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20x microscope objective on a budget

 
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anto74



Joined: 06 Feb 2020
Posts: 27
Location: Italy

PostPosted: Sun Feb 09, 2020 1:19 am    Post subject: 20x microscope objective on a budget Reply with quote

Hello, I'm beginner in microphotography.

I shot macro and closeup with APS-C e Micro 4/3 below 5X (Laowa 25mm 2x-5x and Pentax 100mm 1:1)

Now I've purchased a motorized macro rail and tube lens system with Raynox DCR 150 with 10x microscope objective to learn to shoot at high magnification.

I would buy 20X on a budget but I would like advice. On eBay, I see some 20X (Nikon DIC...). Can I use this?

Thanks,

Antonio
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Chris S.
Site Admin


Joined: 05 Apr 2009
Posts: 3431
Location: Ohio, USA

PostPosted: Wed Feb 12, 2020 1:52 am    Post subject: Reply with quote

Antonio, welcome to the forum!

I see we didn’t do a good job in answering your question here, so that you’ve tried getting similar information in other threads. Let me try to consolidate your questions here in your original thread.

anto74 wrote:
Hello, I'm beginner in microphotography.

Let me mention that inside this forum, we use some words differently from the way they are used elsewhere. In traditional contexts, making photographs with a 10x or 20x microscope objective would indeed be called “photomicrography.” But in our forum, we reserve the word “photomicrography” for the use of traditional microscopes to make photographs.

Your intended use—placing 10x and 20x objectives on a home-made, open system—we call “photomacrography”, or “macro photography” here in our pages. This naming convention helps in the discussions we have here, which include both photography through traditional microscopes and photography on home-made, open macro rigs. We find it useful to distinguish the two because many of the challenges are different.

I bring this up not to make a trivial point, but to make sure that the advice you get is matched to your needs. For our purposes, you are a beginner at high-magnification macro photography, and seek help finding an affordable 20x lens that can be used on your Raynox converging lens assembly.

anto74 wrote:
On eBay, I see some 20X (Nikon DIC...). Can I use this?

You can use some of these lenses—but definitely not all of them.

For starters, on a macro rig such as yours, working distance (WD) is very important. At 20x, you should look for 10mm or more of WD. Among Nikon objectives (a good choice for your purposes), you will want objectives that are labeled “ELWD”. This stands for “Extra Long Working Distance.”

You probably know this already, but a key reason that Nikon objectives are good for your purposes is that all but very old ones are corrected for chromatic aberration (CA) in the objective itself. (Some other brands require CA correction in the intermediate lens (Raynox in your case—which does not correct for CA), or in the eyepieces (which you do not have in your system). Most Mitutoyo objectives are also corrected for CA, but these are out of your $250 Euro ($273 USD) budget. Some (not all) Olympus objectives are also corrected for CA, but I believe these are also beyond your budget. So you are doing well to be looking at Nikon objectives.

When looking at Nikon ELWD 20x objectives, you want one that is of infinity (not finite) design. These will have an infinity symbol on the lens barrel. If the barrel says “210” or “160,” it is designed for finite use—on a bellows or empty lens tube without Raynox or other glass.

Also, you want a lens that is intended for use without a cover slip. Cover slip lenses typically say “/0.17” on the barrel. Most of the Nikon infinite 20x ELWD objectives on eBay have correction collars, and can be adjusted for use with no cover slip, or cover slips of varying thickness, up to and including the thickness of a microscope slide or petri dish. So while these don't say "/0.17", they say things like " 0-2". While you could make one of these work, I’d suggest you avoid them; the correction collar makes these lenses more expensive, decreases the working distance, and has no value in your use.

Currently on eBay, I see two likely looking candidates for you. Both are Nikon LU Plan ELWD 20x/0.40 objectives, with a working distance of 13mm. One is eBay item number 321624712035; the other is eBay item number 124039881908. They are similarly priced--$340-$345 USD. This is a bit above your budget, but both auctions permit “make offer”—so you might make an offer within your budget.

Disclaimer: I have not personally used a lens of this model. I’m assuming they would work for Antonio based on their specifications and experience with other Nikon objectives. If anyone has personal experience, please share it.

We often advise that second-hand microscope objectives should be purchased only with a return privilege, and that the lens must be tested against a known benchmark before final acceptance. This said, in my experience, second-hand Nikon objectives are much less likely to be bad than second-hand Mitutoyo objectives. I suspect they are more durable.

While I often test objectives for forum members, my schedule won’t permit much testing for the next few weeks. I don’t know if there is another forum member who is set up to test these objectives for you.

Pawel wrote:
I Have Nikon TU Plan 20x/0.40 ELWD WD19mm - NEW for sale.

This quote is from your thread in the Equipment Exchange forum. I expect that the Nikon TU plan that Pawel offers would have less chromatic aberration than the LU plan lenses—and 19mm WD is easier to work with than the 13mm WD of the LU plans. However, TU plans are much more expensive than LU plans. There are some TU plans on eBay for less cost than Pawel’s, but they still exceed your budget considerably.

In your post in the Equipment Discussions forum, you asked about “Nikon Plan Fluor 20x/0.50 DIC M” objectives. Avoid these for your purposes. Note that these objectives are not labeled ELWD--and working distance of 2-3mm is far too little for general macro use. (Though a few exceptions have been made at much higher magnifications/numerical apertures by expert macro photographers willing to accept severe lighting constraints for particular uses.) There is nothing wrong with "DIC," and "Fluor" usually indicates a better--if sometimes more fragile--lens.

Cheers,

--Chris S.
(A different Chris from ChrisR, who has also responded in one of your threads.)
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anto74



Joined: 06 Feb 2020
Posts: 27
Location: Italy

PostPosted: Wed Feb 12, 2020 2:28 am    Post subject: Reply with quote

Hello Chris,

Thanks for your answer and for precious info!

I'm an experienced macrophotography user (from close up to 5X ) and now i discovered the magic world of photos at >10X magnification Smile

My goal with 20X is to have the same quality as my Laowa 25mm 2.5-5x or Pentax 100mm macro at 100% view (I print A3+ and A2 my best photos).

Example:
www.antoniodesantis.it/fs/vespa.jpg ( Laowa 25mm at 2.5X )
www.antoniodesantis.it/fs/cimice3.jpg ( Laowa 25mm at 5x)
www.antoniodesantis.it/closeup/colias_crocea.jpg (Pentax 100mm)

The photos with Laowa are first attempts with WeMacro rail and focus stacking technique I used Helicon Focus trial version.

Do you think that with the Nikon lenses you pointed out to me the results will be good?

I saw two items on Ebay, I live in Italy and I have import charges for 120$ Sad
In may I will go to Houston to visit my brother... maybe I could have the item shipped here Smile

Thanks again Chris!

Cheers,
Antonio
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Chris S.
Site Admin


Joined: 05 Apr 2009
Posts: 3431
Location: Ohio, USA

PostPosted: Wed Feb 12, 2020 5:10 am    Post subject: Reply with quote

anto74 wrote:
I'm an experienced macrophotography user (from close up to 5X ) and now i discovered the magic world of photos at >10X magnification Smile

I know you are an experienced macro photographer, Antonio. I only meant to describe you as inexperienced at magnifications higher than 5x--and this only to help other forum members note where you are in the learning curve in order to give you appropriate advice. (Also, I believe you will not be inexperienced at 10x and 20x for long. Very Happy )

anto74 wrote:
Example:
www.antoniodesantis.it/fs/vespa.jpg ( Laowa 25mm at 2.5X )
www.antoniodesantis.it/fs/cimice3.jpg ( Laowa 25mm at 5x)
www.antoniodesantis.it/closeup/colias_crocea.jpg (Pentax 100mm)

The photos with Laowa are first attempts with WeMacro rail and focus stacking technique I used Helicon Focus trial version.

Very fine images! Your Laowa is looking good at 2.5x; but by 5x, it's not as good as a 5x microscope objective would be. This is typical and expected. So given your high standards, you may want to add a 5x microscope objective at some point in the future.

anto74 wrote:
Do you think that with the Nikon lenses you pointed out to me the results will be good?

Yes I do.

This said, any 20x lens in your price range will be an achromat, rather than an apochromat. An achromat is corrected for two points in the visible spectrum, whereas an apochromat is corrected for three points in the visible spectrum. Because of this, achromats (particularly at 20x and above) tend to produce some false color (often purple or violet) along high-contrast edges. When focus stacking with many subjects, much or all of this false color disappears (stacking algorithms select sharp detail, discarding much of the fuzzy false color). You may be left with some edges to retouch. But apochromatic lenses (such as Mitutoyo objectives) cost far more. And many wonderful images have been posted to our fora, taken with achromats.

Good luck!

--Chris S.
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