Objective with lower magnification than it should

[Mindwarp]

Hello all,

I adapted a Zeiss 50x/0.95 dry objective from an Axiomat Zeiss (infinite) to my Axioplan (infinite). It works perfectly but... obviously the magnification I obtain is lower than the one I have with the 40x/0.75 objective !
Is there an explanation or is my 50x damaged ? Contrast, image and resolution are more than perfect only magnification seems lower than it should.

Did it already happened to some of you ?

Thanks you.

[Greg Howald]

The only explanation I know of is this. DIN standard Finite objectives will usually fit in any Finite scope provided they match in focal length.
But... Infinite optics have no international standard. Optics in Infinite systems are often Specific by Brand. So, if you mix brands of optics in an infinite system, what you get may well be different from what you expected. Differences may be in the head as well as in the objective. Each manufacturer of course claims their system is better than others, so the optics you use need to match the manufacturer of the scope.
Greg

[Scarodactyl]

Typically this would mean that your microscope's head has a tube lens of shorter focal length than the objective is specced for. Later Zeiss infinity stands do have an unusually short focal length (165mm) but I don't know if the axiomat would have used a longer focal length.

[Mindwarp]

Hello

@Greg thanks you for these usefull input, it gives me one more motivation to keep as much as I can, every pieces from the same brand on each microscope.
By the way Axiomat an Axioplan are both Zeiss from the same era.

@Scarodactyl, thanks you for the information. This objective is quite special as the thread isn’t on the top but on the first third of his body. It is not made to just be screwed on the head nose of the Axiomat but penetrating in by a third of his size.
In the Axioplan it can’t be penetrating, so the offset might explain the magnifixation lowering.
As it is an Apo with corr I might be able to compensate with a stronger eye piece.

[apochronaut]

The Axiomat was the first Zeiss microscope built with infinity correction. It was launched in 1973, just slightly after Reichert introduced the Univar, heralding their introduction of infinity correction. This was about 10 years after AO.
The Axioplan was launched after they discontinued the Axiomat, so there was a short gap in time when Zeiss did not make an infinity scope again. The Axioplan was the Zeiss reintroduction of infinity correction based on a standardized system of a roughly 165mm reference length. Having used an Axiomat and looking at it, it is unlikely that it has such a short reference length. My guess is that it is somewhat longer and that accounts for your magnification loss.

There are a couple of Axiomat owners on the forum. Perhaps they know the actual reference length of the Axiomat.

[Scarodactyl]

In the Axioplan it can’t be penetrating, so the offset might explain the magnifixation lowering.

One of the nice things about infinity microscopes is that the length of this gap does not matter*.

*for magnification and focus, but longer distances can decrease the size of your image circle and it can have subtle effects on how well corrected your image is, but that doesn't matter much for conventional microscopy.

[Mindwarp]

@Apochronaut, thanks you for these historical information. It seems now that the objective would de more efficient if the tube was a little smaller of 20 mn (the protubing part above the tread)

@Scarodactyl, by the way it is impressive that it lower the magnification of around 25%
Instead of a 50x/0,95 it might be more closer to 35x (I compared to my 40x and my 25x objectives) but the resolution is really good (Apo) with -> eyepiece 10x + optovar 2,5x. But working distance is really small (as I need to play a lot with the correcting ring).

I’d be curious to know if some other members used Axiomat objectives with other more recent Zeiss microscopes ?

[apochronaut]

@Apochronaut, thanks you for these historical information. It seems now that the objective would de more efficient if the tube was a little smaller of 20 mn (the protubing part above the tread)

@Scarodactyl, by the way it is impressive that it lower the magnification of around 25%
Instead of a 50x/0,95 it might be more closer to 35x (I compared to my 40x and my 25x objectives) but the resolution is really good (Apo) with -> eyepiece 10x + optovar 2,5x. But working distance is really small (as I need to play a lot with the correcting ring).

I’d be curious to know if some other members used Axiomat objectives with other more recent Zeiss microscopes ?

If you are getting only 35X, the reduction in magnification is about 30%. That means that the reference focal length of the Axiomat would be in the 240mm range, roughly. The pick up point of the Axiomat eyepieces is also an unknown.

[Mindwarp]

Yes it is far higher than my 25x and a bit lower than the 40x.

Do you think something can be done ? Extension on the objective or at the eyepiece level ?

[apochronaut]

You are looking at 70mm or thereabouts. Do you have an optovar? I would just set it to compensate.

[Mindwarp]

Yes @apochronaut I have an optovar. So with an eyepiece x10 and the Optovar x2,5, I might be around the limit of the Apo dry objective NA 0.95 .