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Raynox DCR-150 tube assembly with flocking
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rjlittlefield
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Location: Richland, Washington State, USA

PostPosted: Sun Sep 30, 2018 1:02 pm    Post subject: Reply with quote

santiago wrote:
Would it be realistic to expect the Mitutoyo 20x to be sharper than my new purchased Nikon CFI Plan 10x/0.25 (MRL00102)? Or at least equally sharp?

It depends on what you mean by "sharp". Because of its larger aperture, NA 0.42 versus 0.25, the 20X objective will resolve much finer detail on subject. But at rated magnification, the combination of 20X NA 0.42 will be running at effective f/24, while 10X NA 0.25 will be effective f/20. (The formula is Feff=mag/(2*NA).) As a result, the 20X image will be more diffracted and will have less crisp pixel-to-pixel detail than the 10X image.

To do a direct comparison, you could resize either image to match the other, or resize both of them to some other standard like 14X. In any of those cases, the image from the NA 0.42 objective should be significantly sharper than the image from the NA 0.25 objective, after resizing so that both of them show the same FOV on subject.

Quote:
He will even send me a test stack so that I can see for myself.

That sounds like a good thing to do. The seller is an experienced user of microscope objectives, so what you get should be a great indication of what the lens will do.

--Rik
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santiago



Joined: 25 Sep 2018
Posts: 42
Location: Nijmegen, The Netherlands

PostPosted: Mon Oct 01, 2018 5:20 am    Post subject: Reply with quote

Great formula, that was very helpful. By "sharp" I meant crisp pixel-to-pixel detail.

Indeed, an effective aperture of 24 should produce a softer/more diffracted image than the Nikon 10x at Feff 20.

Should I then expect the Mitutoyo to ideally score 0.8333... for crispness and the Nikon to score 1 (20/24)? If both lenses where performing at their theoretical maximum potential, how would the quality of the glass/elements impact this 0.8333... vs 1 estimation?

rjlittlefield wrote:
To do a direct comparison, you could resize either image to match the other, or resize both of them to some other standard like 14X. In any of those cases, the image from the NA 0.42 objective should be significantly sharper than the image from the NA 0.25 objective, after resizing so that both of them show the same FOV on subject.


Yes, it would be quite disappointing if such test failed, that would mean that the Mitutoyo 20x is incapable of resolving more detail than the Nikon 10x. But I will perform the test to see the theory confirmed (hopefully).

(Edit: here are the test results.)

I will also take a picture of a flat subject with both lenses at their intended magnifications (with flash) and pixel-peep the RAW files. I asked the seller if he could provide a sample RAW file.

Thanks again.
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Last edited by santiago on Sat Nov 10, 2018 11:48 am; edited 1 time in total
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rjlittlefield
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PostPosted: Mon Oct 01, 2018 11:27 am    Post subject: Reply with quote

santiago wrote:
Should I then expect the Mitutoyo to ideally score 0.8333... for crispness and the Nikon to score 1 (20/24)? If both lenses where performing at their theoretical maximum potential, how would the quality of the glass/elements impact this 0.8333... vs 1 estimation?

I do not recall seeing any quantitative tests of just how close these lenses come to matching the MTF curve of diffraction alone. Mitutoyos in good condition are generally considered to be at least as sharp as any other objective of the same NA, with typically a lot less CA.

Compared to the 10X, the 20X is noteworthy for having a remarkably large field. This means that it can be pushed down to lower magnifications by using it with tube lenses that are shorter than 200 mm. In my kit, for APS-C sensor, the Mitutoyo 20X NA 0.42 used with a 100 mm tube lens to give 10X NA 0.42, is sharper than any other 10X I have, across the entire field.

--Rik
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santiago



Joined: 25 Sep 2018
Posts: 42
Location: Nijmegen, The Netherlands

PostPosted: Mon Oct 01, 2018 1:23 pm    Post subject: Reply with quote

That's great news! So could I use my Canon EF 100mm f/2.8L Macro IS USM as the 100 mm tube lens with the Mitutoyo 20x, to get 10x?

I could also use a Raynox DCR-250 to get 20 * (125/200) = 12.5x. Or is a regular camera lens preferred over bellows + converging lens?

(The best would be to do a test I guess.)

But will this pushed down magnification produce vignetting on FF?

And lastly, will a native 10x Mitutoyo perform better than a 20x Mitutoyo pushed down to 10x? I would expect the 10x to be optimized for that magnification.

Thanks a lot for taking the time to reply!
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Santiago
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rjlittlefield
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Joined: 01 Aug 2006
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PostPosted: Mon Oct 01, 2018 11:20 pm    Post subject: Reply with quote

santiago wrote:
That's great news! So could I use my Canon EF 100mm f/2.8L Macro IS USM as the 100 mm tube lens with the Mitutoyo 20x, to get 10x?

On APS-C, yes. That's a combination I've tested. On full frame I expect you'll get some vignetting, not sure how much.

Quote:
I could also use a Raynox DCR-250 to get 20 * (125/200) = 12.5x. Or is a regular camera lens preferred over bellows + converging lens?

It can go either way. At 12.5X and NA 0.42, the Raynox will be running at effective f/14.9 . It's asking a lot for a 3-element lens to maintain good sharpness even in the corners at that aperture. I've seen lots of reports of successful use of the Raynox DCR-250 this way, but whether it would be better or worse than some different 125 mm lens is definitely a matter to be resolved by testing.

Quote:
And lastly, will a native 10x Mitutoyo perform better than a 20x Mitutoyo pushed down to 10x? I would expect the 10x to be optimized for that magnification.

On APS-C, my experience is that the 20X pushed down is sharper than the 10X at nominal, everywhere in the field.

I agree that each lens is probably optimized for its specifications. But those specifications include a lot more than just magnification. The 20X is optimized not just for 20X, but also for 20 mm working distance and $2055 list price, versus 33.5 mm WD and $885 for the 10X.

In practice, I usually use each lens at rated magnification. That's because I usually don't need the the additional NA of the 20X objective, except on small subjects where I would rather have the additional magnification also.

--Rik
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santiago



Joined: 25 Sep 2018
Posts: 42
Location: Nijmegen, The Netherlands

PostPosted: Tue Oct 02, 2018 11:51 am    Post subject: Reply with quote

rjlittlefield wrote:
On APS-C, my experience is that the 20X pushed down is sharper than the 10X at nominal, everywhere in the field.


That's no minor detail... good to know!

I'm very curious to see how the Mitutoyo 20x + Canon 100mm f2.8 performs compared to the Nikon 10x (MRL00102).

Adding 20mm extension tubes (which I own) to the Canon 100mm would make 12x, which in turn could be fun testing against the Mitu 20x + DCR-250 setup, but then I realized that you lose infinity, so the extension tube is a no-go?

(Most of all, I'm very curious to see how the Mitutoyo 20x performs at its rated magnification.)

Thanks again Rik for the useful information. Let me also tell you that I really like Zerene Stacker, it's an amazing tool, once you get the hang of it nothing seems impossible. I found out that with stacks that are more challenging than usual, what works best for me is making several partial stacks (excluding conflicting frames) to get the different parts of the subject (i.e. antennae, mandibles) nicely stacked and then use those partial stacks as source files during retouching. Then you don't have to resort to PMax that often. It also gives you more flexibility artistically speaking.

Can't wait to have that Mitutoyo 20x and test it on this nice tube assembly.
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Santiago
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rjlittlefield
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PostPosted: Tue Oct 02, 2018 2:24 pm    Post subject: Reply with quote

santiago wrote:
Adding 20mm extension tubes (which I own) to the Canon 100mm would make 12x, which in turn could be fun testing against the Mitu 20x + DCR-250 setup, but then I realized that you lose infinity, so the extension tube is a no-go?

Adding extension might work, might not. Things get less predictable when the rear lens is not focused at infinity. I have not tried the particular configuration you're thinking about.

Quote:
(Zerene Stacker) I found out that with stacks that are more challenging than usual, what works best for me is making several partial stacks (excluding conflicting frames) to get the different parts of the subject (i.e. antennae, mandibles) nicely stacked and then use those partial stacks as source files during retouching. Then you don't have to resort to PMax that often. It also gives you more flexibility artistically speaking.

This sounds closely related to a technique called "slabbing", where you blindly process the full stack as groups of overlapping substacks to make flattened slabs, then do everything else from the slab outputs. Slabbing gives a huge gain in speed of retouching or if you need to make multiple stacking runs. There are third-party utility programs that generate batch files to simplify the process. See http://extreme-macro.co.uk/zerene-slabbing/ for discussion and links.

--Rik
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santiago



Joined: 25 Sep 2018
Posts: 42
Location: Nijmegen, The Netherlands

PostPosted: Wed Oct 03, 2018 9:31 am    Post subject: Reply with quote

Very nice. So an XML file can be generated to let Zerene create x number of equally deep slabs (with configurable overlapping) and then stack these, all in one go. This can be very convenient indeed when "blindly" is not an issue. There might be other cases in which selective slabbing would be necessary to do a more "handcrafted" stack.

Great information as always, thank you!
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bs0604



Joined: 19 Feb 2013
Posts: 14
Location: Sarasota FL

PostPosted: Sun Oct 28, 2018 2:44 pm    Post subject: Reply with quote

I am confused about flocking material. This is put inside the tube or wrapped around the outside of the tubes?
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hero



Joined: 17 Jul 2017
Posts: 44
Location: California

PostPosted: Sun Oct 28, 2018 4:24 pm    Post subject: Reply with quote

bs0604 wrote:
I am confused about flocking material. This is put inside the tube or wrapped around the outside of the tubes?


Most definitely put *inside* the tubes, but only in places where non-image forming reflections occur, which will depend on the tubes and/or adapters used. If something inside the optical assembly reflects light that isn't supposed to, that will result in reduced contrast, increased glare, hot spots or ghosts, etc. The purpose of flocking the interior of the tube is to stop this from happening, and to ensure that only the light refracting through the lenses will reach the sensor.

If you're using step-down rings, for example, the flat surface perpendicular to the optical axis can cause unwanted reflections.

I just bought some doodlebug beetle black cardstock in anticipation of having to create a tube lens setup soon.
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elimoss



Joined: 12 Sep 2018
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PostPosted: Mon Oct 29, 2018 2:12 pm    Post subject: Reply with quote

What is a good glue or glue-ing technique to use with the flocking material?
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santiago



Joined: 25 Sep 2018
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Location: Nijmegen, The Netherlands

PostPosted: Mon Oct 29, 2018 2:27 pm    Post subject: Reply with quote

elimoss wrote:
What is a good glue or glue-ing technique to use with the flocking material?


I bought flocking tape from amazon, it does seem to do the job and the adhesive coating is pretty strong.

https://www.amazon.co.uk/dp/B01B5FNSO8/ref=pe_3187911_189395841_TE_dp_1

You can find this on ebay as well.
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Lou Jost



Joined: 04 Sep 2015
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PostPosted: Tue Oct 30, 2018 12:34 pm    Post subject: Reply with quote

Quote:
I would expect the 10x to be optimized for that magnification.


Santiago, it is iimportant to understand that the stated magnifications for infinity optics are not actual design points, per se. They are just the magnifications you get when you use tube lenses of the reference focal length (200mm for most brands, 180mm for Olympus). There is nothing very special about it. The parameters that really matter are NA and field-of-view on the subject.

The reason the 20x does better than the 10x is bec ause the NA is much higher and the FOV on the subject is still sufficient to cover the APS sensor at 10x.

I think it is easy to get trapped into thinking that the rated m is somehow fundamental. That's just not true for infinity-corrected optics.
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santiago



Joined: 25 Sep 2018
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Location: Nijmegen, The Netherlands

PostPosted: Wed Oct 31, 2018 2:20 am    Post subject: Reply with quote

Lou Jost wrote:

The reason the 20x does better than the 10x is bec ause the NA is much higher and the FOV on the subject is still sufficient to cover the APS sensor at 10x.


Hi Lou, yes, that makes sense, thank you Smile

Compared to a native 10x, the only "disadvantage" would be that the 20x pushed down to 10x will vignette on FF, but that sounds like a trivial tradeoff in exchange for more resolving power/higher NA.

Can't wait for the ring adapter to arrive and use my recently purchased (used) Mitty 20x.

Do you live in Ecuador? That would be like a dream come true with so many beautiful bugs available the entire year!

Regards,
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Santiago
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Lou Jost



Joined: 04 Sep 2015
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PostPosted: Wed Oct 31, 2018 3:48 pm    Post subject: Reply with quote

Yes, Santiago, I live in paradise. Yesterday swarms of colorful hummingbrids swirled around feeders a meter above my head during dinner...today I am in another place to try to get focus-stacked pictures of some new species of orchids that I discovered some years ago.

For some pictures of Ecuador's wildlife see my blog at the link under my name on the sidebar here....
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