Hi there,
Looking for help/advice on what objective lens I should source. I am looking to image stained cells. Not sure on which objective lens units I should buy in (ie what magnification with what N.A should I get?).
Any advice, suggestions or explanation is gratefully appreciated - lacking in optics knowledge but working on it!.
Many thanks in advance
SR
Different cells have very different sizes, so different lenses would be appropriate. For small cells like red blood cells you will want a high magnification and high NA - probably an oil immersion 100x lens. For larger cells a 40x with NA around 0.5 or greater will give enough resolution and a bigger field of view. Big plant cells and larger single celled things like paramecium only need 10-20x or even the simple Pi camera lens with the lens spacer.
For any magnification, higher NA in principle gives better resolution, as long as the lens is designed well. Conversely increasing the magnification without increasing the NA does not help you to see smaller details.
My own preference for most things - and I don’t do cells often - is a 40x to start with. They are easier to use as the working distance is longer and they don’t need immersion oil. 40x is available in quite a choice with pretty high NA and low cost. If that really turns out not to be enough, then go higher.
The other lens parameters - infinity or 160mm tube length and the par-focal distance are not so important, but you need to know the tube length to print the right parts. You probably want to have the same if you have more than one lens. Par-focal distance is often not quoted in the lens specifications. 45mm is most common and the microscope is currently designed around that distance. 35mm is the other standard distance, which means moving the optics module further up the rail towards the sample.
Another point is the illumination. In order to be able to take advantage of a high NA objective lens you also need high NA illumination. The Openflexure microscope illumination is designed to do that with the condenser lens fitted. Then it also needs to be aligned with the point that you are imaging.
According to this paper
fluorescence is subject to fluorophore saturation and photo bleaching effects that do not affect other optical methods, the highest possible light collection efficiency is desirable.