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Thread: Pentax DA 40mm F2.8

  1. #1
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    Default Pentax DA 40mm F2.8

    Hi everyone,

    I would like to seek some of the experts' opinions on the problem I am facing. Your comment and advices will be very much appreciated. I collected this lens yesterday and after taking several photos, I discover something don't seem to be right to me. It seems that photos taken at f4.0 and below (smaller f-stop number) were not sharp at all. Sharpness is ok at f5.6 and above (bigger f-stop number).

    The following photos were taken with a tripot this morning. Auto focus was switched to "manual" once focus is locked on. In others words, all of the photos were taken without any change in focus length. They were also cropped to 100% and then compressed. No PP was done either.

    This test were repeated several times and the results were consistent.

    Taken at f2.8 (cropped to 100% and then compressed)


    Taken at f3.5 (cropped to 100% and then compressed)


    Taken at f4.0 (cropped to 100% and then compressed)


    Taken at f5.6 (cropped to 100% and then compressed)


    Could this due to FF or BF problem at f-stop below 4.0? Please give me some advice before I decide to send the lens and camera for adjustment.

    Many thanks to all of you.

  2. #2

    Default Re: Pentax DA 40mm F2.8

    ya,it is possible you have the FF problem, use this chart to test the focus system http://www.focustestchart.com/chart.html
    Last edited by CSLee; 21st January 2007 at 01:49 PM.

  3. #3
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    Default Re: Pentax DA 40mm F2.8

    Thanks CSLee, I did conducted some tests using the chart earlier but was not able to come to any conclusive results. However, I redo the test a while ago (see photo belwo) and I think it FP about 2-6mm. Am I correct ?


  4. #4

    Default Re: Pentax DA 40mm F2.8

    looks about 6 mm front

  5. #5

    Default Re: Pentax DA 40mm F2.8

    what about other lens ???

  6. #6

    Default Re: Pentax DA 40mm F2.8

    Using the test chart method might be flaw due to how auto focus program in the camera determine focus at 45 degrees angle. Instead take real life shot and determine how soft and sharp is it. In your case, I think you might have a bad copy of the lens. Try changing it. It happen with the 16-45mm lens too. A guy Htyloday in Dpreview got a bad copy of the 16-45mm and I think Walan too. The point is that you can get a bad copy of the lens.

    BTW, what camera are you using?

  7. #7

    Default Re: Pentax DA 40mm F2.8

    Quote Originally Posted by kcsum View Post
    ...
    The following photos were taken with a tripot this morning. Auto focus was switched to "manual" once focus is locked on. In others words, all of the photos were taken without any change in focus length. They were also cropped to 100% and then compressed. No PP was done either.
    ...
    This isn't a right way to test the DA 40 lens. Most modern AF lenses' focusing would change along w/ the change of aperture. You can't lock the focusing to the same point for all different apertures.

    The best way is to leave the camera to AF.S, mount the camera on a tripod, use a cable release if you have one, 2 seconds mirror up, set the SR to OFF, use window or sun light instead of fluorescence light and make sure the light condition is very good, then do the test again.

    If you still get the same results, I'd say either the lens or the camera, or the combo have problem.

    The DA40 is a very sharp lens, it is sharp from wide open to F22. I've had several copies and all perform quite similar (on Ds and K10D).

    Good luck!

  8. #8
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    Default Re: Pentax DA 40mm F2.8

    Thanks for the useful advices from everyone who have responded. I really appreciate the time you all have taken.

    In fact, I did several sets of test under different conditions. All the requirements, for examples, 2 seconds mirror up, switched off SR, used AF.S and conducting the test in the morning under natural light near my windows, were adopted (Actually, also got this from dpreview). Still, the results from the different sets of test showed that the images were soft at f4.0 and below.

    Anyway, I have written to Shashinki to request them to change another one for me. Lets see how it goes.

    Once again, many thanks.

  9. #9
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    Default Re: Pentax DA 40mm F2.8

    Quote Originally Posted by kcsum View Post
    Thanks for the useful advices from everyone who have responded. I really appreciate the time you all have taken.

    In fact, I did several sets of test under different conditions. All the requirements, for examples, 2 seconds mirror up, switched off SR, used AF.S and conducting the test in the morning under natural light near my windows, were adopted (Actually, also got this from dpreview). Still, the results from the different sets of test showed that the images were soft at f4.0 and below.

    Anyway, I have written to Shashinki to request them to change another one for me. Lets see how it goes.

    Once again, many thanks.
    i strongly recommend against this, you should bring down to shirio and see if they can recalibrate for you, both camera and lens.

  10. #10
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    Question Re: Pentax DA 40mm F2.8

    Quote Originally Posted by Vulpix0r View Post
    i strongly recommend against this, you should bring down to shirio and see if they can recalibrate for you, both camera and lens.
    Could you explain why u strongly against it ? I am really curious.

    I did thought of sending both the lens and camera to Shriro for calibration. However, I do not have any problems with my Sigma lens and I just do not feel comfortable sending my K10to the service center for calibration (I try not to fix something that is not really broken). I even decided to accept this lens and work around the lower f-stops rather than sending the camera for service.

    So far, Shashinki's service has been quite prompt and professional . In fact, they had just replied and allow me to send the lens back to them for an exchange.

  11. #11

    Default Re: Pentax DA 40mm F2.8

    Quote Originally Posted by Vulpix0r View Post
    i strongly recommend against this, you should bring down to shirio and see if they can recalibrate for you, both camera and lens.
    Quote Originally Posted by kcsum View Post
    Could you explain why u strongly against it ? I am really curious.

    I did thought of sending both the lens and camera to Shriro for calibration. However, I do not have any problems with my Sigma lens and I just do not feel comfortable sending my K10to the service center for calibration (I try not to fix something that is not really broken). I even decided to accept this lens and work around the lower f-stops rather than sending the camera for service.

    So far, Shashinki's service has been quite prompt and professional . In fact, they had just replied and allow me to send the lens back to them for an exchange.
    i also wanna know why u're strongly against it?

  12. #12

    Default Re: Pentax DA 40mm F2.8

    All Pentax products at ShaShinKi.com is having Pentax International Warranty, so it will be honoured by Pentax distributors worldwide

    I am in the process of writing/finishing an alternative test method for lens, as I find the focustestchart method above is not accurate (influence by camera focus sensor position).
    DR KOH KHO KING

  13. #13
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    Default Re: Pentax DA 40mm F2.8

    I'm strongly against it because the problem might not be JUST the lens. As you all know, the sensor is a moving component as well, and the DPReview people encountered a problem that his sensor had to be repositioned.

    His other lenses might work fine, but it might be because of a variety of reasons.

  14. #14
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    Default Re: Pentax DA 40mm F2.8

    I have just done a test by comparing my lens with another DA 40mm which I got from my brother. The 2 sets of results proved that the lens I got from Shriro is having sharpness problem at smaller f-stop. These photos were all taken under the same conditions (SR off, tripod, 2 secs timer…). The photo were copped 100% and compressed. Due to compression, the different may not be significant.

    For those file numbers that have a “b” behind were taken with my brother’s lens.

    Lens side by side


    First set:

    f2.8 (brother's lens)


    f2.8 (Mine)


    2nd Set:
    f2.8 (brother's lens)


    f2.8 (Mine)


    Thanks for all those who contributed and made me a more knowlegable person with regard to lens testing. Many thanks.

  15. #15

    Default Re: Pentax DA 40mm F2.8

    Hi
    I'm curious. How did you conclude your brother's images are better than yours?
    They look the same to me except a slightly different level of brightness..
    cheers

  16. #16
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    Default Re: Pentax DA 40mm F2.8

    It was very obvious when you look at the 10mp photos at 100% without compression. Those posted here were compressed so it did not really showed much different.

    Anyway, tested three DA40mm lenses at Shriro this evening with 2 very nice gentlemen. Another k10D body was also used (with my lens only). Conclusion was expected - soft image from my lens. Awaiting for my replacement in 3 weeks time.

    Thanks for all the comments. This thread should end.

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