Pentax 560mm lens now listed on Adorama...any takers!

Started Nov 5, 2012 | Discussions thread
Russell Evans Forum Pro • Posts: 12,607
Re: Resolution, diffraction limits, long lens on Q etc...
The ever increasing sensor resolution will end when the best prime lens don't reach their peak center resolution before diffraction limits their performance. Then there will be no point in increasing sensor resolution.

If you look at the photozone.de lens data for a good lens on the m4/3 16mpix sensor , you might notice that the center MTF50 figures are close to 3150, but don't drop to below 2750 even at f8. If we look at the photozone.de center MTF50 figures for the DA * 300mm f4 on the APS-C 16mpix sensor of the K-5 , you'll notice that the highest data point is 2412 for the center at f5.6. It seems even with diffraction effecting the m4/3 sensor at f4-5.6, its not really going to be detrimental in practical terms to use lenses even at f8 on m4/3.

And back to the long lens discussion, as many long lens users have pointed out (falcon wizard, ron...) 600mm is 600mm is 600mm.

And so the Pentax decision for aligning their lens products around the APS-C 1.53x crop is not valid? Just marketing fluff?

You're not going to get that DOF / creamy backgound by mounting a 77 limited on a Q.

Sticking to 4/3 sensor in a K-5 body, as that is the topic of my post you replied to, let's look at DOF on m4/3 at the minimum focus distance of the 560mm, 5.6 meters. That should give the best creamy background.

http://www.dofmaster.com/dofjs.html

Olympus E-PL3

  • Camera: Olympus E-PL3
    Focal length (mm) 300
    Selected f-stop f5.6
    Subject distance 5.6 m
    Depth of field Near limit 5.58 m Far limit 5.62 m
  • Total 0.04 m
  • In front of subject 0.02 m (50%)
  • Behind subject 0.02 m (50%)
  • Camera: Olympus E-PL3
    Focal length (mm) 300
    Selected f-stop f8
    Subject distance 5.6 m
  • Depth of field Near limit 5.56 m Far limit 5.64 m
  • Total 0.08 m
  • In front of subject 0.04 m (50%)
  • Behind subject 0.04 m (50%)

Pentax K-30

  • Camera: Pentax K-30
    Focal length (mm) 600
    Selected f-stop f5.6
    Subject distance 5.6 m
    Depth of field Near limit 5.59 m Far limit 5.61 m
  • Total 0.02 m
  • In front of subject 0.01 m (50%)
  • Behind subject 0.01 m (50%)
  • Camera: Pentax K-30
    Focal length (mm) 600
    Selected f-stop f8
    Subject distance 5.6 m
    Depth of field Near limit 5.59 m Far limit 5.61 m
  • Total 0.02 m
  • In front of subject 0.01 m (50%)
  • Behind subject 0.01 m (50%)

So it looks like we would have 10mm more DOF in the m4/3 wide open with the Da * 300mm, and 20mm more DOF at f8. I used 600mm as the isn't an option for 560mm at the site.

Let go with a subject distance of 15m to move things out.

Olympus E-PL3

  • Camera: Olympus E-PL3
    Focal length (mm) 300
    Selected f-stop f4
    Subject distance 15 m
    Depth of field Near limit 15 m Far limit 15 m
  • Total 0.07 m
  • In front of subject 0.04 m (50%)
  • Behind subject 0.04 m (50%)
  • Camera: Olympus E-PL3
    Focal length (mm) 300
    Selected f-stop f8
    Subject distance 15 m
    Depth of field Near limit 14.7 m Far limit 15.3 m
  • Total 0.59 m
  • In front of subject 0.29 m (49%)
  • Behind subject 0.3 m (51%)

Pentax K-30

  • Camera: Pentax K-30
    Focal length (mm) 600
    Selected f-stop f5.6
    Subject distance 15 m
    Depth of field Near limit 14.9 m Far limit 15.1 m
  • Total 0.14 m
  • In front of subject 0.07 m (50%)
  • Behind subject 0.07 m (50%)
  • Camera: Pentax K-30
    Focal length (mm) 600
    Selected f-stop f8
    Subject distance 15 m
    Depth of field Near limit 14.9 m Far limit 15.1 m
  • Total 0.19 m
  • In front of subject 0.1 m (50%)
  • Behind subject 0.1 m (50%)

So it looks like we would have 2.8 inches more DOF in the m4/3 wide open with the Da * 300mm, and 15.7 inches more DOF at f8. I used 600mm as the isn't an option for 560mm at the site.

Maybe I should use an aperture of f5.6 for the m4/3 to the f8 of the APS-C? After all f8 is more diffraction on the m4/3, so worse performance. We are using f8 on the 560mm to hit the sweet spot right? But, we still want a creamy background?

Olympus E-PL3

  • Camera: Olympus E-PL3
    Focal length (mm) 300
    Selected f-stop f5.6
    Subject distance 15 m
    Depth of field Near limit 14.9 m Far limit 15.1 m
  • Total 0.1 m
  • In front of subject 0.05 m (50%)
  • Behind subject 0.05 m (50%)

That's cool, the same DOF at the sweet spot for the lenses' apertures on the respective sensors. Got to like that, right?

Thank you
Russell

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