Q/Q2 image quality

[sturkel]

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On 9/13/2019 at 2:11 AM, Jared said:

This is easy enough to validate on your own—no special equipment needed.  Shoot an image of something at f/4 or so (the Q2 performs best in the center of the field at around f/4, at least mine does). Make sure your subject is in the approximate center of the field.  Then shoot the same image at f/11.  Import into the computer. Turn all sharpening and noise reduction off.  Examine the images in the middle of the field of view at 200%.  Is there a difference?  Which one is sharper?  In my experience, yes, diffraction is noticeably affecting image quality on the Q2 by f/11.

Keep in mind, diffraction always affects every image, no matter what the megapixel count of your camera and no matter the aperture.  The question is when does diffraction become the dominant factor in MTF. My simple test above should answer that for you—at least in the middle of the frame where the image quality is highest.  

Things get more complicated as you move to the edge of the field.  First, while the lens on the Q2 is extremely good, it’s not as good in the corners as it is in the middle of the field.  There’s nothing unusual in that.  The vast majority of lenses perform best in the middle of the frame.  Often, wide angle lenses like the 28mm on the Q2 get better in the corners as you stop them down.  I would say the Q2 is best in the corners at perhaps f/8 or so.  Again, your sample may differ, so try your own tests.  Keep in mind that lens assembly is never perfect, so you may find that one corner is materially better or worse than other corners.  In any event, the generally lower resolution in the corners may mean that diffraction isn’t the dominant factor at f/11.  Perhaps you would have to go to f/16 or f/22 before you see the image getting worse.  It isn’t because the effects of diffraction are any different in the corners, it’s just that other things might matter more so you don’t notice. Try it with your camera and see when the corners start to get noticeably softer.

Finally, keep in mind that these effects are relatively subtle.  In many images the increased depth of field you get with smaller apertures far outweighs the slight image degradation in the center of the field.  This will depend on the subject.  In a portrait, for example, corner performance rarely matters much at all.  In a landscape?  It could be critical.  Some photographers have turned to focus stacking to get the best of both worlds, but this won’t work for all subjects and it requires additional effort in post processing.  An even more extreme technique is the pixel shift technology incorporated into many cameras with image stabilization now.  The new Sony A7R Mark 4, for example, can produce a 240 megapixel image of a perfectly still subject that contains demonstrably more detail than the native 60 megapixels or so.  At least at certain apertures it does.

Diffraction isn’t a brick wall that you bump up against at some magic number.  It affects all images all the time.  As the aperture gets smaller, the affect gets bigger.  Eventually you get almost nothing by increasing megapixels.  We aren’t there yet (even at f/8), but Jaap’s point is a good one.  With good technique, a good lens, a tripod, and appropriate aperture it is definitely possible to get more details out of a 47 megapixel camera than out of a 24 megapixel camera.  Does it make for a better photograph?   Does your photography even allow that better technique, careful focus, appropriate aperture and perhaps even a tripod?  If you are using the Q for street photography, for example, I’d say the extra megapixels are all but irrelevant.  Portraiture?  Sports?  You’ve probably chosen the wrong camera entirely.  Travel?  Yeah, you can probably benefit, mostly because you have extra room for croppingand would otherwise be stuck at 28mm.  Landscape?  Yeah, the extra megapixels could matter.  

At some point, though, we will probably see megapixel counts stop going up because they are virtually empty in terms of the additional content.  We are already seeing that with cellular phones which have very tiny pixels.  The last three releases of iPhones, for example, have all had 12 megapixel cameras.  The improvements are in better noise control, more focal lengths, better computational photography, and faster lenses rather than increased megapixels.  Clearly, Apple is of the opinion that a chip as small as that in the iPhone has reached its limit at 12.  Any additional pixels add no more relevant detail.  Larger formats will support more pixels, of course, but even full frame will have its limit.

Excellent discussion.  Thank you

[Leica Guy]

5 hours ago, Jared said:

Nope, it’s just the size of the hole, not the angle from the outer edge of the lens.  In fact, the outer edge of the lens is not used at all when shooting stopped down—only the central part of the lens elements illuminate the imaging plane. Light from the outer portions of the lens is simply blocked by the iris and never reaches the imaging plane. 

This also explains why larger formats are less affected by diffraction.  An f/32 aperture on an 8”x10” view camera has a physically much larger diameter opening than the same focal length with a 35mm camera, so shooting at f/11 or f/16 or even f/64 is perfectly reasonable with a larger format.

 

I absolutely stand corrected. Thanks Jared. My knowledge was clearly not accurate. Good to know the real effects. 

This makes me think that smaller sensor cameras are more susceptible to diffraction. The sweet spot aperture setting is more and more open the smaller the sensor. Is that correct? 

Edited September 19, 2019 by Leica Guy

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[jaapv]

6 minutes ago, Leica Guy said:

I absolutely stand corrected. Thanks Jared. My knowledge was clearly not accurate. Good to know the real effects. 

This makes me think that smaller sensor cameras are more susceptible to diffraction. The sweet spot aperture setting is more and more open the smaller the sensor. Is that correct? 

Post #28

[bags27]

6 hours ago, Jared said:

This also explains why larger formats are less affected by diffraction.  An f/32 aperture on an 8”x10” view camera has a physically much larger diameter opening than the same focal length with a 35mm camera, so shooting at f/11 or f/16 or even f/64 is perfectly reasonable with a larger format.

Hence Willard Van Dyke and Ansel Adams's Group f/64! 😃

Edited September 19, 2019 by bags27

[Jared]

1 hour ago, Leica Guy said:

I absolutely stand corrected. Thanks Jared. My knowledge was clearly not accurate. Good to know the real effects. 

This makes me think that smaller sensor cameras are more susceptible to diffraction. The sweet spot aperture setting is more and more open the smaller the sensor. Is that correct? 

Yes, smaller sensor cameras are absolutely more susceptible to the effects of diffraction.  Just as an example, years ago in the Big Sur/Carmel/Monterey Bay area there was a group of photographers known as Group f/64 consisting of the likes of Ansel Adams, Imogen Cunningham, and Edward Weston.  They were all proponents of sharp focus with plenty of details.  They favored higher focal ratios for increased depth of field, particularly in landscape work.  They were able to use apertures like f/64 because they were mostly shooting 8”x10” view cameras, so diffraction at f/64 was quite manageable.  Obviously, that would not be the case with 35mm film.

As far as your memory of the steeper angles from the edges of lenses... I suspect you were thinking about how depth of field is affected by aperture rather than diffraction.  Depth of field does decrease as the aperture gets physically larger because of the steepness of the light cone.  You had probably just mixed these in your head.  I do that sort of thing all the time.

[Jared]

55 minutes ago, bags27 said:

Hence Willard Van Dyke and Ansel Adams's Group f/64! 😃

You beet me to it!  I was just typing about Group f/64.