some good lens info

[rjlittlefield]

I have used the Olympus for a few weeks now and I have to say I am very satisfied with this lens; however, having it a pupil ratio of 0.85 does not mean that it actually works at f4.7? please, correct me if I am wrong

That's close enough for practical purposes. The f-number equivalent to a lens with P=1 varies with magnification. At a nominal setting of f/4, equivalent f/4.7 is worst case at high magnification. At 2.3X (rated minimum magnification on bellows) it's a little wider than f/4.5. At 5X I calculate f/4.57.

--Rik

[seta666]

Thank you Rik, that iexplains why I find the Olympus 38mm so pleasant to work with. The JML 21mm works very well and does very clean stacks but the Olympus may work even better, being 4.5 aprox is not much of surprise
The JML on the other hand should give better resolution figures, at least in practice; I could also use the Olympus at 2.8 which would become a f3.3 or something
I was using 0,06mm steps with the Olympus at 4-5X, Do you think is a bit conservative then?

[rjlittlefield]

I was using 0,06mm steps with the Olympus at 4-5X, Do you think is a bit conservative then?

At a ring setting of f/4, I'd probably go with 0.04mm. Standard calculation says DOF=0.0439mm given CoC = 0.02mm and 5X. But ultimately the question is just whether you see focus banding on things like compound eyes. If you don't, the step size is fine.

--Rik

[mgoodm3]

Here is an image of a measurement slide angled at about 20 deg. "0" is closer and "10" is farther. Shot at f/5.6. There is certainly a bit of Long CA at the focus plane with a bit of magenta fringing, but not a massive amount.

[mgoodm3]

Second test: Images shot back to back (no change except for those listed). First pic, like the samples in the test. Second pic, adding diffusion to the lighting.

The fringe lessens considerably with the diffusion, suggesting to me that it represents purple fringing. Since this is supposed to be a detector issue, it should only show on the images and not through the viewfinder. Can't see any of this through the viewfinder.




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[rjlittlefield]

I was using 0,06mm steps with the Olympus at 4-5X, Do you think is a bit conservative then?

At a ring setting of f/4, I'd probably go with 0.04mm. Standard calculation says DOF=0.0439mm given CoC = 0.02mm and 5X. But ultimately the question is just whether you see focus banding on things like compound eyes. If you don't, the step size is fine.

I just noticed elsewhere that you're using 5D mkII. My DOF number would be for a 1.6 crop sensor. On a full-frame sensor like the 5D mkII, CoC would be more like 0.03mm, so your 0.06mm for DOF would be right on target.

--Rik

[seta666]

Thanks Rik, I had not trouble with those 0,06mm steps
Which formula are you using for DOF?

[ChrisLilley]

Doing numerical testing has taught me a lot over the last couple years.

I just wanted to say that your macro-range ematest results are very interesting and I am not aware of any other sites where this is done - congratulations. Very clear and informative.

A post on what adaptations you needed to do and what pitfalls you found would also be very welcome,i am sure (in your copious free time, of course).

[rjlittlefield]

The one from Lefkowitz, page 258. He has it as:

TDF = 2 C f_r (m+1)/m^2

TDF = Total Depth of Field
C = Circle of Confusion
f_r = relative (marked) aperture
m = magnification

There are corresponding variations for pupil ratio different from 1.

This is a pure geometry model based on ray tracing, ignores diffraction and everything else. But it's a good starting point.

--Rik

[ChrisLilley]

In your review of the Nikon 135mm f/4 bellows lens, my monitor shows prominent magenta fringing on some portions of the example image, while your findings indicate: "Chromatic Aberration: This lens show minimal color fringing in the center (about 0.25 pixel) and minimal on the periphery (0.10 - 0.20 pixels)."

I assumed that here "chromatic aberration" = "lateral chromatic aberration" due to the mention of how it varies across the image rather than through the depth of field.

[mgoodm3]

Doing numerical testing has taught me a lot over the last couple years.

I just wanted to say that your macro-range ematest results are very interesting and I am not aware of any other sites where this is done - congratulations. Very clear and informative.

A post on what adaptations you needed to do and what pitfalls you found would also be very welcome,i am sure (in your copious free time, of course).

A good glass slant edge target is necessary (Applied Image has them available). One problem is that as you go up in magnification, say much above 5x, the straight line of the slant edge starts to get kinda rough. I would guess that this skews the results a little, but they seem to be pretty consistent despite that.

Otherwise it is just time consuming to do the testing because every data point has to be separately performed (20-50 pictures each to find the sharpest of the bunch). When I added in corner testing, it effectively doubled the work involved. I have already done center of field testing on 60+ lenses, but only those that are online have the corner testing also.

I try to keep the lighting and conditions of testing consistent (same camera, same lighting position, conditions in the room) so my results are more consistent.

[SONYNUT]

as i focus up and down the blown reflection will glow green to purple..i just drop the light down and its gone...but this is pretty typical with the best of lenses vs curved reflective surfaces..my big zeiss non macro lenses do the same..

minolta 100mm bellows lens

[Chris S.]

Mark, your three test images are really interesting. On the test slide, it appears on my monitor that the area immediately around the numeral "5" is neutral, but that, pretty quickly, the out of focus numbers become purplish to the left and greenish to the right. It's not dramatic, but this is not a high contrast situation--certainly no highlights; and the effect on the coin does seem to affect the highlights most. Is it possible that longitudinal CA is here demonstrated pretty clearly, but it requires higher contrast to make it appear more striking?

In your two coin shots, you seem to be demonstrating something I've seen with some of my lenses: Strong purple fringing in high-contrast areas, which can be reduced, but not removed, with softer light.

In standard, non-macro photography, I find CA to show up quite differently in various areas of a single image, depending that that area's contrast. CA stands out to me as color fringes in high-contrast areas of the image, and as a loss of sharpness in medium to low contrast areas. My assumption has been that it simply shows up most dramatically in the very light and very dark areas because they lack much color information, other that that produced by CA. But I don't know if this is assumption is correct.

With a few of my finite microscope objectives on the bellows, I get purple fringing similar to what you are getting in your coin tests. Like you, I've used softer light to minimize it, but the fringing can still drive me nuts (I no longer use those lenses much). My current thinking is that the fringing is produced by longitudinal CA, and that the soft light provides less of the near-white or near-black areas in which this CA shows up most clearly. If I'm wrong, I'd love to be corrected. I've asked about it on this forum, and recall one or two other posts with similar questions, but don't recall a solid answer.

The fringe lessens considerably with the diffusion, suggesting to me that it represents purple fringing. Since this is supposed to be a detector issue, it should only show on the images and not through the viewfinder. Can't see any of this through the viewfinder.

This is intriguing--I didn't know about this being a detector issue. Any chance you could you elaborate on this?

Best,

--Chris

[Chris S.]

as i focus up and down the blown reflection will glow green to purple..i just drop the light down and its gone...

Makes sense, Sonynut. But in my (non-coin) subjects, I can rarely drop the light enough to get rid of the fringing without losing the darker regions. Also, I get purple shadows in out of focus areas with some lenses. So far, the only answer I've found is to prefer lenses that don't exhibit this behavior--and I've got some of those. But I'd love another answer.

Cheers,

--Chris

[mgoodm3]

Most things that I have read have blamed purple fringing on overloading the microlenses at the front of the detector with light (CA at these lenses). sometimes blaming it on UV. there seems to be a lot of confusion about this effect online as it is commonly mixed around with just plain magenta/green long CA.

The argument that best puts it at the detector for me is that with a microscope objective I can create a very large fringe that I can mostly cure with softening the light. This large fringe is only visible on images and not at all through the viewfinder.