Diffraction Limit Discussion Continuation

Started 6 months ago | Discussions thread
Mike Davis
Contributing MemberPosts: 690
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Re: Enlargement factor has been ignored
In reply to Ulric, 6 months ago

Ulric wrote:

Mike Davis wrote:

And that's what's been missing from this discussion - a consideration of the impact of

enlargement factor on diffraction's ability to inhibit a desired print resolution.

I considered that on the very first page of the previous thread.

http://www.dpreview.com/forums/post/53151772

Hey, I missed that.  Good for you!

Actually, pixel pitch can matter even when viewing at enlargement factors far less than 1:1.

Rather than repeat myself, see my post, above.

But yes, you touched on the subject of enlargement factor.  Hooray!  Nobody else seems to care that any comparison that omits specification of the enlargement factor and desired print resolution makes for an apples and orange discussion of either DoF or the impact of diffraction.

Small enlargement factors (had with large sensors and/or small prints) and/or large viewing distances might allow the use of any f-Number available with a given lens and camera, without any fear of diffraction inhibiting a relatively high desired print resolution.  The larger the sensor, the less will be the enlargement factor for any given print size and viewing distance, and thus, the larger the f-Number that can be used before diffraction will begin to inhibit your desired print resolution.

If two sensors are the same size, but one has more pixels than the other, there's some probability that sooner or later, the guy equipped with the higher pixel count is going to make a larger print than the guy who has the lower pixel count on the same size sensor.  Using the higher number of pixels on the same size sensor to produce a larger print causes the Airy disk diameters at the sensor, for any given f-Number, to suffer more magnification in the final print than they would in a smaller print, and thus a greater likelihood of diffraction inhibiting a desired print resolution.  The photographer has to shrink the Airy disks at both the sensor and in the final print (after enlargement), by opening up so that his desired print resolution is not compromised by the larger Airy disks that come with the greater enlargement factor.

Beating the dead horse...

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