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08-08-2007, 09:28 AM   #1
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Pentax/Nikon/Canon - Sigma AF issues

I'll try to be brief with my question. I'm in the process of picking a new lens and I've been pouring over reviews. I've noticed that alot of Canon and Nikon users have complained of front-focusing on some EX Sigma lenses. My question is this:

Is that issue a moot point since they have on-board focusing motors vs. our (Pentax) on-body focusing motors? I can't find any gripes regarding similar issues coming from Pentax owners...

Thanks!

08-08-2007, 09:53 AM   #2
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Probably because Pentax users tend to be a more mellow lot lol.

I have 2 Sigma lenses for my 20D, and no problems with front or back focusing issues.

However, I am sure if I start to pixel peep and measurbate, I could probably find something wrong to complain about. I have long since figured out that this sort of behaviour just ruins a good hobby.

Since there are more Nikon, and Canon users out there then Pentax users, you will hear more complainers out there not happy about something or other.
08-08-2007, 10:03 AM   #3
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QuoteOriginally posted by Chako Quote
Probably because Pentax users tend to be a more mellow lot lol.

I have 2 Sigma lenses for my 20D, and no problems with front or back focusing issues.

However, I am sure if I start to pixel peep and measurbate, I could probably find something wrong to complain about. I have long since figured out that this sort of behaviour just ruins a good hobby.

Since there are more Nikon, and Canon users out there then Pentax users, you will hear more complainers out there not happy about something or other.
Thanks Chaco... that makes sense.

I was thinking that the lens and it's internal chip handle more of the focusing when the motor is internal but you can't discount the measurbation issue among most reviewers. Coincidentally, I just found a (negative) reviewers personal blog in which he took photos of a measuring tape so you could quantify the front focus. I'm henceforth ignoring his reviews.
08-08-2007, 10:34 AM   #4
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QuoteOriginally posted by matiki Quote
Coincidentally, I just found a (negative) reviewers personal blog in which he took photos of a measuring tape so you could quantify the front focus. I'm henceforth ignoring his reviews.
I find this view somewhat astonishing.

One of the assumptions we implicitly make as we endeavour to improve our photographic skills is that faults in the photograph are due to shortcomings in our technique. If this were not true, striving for better pictures would be pointless.

Usually it's a safe assumption, since most cameras and lenses do not have manufacturing defects, and most of the time the cause of the flaw is rather obvious, and the technique correction not difficult to achieve with practice.

But occasionally, we find something in our photographs that causes doubt. Strange exposures that we can't explain, focusing that's a bit off - I'm sure we all encounter this from time to time. But if the problem recurs frequently there's a risk that our confidence in the equipment will be undermined.

This is the point at which some careful investigation is warranted, and 'careful' means under controlled, repeatable conditions - since in the field, it is usually impossible to check things reproducibly, and then you end up with pointless conjecture and argument.

Measurbation, as we love to ridicule it, has its place. It's not the sort of photography we want to have to do, but if you suspect that there's something wrong, what would you rather do - trust blindly that you don't have one of the duds that occasionally escapes the QC process, and continue producing sub-standard pictures, or know for sure?

Usually, of course, even after you've checked carefully, the conclusion is still that it's the technique that's at fault. Which is a good thing

But occasionally it's not. K10D stop-down-metering, anyone?

08-08-2007, 11:11 AM   #5
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Your camera is a tool. It has limitations, just like me. Auto-focus is only an aid to making things simpler, reducing the work-load. It's a bit like auto-pilot, you know it could land the plane if you let it, but you're still glad to see the pilot taking control. I almost never trust auto-focus, even if I use it, I still like to check visually with the non-automatic No.1 eyeball. It's all part of the craft, which I enjoy.

Sympathy to sports photographers, who probably think they need auto-focus more than landscape artists, or portrait photogs, but we made great sports pictures before automation began to down-skill our art, and we still can; auto-focus or no auto-focus.

No flames please, I'm old and stuck in my ways, I mourn the passing of the smelly darkroom and silver-stained fingers, tilting baseboards, real dodging and burning..........sob, sob
08-08-2007, 11:14 AM   #6
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QuoteOriginally posted by ChrisA Quote
I find this view somewhat astonishing.

One of the assumptions we implicitly make as we endeavour to improve our photographic skills is that faults in the photograph are due to shortcomings in our technique. If this were not true, striving for better pictures would be pointless.

Usually it's a safe assumption, since most cameras and lenses do not have manufacturing defects, and most of the time the cause of the flaw is rather obvious, and the technique correction not difficult to achieve with practice.

But occasionally, we find something in our photographs that causes doubt. Strange exposures that we can't explain, focusing that's a bit off - I'm sure we all encounter this from time to time. But if the problem recurs frequently there's a risk that our confidence in the equipment will be undermined.

This is the point at which some careful investigation is warranted, and 'careful' means under controlled, repeatable conditions - since in the field, it is usually impossible to check things reproducibly, and then you end up with pointless conjecture and argument.

Measurbation, as we love to ridicule it, has its place. It's not the sort of photography we want to have to do, but if you suspect that there's something wrong, what would you rather do - trust blindly that you don't have one of the duds that occasionally escapes the QC process, and continue producing sub-standard pictures, or know for sure?

Usually, of course, even after you've checked carefully, the conclusion is still that it's the technique that's at fault. Which is a good thing

But occasionally it's not. K10D stop-down-metering, anyone?
I'm cool with careful, objective analysis. But one bad copy does not make a bad line of lenses. Unfortunately, the review I discussed, is referred to a number of times by other unsatisfied lens reviewers. It's one thing to say:

"My copy of lens xyz had the following flaws and following strengths..."

It's another to say:

"These lenses all have critical flaws... they all do this:..."

I guess my real gripe isn't with the methodology used to arrive at his conclusion that his lens is bad. It's with his decision to pooh-pooh the lens everywhere he can find. By ignoring his reviews, and the reviews of others who simply cite his experience... I find absolutely no surprising reviews of the lens in question.

Perhaps I'm just venting because his widespread web of pooh-pooh reviews has delayed my much anticipated 2nd lens purchase.
08-08-2007, 11:20 AM   #7
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Oh, there are examples. Reading for you:
Sigma 30/1.4 EX DC - good?: Pentax SLR Talk Forum: Digital Photography Review
08-08-2007, 11:20 AM   #8
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QuoteOriginally posted by keithlester Quote
Your camera is a tool. It has limitations, just like me. Auto-focus is only an aid to making things simpler, reducing the work-load. It's a bit like auto-pilot, you know it could land the plane if you let it, but you're still glad to see the pilot taking control. I almost never trust auto-focus, even if I use it, I still like to check visually with the non-automatic No.1 eyeball. It's all part of the craft, which I enjoy.

Sympathy to sports photographers, who probably think they need auto-focus more than landscape artists, or portrait photogs, but we made great sports pictures before automation began to down-skill our art, and we still can; auto-focus or no auto-focus.

No flames please, I'm old and stuck in my ways, I mourn the passing of the smelly darkroom and silver-stained fingers, tilting baseboards, real dodging and burning..........sob, sob
LOL

My dad just gave me his old Yashica from Vietnam (The War, I think it was made elsewhere). He has some amazing photos and slides that were taken with it. I've bought my first roll of black and white (yes you are talking to someone who's never owned a film camera, if you don't count APS, which I don't) and I can't wait to mess around with it. He has some amazing photos from helicopters flying low over landing zones and other "full of action and movement" scenes, all taken with a manual focus, cocking diaphram camera.

I think if I found a lens had a "front focus" issue at some range of zoom, I'd learn to turn the focus ring manually in those situations and move on, but that's just me.

08-08-2007, 11:26 AM   #9
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There is so much sample variation. Nikon's initial run of their excellent 18-70 DX lens was plagued with noticeable BF issues, but they were easily correctable.

I believe there is a lens callibration setting in the new Canon sports camera so BF/FF plagues many manufacturers.
08-08-2007, 11:59 AM   #10
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QuoteOriginally posted by Jonas B Quote
Thanks Jonas. That's quite a thread (long).
08-08-2007, 01:09 PM   #11
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Wow haha...and I thought the BF/FF issues on the DA lenses were serious.

I agree that autofocus is an only aid and to totally depend on it spoils the charm of having an SLR for photography. Like why do I see so many threads on the DA*s where SDM takes precedence over other elements far more crucial in terms of photographic weight. Not just sharpness but stuff like colour rendition, CA/PF, etc.
08-08-2007, 06:08 PM   #12
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At one point I had three consumer Sigma lenses, and they all focused fine. Certainly no worse than any Pentax lens I have, and better than a handful!
08-08-2007, 06:17 PM   #13
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QuoteOriginally posted by FotoPete Quote
Wow haha...and I thought the BF/FF issues on the DA lenses were serious.

I agree that autofocus is an only aid and to totally depend on it spoils the charm of having an SLR for photography. Like why do I see so many threads on the DA*s where SDM takes precedence over other elements far more crucial in terms of photographic weight. Not just sharpness but stuff like colour rendition, CA/PF, etc.
Hey Pete,
It's a tough call for me. I used an MX with a 50mm for the longest time and the only time MF remotely bothered me was when shooting sports.

Once you're "spoiled" with AF though, it becomes a useful tool much like autoexposure (which my MX didn't have either). I guess 1) It's almost always faster 2) easier to focus off centre and 3) digital SLRs are much harder to manual focus.

With the stock focusing screen, MF is quite tricky, but with a custom screen matching the MX, I'm not as reluctant anymore, even though the MX viewfinder is still worlds better in terms of size and clarity in general, especially with fast lenses.
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