know how it went.

Make sure that you have an unambiguous focus target. Using a ruler, for instance, is out of the question. You can use a ruler to judge front-focus/back-focus, but you must not focus on any part of a ruler because the camera cannot know which part of it you intend to focus on. Your focus target needs to be isolated so that the camera cannot get confused by nearby targets. If you follow the instructions of a focus chart, you should be fine. Or just do a series of shots (with varying focus adjustment values) on a single target.

Bear in mind, that the subject to camera distance matters, i.e., if you optimise the AF fine adjustment for 1.5m, it may not be optimal for 4m. I have collected some AF adjustment hints but don't let yourself get overwhelmed with them. Any change you'll do, will probably be for the better by the look of your sample photo.

Bear in mind, as CarlJF already suggested, that you should choose manual AF point selection. If you let the camera choose a focus point automatically, chances are that it will pick a high contrast area to focus on instead of the area you intend it to focus on. You can first just use the centre focus point (in manual focus point selection mode) and use the "focus recompose" technique, and later you can move the AF point around (which is particularly useful with moving subjects that you don't want to end up in the centre of the image).

Again, good luck with fixing your problem. Your camera is certainly capable of taking sharp shots. No need to leave Pentax. I hope you can make your lens work with the camera yourself. As an option, you can also take both lens and camera to a Sigma service centre and have the lens calibrated to your camera. This won't take long and won't cost much.

Last edited by Class A; 09-22-2014 at 06:01 PM.
09-22-2014, 06:42 PM   #37
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QuoteOriginally posted by adwb Quote
Is this correct? In all threats of residing threads on back/ front focus and adjusting this has never been mentioned before, If that's the case I have wasted hours setting individual 3rd part lenses and if that's the case which one is the non pentax one? The first one you set or which one?
I only have one non Pentax AF lens, so I really can't confirm this. Having said that, I do remember reading about this, so I went looking. This is what I found.
  • Page 126 in the Pentax K5 Users Manual, indicates that the body can index based on lens ID up to 20 separate lenses.
  • Apparently the problem is somewhat isolated to Sigma who makes it a habit of reusing lens ID across more than one lens type. This is discussed in the following post.
This is not a problem that Pentax can fix. Using the lens ID is a reasonable index (identifier) into the correction table. I really do not see any other item available that would identify the lens mounted. If the lens' manufacturer reuses the same lens ID across different lenses, then what is Pentax to do. Apparently, this is isolated to a few Sigma lenses. I would also think that the post processing utilities would have the same problem in identifying lenses for the application of correction factors. If Pentax had expected non Pentax lenses to reuse lens ID values, they could use the focal length to try to distinguish between the various lenses - but that is spilled milk.Also, the problem is not isolated to Pentax. Nikon has suffers from the same problem - but worse, except 3rd party lenses (guess who - Sigma) reuse Nikon lens IDs. At least, here in Pentaxland, we don't have Sigma lenses popping up being identified as Pentax lenses.

Last edited by interested_observer; 09-22-2014 at 06:57 PM.
09-22-2014, 09:44 PM   #38
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QuoteOriginally posted by Class A Quote
No, they will not.
They do, I'm talking from actual experience with brand and off-brand lenses here. Canon designs their lenses so the camera body will communicate to the lens and adaptively "learn" how to focus accurately with it* - this is why third party lenses have a higher incidence of issues related to AF accuracy**. Sigma and other third party manufacturers cannot copy this due to patent laws.

QuoteOriginally posted by Class A Quote
All my third-party lenses autofocus just as well as my Pentax lenses.
Well that isn't just fantastic, good for you! I'm just so happy to hear that. None of my sigma lenses had AF that was anywhere near accurate on any of my pentax camera bodies out of the box***. While we are on the subject: none of my Sigma lenses for Nikon F or Canon EF mount were perfectly accurate either****.

But then again I have a reputation around here for complaining about sigma all the time: So my opinions are invalid because i'm incapable of making any objective statements on third party lenses. I dare you to buy as many lenses as I have and maintain an objective view on lens makers. I think I'm justified in being more than a tad annoyed with sigma. Why do I have to be pegged as a malcontent?

* However, in extreme situations AF adjustment will still be needed, but over time the camera body will rein the lens in.
** Especially zoom lenses which are not parfocal - focus will drift over time.
*** Pentax K10D, Pentax K7, Pentax K5IIs, Pentax K3.
**** Canon 20D, Canon 1D, Canon 1Ds MKII, Canon 1D MkIIn, Canon 1Ds MKIII, Canon 1DX. Nikon D2x, Nikon D200, Nikon D3s, Nikon D4s.


Last edited by Digitalis; 09-22-2014 at 10:07 PM.
09-22-2014, 09:51 PM   #39
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Well? What was the result?
09-22-2014, 10:00 PM   #40
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QuoteOriginally posted by Digitalis Quote
Back button focusing is great for moving subjects especially when combined with continuous autofocus - but bear in mind you should never use continuous AF when the subject isn't moving. Canon and Nikon DSLRs have an automatic switch that change between the two modes if motion (or a lack of it) is detected. Pentax only recently developed this protocol for the SAFOX AF system. The K5, being an older camera doesn't have this functionality.

I've got 3 Nikon cameras and I'm not familiar with this Doug. Can you point out the menu/function please?
09-22-2014, 10:15 PM   #41
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QuoteOriginally posted by bossa Quote
I've got 3 Nikon cameras and I'm not familiar with this Doug. Can you point out the menu/function please?
For Nikon cameras I think it appears in the menu for the DXXXX series cameras the FN button can be customized to switch between AF modes. Entry level nikon bodies have AF-A ( automatic) setting by default.

Last edited by Digitalis; 09-22-2014 at 10:26 PM.
09-23-2014, 02:11 AM   #42
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The trouble with Sigma is their Retro engineering. There seem to be much less problems with Tamrons who just license the mounts.
09-23-2014, 04:01 AM   #43
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QuoteOriginally posted by D1N0 Quote
The trouble with Sigma is their Retro engineering. There seem to be much less problems with Tamrons who just license the mounts.
Do you have any corroborating evidence or are you just parroting an unfounded conjecture that circulates around forums?
09-23-2014, 04:19 AM   #44
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QuoteOriginally posted by Class A Quote
Do you have any corroborating evidence or are you just parroting an unfounded conjecture that circulates around forums?
This is a well known fact. Are you trying to pick a fight with me?
09-23-2014, 04:20 AM   #45
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QuoteOriginally posted by Digitalis Quote
Canon designs their lenses so the camera body will communicate to the lens and adaptively "learn" how to focus accurately with it* - this is why third party lenses have a higher incidence of issues related to AF accuracy**. Sigma and other third party manufacturers cannot copy this due to patent laws.
I don't want to comment on Sigma and Canon. This is a forum for Pentax users and the OP has a problem with a Pentax camera.

Pentax AF protocols have been known for a long time and there is zero evidence that third-party manufacturers have any difficulty to replicate the lens behaviour as required.

Again: Professional photographers use Sigma lenses. They would not do that if it implied any kind of compromise.

QuoteOriginally posted by Digitalis Quote
None of my sigma lenses had AF that was anywhere near accurate on any of my pentax camera bodies out of the box***.
This is unfortunate, but does not prove that Sigma has difficulty replicating AF protocols.
It also, BTW, does not prove that Sigma QC is worse than Pentax QC (or any other lens maker's QC, for that matter).

Your personal experience only means something in terms of a systemic effect, if it is backed up by other similar experiences, adding up to statistical significance.

QuoteOriginally posted by Digitalis Quote
So my opinions are invalid because i'm incapable of making any objective statements on third party lenses.
No, your opinions are not invalid at all.

However, your personal experience does not constitute absolute truth. It is just a single data point. Nothing more, nothing less.

QuoteOriginally posted by Digitalis Quote
I dare you to buy as many lenses as I have and maintain an objective view on lens makers.
I'm not sure what the challenge is, but one thing seems to be clear:

Despite your apparently almost unlimited funds for photography (with several camera systems and extremely expensive lenses such as from Leica), you choose to have multiple lenses from Sigma. You actually own more Sigma lenses than I do. So despite your unfortunate history with AF accuracy, you are still holding on to these lenses.

From this I conclude that
  • at least after AF calibration, AF accuracy must be at least acceptable, and
  • optically these lenses must be very good, if not exceptional.

But all we hear from you thread after thread is how idiotic Sigma designers are and how terrible Sigma AF is, etc.
It just doesn't make sense. Now, if you were complaining about your other lenses just the same, I'd understand. But you seem to have an axe to grind with Sigma in particular. Why don't just sell all that inferior gear and avoid being annoyed?

QuoteOriginally posted by Digitalis Quote
I think I'm justified in being more than a tad annoyed with sigma.
You are entitled to be annoyed about whatever you want and you are also entitled to continue to be annoyed even though you could just end it all by selling this annoying gear (instead of buying more Sigma lenses, as you just recently did).

What you cannot expect is to spread unfounded pejorative rumours about Sigma technology without people objecting to it.
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