Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
03-03-2011, 03:51 PM   #46
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
Original Poster
QuoteOriginally posted by Class A Quote
I'd ask Sigma what to do, i.e., whether they need your camera to calibrate the lens or not. I've heard good user reports from Sigma service centres, so I'd give it a try.

Good luck with the lens, hope it won't disappoint!

I've seen some very nice shots from the Sigma. Not such a fan of the DA* 55/1.4.

N.B., by looking for 55/1.4 shots, I found this mini thread in which other DA* 55/1.4 users report about focus problems.
Thanks for the link. Here is what one of the users said in that thread:

QuoteQuote:
This lens is capable of very sharp results with pleasing colours & bokeh, etc. I really want to love this lens but today I have given it to my Pentax dealer in London to send to Pentax and sort it out.
With my copy, you can take the same shot from the same location at the same aperature value; i.e all the same, etc and it will focus slightly differently every time. Also, it will give perfect infinity focus with zero AF correction set on my K7, but then it is out of focus for mid to close-focus shots. Then if I adjust the AF correction to +7, then the mid to close shots are sharp but infinity focus is blurred. I also have the 16-50 and the 50-135 and the FA77 and they all focus perfectly.
This matches my experience with four copies of that lens. Backfocusing was not the only problem. Erratic focusing was another. I really wanted to love it and to keep it, but there was no way that I could trust it.

Rob

03-03-2011, 03:54 PM   #47
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
Original Poster
QuoteOriginally posted by creampuff Quote
With Sigma's QC, you really got to test thoroughly. I got friends using Canon, Nikon and Pentax who had to send their Sigma 50mm f/1.4 for re-calibration for focus issues with my local Sigma service center. This is a known issue and using the camera's AF fine adjustment is not the solution. Having said that, once calibrated, it is a stellar lens, just like the DA* 55mm f/1.4.
A question regarding the Sigma 50/1.4: Have you found focus shift to be much of an issue, i.e. does the focus point shift backwards as the aperture is stopped down? This was reported to be the case by Photozone.

Rob
03-04-2011, 02:52 PM   #48
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
Original Poster
The saga continues.

Well, I received the Sigma 50/1.4 last night. This lens is built like a tank and is much heftier than the Pentax. It is exceptionally sharp from f2-f5.6. Focusing calibration is possible without too much trouble. However, the focusing accuracy is abysmal. Ten consecutive shots using the LensAlign system at a constant aperture with the camera mounted on a tripod show the focus points to be all over the map. Just to assure myself that I was not losing my mind, I tested my DA* 16-50 in the same way and found it to consistently focus at the exact same point. In addition, Sigma lens does indeed exhibit significant focus shift, meaning that one has to compensate for it depending on the aperture and DOF. So, I do not believe that this lens will be suitable. Call me picky.

I spoke with Pentax's Customer Care in Chandler, AZ. They assured me that if I purchase another DA* 55/1.4 that does not perform up to standards, they will repair or replace it as necessary, so that I will get a satisfactory copy. (Promises, promises.) If service is needed, I will send the camera with the lens. So, acting against my better judgement, I have placed an order with Adorama--fifth lens, third vendor.

Rob
03-04-2011, 03:15 PM   #49
Veteran Member




Join Date: Apr 2010
Location: Tennessee
Posts: 1,994
Well, I admire your commitment. I just hope you don't end up being committed.

03-04-2011, 04:28 PM   #50
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
Original Poster
QuoteOriginally posted by DogLover Quote
Well, I admire your commitment. I just hope you don't end up being committed.
I hear you. The only saving grace is that return shipping for defective units, is free, so I'm still not out of pocket any money for all the lenses that I have tested. It's just the aggravation of getting one lemon after another that is bugging me. On the other hand, I'm getting really good at setting up the LensAlign kit. I can get it completely ready to go in about 5 minutes. It is pricey but far superior to simple focus test charts and, for those who care about precision, well worth the investment. In fact, I would say that the cost is trivial compared to the cost of several high quality lenses.

Rob
03-04-2011, 04:53 PM   #51
Veteran Member




Join Date: Apr 2010
Location: Tennessee
Posts: 1,994
QuoteOriginally posted by robgo2 Quote
I hear you. The only saving grace is that return shipping for defective units, is free, so I'm still not out of pocket any money for all the lenses that I have tested. It's just the aggravation of getting one lemon after another that is bugging me. On the other hand, I'm getting really good at setting up the LensAlign kit. I can get it completely ready to go in about 5 minutes. It is pricey but far superior to simple focus test charts and, for those who care about precision, well worth the investment. In fact, I would say that the cost is trivial compared to the cost of several high quality lenses.

Rob
Yeah, I imagine I will break down and get one someday. Thing is, I've never noticed any focus issues with any of my lenses. I have double-checked a few of them using that online moire pattern (if you know what I'm talking about) and they looked spot-on. I just hope my luck holds and the K5 I'm expecting on Monday works as well with my lenses. But I am pretty anal and the idea of verifying perfect functionality (in any area) definitely appeals to me.
03-04-2011, 07:28 PM   #52
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
Original Poster
QuoteOriginally posted by DogLover Quote
Yeah, I imagine I will break down and get one someday. Thing is, I've never noticed any focus issues with any of my lenses. I have double-checked a few of them using that online moire pattern (if you know what I'm talking about) and they looked spot-on. I just hope my luck holds and the K5 I'm expecting on Monday works as well with my lenses. But I am pretty anal and the idea of verifying perfect functionality (in any area) definitely appeals to me.
You may be lucky in that all of your lenses are spot on, but I, too, thought that until I started checking mine with LensAlign. After making the appropriate adjustments, I discovered that my lenses were actually much sharper than I had realized.

Rob
03-04-2011, 07:43 PM   #53
Veteran Member




Join Date: Apr 2010
Location: Tennessee
Posts: 1,994
QuoteOriginally posted by robgo2 Quote
You may be lucky in that all of your lenses are spot on, but I, too, thought that until I started checking mine with LensAlign. After making the appropriate adjustments, I discovered that my lenses were actually much sharper than I had realized.

Rob
Now why would you have to go and tell me something like that? You should send me your phone number so I can call you tonight when I'm not sleeping and I can explain to you the consequences of telling something like this to someone as anal as myself.

03-04-2011, 11:21 PM   #54
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
Original Poster
QuoteOriginally posted by DogLover Quote
Now why would you have to go and tell me something like that? You should send me your phone number so I can call you tonight when I'm not sleeping and I can explain to you the consequences of telling something like this to someone as anal as myself.
I want someone to feel my pain as I work through this DA* 55/1.4 business. Seriously, I do think that LensAlign is a good investment for someone who owns quality glass and cares deeply about sharpness. You may be one of those people. There is a similar, but less expensive, device called the Spider or something like that, but I know nothing about it.

Rob
03-05-2011, 12:22 AM   #55
Pentaxian
Class A's Avatar

Join Date: Aug 2008
Location: Wellington, New Zealand
Posts: 9,193
DogLover, LensAlign is a nice tool but it a) doesn't make one's lenses sharper and b) can be replaced with a bit of DIY. Alternatively, just use AF adjustment bracketing on a flat target or one that interests you in practical situations (I already posted a pointer to my AF adjustment hints).

A successful AF adjustment will just move the point of focus where it belongs. You'd notice if it isn't where it belongs. So again, LensAlign is useful (but not perfect) for making quick and consistent adjustments but it is in no way irreplaceable If you want to be anal about your AF fine adjustment you could have that right now.

Last edited by Class A; 03-05-2011 at 03:45 AM.
03-05-2011, 03:53 AM   #56
Pentaxian
Class A's Avatar

Join Date: Aug 2008
Location: Wellington, New Zealand
Posts: 9,193
QuoteOriginally posted by robgo2 Quote
There is a similar, but less expensive, device called the Spider or something like that, but I know nothing about it.
The Spyder LensCal lacks the alignment aids of the LensAlign tool. If I were to burn money on such a tool, I'd go for the real McCoy and get the LensAlign.

Robgo2, I'm sure you are doing it, but just to make a 100% sure: Are you putting the sighting gate of the LensAlign down before you take measurement shots?

How do the lenses obtain different focus? Do they seek a new focus point just because you trigger "AF" again, or is it a result of letting the lens run from the MFD or infinity to the target again? I could imagine that the latter would result in quite some variation for very fast lenses (which the 16-50 is not). I'd be worried if a lens couldn't home in on the correct focus point after a few AF attempts, but I wouldn't necessarily expect it to hit the sweet spot from one of the extreme ends in a consistent manner. I believe the AF system of the K-7/K-5 says "good enough" before optimal focus can be obtained in such scenarios.
03-05-2011, 05:30 AM   #57
Pentaxian
RonHendriks1966's Avatar

Join Date: Jan 2009
Photos: Gallery
Posts: 8,714
QuoteOriginally posted by robgo2 Quote
You may be one of those people. There is a similar, but less expensive, device called the Spider or something like that, but I know nothing about it.
I bought this Spider thing and basicly you can't go wrong with it. You just make it level, as your camera and AF on the vertical and reed out on bigger screen where the sharpest point/shift is. I make it simple to my self and make 5 shots: -10 -5 0 5 and 10 then I look in PC where I have to look and then make a serie of say 0 1 2 3 4 5 and look where it is precise. Then I just take another small serei of 2 and 3 to make a discision. For DA*55 I did this with f1.4 and for FA*85 I did this with f2.0 since I'm not using that lens at open apperture.
03-05-2011, 01:01 PM   #58
Veteran Member




Join Date: Jan 2007
Location: New Mexico
Photos: Albums
Posts: 1,125
Original Poster
QuoteOriginally posted by Class A Quote
The Spyder LensCal lacks the alignment aids of the LensAlign tool. If I were to burn money on such a tool, I'd go for the real McCoy and get the LensAlign.

Robgo2, I'm sure you are doing it, but just to make a 100% sure: Are you putting the sighting gate of the LensAlign down before you take measurement shots?

How do the lenses obtain different focus? Do they seek a new focus point just because you trigger "AF" again, or is it a result of letting the lens run from the MFD or infinity to the target again? I could imagine that the latter would result in quite some variation for very fast lenses (which the 16-50 is not). I'd be worried if a lens couldn't home in on the correct focus point after a few AF attempts, but I wouldn't necessarily expect it to hit the sweet spot from one of the extreme ends in a consistent manner. I believe the AF system of the K-7/K-5 says "good enough" before optimal focus can be obtained in such scenarios.
Yes, I am careful to lower the gate before doing the actual test shots. My technique is to defocus the lens slightly before each shot, so as to force the camera to refocus. I do not defocus to either extreme. And just to give the lens the benefit of the doubt, I often release and repress the shutter button to allow for fine tuning of focus.

For the record, the Sigma is erratic even at f2.8, which is the same as the maximum aperture of the DA* 16-50. One of the beauties of the LensAlign device is that you can actually see the focus point moving forward and backward, which you cannot see with a simple focus chart. All that the latter tells you is that you are either in or out of focus. For a lens that focuses in a consistent manner, that will be enough. For one that is inconsistent, it leads to a state of confusion. I'm not claiming that a special system, such as LensAlign, is essential for proper lens calibration, but it is very nice.

Rob
03-06-2011, 02:54 PM   #59
Pentaxian
Class A's Avatar

Join Date: Aug 2008
Location: Wellington, New Zealand
Posts: 9,193
QuoteOriginally posted by robgo2 Quote
For the record, the Sigma is erratic even at f2.8, which is the same as the maximum aperture of the DA* 16-50.
Any lens that shows erratic focusing should do this at every aperture. Focusing occurs wide open so if the camera has trouble to find the same focus point consistently, this should happen for any shooting aperture. Of course, the higher DOF better masks small errors when using smaller apertures. If there are differences between wide and small shooting aperture focusing then they stem from the AF algorithm in the camera, but not from the lens.

QuoteOriginally posted by robgo2 Quote
One of the beauties of the LensAlign device is that you can actually see the focus point moving forward and backward, which you cannot see with a simple focus chart.
Every tilted focus chart allows you to see the focus point moving forward and backward. In fact, I'm not aware of any focus charts (except the moiré-based ones) that are not to be used in a tilted setup.

QuoteOriginally posted by robgo2 Quote
I'm not claiming that a special system, such as LensAlign, is essential for proper lens calibration, but it is very nice.
Agreed, it is nice. For utmost precision, however, I recommend to do follow up the LensAlign procedure with AF adjustment bracketing on a flat target, using the AF area to read out the best focus, as opposed to the ruler which might be in a slightly different focus plane due to field curvature.
03-06-2011, 03:26 PM   #60
Veteran Member




Join Date: Apr 2010
Location: Tennessee
Posts: 1,994
Can you guys offer any insight on the different versions of the LensAlign? I think I was only aware of the $80 version, but now see that there is the $180 Pro version with an "enumerator" (which is what, exactly?), and a $250 Pro Plus version that adds the 47" long ruler. I'm guessing that would be the one to use for my 100-300, but can that lens be done on the others? Even the cheapest one says there is a 24" long ruler option (though I don't see it listed at B&H). Would that be enough to do my long lens?
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, copy, da*, k-mount, lenses, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
GX20/K20D Shake Reduction OIS SR erratic operation chhayanat Pentax DSLR Discussion 5 07-15-2011 11:34 AM
For Sale - Sold: K10D (with focusing problem), BG2 Grip, DA 18-55mm (Worldwide) Aegon Sold Items 0 08-28-2010 02:15 PM
For Sale - Sold: Pentax Brand Focusing Screens and Katz Eye Focusing Screen K10D/K20D (Worldwid superbass Sold Items 8 03-26-2010 01:42 PM
Question regarding types of Focusing and Focusing Points stl09 Troubleshooting and Beginner Help 1 01-31-2010 09:22 PM
For Sale - Sold: K100d and 18-55mm kit lens + split focusing screen installed + glass screen pr vanchaz2002 Sold Items 1 07-24-2008 07:09 AM



All times are GMT -7. The time now is 07:06 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top