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Question about microscope objective

 
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MSims



Joined: 16 Nov 2013
Posts: 3
Location: Bay Area

PostPosted: Sun Nov 17, 2013 9:28 pm    Post subject: Question about microscope objective Reply with quote

Newish to macrophotography and had a few questions. I am recently picked up a Nikon D800 and a Nikon 105mm 2.8d to continue a project I was working on. I was considering the TC-20E III to take it to 2:1 but then found this forum and am now considering a Nikon's CFI Plan Achromat 10x to get to 5:1 if I am understanding the overwhelming amount of information I am reading here.

If I am reading correctly, if I were to use the 10x on a 200mm tube it would give me 10x and on my 105mm it will yield a 5x?

Will I be able to use the Nikon's CFI Plan Achromat 10x without a rail such as the StackShot?

Here are my first 2 attempts at focus splicing using a H3D-II 31 and the 120mm Macro lens. This is what got me hooked on macro and want to explore further. Both subjects are about the size of my palm so 1:1 was enough for these images. But I am looking to shoot things much smaller.

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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18094
Location: Richland, Washington State, USA

PostPosted: Sun Nov 17, 2013 10:09 pm    Post subject: Reply with quote

MSims, welcome aboard -- your images look great! Very Happy

You're correct about the magnifications: 10X on 200mm; 5.25X on 105mm.

The wrinkle is that the CFI Plan Achromat 10X only covers a field around 5 mm diameter with high quality image. So at 5X it would be OK on your D800 in DX mode using the APS-C sized center of your sensor, but the corners would go bad in FX mode using the full frame.

The required focus step is about 0.005-0.010 mm in both cases, so you'll be needing some sort of screw-driven focus rail, micrometer driven linear stage, or microscope focus block. Once upon a time I used to stack 10X on sensor using a milling table with 0.1" per turn of the handscrew, but that got pretty fiddly because the required focus step was then about 1/500 of a full turn (giving 0.005 mm focus step).

--Rik
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MSims



Joined: 16 Nov 2013
Posts: 3
Location: Bay Area

PostPosted: Mon Nov 18, 2013 8:17 am    Post subject: Reply with quote

Rik,

Thank you for your quick response. I am so glad I have found this forum. I must say though its a bit like going down the rabbit hole.

I guess that brings up another question then. I will need to be in full frame FX mode due to my output size requirements, is there a better objective that will cover the full frame sensor of the D800? I do not foresee myself needing an objective that is capable of more than 5x on my 105mm, but I do need it to cover the full frame sensor.

How do you calculate the coverage of the objectives compared to the sensor?

I was also contemplating the PB-6 nikon bellows where my initial thoughts were that it might give me a more flexible range.

Most of the things I will be shooting will range from 20mm to 50mm in length and 5mm to 10mm thick with varying widths that I will stack and then merge into panoramas as I did with the long wingspan in the image above.
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Mon Nov 18, 2013 12:32 pm    Post subject: Reply with quote

This answer will seem a bit indirect, but I think it's best if we start back with some basics.

The point of a microscope objective is to cover a small area at high resolution. You can think of the Nikon CFI 10X NA 0.25 as being a reversed 20 mm f/2 lens whose design is optimized to run best wide open, resolving roughly 700 line pairs per mm but with that high quality only within a circle of roughly 5 mm diameter.

You can change the overall magnification by changing the length of the tube lens (rear lens), but that doesn't change the size of the high quality image circle on subject.

Quote:
How do you calculate the coverage of the objectives compared to the sensor?

The coverage of an objective on subject is fixed by its design. Even for the best objectives this will be no more than about 50 mm divided by the objective's nominal magnification. For most objectives it is significantly smaller, more like 30 mm divided by the nominal magnification.

This coverage on subject maps to coverage on sensor simply by multiplying by the actual magnification. If you run that Nikon CFI 10X at actual 5X by sticking it on a 100 mm tube lens, then the coverage on sensor becomes 5 mm on subject * 5X = 25 mm on sensor. This is why it covers an APS-C sensor at 5X, but not full frame.

Quote:
is there a better objective that will cover the full frame sensor of the D800? I do not foresee myself needing an objective that is capable of more than 5x on my 105mm, but I do need it to cover the full frame sensor.

Yes, there are better objectives for 5X on full frame, but they won't be nominal 10X pushed down with a short tube lens. To cover full frame at actual 5X, you need coverage on subject of about 8 mm diameter. That calls for a lower magnification objective, a 4X or 5X, and then you'll be needing to use it on a 200 mm tube lens in order to run at actual 4X or 5X.

Arguably the best microscope objective in that regime is the Mitutoyo M Plan Apo 5X NA 0.14, working distance 34mm.

However, the Mitutoyo 5X is essentially just a 40 mm f/3.5 apochromat fitted into the Mitutoyo standard objective mount.

So, it's a good question whether you'd be better off with the Mitutoyo 5X on a 200 mm tube lens, or better off with some other roughly 40 mm f3.5 apochromat used by itself on bellows. For discussion relative to that topic, see for example http://www.photomacrography.net/forum/viewtopic.php?t=21874 and the links therein.

Quote:
merge into panoramas

For some discussion of pano merging in macro settings, see our FAQ What is "stack-and-stitch", and how can I do it?. There are some issues regarding parallax that you may not have run into yet.

--Rik
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soldevilla



Joined: 16 Dec 2010
Posts: 460
Location: Barcelona, more or less

PostPosted: Mon Nov 18, 2013 4:01 pm    Post subject: Reply with quote

fantastic first image!
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MSims



Joined: 16 Nov 2013
Posts: 3
Location: Bay Area

PostPosted: Mon Nov 18, 2013 7:40 pm    Post subject: Reply with quote

Rik,

Thank you for the clarification and insight, its starting to make sense. You have given me a lot to think about.

Soldevilla,

Thank you
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