Diffraction f/Entekaphobia

Started Feb 5, 2014 | Discussions thread
Scott McMorrow Regular Member • Posts: 366
Falk is right

Roger measures MTF50 directly from RAW without sharpening.  With sharpening, contrast is increased, as low pass filtering of the optical system is removed.  It is not uncommon that MTF10 to MTF20 measured RAW becomes much higher contrast after sharpening, and quite visible in the final photo.  Falk shows this in a whitepaper on D800/D800E sharpening and AA-filter.

Several things must always be asked when viewing MTF measurement plots

1) is the result with or without sharpening? (Roger uses no sharpening, photozone uses sharpening, but does not specify how it is done)

2) if sharpened, was the sharpening performed with a sharpening tool (camera jpg engine, ACR ...) or using an ideal mathematical filter? (Imatest can provide resolution results based on an ideal mathematical filter.  In camera JPG sharpening results tend to be overly hot, but uniform for a particular camera.  ACR and other sharpening will depend on settings and user preference.)

3) For edge and corner measurements, where was the focus point placed? (at the center, at the edge, at the corner)? (Roger uses center focus for all measurements.  Photozone uses best focus for each measurement zone.)

5) what method was used and what are it's assumptions and limitations.  (Imatest methods are well documented.  Target size, contrast and sharpness dictate the potential resolution limit of testing.  Testing is near field with a flat subject, which is good for comparison to portrait photography, but may not relate to city or landscape photography, where focus is at or near infinity.)

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