Mitakon 20mm f/2 4.5X Super Macro Lens

Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.

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ChrisR
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Post by ChrisR »

ChrisR, not sure if you can do that because if you shoot the aperture opening through the glass from front, its size will change and the back end does not have any glass, even if it does, it will not be shot in the same condition as the front, so the ratio will not be right.
I believe that IS the correct way to do it, so you get the two images of the same thing showing how big it appears to be, which is what (it turns out) matters. If there were no glass, then it would of course look the same from both sides :D.

If they put the iris in at the back as an afterthought, so it's not in the "right place", then heaven knows - you'll have to wait for Rik! I'd guess the PMR may change when the lens is wide open because the limiting aperture moves.
I can't think of a good reason for using such a mean iris.
(Though I do have a lens with a two blade iris!)
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mjkzz
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Post by mjkzz »

OK, so you are saying that it is the apparent size of aperture that matters, right? make sense. I was taking the approach of using the size of front and back element to estimate PF.

Sorry, the iris are NOT at the back, it was so with that defective one, the replacement has it in the middle of the lens, I have been using it wide open, so I did not check that part.

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Post by mjkzz »

OK, here are apparent size of the lens iris, physical aperture set to f/16, front and back, cropped but no resize. Measure tips of the triangle to the base, I get 364/498 = 0.731

Image

Image

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Post by mjkzz »

JohnyM, here is a pic of it on one segment of extension tube, so if your bellow has the right camera mount, it should work.

Image

JohnyM
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Post by JohnyM »

Great, can you shoot it at various apertures and various bellows lenght added? Something like USAF test? Im especially interested in wide open performance. And at magnification with bellows added so the lens maitain 10mm working distance.

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Post by mjkzz »

JohnyM, USAF is so expensive in China, of course, there are cheap (knock-off) ones, but I doubt they are any good and can lead to misleading results.

At 10x, WD is definitely more than 10mm, I did some stack, but I need a good subject to shoot, it is winter time, so hard to catch one. Maybe later I can get a house fly or something.

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Post by mjkzz »

Here is demonstration of "doughnut" shaped bokeh video. It is shot with aperture wide open, so bokeh is round instead of triangle.

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Post by rjlittlefield »

ChrisR wrote:If they put the iris in at the back as an afterthought, so it's not in the "right place", then heaven knows - you'll have to wait for Rik! I'd guess the PMR may change when the lens is wide open because the limiting aperture moves.
Correct, the PMR would change in that case, because the limiting aperture would move and thus would be treated differently by the optics (if any) on each side of the lens.

As an extreme example of this situation, consider a lens that has been modified to be telecentric, by adding a limiting aperture at the rear focus distance. In this case the lens with telecentric aperture has PMR=0 because the apparent rear diameter = physical diameter while apparent front diameter is infinite. But if you open that added aperture far enough that it does not limit the ray cones, then the lens reverts to its normal non-telecentric behavior with two finite diameter pupils.

In the last set of pictures showing the triangular aperture, I would be happier if the aperture were focused sharply instead of being fuzzy. But the computed value of 0.731 is close enough to that of the Oly 20 mm to support the claim that the new lens is a clone of that.
mjkzz wrote:...demonstration of "doughnut" shaped bokeh
Interesting -- thanks for this. Apparently a significant amount of remaining spherical aberration when used wide open.
Oh boy, three blade aperture . . . but as stacking progresses, it is getting smaller and smaller, kind of weird but final stacked image looks fine, so for single shot image, like stack #63, it is probably "dreadful" :-) But for final stacked image, it is not a problem at all
Correct. The shape of the aperture has little effect on the appearance of in-focus detail, because that appearance is determined by diffraction and lens aberrations and not by geometric blur due to spreading of the ray cones. It is the same reason that you can use a phase objective (phase ring = annular aperture) and still get good stacked results within the in-focus slab.

--Rik

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Post by ChrisR »

0.731
Same as the Olympus, then, near enough. Thanks for doing that.
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Post by Charles Krebs »

Peter,

Thanks... all very interesting.

You are getting a lot of requests to try different things :wink:

For me I would be curious about performance at 2.8 or even 4. Wide open performance is important to determine, and it would be great if it were "killer" wide open. But sometimes a relatively "fast" lens like this can surprise with much better image quality when stopped down just a little.

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Post by mjkzz »

Charles, here we go, stacked 141 images at f/2.8 (no f/4 mark and it is continuous, so did not try f/4) 20um step size. Still think it is soft, I will use flash next time as I am in the middle of changing setup.

Rumor has it that Laowa will introduce a 5x lens next May, not sure if it is a clone of MPE or just a 5x to compete with this, so things will be interesting.

Image

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Post by Chris S. »

Chris S. wrote:The three-bladed iris also seems a questionable design decision--I'd fear that the out-of-focus highlights will be dreadful.
rjlittlefield wrote:
Oh boy, three blade aperture . . . but as stacking progresses, it is getting smaller and smaller, kind of weird but final stacked image looks fine, so for single shot image, like stack #63, it is probably "dreadful" :-) But for final stacked image, it is not a problem at all. . . .
Correct. The shape of the aperture has little effect on the appearance of in-focus detail. . . .
Agreed that aperture shape has little effect on in-focus detail; my concern is out of focus highlights, which do take the shape of the iris. Given a stacked subject where sufficient detail exists around such highlights, we know that stacking software will selectively include in-focus detail and exclude OOF artifacts, effectively eliminating the latter. But I've photographed quite a few subjects where little enough competing detail existed that OOF highlights were problematic in the stacked output. So I still question if this lens will prove troublesome in these cases.

If Mitakon had spent a tiny bit more money to put a many-bladed, roundish iris on this lens, it might have made the lens far more forgiving with difficult subjects.

This said, I am of course speculating.

--Chris S.

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Post by mjkzz »

Thanks Rik for explanation, great insights! I just tried to do it again and again, I think I had too much coffee, even the camera is mounted on a tripod, I hear the in-focus beep (lens is set to manual to prevent change of magnification), by the time the shutter is pressed, it is out of focus. Darn it, need to get a remote.

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Post by mjkzz »

If Mitakon had spent a tiny bit more money to put a many-bladed, roundish iris on this lens, it might have made the lens far more forgiving with difficult subjects.
Do you mind doughnut shaped out of focus highlights (bokeh?)? If you watch the video in my previous post, doughnut shaped highlights are kind of annoying for single shots.

Yeah, for stacked image, this is not an issue.

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Post by mjkzz »

Pushed it to 10x

Image

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