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06-15-2009, 07:21 AM   #1
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DA* 50-135 is not as good as people think

I just purchased my DA* 50-135 F2.8 3 days ago and done some test shot vs my Sigma 70-300 F4-5.6

I use a K110D and I found that my sigma can focus much better than the pentax, the DA* temp to focus a little behind where it suppose to focus to. and in term of image quilty I find that they are the same at 135mm set at F4

I do not know if anybody out there have the sigma 70-300 F4-5.6 as well but I can either say the sigma is a super good deal or the DA* is super expensive.

Give give me some idea

06-15-2009, 07:30 AM   #2
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You have a bad sample, I have seen thousands of images from both lenses and there is no comparison at f/4.
06-15-2009, 07:42 AM   #3
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If I have a bad copy then what will pentax do about it? exchange one for free to me or what?
06-15-2009, 07:43 AM   #4
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QuoteOriginally posted by m42geo Quote
I just purchased my DA* 50-135 F2.8 3 days ago and done some test shot vs my Sigma 70-300 F4-5.6

I use a K110D and I found that my sigma can focus much better than the pentax, the DA* temp to focus a little behind where it suppose to focus to. and in term of image quilty I find that they are the same at 135mm set at F4

I do not know if anybody out there have the sigma 70-300 F4-5.6 as well but I can either say the sigma is a super good deal or the DA* is super expensive.

Give give me some idea
K110D has no SDM. AF is just a bit better than ist DS. DA*50-135 is not very quick lens and K110D is not camera with very fast AF.
And...
It's hard to find difference at 6 MP pictures from zoom lenses out of camera with strong AA filter.

06-15-2009, 07:44 AM   #5
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QuoteOriginally posted by m42geo Quote
If I have a bad copy then what will pentax do about it? exchange one for free to me or what?
Do you shoot in RAW?
Check back/front focus of 50-135 and try Light Room as RAW convertor.
06-15-2009, 07:46 AM   #6
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QuoteOriginally posted by ogl Quote
K110D has no SDM. AF is just a bit better than ist DS.
It's hard to find difference at 6 MP pictures from zoom lenses out of camera with strong AA filter.
Yes but My sigma can focus better than pentax. So if I only have 6mp sensor then there are no reasons to get * grade lens?

What is AA filter by the way?

I shot in raw to compare the photos
06-15-2009, 07:50 AM   #7
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QuoteOriginally posted by m42geo Quote
Yes but My sigma can focus better than pentax. So if I only have 6mp sensor then there are no reasons to get * grade lens?

What is AA filter by the way?

I shot in raw to compare the photos

Sigma could be faster. I don't see any miracle...

Check back/front focus of DA*.

All Pentax 6 MP cameras has strong AA filter.
Anti-aliasing filter - Wikipedia, the free encyclopedia

Help with moire and artifacts, but it lowers the resolution.

http://en.wikipedia.org/wiki/Moire

Compare DA*50-135 and Sigma at f5.6-11 range. The zooms at 6 MP should be closed till f5.6-11 (IMO) to get better results.

Last edited by ogl; 06-15-2009 at 07:56 AM.
06-15-2009, 07:53 AM   #8
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QuoteOriginally posted by ogl Quote
Sigma could be faster. I don't see any miracle...

Check back/front focus of DA*.

All Pentax 6 MP cameras has strong AA filter.
Anti-aliasing filter - Wikipedia, the free encyclopedia
Please let me know how to check back/ front focus of my lens? The is the buiggest issue for me for this lens, It focus at the back of the object a little. Need help

Thanks

06-15-2009, 07:58 AM   #9
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http://focustestchart.com/focus10.pdf
06-15-2009, 08:08 AM   #10
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QuoteOriginally posted by ogl Quote
but it doesn't tell me how to fix the issue after checking if the lens have back focusing problem or not
06-15-2009, 08:20 AM   #11
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QuoteOriginally posted by m42geo Quote
Please let me know how to check back/ front focus of my lens? The is the buiggest issue for me for this lens, It focus at the back of the object a little. Need help

Thanks
Try this: zoom in to 135mm then hold focus. recompose back to 50mm or wherever you want. then compare your shot with the same shot but instead, holding focus at the FL you wish to take (50mm is good to insure the same FL). I once thought my 50-135 back focused badly, but then learned this, and things were just dandy. Same with the 16-50, thought it was misfocusing a lot, but zooming in to focus first makes things all right However, I found that when I used my lenses with the K100D, things were generally sharper, meaning I don't have to zoom in that often to focus first, than on my K20 or K10 (must be SDM problems).
06-15-2009, 08:59 AM   #12
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Funny, I was just thinking about how good a lens the 50-135 is, especially in terms of wide open performance. I did a quick non-scientific test comparing the 50-135, 16-50, and FA50 at f2.8.

On a scale of 1-to-10 (with 10 being the sharpest): the FA50 is a 10, the 50-135 is a 9, and the 16-50 is a 6. My 16-50 is a good copy....very sharp. It just can't light a candle to the 50-135 wide open.
06-15-2009, 12:34 PM   #13
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QuoteOriginally posted by m42geo Quote
I just purchased my DA* 50-135 F2.8 3 days ago and done some test shot vs my Sigma 70-300 F4-5.6
Feel free to post the results (100% crops). I'm guessing that others will be able to see differences you are not. It's also possible that only having 6MP resolution isn't enough to see the differences as clearly as you could with a K20D.

But if nothing else, the mere fact that the 50-135 has f/2.8 and the Sigma does not makes the 50-135 infinitely preferable for many types of situations (eg, low light, portraits, etc). as does the fact that it has the 50-70 range the Sigma lacks. On the other hand, the fact that the 70-300 goes to 300 makes it much preferable for other types of situations. the are different lenses with different strengths. The fact that results might be comparable at 135mm and f/4 (and I say *might* - again, I'm guessing others will see differences you don't) doesn't mean they are equally useful in all situations.

QuoteQuote:
I use a K110D and I found that my sigma can focus much better than the pentax, the DA* temp to focus a little behind where it suppose to focus to.
It's possible that the fact that the 50-135 has less DOF at f/2.8 is causing you to notice a focus issue the Sigma would have been unable to display, because it can't go to f/2.8. In any case, most focus issues - assuming you do have on - are due to the camera, not the lens. but it's also very likely you don't have a focus issue, but are simply getting unlucky with the camera happening to choose a different target than you intended. It cannot read your mind, and the AF sensor is so large that you cannot usually place it precisely enough.

By all means, do use the test chart, and post the results. The K100D doesn't support the focus adjustment feature the K20D does, but there are special undocumented/unsupported ways of doing some focus adjustment - search on the terms "K100D", "focus adjustment", and "debug".
06-15-2009, 01:38 PM   #14
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QuoteOriginally posted by m42geo Quote
I just purchased my DA* 50-135 F2.8 3 days ago and done some test shot vs my Sigma 70-300 F4-5.6

I use a K110D and I found that my sigma can focus much better than the pentax, the DA* temp to focus a little behind where it suppose to focus to. and in term of image quilty I find that they are the same at 135mm set at F4

I do not know if anybody out there have the sigma 70-300 F4-5.6 as well but I can either say the sigma is a super good deal or the DA* is super expensive.

Give give me some idea
All zooms are compromises, even good ones. They can impossibly be optimised so that they offer the same quality for all focal lengths. As a almost perfect rule, they are best in the middle of the focal length range, and are suffering most from compromises in the short and long ends. I've shot the DA*50-135 against some of the best prime lenses Pentax made in this focal range: A50/1.7, A*85/1.4, A100/2.8, A*135/1.8. When I say that I shot them against each other I mean identical settings, multiple motives, brick walls on tripod with SR off and remote controle to remove all random differences... Not just one focal length, multiple appertures and iso's etc.

In the middle of the focal length range at f4 or more, it is comparable to the A100/2.8 and close to the legendary A*85/1.4. That a zoom rival excellent primes in this way is rare. In the 50mm end, it is OK, but not as sharp as the A50/1.7, and it has some corner softness. The 135mm end is its worse end: more corner softness, some distorsion. This is not strange: correcting this would have required more glass and made the lens more expensive and heavy and perhaps not as good in some other aspect. It get's noticeably better quite soon when you zoom away from 135mm towards 100mm.

Your consumer sigma zoom on the other hand has 135mm somewhere in the middle of its focal length range. Usually these ~70 to ~300mm lenses are quite bad above 200mm and quite good below 200mm. I don't know this lens first hand, but it is reasonable to assume that you are somewhere near its best range. So you have compared the worst part of an excellent zoom with the best part of another zoom. Not the best way to evaluate the lens.

As for autofocus speed. I don't know your sigma, but what I can say about the DA* lens is that is has a rather long ...searching for the right word in English...focus ring turning (?), and a lot of glass, which means that it takes some time to turn it, especially with the week screwdrive AF engine of the K110 and its old focus algorithms. If the sigma is faster it may be because of a shorter focus ring range and lighter construction(?).
Some times I'd wish my DA*50-135 would focus faster even on the K20D, but on the other hand it is a dream to focus manually, and I hope it will be a bit faster on the K-7.
06-15-2009, 01:46 PM   #15
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Just another data point. I have the Sigma and I rented the 50-135. In short, the 50-135 was in another galaxy as far as better image quality, sharpness, and just about every other category. Either you were doing something wrong or you had a bad copy.

Last edited by user440; 06-15-2009 at 01:58 PM.
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