Question about specific objective lens


I build my openflexure microscope (v6) using raspberry pi camera & lens.
I wanted to upgrade for a large objective lens (high resolution) and hastily bought this one:

It seems that this one has a parfocal length of 45mm. I tried to use it - without success.
In the stl configurator I found options 40 or 50 mm. Is that mean that my objective is not feasible for that build? Is there anything I could do to make it work? (I did not use immersion oil, maybe that is also a mistake?)

Would be grateful for some answers.


45mm is one of the standard parfocal lengths, and will work with the microscope V6 with the slide riser installed.

In the optics modules there is no need to have an difference for lenses with a different parfocal distance, so the STLs are the same. The f40 and f50 in the STL names (eg optics_picamera_2_rms_f50d13.stl) denote the tube lens that you will need to put into the optics module. f=50mm and 13mm (or 1/2") diameter are the ones we usually use.

The other important objective lens parameter is the tube length, which for the objective you link to is 160mm. So that is not infinity corrected and will need the normal optics_picamera_2_rms_f50d13.stl optics module.


Dear William,

Thank you so much for the answer.

So it seems that the reason my setup is not working is that I have F=50mm tube lens (thorlabs) and F=45mm objective lens (linked before).
So I should match that parameter either by buying different tube lens or objective, is that right?

Do you think I will need to use oil immersion for the mentioned objective to work?
I am trying the reflected light setup.

Also do you know what would be a magnification of a 100x objective in comparison to the raspberry pi V2 camera? I measured that the raspberry camera’s field of view was around 0,8-1mm. Do you know what it would be for 100x standard objective lens? (If that’s a dumb question - plese excuse me, I am a beginner in that topic:))

PS. I love what you do in Openflexure.

Have a great day,
Piotr Grygo

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Your objective has a pretty standard focal length of 160mm, not 45mm. The parfocal length is the distance between the shoulder of the objective and the object focal plane, not anything to do with the image plane. As WilliamW said, the optics module does not need to be modified in any way. The only issue with your 100x objective is how far away from the sample it needs to be. As long as the end of your objective can touch the cover slip on your slide, and you have the correct immersion oil, your setup is fine.

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You have the right objective and tube lens. As @tkircher says, the 100x objective needs to get very close to the sample. You will need to have your slide with the sample and cover slip on the underside so that there is only a thin coverslip between the sample and the lens. With your Raspberry Pi lens the working distance between the lens and the sample is a bit more than 1mm, so you will have been able to have a sample on top of a standard microscope slide.

The 100x lens is designed to work with immersion oil between the lens and the coverslip over the sample. You should be able to get an image without oil, but it will not get the full resolution and it will probably have various aberrations in colour or focus. If you need the highest resolution, you will need to use immersion oil, if you don’t need the very highest resolution then it is usually best to use a x40 or x60 lens which give the best resolution that you can get without oil.

For your other question, the the field of view of the basic optics with the Pi camera lens is similar to a x20 microscope objective in the high resolution optics module (Comparison of a pi-camera and a 20x optical lens - Contributions - OpenFlexure Forum). So the 100x lens will be about five times smaller field of view.

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Thank you again for replies William & tkircher!

I already bought the immersion oil.

So it seems that the standard glass slides that I own are too thick (which could be the main reason of me seeing almost nothing :slight_smile: ).
Do you know what is the optimal thickness of an underside coverslip for the 100x objective? Could you send some example link?

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The required thickness of the coverslip is specified on the objective. In your case, it’s 0.17mm. The thickness of the slide is not as important, because the objective is always on the coverslip side of the sample.