lens diffraction settled once & for all

01/12/2015 04:40:53 PM · #1

I always hear a version of this idea:

"oh, the new high resolution camera has too many megapixels...lens diffraction makes it blurry"

"it's a waste to use poor lenses with a high megapixel camera because of lens diffraction"

"my low megapixel camera is better for this lens, because on a higher res camera the images blur due to diffraction"

I don't see how this is possible. Yes, I understand that diffraction can cause some loss in sharpness: but I simply don't see how a low megapixel camera can outresolve a high megapixel camera with the same lens. Surely the diffraction issue is not as limiting as the advantages you get from increased resolution?

Am I wrong to think this? Or is everyone else wrong.

Someone is going to be wrong today, and I am going to find out WHO.

Message edited by author 2015-01-12 16:41:45.

Nikon AF-S DX Nikkor 35mm f/1.8G

01/12/2015 05:05:06 PM · #2

I think the idea is more akin to running the old tires on the farm truck, and getting new tires for your personal truck.

damjanev

Nikon D3200

01/12/2015 05:14:32 PM · #3

The two key points are (from what i know about diffraction):

- It is not the megapixel/resolution that is a factor in diffraction. Its the actual physical pixel size. and some additional sensor elements such as presence of an AA filter. It becomes a bit complicated when the layout of the coloured pixels on the sensor is taken into account, but still, the key factor is not the megapixel count it is the pixel size.

- It happens at small apertures. How small, actually depends on the lens and the sensor.

//www.cambridgeincolour.com/tutorials/diffraction-photography.htm
//www.cambridgeincolour.com/tutorials/diffraction-photography-2.htm

Message edited by author 2015-01-12 17:21:28.

01/12/2015 05:19:05 PM · #4

Originally posted by Cory:

I think the idea is more akin to running the old tires on the farm truck, and getting new tires for your personal truck.

im a simple boy, don't rightly now about big city folk things seech as farm trucks n' tires

Canon RF 24-70mm f/2.8 L IS

01/12/2015 05:19:37 PM · #5

so, could a lower resolution sensor with larger pixels out-resolve a higher resolution sensor with smaller pixels?

given the same lens, aperture settings etc....

Message edited by author 2015-01-12 17:19:56.

kirbic

Canon EOS R5

01/12/2015 05:28:10 PM · #6

A given lens always produces the same quality image, regardless of the sensor behind it. There is always some limit to the resolution of the lens. For example, a given lens might blur a sharp edge across a distance of, say, 10 microns at the sensor. A low-density sensor, like the original 5D, has a pixel pitch of about 8.2 microns, so that 10 micron blur is only about 1.2 pixels, and will be barely noticeable. A high-density DSLR sensor has a pixel pitch of more like 4.2 microns, and the blur will be more like 2.4 pixels, and that will be very noticeable.
The above applies whether the blur is due to lens quality or diffraction (diffraction applies even for an optically perfect lens).
So, how do I apply this in practice? Some "rules of thumb":
- Lenses are almost always lower in resolution at the corners, so FF sensors will show up issues there when APS-C sensors will not. The poster child for this difference is the Tamron 28-75 f/2.8, which folks using APS-C cameras loved, but those with FF cameras decidedly did not.
- High-density sensors will start to show effects of diffraction at lower f-stops than cameras with lower density sensors. For the highest density DSLR sensors, careful analysis might show some diffraction effects at f/11 or possibly f/8. For lower density sensors, f/16 is where it starts to be visible.
- In order to get the most from a high-density sensor, you will need glass that exceeds the resolution of the sensor across the portion of the image circle that the sensor uses, either the whole enchilada for FF (a circle about 43mm across), or a little less than half the area for APS-C (a circle about 27mm across)

damjanev

Nikon D3200

Nikon AF-S DX Nikkor 35mm f/1.8G

01/12/2015 05:29:27 PM · #7

Originally posted by LanndonKane:

so, could a lower resolution sensor with larger pixels out-resolve a higher resolution sensor with smaller pixels?

given the same lens, aperture settings etc....

I'm going to quote the conclusion part of the second article. I think it'a a direct answer to your question.

Originally posted by //www.cambridgeincolour.com/tutorials/diffraction-photography-2.htm:

Thus far, you're probably thinking, "diffraction more easily limits resolution as the number of camera megapixels increases, so more megapixels must be bad, right?" No â�� at least not as far as diffraction is concerned. Having more megapixels just provides more flexibility. Whenever your subject matter doesn't require a high f-stop, you have the ability to make a larger print, or to crop the image more aggressively. Alternatively, a 20MP camera that requires an f-stop beyond its diffraction limit could always downsize its image to produce the equivalent from a 10MP camera that uses the same f-stop (but isn't yet diffraction limited).

Regardless, the onset of diffraction is gradual, and its limiting f-stop shouldn't be treated as unsurpassable. Diffraction is just something to be aware of when choosing your exposure settings, similar to how one would balance other trade-offs such as noise (ISO) vs shutter speed. While calculations can be a helpful at-home guide, the best way to identify the optimal trade-off is to experiment â�� using your particular lens and subject.

kirbic

Canon EOS R5

Canon RF 24-70mm f/2.8 L IS

01/12/2015 05:34:05 PM · #8

Originally posted by LanndonKane:

so, could a lower resolution sensor with larger pixels out-resolve a higher resolution sensor with smaller pixels?

given the same lens, aperture settings etc....

With the same lens, No.
Resolution is defined as lines (or line pairs) per millimeter. The resolution obtained in the final image is largely determined by the worst part of the system. So a razor-sharp lens projecting onto a low-resolution sensor produces a low-resolution image, and a low-resolution lens projecting onto a high-resolution sensor produces a low-resolution image.
If by "resolution" you mean the total detail present in the output image, then the answer is different. If we have a lens that projects a very large image circle (think medium format) and a low-density sensor that, because of the large area still contains a large number of pixels, then yes, you can have more detail from a low-density sensor. But you are using a completely different lens (one with a larger image circle) and a much larger sensor.

01/12/2015 06:49:56 PM · #9

Originally posted by LanndonKane:

Originally posted by Cory:
I think the idea is more akin to running the old tires on the farm truck, and getting new tires for your personal truck.

im a simple boy, don't rightly now about big city folk things seech as farm trucks n' tires

I suspect you might be makin' fun of me. ;)

01/12/2015 06:50:56 PM · #10

Originally posted by kirbic:

Yeah, like he said, putting the new tires on the farm truck just don't make sense. :-D

Olympus OM-D E-M5 Mark III

01/13/2015 09:14:36 AM · #11

Originally posted by kirbic:

Originally posted by LanndonKane:
so, could a lower resolution sensor with larger pixels out-resolve a higher resolution sensor with smaller pixels?

given the same lens, aperture settings etc....

With the same lens, No.
Resolution is defined as lines (or line pairs) per millimeter. The resolution obtained in the final image is largely determined by the worst part of the system. So a razor-sharp lens projecting onto a low-resolution sensor produces a low-resolution image, and a low-resolution lens projecting onto a high-resolution sensor produces a low-resolution image.
If by "resolution" you mean the total detail present in the output image, then the answer is different. If we have a lens that projects a very large image circle (think medium format) and a low-density sensor that, because of the large area still contains a large number of pixels, then yes, you can have more detail from a low-density sensor. But you are using a completely different lens (one with a larger image circle) and a much larger sensor.

this makes sense.

Yo_Spiff

Olympus 12-100mm f/4.0 M.Zuiko ED IS PRO

01/13/2015 03:06:39 PM · #12

I think it is simply a matter of human perception. Just like on a tiny screen everything looks razor sharp, but when you put it on the big monitor, all the imperfections jump out at you.

Message edited by author 2015-01-13 15:07:57.

tanguera

Nikon D750

Nikon AF-S Nikkor 17-35mm f/2.8D IF-ED

01/13/2015 03:24:33 PM · #13

Checking in to see if it's been settled....

Mike

Canon EOS-5D Mark II

Tamron SP 24-70mm f/2.8 Di VC USD Canon Mount

01/13/2015 03:42:33 PM · #14

Originally posted by Yo_Spiff:

I think it is simply a matter of human perception. Just like on a tiny screen everything looks razor sharp, but when you put it on the big monitor, all the imperfections jump out at you.

its real thing, countless message board threads are built upon its existence.