SLR versus mirrorless - the gap is closing fast.

heartyfisher · January 2015

Diffraction is primarily a function of absolute aperture, not f-stop. The circumference of the aperture where diffraction happens is linear at 2 Pi R where the area (where light gets in) is Pi r square. That is why astronomical lenses are specified in size to determine resolution limits, their f stop (such as it is) becomes a function of magnification.

Modern telephoto camera lenses are similar in employing magnifying elements (like internal extenders), otherwise an 800mm lens would be at least 32 inches long.

Magnification, optical design, and placement of aperture all affect this in real terms which is hy you see the measurements you do, but the physics is simple, and all the lenses we discuss are 'small'.

This is also why the sharpest lenses are often the really big ones (200/2, 400/2.8), despite lots of glass, because the upper diffraction limit of a 6 inch lens (400/2.8) is so much higher than that of a 1 inch (50/2.0).

.... H

Well said.. I always thought that that was the case .. but was not able to state it. I knew that the huge radio telescopes were that huge because of the "efficiency" gained by the size vs diffraction of the wave length over the "aperture" (which are miles and miles wide).

mikep · January 2015

i think that on the subject of dslr vs mirrorless lenses, we can also look at dslr vs rangefiner. the rangefinder having a similar smaller flange distance

http://www.kenrockwell.com/tech/rangefinder-vs-slr.htm

assuming he is correct, there seems to be some advantages to both small and large cameras?

WestEndFoto · January 2015

You are correct HaroldP.

heartyfisher · January 2015

You are correct HaroldP.

yup it is 42 .. :-B

Sorry, what is he correct about ? :-)

WestEndFoto · January 2015

His latest post that you quoted.

heartyfisher · January 2015

His latest post that you quoted.

Yes, that gives me a logical explanation for some differences I have noticed between Macro lenses and normal or zoom lenses when tiny apertures like F22 or 32 are used. Ie the Macro lenses perform better at tiny apertures. Whatever the distance. I believe this is due to the placement of the aperture opening and the absolute size of the openings.

Paperman · January 2015

Diffraction is primarily a function of absolute aperture, not f-stop. The circumference of the aperture where diffraction happens is linear at 2 Pi R where the area (where light gets in) is Pi r square. That is why astronomical lenses are specified in size to determine resolution limits, their f stop (such as it is) becomes a function of magnification.

Modern telephoto camera lenses are similar in employing magnifying elements (like internal extenders), otherwise an 800mm lens would be at least 32 inches long.

Magnification, optical design, and placement of aperture all affect this in real terms which is hy you see the measurements you do, but the physics is simple, and all the lenses we discuss are 'small'.

This is also why the sharpest lenses are often the really big ones (200/2, 400/2.8), despite lots of glass, because the upper diffraction limit of a 6 inch lens (400/2.8) is so much higher than that of a 1 inch (50/2.0).

.... H

Food for thought ...... From some website explaining diffraction

Technical Note: Independence of Focal Length

Since the physical size of an aperture is larger for telephoto lenses (f/4 has a 50�mm diameter at 200�mm, but only a 25�mm diameter at 100�mm), why doesn't the airy disk become smaller? This is because longer focal lengths also cause light to travel further before hitting the camera sensor -- thus increasing the distance over which the airy disk can continue to diverge. The competing effects of larger aperture and longer focal length therefore cancel, leaving only the f-number as being important (which describes focal length relative to aperture size)

I say I have to agree with this otherwise diffraction calculators would have required info on actual lens opening :-? The perimeter of aperture of a 200/2.8 lens being 6 times ( the area being 36 times ) of a 50/2 lens, actual aperture size could not have been sth that could be left out of the equation. Have read numerous articles on diffraction and never seen anywhere actual size of lens mentioned as being a factor.

I am sure the size of opening & amount of light going in a lens is a huge factor in astronomy / telescopes but probably unrelated to diffraction. ( one naturally sees better when there is more light )

So I'd have to sadly disagree with your above comments as well Heartyfisher :-S :-S :-S

sevencrossing · February 2015

An interesting review on the 7D2 by the man we love to hate, KR
He suggests that while many mirrorless cameras can match it on fps
none can actually focus anywhen near as as fast

FrenchRiviera · February 2015

Diffraction is an optical issue .

The smaller the pixels are , the sooner diffraction will be seeable . ( aperture )

It doesn't mean quality is getting worse with higher resolution , just it won't improve that much anymore

FrenchRiviera · February 2015

From a technical user point of view , biggest difference between mirorless and DSLR is AF behaviour in AF-C mode .

Rest is just personnal preference for particular use .

heartyfisher · February 2015

@paperman .. so its all back to being all in my mind ... 8-}

Howdy, Stranger!

Categories

In this Discussion

Who's Online (0)

SLR versus mirrorless - the gap is closing fast.

Comments