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Choice of microscope objective for bellows and SLR
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Enoplometopus



Joined: 31 Mar 2010
Posts: 48
Location: Germany

PostPosted: Wed Apr 07, 2010 1:37 pm    Post subject: Choice of microscope objective for bellows and SLR Reply with quote

Hi All

I am totally new in this list. I'm trying to work myself into photomicrography and I am now assembling my first setup. What's missing is a microscope objective. I plan to get a 10x and maybe a 20x, but since I work without a microscope I cannot use an eyepiece to do any optical corrections. Therefore I need to ensure it is an objective that has included lenses doing this final corrections.

As far as I have understood this is generally expressed by the term "finite". What microscope lenses can I use with a bellows system and an SLR? Do they generally have the word "finite" engraved? How can I be sure of not buying an objective that needs an eyepiece for optical corrections?

I read the wonderful articles of Charles Krebs, but I still feel insecure buying an objective and just assuming it is what I need, because most are not. What in particular do I need to look for if searching for it in Ebay?

(Or does anybody plan to sell a good 10X and maybe 20x of this type?)

Thanks for any help.

Cheers, Daniel
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ChrisR
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Joined: 14 Mar 2009
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PostPosted: Wed Apr 07, 2010 3:26 pm    Post subject: Reply with quote

Welcome Daniel
This is truly a frequently asked question - we need a reference post!
I think you'll find all the answers, or links to them, in this recent thread:
http://www.photomacrography.net/forum/viewtopic.php?t=9290

Do be aware, if you aren't already, that buying things like microscope objectives on ebay can be a frustrating experience. I've had to send 3 back, which is costly. One had been returned by a previous "winner"- it seems the seller would just keep trying until someone didn't notice the problems.


Last edited by ChrisR on Wed Apr 07, 2010 3:36 pm; edited 1 time in total
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Wed Apr 07, 2010 3:28 pm    Post subject: Reply with quote

Daniel, welcome aboard! Very Happy

This question is turning up often enough lately that maybe we should package the answer into a FAQ entry. Not today, though.

As a quick summary...

A "finite" type objective is needed to project directly onto the camera sensor. These objectives are designated as 160/ or 210/, followed by the nominal cover glass thickness, typically either - (don't care), 0 (none), or 0.17 (standard cover glass).

For your purposes, the best objectives will be designated 160/0, 210/0, 160/-, or 210/-, although at 10X and below you can also use 160/0.17 and 210/0.17 and retain excellent image quality.

Avoid "infinity" type objectives. These are designated with the sideways-8 infinity symbol instead of 160 or 210.

Regarding corrections, the Nikon CF series of finite objectives can be trusted to perform well by themselves. A brochure showing these objectives is currently posted at http://www.krebsmicro.com/Nikon_CF.pdf. Many of us are particularly fond of the CF N Plan Achromat 10X NA 0.30 as the next step in magnification beyond high end macro lenses such as the Olympus 20 mm f/2 bellows macro lens. At higher powers like 20X and 40X, the ELWD's are needed to give enough working distance for front-lighting.

Choosing objectives other than the Nikon CF's is pretty much like playing dice. Some of them work well, others do not, and I am not aware of any good source of information.

What are your main interests? We can give better advice if we know more about what you want to do.

--Rik
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bklein



Joined: 16 Feb 2010
Posts: 94
Location: Trabuco Canyon, CA

PostPosted: Wed Apr 07, 2010 10:19 pm    Post subject: Reply with quote

I think we need a photo or a new thread with photos -
"this one is good, this one isn't."

I've struck out it seems with the vendor Charles recommended for the CF.
Doesn't return calls or emails.
As infinites seem the way things are going with microscopes and objectives I hope DIY'rs figure out a cost effective solution using them.

Barry


Last edited by bklein on Thu Apr 08, 2010 1:38 am; edited 2 times in total
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rjlittlefield
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PostPosted: Wed Apr 07, 2010 10:46 pm    Post subject: Reply with quote

bklein wrote:
Not all marked with a "160" are finites.

I suspect there's some confusion about what "finite" means. Objectives that are marked "160" are designed to project a real image to an eyepiece mounted on the end of a 160 mm mechanical tube. This is the definition of "finite": that the objective is designed to project a real image at some finite distance. It contrasts with "infinity" designs, in which the objective is designed to create a virtual image at infinity, and it is only the matching tube lens that projects a real image for use by the eyepiece. Neither "finite" nor "infinity" have anything to do with color aberrations -- that is a separate issue.

Does this clear up the confusion, or can you give an example or expand on what you mean when you write that "Not all marked with a "160" are finites"?

Quote:
As finites seem the way things are going with microscopes and objectives I hope DIY'rs figure out a cost effective solution using them.

Did you mean "As infinites..."?

--Rik
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bklein



Joined: 16 Feb 2010
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Location: Trabuco Canyon, CA

PostPosted: Thu Apr 08, 2010 2:00 am    Post subject: Reply with quote

rjlittlefield wrote:
bklein wrote:
Not all marked with a "160" are finites.

I suspect there's some confusion about what "finite" means. Objectives that are marked "160" are designed to project a real image to an eyepiece mounted on the end of a 160 mm mechanical tube. This is the definition of "finite": that the objective is designed to project a real image at some finite distance. It contrasts with "infinity" designs, in which the objective is designed to create a virtual image at infinity, and it is only the matching tube lens that projects a real image for use by the eyepiece. Neither "finite" nor "infinity" have anything to do with color aberrations -- that is a separate issue.

Does this clear up the confusion, or can you give an example or expand on what you mean when you write that "Not all marked with a "160" are finites"?

Quote:
As finites seem the way things are going with microscopes and objectives I hope DIY'rs figure out a cost effective solution using them.

Did you mean "As infinites..."?

--Rik


Hi Rik,
Yes, combination brain fade and screw up...
I did mean "INfinintes".
I removed (edited) the "160" reference. What I was referring to within my fuzzy brain is that some Olympus are marked "f=180" but are infinites (usually?). Like this item in ebay: 170468447132. Also, Nikon has the CFI60 series scopes with objectives referred to as CFI and CFI60 (which looks alot like CF160). The ones we seem to be desiring are CF, no "I". And with "N Plan" even better. Just no infinity symbol hiding on the other side (missing 2nd photo in the ebay ad....) Sad

Barry
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Enoplometopus



Joined: 31 Mar 2010
Posts: 48
Location: Germany

PostPosted: Thu Apr 08, 2010 2:59 am    Post subject: Reply with quote

ChrisR:
Thanks for the thread about the objective choice, that fits. I‘ll read it in detail.

>>Do be aware, if you aren't already, that buying things like microscope objectives on ebay can be a frustrating experience. I've had to send 3 back, which is costly. One had been returned by a previous "winner"- it seems the seller would just keep trying until someone didn't notice the problems.<<

I know! I‘ve sent back two already before completing my setup...




Rik:
>> This question is turning up often enough lately that maybe we should package the answer into a FAQ entry. Not today, though. <<

That sounds great. Maybe also with a list including all the specifications of those objectives that are recommended, so one can exactly see what he can read engraved in the objectives.

>>What are your main interests? We can give better advice if we know more about what you want to do.<<

Well, I do living marine organisms, up to now I do close up and macro photography 5:1 (MP E 65mm). I‘ve seen the fantastic works of Charles Krebs and immediately understood this technique as an extension or continuation of my macro shots, though this requires to either work with dead or somehow immobilized organisms. But the magnification I need will mainly be between 10x and 20X, I guess.

>>For your purposes, the best objectives will be designated 160/0, 210/0, 160/-, or 210/-, although at 10X and below you can also use 160/0.17 and 210/0.17 and retain excellent image quality. <<

Does this mean all objectives 160/... or 210/... are finite? And then it just depends on the question whether they do chromatic aberration corrections inside the objective? In this case I could try one of those I have in my compound microscope and see what chomatic aberrations they produce (I tried to upload two pics of my 10X objectives here, hope that upload works).

One of the problems I may face over here in Germany is that Nikon has a wide coverage in Asia and North America, while here in Europe we almost always have Zeiss and Leitz. Nikon objectives are almost not present in this market...

Cheers, Daniel
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morfa



Joined: 12 Oct 2009
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Location: Stockholm, Sweden

PostPosted: Thu Apr 08, 2010 3:15 am    Post subject: Reply with quote

Enoplometopus wrote:

ChrisR wrote:
Do be aware, if you aren't already, that buying things like microscope objectives on ebay can be a frustrating experience. I've had to send 3 back, which is costly. One had been returned by a previous "winner"- it seems the seller would just keep trying until someone didn't notice the problems.


I know! I‘ve sent back two already before completing my setup...

Cheers, Daniel


Chris, Daniel and anybody else with similar experiences: may I ask what seems to be the problem with the objectives you are returning? Just curious if there is something in particular you should look carefully at when buying used objectives.
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Enoplometopus



Joined: 31 Mar 2010
Posts: 48
Location: Germany

PostPosted: Thu Apr 08, 2010 3:30 am    Post subject: Reply with quote

>>Chris, Daniel and anybody else with similar experiences: may I ask what seems to be the problem with the objectives you are returning? Just curious if there is something in particular you should look carefully at when buying used objectives.[/quote]<<

Actually I purchased a 10x and a 20x, both Nikon CF, but later found out they were infinites. I was able to convince the seller not to send me the objectives and send my money back. In this case it was caused by sparse detail information about the objective specifications, paired with sparse understanding of the optical principles behind it. I will now try to get held of a CF N Plan Achromat 10X NA 0.30...

Daniel
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rjlittlefield
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PostPosted: Thu Apr 08, 2010 8:30 am    Post subject: Reply with quote

bklein wrote:
What I was referring to within my fuzzy brain is that some Olympus are marked "f=180" but are infinites (usually?). Like this item in ebay: 170468447132.

Thanks for the example. I have not run into that particular notation before. I'm pretty sure that the "f=180" refers to the focal length of the matching tube lens. This is roughly analogous to tube length in a finite scope. An infinite objective gives its rated magnification only with some specific tube lens focal length. Tube lens lengths vary between manufacturers: Nikon likes 200 mm, Olympus uses 180 mm, Zeiss uses 164.5 mm, probably there are others.

--Rik
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rjlittlefield
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PostPosted: Thu Apr 08, 2010 9:42 am    Post subject: Reply with quote

Enoplometopus wrote:
I will now try to get held of a CF N Plan Achromat 10X NA 0.30...

Yes, I think this would be the best solution for you. Your interests require having a flat field to allow single shots. Objectives with flat field are called "plan". The lens you mention has a very flat field with good resolution everywhere. The only drawback is that you can expect to wait a while before one comes up.

If you were interested mainly in stacking and wanted to get started quickly, then I might also suggest a 10X NA 0.25 "Nikon Achromatic Finite Conjugate Objective" currently available new from Edmund Optics (HERE).

Edmund's tech support tells me that "There isn't very much data currently put out by Nikon on this particular line of objectives." However, they appear very similar to Nikon's earlier "E Achromat" objectives as shown in the CF series brochure linked above.

I recently bought one of these new objectives for evaluation. On quick look, it has significant curvature of field (typical of non-plan) and slightly less resolution than the now discontinued CF N Plan Achromat 10X NA 0.30 (as expected with the smaller aperture). However, the color fringing is about the same, quite good. The new objective has slightly better resolution and far less color fringing than an older aus Jena 10X NA 0.25 achromat that I used to use successfully (see HERE).

--Rik
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Enoplometopus



Joined: 31 Mar 2010
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Location: Germany

PostPosted: Thu Apr 08, 2010 10:21 am    Post subject: Reply with quote

Rik:

>>If you were interested mainly in stacking and wanted to get started quickly, then I might also suggest a 10X NA 0.25 "Nikon Achromatic Finite Conjugate Objective" currently available new from Edmund Optics (HERE). <<

Well, I forgot to tell that I am planning to do stacking with that objective. Probably only stacking. What I want to do is pretty much the same like Charles has done with insects here, only I work with marine organisms: http://www.krebsmicro.com/obj_bellows/index.html. If the "10X NA 0.25 Nikon Achromatic Finite Conjugate Objective" will allow me to do this, and the sharpness is not much lesser than the other one, I'd be interested.

And how do those microscope objectives in general compare with a Zeiss Luminar 16 or 25? Much more sharpness?

Cheers, Daniel



--Rik[/quote]
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rjlittlefield
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PostPosted: Thu Apr 08, 2010 11:12 am    Post subject: Reply with quote

Enoplometopus wrote:
And how do those microscope objectives in general compare with a Zeiss Luminar 16 or 25? Much more sharpness?

Yes, much more. See for example HERE, in the third panel, "direct comparison of center resolution". Another comparison HERE. These are with biological specimens. I am currently looking at a different test subject -- a piece of freshly smoked glass covered with tiny soot particles of various sizes and shapes. The improvement of the objectives over the Luminar 16/2.5 is so extreme that I'm not going to show the results until I go back and confirm that they are correct.

--Rik
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Enoplometopus



Joined: 31 Mar 2010
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PostPosted: Thu Apr 08, 2010 11:22 am    Post subject: Reply with quote

>>Yes, much more. <<

Good to know. The Luminars are quite abundant and relatively easy to get here in Germany and neighbour countries, and whoever works with those praises the sharpness, probably not being aware of microscope objectives at all. Those guys usually work in lower magnifications, I guess...


>>The improvement of the objectives over the Luminar 16/2.5 is so extreme that I'm not going to show the results until I go back and confirm that they are correct.<<

Wow!

And you think with the "10X Nikon Achromatic Finite Conjugate Objective" I won't need to be afraid of chromatic aberrations when using it on a bellows system? Do you have personal experience with that? If you say it would be suitable for stacking works, I'd be willing to get it and start with it while waiting for a good opportunity of getting the "Plan" version...

Daniel
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rjlittlefield
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PostPosted: Thu Apr 08, 2010 11:44 am    Post subject: Reply with quote

Luminars are very sharp compared to lesser lenses of the same general type. The key difference is that compared to microscope objectives the Luminar and similar lenses cover a wider angle of view at lower resolution.

I have a lot of experience using various objectives on bellows. Based on that experience, I have high expectations for the new Nikon. But I have not yet run a deep stack with that particular objective, and I have been surprised enough times to be cautious. I expect to have some tests ready for posting after the weekend.

--Rik
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