We are working on reflective DHM and the system looks like the setup in figure 1. We are facing a severe problem of reflection in the system.
Apart from the reference beam and object beam, there is a unknown strong spot on the CCD. In figure 2, the black bar is the object, the bright concentric spot is the reflection of the objective lens (if a plano-convex replaces the objective, the bright spot still exists). When the distance between the objective and condenser changes, the radius of the spot changes as well. We guess it originates from this lens, but we have no idea how to remove it.
In addition, in figure 3, the condenser is placed above the BS and the reference beam is blocked. The bright concentric spot changes to interference pattern. Does anybody have any clue on this problem? Thanks.
Hello, Zhenbo.
It happens in general and fluorescent microscopy. Sorry! I am afraid you have to get an optical specialist from the company to disassemble and clean the system suspected. Usually the problem comes from careless opening the system, causing dusts or particles in or under humid condition during rainy season and condensing water vapor and drying with fungi during rainy season. It could get worse without careful ventilation and thermostatic condition and a complete covering the system when not in use.
Best wishes.
Hi, Prof. Sang Ho Lee,
Thanks for your advice. We'll check the humidity and ventilation. Apart from the contamination of optical components, do you think is it possible that the spot is due to the reflection of the objective's internal lens, or misalignment of components in the optical path? Thanks.
Hi, Zhenbo.
With lens paper or cloth briefly dipped in isopropyl alcol (99%), can you try to clean the eye pieces, objectives, condenser parts (without removing), and any filters or slip-in filter system (removable) where easily accessible in the path? If you still see the spot, it would be internal one. Check the centering by adjusting objectives revolver and diaphragm since you are asking about the alignment.
I am also wondering by noticing small cell-like structures, debris and rod-like structure. Do they come from your sample, then it's ok. Finally, check the light source box by opening whether it's clean in the reflective thing at the back of the bulb (All these can be done for general cleaning of microscope for maintenance until an expert comes).
I wish your best of luck.
Hi, Prof. Sang Ho Lee,
Thanks. We've tried to figure out the origin of the spot by cleaning and using new components. Finally, by changing the plano-convex lens to a doublet one and move it to the other side of BS, the annoying spot disappears. Unfortunately, however, when the doublet is placed as the figure above, that spot is still there. This is weird, but the solution of placing the doublet and the objective at different sides of BS is pretty good to us. Hope this can help anyone who has similar trouble.
Hi Zhenbo Ren,
I have a similar issue with my set up as yours. I wonder if you could share the modified setup sketch, that might help me a lot. Thanks in advance.
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