Dear all,
First of all, thanks a lot for this great project. I was looking into it and start building it for a private school in Belgium. And that for two reasons: to enhance kids experience by helping them to obtain quality observations in relative quick time (auto-focus) and to discuss with them your great idea of sharing knowledge and time for a good cause showing than not all is about money.
Now, my problem: all went just fine with the print of latest high-resolution OpenFlexure Microscope v7. I was using the indicated Plan corrected 40x (195mm conjugate distance) objective lens and all went without problems.
Now, the biology teacher was asking me if we can change the magnification as she was looking to show some more details, so I first bought a 60x (195mm conjugate distance). I didn’t pay attention and the objective was not plan corrected, but anyhow I could not focus the same samples as before. Then I bought a 100x (oil drop) objective lens but I was facing the very similar issue: i got a blur image that can’t be enhanced no matter if I try to move up or down the objective.
As samples I was trying with Escherichia Coli Smear, Bacteria Smear or Yeast Smear.
I placed the sample face down, same as with 40x objective.
I’ll much appreciate some indications that will help me to solve the issue. Please let me know if you need any other info.
With kind regards,
Marius
This is odd. 60x should work if 40x works. Have you made a new optics module or just changed the lens on the old module?
A good test sample is a blank slide with drywipe marker scribbled on it, then a fingerprint to add finer detail. This is a flat sample with surface detail, so will show you whether the problem is the working distance or something else.
Hi William,
Thanks a lot for your quick and clear advice.
To answer to your question: I just changed the lens on the old module. I am thinking to build a second microscope, the upright model and use a lower magnification for a different kind of samples.
For most of the “issues” things are evident, but only to those that had the experience. Indeed, with a blank slide prepared as you instructed me I was able to focus all three lenses without any problem. I extend the test by adding a cover glass (about 0.13-0.17 mm thick) and I was again able to focus, but not on the slides with permanent preparations for microscope. With those ones, only the 40x is Ok. I measured and the cover glass is about 0.30-0.40 mm thick. Could it be that those about 0.20mm difference bring me outside of the measurement capacity for 60x and 100x ?
I am waiting your answer but in principle I can consider the topic closed.
With kind regards,
Marius
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That is very useful detailed testing information @marius4m, thank you.
The usual thickness for a cover glass is 0.17mm, and lenses are usually designed to give the best images (colour aberration and field flatness) with that thickness. It will be marked on the lens - the 0.17 in a marking like ‘160/0.17’. A 40x objective will then have maybe 0.5mm air space between the coverslip and the lens face. A 60x or 100x lens will have less than 0.2mm air (or oil for your 100x) space between the 0.17mm coverslip and the lens face. The thick coverslip on your prepared samples is the problem.