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Magnification Changer

Posted: Tue Aug 21, 2018 9:00 pm
by nxp
I have Olympus BX40 with:
Plan 20x/.40 Ph1
Plan 40x/.65 Ph2
Plan 100x/1.25 Ph3 oil

The microscope also have a Magnification Changer (Olympus Microscope U-CA Magnification Changer 1x, 2x, 1.6x, and 1.25x). Something like this: ... lv37367849

Does this magnification changer realy help or i just loose quality?

Should i sell it (may be 800usd?) and buy a better objective like a plan apo?

I use it for microphoto.

Re: Magnification Changer

Posted: Tue Aug 21, 2018 9:47 pm
by apochronaut
so, the rule of thumb is that for achromatic objectives, you can push the magnification 1000X the N.A., so Olympus has deliberately put a 1.25X in the changer, so you can maximize the magnification of your 1.25N.A. objective with 10x oculars. The same is true with the 20x .40 , using the 2X mag. changer and the 40x .65 , using the 1.6X mag. changer. Each magnification is dovetailed to a specific objective, without overdriving it's resolution capacity.

In the old days, the same thing was done by using different eyepieces. It might seem odd that 30X eyepieces were supplied with older microscopes but a 30x eyepiece with a 10x .30 apo objective is still within spec. That was the only objective you would normally use it with , though.

Going to apochromats, is a whole other thing. Not only does the resolution potential go up but you would also be able to use one of your mag. changer magnifications with a higher magnification objective; for instance: the 2X with a 40x apo, which would have an N.A. of .80 or higher likely. You also might be able to stretch higher N.A. 100X apos to 1600X with the 1.6x mag changer, because with the more highly colour corrected objectives, there is a higher tolerance for magnification increase; somewhere +- 1100X the N.A., depending on the objective. Olympus probably knows that their 1.4 N.A. 100X objectives can be pushed that far.

Re: Magnification Changer

Posted: Wed Aug 22, 2018 3:07 am
by Tom Jones
In addition to apochronaut's comments, mag changers also can be quite useful to aid in framing your photographs or videos in that they will allow you to more easily fill the sensor frame so you don't lose as much as when cropping in post. Particularly handy when shooting video as cropping in post is a pain. I use them on both my BX's and BH2's. They come as part of the system on the Oly IMT-2 inverted scope (1x and 1.5x), the IX71 (1x and 1.6x or 1x and 2x) and optivars on Zeiss Universals and Photomicroscopes. Others, too, I'm sure.

Hang onto the mag changer. They're pretty rare. Save up your pocket change for additional objectives. You won't regret it.

Re: Magnification Changer

Posted: Wed Aug 22, 2018 7:46 am
by 75RR
re-posting this (from 2015) with a couple of changes as I thought it might help

This is a quote from Fundamentals of Light Microscopy by Douglas B. Murphy

"Oculars or eyepieces are needed to magnify and view the image produced by the objective.
To make optimal use of the resolution afforded by the objective, an overall magnification equal to 500–1000 times the NA of the objective lens is required.
More magnification than this gives “empty” magnification, and the image appears highly magnified but blurry.
For most applications, 10x eyepieces work well. When higher magnifications are required for a specific objective, a magnifying booster lens (in Zeiss microscopes, an Optovar lens magnification system) can be rotated into the optical path.
Alternatively, a different set of higher-magnification eyepieces can be employed."

This is the formula: (well, a rule of thumb really)

Range of Useful Magnification (500 to 1000 x NA of Objective)

In which the 500 x NA (Numerical Aperture) is the minimum necessary for the detail present in an image to be resolved,
and anything over 1000 x NA tends to give empty magnification.

as an example:
For a Plan 40/0,65NA Objective
the range would be between
500 x 0,65 = 325 and
1000 x 0,65 = 650 so
below 325x total magnification, detail will not be resolved
above 650x total magnification, no additional detail will be resolved

best Useful Magnification Range for this objective is between 325x and 650x

A quick test is to multiply the NA of an objective by 1000,
then multiply the magnification of the objective by the magnification of the eyepiece* (and the magnification changer if used).
if the second figure is higher then using that objective with that eyepiece* will result in empty magnification.

Another useful test is to divide the max magnification by the objective's magnification, this gives you the max eyepiece magnification for that objective.
In this case 650/40 = 16. Therefore a 16x eyepiece would be ok (or a 10x with 1.6 magnification changer) but a 20x eyepiece (10x with 2x magnification changer) would give empty, i.e. ‘too much’ magnification with this objective.

It is good to keep an eye on this, especially as one can not only slip into empty magnification without realizing it but one can also drop below the minimum magnification needed for optimal resolution.

* Note that in these formulas one should multiply any additional magnification brought about by the magnification changer to that of the eyepieces.

For example:
10x eyepieces x 1.25 = 12.5X
10x eyepieces x 1.6 = 16X
10x eyepieces x 2.0 = 20x

It is good to remember that it is the objective that provides the image.
What the eyepiece does is present it to us at a magnification that allows us to appreciate it at its best possible advantage.

Note: As one gets older and ones eye deteriorate it helps to be a little more flexible with this rule of thumb.

Re: Magnification Changer

Posted: Sun Aug 26, 2018 1:17 am
by einman
I have the mag changers on two of my Leitz scopes. They are useful but Apo's quick explanation makes perfect sense now why the specific magnifications were chosen.

Re: Magnification Changer

Posted: Thu Aug 30, 2018 7:09 am
by hkv
I would keep it. I use mine all the time especially when shooting video.

Re: Magnification Changer

Posted: Thu Aug 30, 2018 12:46 pm
by Crater Eddie
I would keep it also, you will use it more than you think you would. I have two LOMO heads with the built in mag changers and they do come in very handy. Wish I had a similar one for my BH2.

Re: Magnification Changer

Posted: Sun Sep 02, 2018 1:21 pm
by GaryB
Just to add to this, as I understand things, the head and any other attachments need to be taken into account as well. My heads are 1.25x and 1.6x magnification, some epi attachments are also around 1.5x.

So that would be 40x objective times a 10x eyepiece times a 1.25x head times the mag changer number times any other attachments would be the real total. Correct me if I'm wrong on this as I get all my info from the interwebs :oops: