SDM issues? A straw poll.

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loskeran

Link Posted 01/10/2009 - 10:01
Quote:
As for your problem, it's quite normal and it's called haunting.

I love that one, a Ghost in the lens, I've heard of Gremlins before.

Anvh

Link Posted 01/10/2009 - 10:03
loskeran wrote:
Quote:
As for your problem, it's quite normal and it's called haunting.

I love that one, a Ghost in the lens, I've heard of Gremlins before.


That's what you get when your are dyslectic and English is not your first language.
I sometimes do think the camera/lens has a mind of his own though and in such it might have a ghost (soul)

Hunting is the word we are looking for.
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ
Last Edited by Anvh on 01/10/2009 - 10:04

FredEriksson

Link Posted 01/10/2009 - 10:04
Thanks for your reply, Stefan. I know of haunting, especially when there is not enough light, but what I tried to describe is not that I believe. Basically what happened was that there was scene with lots of daylight and stuff and it should focus with no problems, but it never settled and I could hear the lens' AF motor go back and forth in quick tiny repetive movements like it's stuck in a machine gun-like infinite loop. If it did try to refocus itself I'm sure it would be able to find focus again but I need to give it a nudge by refocussing on something else first and then try again. It's not really a huge problem if it doesn't escalate and I'm not too worried.

Anvh wrote:
Fred that is an auto focus failure not a SDM one, SDM is simply the motor that drives the focus system of the lens, nothing more nothing less.

As for your problem, it's quite normal and it's called haunting.
The AF sensor needs contrast to see if the focus is "sharp" or not and it does not like low light since contrast will drop as well and it reads the light that reflects from the subject.
It simply is not able to see sometimes so it will miss the focus.

Anvh

Link Posted 01/10/2009 - 10:07
the AF sensor also needs contrast, it will for example not lock on the blank walls here, might that have been the problem?
I also found that it helps when you manually put the focus nearly correct, it mostly snap on instantly.
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ

FredEriksson

Link Posted 01/10/2009 - 10:15
LOL, I just went and continued to use "haunting" and in the same sentence where I mention "when there is not enough light"! Ghost do come out when it's dark, right?


Anvh wrote:
loskeran wrote:
Quote:
As for your problem, it's quite normal and it's called haunting.

I love that one, a Ghost in the lens, I've heard of Gremlins before.


That's what you get when your are dyslectic and English is not your first language.
I sometimes do think the camera/lens has a mind of his own though and in such it might have a ghost (soul)

Hunting is the word we are looking for.

FredEriksson

Link Posted 01/10/2009 - 10:20
The scene was full of contrast and the lens started focusing and the scene was pretty much in focus but the focus never settled. And, the AF mode was NOT AF.C I might add.

/F

Anvh wrote:
the AF sensor also needs contrast, it will for example not lock on the blank walls here, might that have been the problem?
I also found that it helps when you manually put the focus nearly correct, it mostly snap on instantly.

Anvh

Link Posted 01/10/2009 - 10:21
Very strange Fred, hopefully it isn't much of a problem.
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ

FredEriksson

Link Posted 01/10/2009 - 10:40
If it stays at this level it's only a very samll nuisance that I can live with. Otherwise the lens is pretty quick to focus with and quiet. And hopefully it will stay that way!

/F

Anvh wrote:
Very strange Fred, hopefully it isn't much of a problem.

RichardDay

Link Posted 01/10/2009 - 13:01
jamesm007 wrote:
Hello, Richard nice site! Nice poll! One suggestion to make it IMO a bit more accurate. No one disputes the DA*300mm, DA*200mm or DA*60-250mm are for the most problem free. The main complaints are toward the DA*50-135mm and DA*16-50mm. I would aggregate all of those lens for you percentage as this will more accurately reflect what we already know, and what we don't know; or in other words get your figure closer to the actual failure rate of those two lens.

Also if you consider any QC problem, SDM or not, say slow AF, as we are not able to separate issues with the facts we have that may have a root cause in the SDM system, or at least for the owner it does not matter as it may still be poor QC there is no way to separate the two. the percentage of DA*16-50mm and DA*50-135mm no matter how you want to add it, on your own poll, is kinda high. I won't say the exact figures as this is your show and I may have added wrong, I for sure am not perfect at 2:00am. Just my two cents

Hi James

Nice to see you here, it's a very friendly and civilised place compared to some!

The challenge I had with setting this poll, is that the poll system is very simple, only a single topic with a single choice (from many) is allowed, it would be much nicer if we could have multiple selectable choices and multiple topics/questions.

I do think however, that no-one so far has felt that they have been dealt with unfairly by either their dealer of Pentax (UK).

I agree that the reliability of any product decreases with usage and time and also that the main problem lenses are the first two SDM models. I also agree that optical alignment issues are quite common and that the SDM system as implemented is certainly not that fast. But alignment (and AF speed) are evident from new and can be dealt with at the time of purchase, whereas motor failure (like any other electrical/mechanical fault) is a potential failure and we should reasonably expect a low incidence of failures (under 1%) over a few years of reasonable use equating to say the same expected life of the shutter mechanism. i.e. around 100,000 actuations for a pro grade product.

I always advocated the use of ultrasonic ring motors rather than a micro motor as they are designed specifically for fast AF systems, but they do add bulk around the lens and are probably more expensive to implement.

I think that the confusion about AF speed arises from the use of the word Supersonic. SDM really stands for Silent Drive Motor rather than fast, maybe one day Pentax will release designs with ring motors? Maybe call them SRM lenses i.e. Supersonic Ring Motor.
Best regards
Richard Day

Profile - link - (click on About for equipment profile) - My Flickr site - link
Last Edited by RichardDay on 01/10/2009 - 13:18

Dr. Mhuni

Link Posted 01/10/2009 - 13:24
Just a thought - has anyone heard anything about the reliabilty (or otherwise) of the Tokina versions of these lenses?
Mhuni

500px

Anvh

Link Posted 01/10/2009 - 13:37
Dr. Mhuni wrote:
Just a thought - has anyone heard anything about the reliabilty (or otherwise) of the Tokina versions of these lenses?

They are only screwdriven
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ

Dr. Mhuni

Link Posted 01/10/2009 - 14:11
Anvh wrote:
Dr. Mhuni wrote:
Just a thought - has anyone heard anything about the reliabilty (or otherwise) of the Tokina versions of these lenses?

They are only screwdriven

Lucky Canikon users, judging by all the sdm issues!
Mhuni

500px
Last Edited by Dr. Mhuni on 01/10/2009 - 14:12

Anvh

Link Posted 01/10/2009 - 14:20
Dr. Mhuni wrote:
Lucky Canikon users, judging by all the sdm issues!

Well the Canon mount has a AF micro-motor in the lens but the nikon version does not so the budget cameras of Nikon (D40, D60, D3000) aren't able to auto focus since they don't have a screwdrive in the body.

As for the problems with SDM it's 15% of the user that voted that had a problem with one of there lenses.
Some have more SDM lenses but only one failed.

Also I shouldn't be laughing since there are coming more and more SDM lenses on the market.
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ

Dr. Mhuni

Link Posted 01/10/2009 - 14:27
It might be more than 15% of 16-50 & 50-135 owners though.

Also, might the screw-drive improve the slow focusing that some complain about?
Mhuni

500px

Anvh

Link Posted 01/10/2009 - 14:55
Dr. Mhuni wrote:
It might be more than 15% of 16-50 & 50-135 owners though.

Also, might the screw-drive improve the slow focusing that some complain about?

Those are simply numbers, probable only Pentax know how many faulty came back for repairs. Although a number of 15% is very high though, when reading the topic most owners with a broken SDM have 2 or more lenses and others commenting even have 4 or 5 so the number will probable be around the 5% though of the lenses.

As for the speed, I don't know if the AF system is used differently, if so then that might be the problem.
The way SDM AF system works is.
- AF meters and give a signal to move the focus, it says so many turns at that speed. they could optimize this but Pentax keeps that low to insure accuracy and to get a better one hit lock.
- It can also be the problem that the PZ contacts can not carry enough power so the motor works sluggish. There are some comments that SDM works faster with Full batteries.
- KAF2 system is faulty. the system is designed to work on SDM and screwdrive so the focusing mechanism in the lens is quite complex for that reason. Maybe KAF3 (SDM only) lenses like the DA*55 and DA17-70 work better. I don't have those lenses so don't know for sure.
The DA*55 seems to be only a tiny bit slower then the FA50 lens as for the DA17-70?

ps. pure speculation this, no facts!
Stefan


K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
AF-540FGZ
Last Edited by Anvh on 01/10/2009 - 14:55
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