Use of telephoto lens and adapter for microscope objectives

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VinodkumarSelvaraj
Posts: 18
Joined: Tue Feb 19, 2019 10:18 pm

Use of telephoto lens and adapter for microscope objectives

Post by VinodkumarSelvaraj »

Hi Guys!!
I am happy to be in the forum. I am reading a lot and gaining knowledge in extreme macro. I should first thank the family of photomacrography.net.

I have a question regarding magnification and I am confused with that. The things which we see through a microscope eye piece may have a magnification of eg. 100x (eye piece - 10X multiplied with objective 10X). SO now comes to mind a few questions. The questions may be silly. But please consider and clear my doubts :-)

1. I have seen microscopes with fitted camera for eg. Olympus having a lens (0.63x) between the camera and the mount. So what will be the magnification we get on the camera?
2. People use telephoto lens and raynox as tube lens to couple microscope objectives with the DSLR. Raynox have 1.5x (DCR-150), 2.5X (DCR-250) magnification. similarly the telephoto lens have various magnification ranges for example canon 70-200mm (0.27x), canon 200mm (0.16x). So will there be a difference in magnification when using different telephoto lens / raynox? Or these diopters do work only to focus the images in the sensor? People use objectives with bellows or extension tubes without any lens and here what happens?

I am a bit lagging in physics. I would like to know simple explanation that makes me understand. Kindly bear with me guys ;-). Thanks in advance.

Pau
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Joined: Wed Jan 20, 2010 8:57 am
Location: Valencia, Spain

Post by Pau »

1- At the microscope the through-the-eyepieces visual image magnification is computed by comparison of the same object viewed with the naked eye placed at 250mm. It is the result of the product of objective magnification x eyepiece magnification (and x whatever intermediate magnification device inside the microscope if present).

At the camera sensor things are a bit different. If you directly project the primary objective image(*) onto the sensor you get just the objective magnification.
Most microscopes do use lenses to project the objective image onto the sensor, mainly to match the image size to the sensor size, for example, a 0.63X lens is meant for C mount small sensor cameras.

Of course no one see the image at the same sensor size, you further magnify it when printing or looking it at the camera or computer screen

2- All those lenses are used focused to infinite with infinite corrected microscope objectives, we call them tube lenses or converging lenses and their function is to focus the objective image "at infinite" at the camera sensor. You can do better forgetting about their stated magnification and just consider their focal length.

Therefore, if you use a Nikon infinite 10X objective with a 200mm tube lens you will get 10X on sensor, if you use it with a 150mm lens you will get 7.5X and so.
Of course this has its limits: if you use too high magnification you will get a less sharp image because of diffraction and if you use a too short tube lens you will get vignette and/or corner degradation due to the limited objective good quality image circle. This depends of the objective NA and magnification in the first case and of the objective design and/or the tube lens construction in the second case.

Infinite corrected objectives have the infinite symbol marked and do need converging lenses.
Finite corrected objectives have the tube length in mm marked (160 in most cases, but it can also be 210, 170 and others). They are to be used without tube lens, so if full corrected like the Nikon CF series, they can be used for direct projection with bellows or tubes.


(*) objective alone at its right distance with finite corrected objectives or objective + tube lens of the adequate focal length with infinite objectives, for example with a 200mm tube lens focused to infinite with Nikon or Mitutoyo objectives, or 180mm with Olympus

Edit: corrected 25mm for 250mm
Last edited by Pau on Tue Mar 05, 2019 8:49 am, edited 1 time in total.
Pau

VinodkumarSelvaraj
Posts: 18
Joined: Tue Feb 19, 2019 10:18 pm

Post by VinodkumarSelvaraj »

Pau wrote:1- At the microscope the through-the-eyepieces visual image magnification is computed by comparison of the same object viewed with the naked eye placed at 250mm. It is the result of the product of objective magnification x eyepiece magnification (and x whatever intermediate magnification device inside the microscope if present).

At the camera sensor things are a bit different. If you directly project the primary objective image(*) onto the sensor you get just the objective magnification.
Most microscopes do use lenses to project the objective image onto the sensor, mainly to match the image size to the sensor size, for example, a 0.63X lens is meant for C mount small sensor cameras.

Of course no one see the image at the same sensor size, you further magnify it when printing or looking it at the camera or computer screen

2- All those lenses are used focused to infinite with infinite corrected microscope objectives, we call them tube lenses or converging lenses and their function is to focus the objective image "at infinite" at the camera sensor. You can do better forgetting about their stated magnification and just consider their focal length.

Therefore, if you use a Nikon infinite 10X objective with a 200mm tube lens you will get 10X on sensor, if you use it with a 150mm lens you will get 7.5X and so.
Of course this has its limits: if you use too high magnification you will get a less sharp image because of diffraction and if you use a too short tube lens you will get vignette and/or corner degradation due to the limited objective good quality image circle. This depends of the objective NA and magnification in the first case and of the objective design and/or the tube lens construction in the second case.

Infinite corrected objectives have the infinite symbol marked and do need converging lenses.
Finite corrected objectives have the tube length in mm marked (160 in most cases, but it can also be 210, 170 and others). They are to be used without tube lens, so if full corrected like the Nikon CF series, they can be used for direct projection with bellows or tubes.


(*) objective alone at its right distance with finite corrected objectives or objective + tube lens of the adequate focal length with infinite objectives, for example with a 200mm tube lens focused to infinite with Nikon or Mitutoyo objectives, or 180mm with Olympus
Thanks a lot Pau. Now I understood :)

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