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Sharper Images Article page 44 tip 4

Discussion in 'AP Magazine Feedback & Suggestions' started by P_Stoddart, Aug 13, 2011.

  1. P_Stoddart

    P_Stoddart Well-Known Member

    The comment in this section on APS-C sensor and 1.5x affect in relation to focal length does not make sense.

    Let's take two camera from the same maker the Sony A900 and the A500.

    They I believe can take the same lens so the optical are not changing.

    The only thing that is happening as far as I can see is a form of digital cropping to half frame.

    If you took a shot using the A900 say on a 300mm at 1/300 and then digital cropped the 6080x4048 down to 4272x2848.

    You would end up with I believe a identical image to taking that shot on a A500 1/300 with the same 300mm.

    Both would look like they have been shot on 450mm but if it is ok for the A900 to be at 1/300 why would it not be ok for the A500. That is doing the same thing except using the sensor instead of software to crop to 4272x2848.

    This was discussed on on here 30/06/2008 including Roger Provins (Sony user) who put the same point. The thread did not come to any conclusion.

    One arguement I have seen for applying the crop factor is that the image is enlarged. But it is not because we end up with same number of pixels for both outputs, the software crop and the sensor crop ie 12MP. In fact there are same number of pixel/mm when captures by the cameras.

    When it comes to larger focal lengths it is critical to know where we are. Because it could be the different between forcing the camera to cross into it's noise zone or not in certain conditions. Of cause some photographers are lucky and have a steadier hand.

    Has anyone had experience on two cameras like this one with say a crop sensor of 10MP and another with FF at 20MP or there about?

    I came across this discussion as well in my search.


    What does Prof Newman say about this?
  2. beejaybee

    beejaybee Marvin

    Not directly but what you say makes perfect sense.
  3. P_Stoddart

    P_Stoddart Well-Known Member

  4. daft_biker

    daft_biker Action Man!

    Yes....and yes, there seems to be a similar amount of detail at any given magnification.

    These first three are all 100% crops....the first with a 50mm and the other two with a 5x macro lens.

    You could replace the 40D section of this image with a crop from a 5D2 image and end up with as near as makes no difference the same thing:
    'scuse the WB!

    Why do I say the 40D and 5D2 resolve a similar amount of detail?....



    ....because when looking for detail at a fixed magnification on a small area of the sensor a test between a 40D and a 7D gives much the same result as a test between a 5D2 and 7D.

    I don't have a direct comparison between the 40D(10MP on APS-C) and the 5D2(21MP on FF). The closest thing to the same shot I could find online are these....



    Although the one shot on the 40D is a sub-adult that was a wee bit smaller than the one shot on the 5D2 (springtails often get darker with age)....a fully grown one pretty much fills the frame at 5x on APS-C.
  5. P_Stoddart

    P_Stoddart Well-Known Member

    Thanks for the input Daft_biker.

    But are you saying that the article could be wrong on putting the 1.5x into guideline on focal length and shutter speed?

    Given that lot of lenses are designed in terms of pro gear for FF sensor and then can be used on APS.
  6. daft_biker

    daft_biker Action Man!

    I haven't seen it but such guidelines usually refer to using the full image from each sensor to produce something like an A4 print, in which case the MP doesn't matter as it's the sensor size which dictates how much you need to magnify to get the print and a smaller sensor magnified more is more likely to show shake so you need a higher shutter speed.

    However, doing things a bit more properly the speed of the subject accross the sensor and the pixel density of the sensor should dictate how fast a shutter speed you need - to get things approaching 'properly' sharp the subject should move less than the distance between photosites during the exposure. Or something like that;)

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