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Thread: Sony NEX-7/A7R Technical Question

  1. #1

    Sony NEX-7/A7R Technical Question

    Hi all,

    Im looking at getting the Sony NEX-7 or A7R, combined with a 18-55mm lens, to use for an inspection/survey job. What I need to know, and what I cant seem to find info on elsewhere, is the scale of the pixel size. Can these cameras achieve sub-cm resolution, or preferably sub-mm, at full zoom and 10-30 metres away (the further the better)?

    Cheers

  2. #2
    Hello Swizzle, welcome to SonyAlpahLab.

    Quote Originally Posted by Swizzle View Post
    what I cant seem to find info on elsewhere, is the scale of the pixel size. Can these cameras achieve sub-cm resolution, or preferably sub-mm, at full zoom and 10-30 metres away (the further the better)?
    Sorry, I am not exactly following you.
    So, you want the picture to be clear enough to cm or mm resolution (when zoom into pixel) at 10-30 metres distance? You will need much powerful zoom lens (than the 18-55mm lens)?
    Amateur and unskilled photographer with a very small collection of gears.

  3. #3
    Super Moderator Obelix's Avatar
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    I agree with Antony.
    Your best option would be A7R with 70-200mm f4.0, or you could use older manual macro lens in 180-200mm range for resolution.
    Later today I could do this test with a6000 (24MP same as NEX-7) and 18-55mm lens, and few other lenses.

  4. #4
    Super Moderator Obelix's Avatar
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    Sony a6000 with 18-55 lens at 55mm from 10m away, full image

    Test 55_10
    by Dalibor M, on Flickr

    100% crop

    Test 55_10_100
    by Dalibor M, on Flickr

    55mm from 20m 100% crop

    Test 55_20_100
    by Dalibor M, on Flickr

    Sony a6000, Tamron SP 70-200mm f2.8
    200mm from 30m, 100% crop

    Test 200_30_100
    by Dalibor M, on Flickr

    200mm from 10m, 100% crop

    Test 200_10_100
    by Dalibor M, on Flickr
    Last edited by Obelix; Mar 21 2015 at 01:19 PM.

  5. #5
    Obelix,
    Thank you for the test results.
    I am surprised with the result of 18-55 mm lens at 10m and 20m.
    Amateur and unskilled photographer with a very small collection of gears.

  6. #6
    I hate to be a dummy, but what exactly is a 100% crop. Obviously it is a cropped portion of an original shot, but how is the 100% figured?

  7. #7
    Super Moderator Obelix's Avatar
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    1:1 pixel, one pixel from image is one pixel on your computer display
    Images out of a6000 are 6000 X 4000 pixels, so to view that image in 1:1 you would need 6000 X 4000 pixel display
    Above images are around 1000 pixels wide, cropped from 6000 pixels image at 1:1

  8. #8
    Thanks for the responses everyone, and many thanks to Obelix for that test, its exactly what i was looking for. The 55mm may end up being good enough for the job, but ill look into some larger lenses.

    Thank you all again.

  9. #9
    Elite Member leuius's Avatar
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    Quote Originally Posted by Swizzle View Post
    Thanks for the responses everyone, and many thanks to Obelix for that test, its exactly what i was looking for. The 55mm may end up being good enough for the job, but ill look into some larger lenses.
    Consider the fact that Obelix tests were with an A6000. The APS-C size sensor gives you a "boost" of 1.5X (crop factor). So if you pick a full frame camera such as A7 you will need a lens 1.5X longer focal length to achieve the same scene coverage.

    Regards,

  10. #10
    Quote Originally Posted by leuius View Post
    Consider the fact that Obelix tests were with an A6000. The APS-C size sensor gives you a "boost" of 1.5X (crop factor). So if you pick a full frame camera such as A7 you will need a lens 1.5X longer focal length to achieve the same scene coverage.
    Thank you leuius. I thought about this the other day, but decided not to add further confusion.
    If Swizzle is eyeing on A7r (36MP) as indicated on the first post, which is 1.5x of a6000 (24MP).
    Assuming using full frame equivalent of the lens at 55mm, I believe the 1.5X (crop factor) thing should get cancelled out roughly.

    Again, I could be wrong, and I am always happy to be proven wrong.
    Amateur and unskilled photographer with a very small collection of gears.

  11. #11
    Super Moderator Obelix's Avatar
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    A7R with with full frame 80 or 85mm (55mm equivalent) lens would give him full 36 MP resolution
    A7R with 18-55mm kit lens would give him around 15 MP crop image

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