Diffraction test: I just did a very unscientific diffraction test on my new Mitakon Zhongyi 20mm macro lens. Looking at images of the same subject at various f/ stops, I could see no...

jackm1943 Loc: Omaha, Nebraska

I just did a very unscientific diffraction test on my new Mitakon Zhongyi 20mm macro lens. Looking at images of the same subject at various f/ stops, I could see no difference between f/2 and f/2.8, a very slight fall off at f/5.6, and very noticeable fall off at f/8 and f/16.

PixelStan77 Loc: Vermont/Chicago

So Jack what is your bottom line on that copy of your Mitakon Zhongyi 20mm macro lens?

bleirer

It shouldn't be the lens that causes the diffraction, but the f stop related to the pixel size. Even the best lens should have the same diffraction at the same f-stop on the same camera. At least from what I've learned.

naturepics43 Loc: Hocking Co. Ohio - USA

Great info. Thanks for posting.

jackm1943 Loc: Omaha, Nebraska

PixelStan77 wrote:

So Jack what is your bottom line on that copy of your Mitakon Zhongyi 20mm macro lens?

Thanks for checking in Stan. Right now, I'm thinking it might be the best $150 I've ever spent on photography, along with the SWEBO focus rail. If for no other reason, it might get my photo juices flowing after being hunkered down for nearly a year due to COVID and several not so serious but very irritating medical issues during 2020. I think I may have gotten it right near the end of B&H's sale on this lens.

jackm1943 Loc: Omaha, Nebraska

bleirer wrote:

It shouldn't be the lens that causes the diffraction, but the f stop related to the pixel size. Even the best lens should have the same diffraction at the same f-stop on the same camera. At least from what I've learned.

Sorry but I'm not certain I understand what you are saying. I don't know the math or physics involved, but I don't think f/2.8 on a macro at 4X is the same as f/2.8 on a "regular" lens. One source indicates it's similar, diffraction wise, to f/10 on a normal lens. That's why diffraction sets in quicker on these high magnification lenses than on regular lenses (I think).
Thanks for commenting, JackM

jackm1943 Loc: Omaha, Nebraska

naturepics43 wrote:

Great info. Thanks for posting.

You're welcome naturepics.
JackM.

Mark Sturtevant Loc: Grand Blanc, MI

this is becoming a very interesting story. A very good deal! I did not know this thing about shooting wide open or nearly wide open with these lenses, so I appreciate learning that.
There are now several manual super macro lenses out there. All are very good, optically. Its hard to know which to choose! I personally still have my heart set on the venerable Canon mpe 65mm, which is still highly competitive and it has the automatic aperture.

bleirer

jackm1943 wrote:

Sorry but I'm not certain I understand what you are saying. I don't know the math or physics involved, but I don't think f/2.8 on a macro at 4X is the same as f/2.8 on a "regular" lens. One source indicates it's similar, diffraction wise, to f/10 on a normal lens. That's why diffraction sets in quicker on these high magnification lenses than on regular lenses (I think).
Thanks for commenting, JackM

Check out the calculator far down this page. The way I see it hitting the diffraction limit happens for a given sensor at a certain f stop with both good and bad lenses.

https://www.cambridgeincolour.com/tutorials/diffraction-photography.htm#calculator

jackm1943 Loc: Omaha, Nebraska

bleirer wrote:

Check out the calculator far down this page. The way I see it hitting the diffraction limit happens for a given sensor at a certain f stop with both good and bad lenses.

https://www.cambridgeincolour.com/tutorials/diffraction-photography.htm#calculator

I haven't read the article yet - and I will read it later - but yes, all lenses, good and bad, have diffraction issues at small apertures but I'm not certain how the sensor has anything to do with it. It's just the physics of light passing thru a small hole. Maybe the article explains?
Thanks for the send, JackM

bleirer

jackm1943 wrote:

I haven't read the article yet - and I will read it later - but yes, all lenses, good and bad, have diffraction issues at small apertures but I'm not certain how the sensor has anything to do with it. It's just the physics of light passing thru a small hole. Maybe the article explains?
Thanks for the send, JackM

The sensor part I think has to do with the size of the pixel. So if two sensors have the same number of pixels the small sensor's pixels have to be smaller. A sensor with smaller pixels reaches the diffraction limit at a larger aperture than a sensor with larger pixels.

At least that's how I read it, not claiming to be an expert. This one is supposedly more accurate for macro, calculating the 'effective aperture' as well https://www.photopills.com/calculators/diffraction-macro

chrisg-optical Loc: New York, NY

jackm1943 wrote:

I just did a very unscientific diffraction test on my new Mitakon Zhongyi 20mm macro lens. Looking at images of the same subject at various f/ stops, I could see no difference between f/2 and f/2.8, a very slight fall off at f/5.6, and very noticeable fall off at f/8 and f/16.

Interesting...this is one reason why focus stacking is used for stationary subjects, another is to get an incredible focus range/DOF that would be impossible even with the smallest apertures on most lenses....especially for tiny subjects such as (dead) bugs.

sippyjug104 Loc: Missouri

jackm1943 wrote:

I just did a very unscientific diffraction test on my new Mitakon Zhongyi 20mm macro lens. Looking at images of the same subject at various f/ stops, I could see no difference between f/2 and f/2.8, a very slight fall off at f/5.6, and very noticeable fall off at f/8 and f/16.

Interesting post and comments. Diffraction is obedient to the physical laws of light passing through an opening or barrier and also as the glass acts as a prism. It is inherent to all lenses so even the expensive lenses will show diffraction at some point and the effect is amplified by the amount of magnification due to the "effective f/stop".

Lenses do vary from one another so the points at which diffraction and softness become noticeable will not always be the same yet they are not immune to it.

Attached is a spreadsheet that I made and posted last week that shows where diffraction is likely to start based on the lens aperture setting indication and the amount of magnification obtained such as extending the lens or when using a variable magnification lens such as those that are 1X to 5X.

I've come to understand that the Laws of Physics are not just good ideas...they are the LAW.

Your experiment with the settings of your lens shows that it too must obey the law.

(Download)

jackm1943 Loc: Omaha, Nebraska

chrisg-optical wrote:

Interesting...this is one reason why focus stacking is used for stationary subjects, another is to get an incredible focus range/DOF that would be impossible even with the smallest apertures on most lenses....especially for tiny subjects such as (dead) bugs.

Yes, and focus stacking, at 1X or less, is so darn easy what with the good software available (Zerene, Helicon, etc.). Focus stacking at greater than 1X is more tedious than difficult, although lighting can be troublesome.
JackM

jackm1943 Loc: Omaha, Nebraska

sippyjug104 wrote:

Interesting post and comments. Diffraction is obe... (show quote)

Thanks for the chart Sippy. I didn't realize that the increased "effective" f/ stop starts at 1X. Good to know. I should add that my test was done at 4X.
JackM