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Comparing macro lenses using MTF - Part VII - Tube lenses
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Miljenko



Joined: 01 Jun 2013
Posts: 82
Location: Zagreb, Croatia

PostPosted: Thu Oct 11, 2018 4:41 am    Post subject: Comparing macro lenses using MTF - Part VII - Tube lenses Reply with quote

Basically, my lens comparison series approaches the end. Magnification range 0.66x to 3x was personally of greatest importance while I was not satisfied with knowledge base of lenses in that range. That's why I concentrated mostly on enlarger, microfiche and industrial lenses in 20 to 80mm range that seemed promising. Well known lenses performed more or less as predicted while those less known provided few pleasant surprises. Next category is 4x where I'm pretty much satisfied with Lomo 3.7x finite objective. As new lenses appear in my lab almost on daily basis, I might find better solution for 4x in the near future or just might decide on proven Mitty 5x solution.



Now I've entered infiite objective area where tube lens is still a subject of discussions. Many solutions were tried and ranked but there are still many 200mm lenses worth trying. Since no one measured actual resolution variations while swapping those lenses, I consider this series of tests a nice opportunity to try a few; some well known and some new.



Nikon 200mm f4 Ai(S) is definitely one of those better known and as former Nikon shooter I was lucky to have it with me for quite some time. Second tube lens everybody is familiar with is Raynox DCR-150 close-up „filter“. To me this lens serves great as add-on in a way it was designed for: an addition to my Fujinon 55-200mm telezoom while doing live bugs in-camera focus stacking in the field. It provides 1:1 stacked magnification while shooting slow moving insects which is both fun and pain in the neck.



I have added another 4 lenses of very different breeds to this roundup: mentioned Fujifilm tele zoom 55-200mm f4.8, two Rodenstock repro lenses: Rodagon R 210mm f5.6 and Apo Gerogon 210mm f9 along with Kenko AC No.5 Close-up filter. Microscope objective tested on all those lenses was Nikon LU Plan 5x NA 0.15 EPI Infinite WD23.5. All the lenses were extended to a point where focus plane is at infinity distance. Besides measuring resolution and CA I did an interesting side test. All the lenses were placed on camera and tripod while shooting at distant objects.



The idea was to compare measured figures and subjectively perceived sharpness at infinity setting. I was expecting some kind of correlation but you'll see it was not always the case.



Nikon lens from 70's was overall the best performer which was not a big surprize. It produced the best center resolution and when stopped down to f5.6 edge resolution went up and scored 5.1 with Nikon LU Plan 5x objective. Chromatic abberations are just average but this anomaly is easy to rectify as you already know.
Next on the hall of fame chart is Fujifilm 55-200 tele zoom which shows best sharpness edge to edge but with two shortcommings: relatively strong CA and heavy corner light falloff. Since this lens might be interesting to Fuji users only, I won't elaborate it any further.
OTOH, Raynox DCR-150 is surelly interesting to many since it's cheap, tiny and supposedly good as the tube lens. Contrary to expectations, the performance was just average. Not bad but not exceptional either. And I believe that due to it's simple design there are no major sample differences. This lens performed better when reversed, so this test answers the long discussed normal vs reversed DCR-150 discussion.
Bigger dissapointment happened with both Rodenstock repro lenses. Those sofisticated, relatively expensive lenses performed below average. Rodagon R had just slightly higher resolution while Apo Gerogon was much lower at CA as expected.



Definitely a great positive surprise came from Kenko AC No.5 close-up „filter“, an attachment similar to Raynox add-ons. There are No. 1, 3 and 5 varieties with corresponding 1000, 330 and 200 mm focal lengths along with different diameters. I was using 55mm thread diameter version. This lens performs better than Raynox DCR-150 in all parameters while having the lowest CA of all the tube lenses tested. And it can be bought on Ebay for 1/3 Raynox price. Kenko as well performs better when reversed but the funny part is performance when used as tele-lens when reversed performance is terrible!
As you can see, I have none of the specialized tube lenses which might perform better than any of the lenses tested here. However, I believe Nikkor 200mm f4 Ai performs good enough for my needs so I don't plan to invest in any of those 200mm „dream tubes“ available. BTW, best to worst center resolution difference measured 13% only so my conclusion would be that tube lenses do not influence total performance that much.
Part VIII of this MTF based test series will deal with Lomo 3.7x microscope objective pushed from 2x all the way to 5x magnification.
Enjoy.
Miljenko
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Lou Jost



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PostPosted: Thu Oct 11, 2018 6:03 am    Post subject: Reply with quote

Nice tests. The Kenko performance is a big surprise.

The Raynox performance in normal vs reversed orientations is a bit ambiguous, perhaps explaining the lack of general agreement about which way is best. Reversed orientation has slightly better resolution (not sure how noticeable this would be) but the forward orientation has lower CA. I think many of our controversies are of this kind; there is no "best", it depends on what qualities we value most.
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Pau
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PostPosted: Thu Oct 11, 2018 8:05 am    Post subject: Reply with quote

I have it not clear: do your results refer of the lenses used as tube lenses with the LU Plan 5X? (the only posted images are with them used as teles)
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Adalbert



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PostPosted: Thu Oct 11, 2018 8:37 am    Post subject: Reply with quote

Hello Miljenko,

Very interesting test, many thanks!

Could you please test the CANON EF 70-200L too?
https://global.canon/en/imaging/l-lens/line-up/ef70-200mm_03_is_usm.html

I have already tested the LU Plan 5x with the DCR-150, LSA and the CANON mentioned above. CANON was the best one. Would you check please?

Thank you in advance.
BR, ADi
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Miljenko



Joined: 01 Jun 2013
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Location: Zagreb, Croatia

PostPosted: Thu Oct 11, 2018 11:13 am    Post subject: Reply with quote

Pau wrote:
I have it not clear: do your results refer of the lenses used as tube lenses with the LU Plan 5X? (the only posted images are with them used as teles)

Careful reading gives you all the details about this and other tests I presented lately: "...Microscope objective tested on all those lenses was Nikon LU Plan 5x NA 0.15 EPI Infinite WD23.5"...
There are no IC wafer, butterfly wing or any other structures images in my tests. The main idea is to avoid visual lens comparisons and replace it with numerical measured values for each lens in test. I believe I have explained the concept in Part I of this series. One of the advantages is possibility of comparison at the later date with the lenses tested (much) earlier.
The only comparison image you could see in those 7 test parts is this 8 segment pic of distant object that comes with explanation. I have shown that lens performance when used as a tube lens does not correlate well with it's performance as the tele lens.
Best.
Miljenko
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Miljenko



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PostPosted: Thu Oct 11, 2018 11:54 am    Post subject: Reply with quote

Adalbert wrote:

Could you please test the CANON EF 70-200L too?

Unfortunately, Adi, my equipment is not capable of testing Canon lenses. I'm using Fujifilm X-T2 camera with various adapters, none of those being Canon to Fuji. Canon EF lenses use "control by wire" aperture adjustment which can only be provided by Canon cameras.
I believe EF70-200L can succesfuly serve as the tube lens. Sort of proof can be Fuji XF55-200 I've tested here which performed very well. That zoom is much less ambitious than EF70-200L you are talking about. Zoom lenses have gone a long way since '80s and now perform much closer to prime lenses than ever before.
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Macrero



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PostPosted: Fri Oct 12, 2018 1:04 am    Post subject: Reply with quote

Thanks for your time, but to be honest, IMO, comparison is pretty meaningless when it comes to using those optics as tube lenses. Bear in mind that the "tube lens" is stopped down by the microscope objective, so it is not working at its maximum aperture, not even close. For instance, the Apo-Gerogon is optimized for 1:1, but it works very well at infinity when stopped down to at least f/22, just like G-Clarons and other similar optics.

The only way to assess the performance of a given lens as a tube lens, is testing it as such. In that case, I can assure you that result will be pretty different.

- Macrero
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ChrisR
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PostPosted: Fri Oct 12, 2018 5:27 am    Post subject: Reply with quote

Well I find it interesting, even if it's not particularly valuable, to see what happens.
I would (perhaps incorrectly) assume that a well corrected lens which works well all the way down to below f/22 (within the limits of diffraction) would also be good as a tube lens. We have had reports where that perhaps wasn't the case; one was something like a Laowa 135mm iirc.

Some years ago, Rik postulated that a more appropriate test was to put a limiting aperture on the front of the 200mm lens, say 10mm diameter, which would force the use of the rays which would actually be used when the lens is repurposed as a tube lens. Some results were shown, but we know about a lot more prospective "tube" lenses now - it may be worth revisiting.

Here's a test of an MT-1, straight
http://www.photomacrography.net/forum/viewtopic.php?t=16718

This is very relevant:
http://www.photomacrography.net/forum/viewtopic.php?

But I can't find the post I wanted.
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Lou Jost



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PostPosted: Fri Oct 12, 2018 7:15 am    Post subject: Reply with quote

Macrero, I am not sure I understand your comment. The tests reported by Miljenko WERE done with the lenses used as tube lenses. As such they are quite valid and useful. Yes, tube lenses probably interact differently with different objectives, but the objective he used gives a valid data point.
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Macrero



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PostPosted: Fri Oct 12, 2018 8:05 am    Post subject: Reply with quote

Lou,

I just re-read the OP and as far as I understand, the lenses were tested as "taking" lenses, wide-open or stopped down a bit. Hence my comment, since that is not a valid indicator of their performance when used as tube lenses.


- Macrero
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Lou Jost



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PostPosted: Fri Oct 12, 2018 8:11 am    Post subject: Reply with quote

No Macrero, he tested them all as tube lenses and the numbers reflect their performance in that role. The photos taken through the lenses (without the objective) are "an interesting side test", just provided for additional information. The reason he includes them is to see whether there is a correlation between the two results. He notes that, as you suspected, there is no correlation between the performance as a tube lens and the performance as a taking lens.
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JH



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PostPosted: Fri Oct 12, 2018 9:03 am    Post subject: Reply with quote

Interesting - thanks for this!
There seems to be a negative correllation between CA and edge sharpeness, I wonder why.

Best regards
Jörgen Hellberg
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Macrero



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PostPosted: Fri Oct 12, 2018 9:33 am    Post subject: Reply with quote

Lou Jost wrote:
No Macrero, he tested them all as tube lenses and the numbers reflect their performance in that role. The photos taken through the lenses (without the objective) are "an interesting side test", just provided for additional information. The reason he includes them is to see whether there is a correlation between the two results. He notes that, as you suspected, there is no correlation between the performance as a tube lens and the performance as a taking lens.


Oh, my bad then, sorry. It would be interesting to see the stacked test pics, though.

- Macrero
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Miljenko



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PostPosted: Fri Oct 12, 2018 8:49 pm    Post subject: Reply with quote

Macrero wrote:
Lou Jost wrote:
No Macrero, he tested them all as tube lenses.


Oh, my bad then, sorry. It would be interesting to see the stacked test pics, though.

- Macrero

Thanks for clarifying, Lou. Macrero, you can bet I will try all those lenses in real use. I've spent way to much for them so letting them go just like that is not an option.
Miljenko
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Lou Jost



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PostPosted: Sat Oct 13, 2018 10:24 am    Post subject: Reply with quote

Miljenko, can you explain what the CA numbers mean? Unlike the resolution numbers. I suppose they are nonlinear with respect to anything that photographers can easily interpret. This means that it is difficult to know if the difference between, for example, 0.50 and 0.55 is large or small. The scale range from 0 to 1, right?
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