Proper Objective to film plane distance

[McMacroBigMac]

Been a long time since i've been on. I see I've been missing out on a lot!

I was given a Leitz LL 20X and I was looking into adapters to go from the RMS mount to t-mount (is this right?) and using a t-mount fine focus adapter (http://www.edmundoptics.com/optomechani ... ube/52-300) and t-mount to EOS adapter. I am using a Canon 5D Mark II

I started wondering if there is a way to find out the proper distance the microscope objective is supposed to be away from the film/sensor plane to minimize distortion, aberrations while maximizing sensor area coverage. I understand the distance from the the sensor will directly affect the working distance to the subject and am only worried if it causes the front objective to contact subject.

With 25mm of extension from the mount on the camera with a homemade mount i was able to focus about 5cm away but saw a lot of pincushion distortion and chromatic aberrations in the the corners. I believe a lot of it was due to the sloppiness of the construction and being hand held.

I have not ordered any of the adapters or the focusing tube yet. This will be my first microscope objective so I'm very excited but want to do it right. Any advice is appreciated.

[Charles Krebs]

I believe this is an "infinity" objective. Can you give us the markings on the objective?

If this is the case, it is more complex than simply adapting it to the proper length extension tube/bellows.

In any event it will be a real long-shot to cover a 24x36mm sensor, but you can give it a try.

[rjlittlefield]

Be sure to read our FAQ: How can I hook a microscope objective to my camera?

From the numbers listed in your posting, I strongly suspect you haven't done that yet.

--Rik

[McMacroBigMac]

I don't know how I missed that in the FAQ that's a very extensive article.

Thanks I'll start there.

--Keegan

[Pau]

I was given a Leitz LL 20X and I was looking into adapters to go from the RMS mount to t-mount ....
... and t-mount to EOS adapter. I am using a Canon 5D Mark II

Leitz objectives aren't adequate to work as macro lenses (direct projection on sensor) because they need complementary aberrations correction done by a Leitz Periplan compensating eyepiece. And they likely will not cover full frame sensor: usually thery are designed for 20mm image circle eyepieces or in the best case (Pl designed for Orthoplan) 28mm image circle.
In the best case you will get a good image centre with nasty periphery.

Another important point is the "coverglass" correction: if it is intended for inverted microscopes (170/1 or similar) they are designed to see through a 1mm thick glass and will be afected by heavy spherical aberration. If designed for 0.17 coverglas this will be not as important if the NA is up 0.30, if it's a metallurgical objective (210/0 or 170/0) this isn't an issue because they are designed to work without coverglass.

And of course if it is infinite corrected as Charles sugests you need a "tube lens", but the former caveats still apply.

Please post the complete specification if you want further clarifications.

[McMacroBigMac]

Pau,

The markings are

LL 20X / 0.40

∞/0/30

If it requires additional lenses and accessories I might see about getting a different one. I helped a guy out and he gave it to me, he has others he said. anything you recommend? I'm gonna read thru the equipment section too. I have a canon 65mm 2.8 mp-e and am looking for something maybe a little higher magnification.

Thanks for all the info,

-Keegan[/b]

[Pau]

The markings are

LL 20X / 0.40

∞/0/30

It's a metallographic objective
LL means long (or very long) working distance, a desirable feature for macro
∞/0 infinite corrected an no cover glass. It needs an adequate tube lens (I don't kow its focal lengh) and no glass covered specimen
/30 I dont know. If it means the working distance it will be a very long one for a microscope objective (again good)

But as I said it do need a tube lens and a compensating eyepiece (ie to be used in the adequate microscope) so it will be problematic for direct projection. Because you already own it you can test it, but I wouldn't expect good performace.

Few objectives are adequate for direct projection on full frame. Other members would give you better advice. For APSC many Nikon CF finite series are very good, but I don't know for FF.