Powers of 10 (Cambridge Silicon Radio BC4-EXT)

[Andy Resnick]

Thanks for the info. I have sometimes considered building a custom epi-illuminator for just this purpose, but it seemed like a lot of trouble for uncertain result. This is definitely a good result!

Is your illuminator commercial or custom? If the latter, can you share the design?

--Rik

Commercial. (Zeiss Ultraphot III/b).

[Andy Resnick]

Huh, I would not have expected that hillshade effect from epi brightfield. I wonder if somethjng is a but off-center.

Yeah, most likely the aperture stop is slightly off-center, or the lamp housing is slightly tilted wrt to the optical axis. It's not something I could easily correct (nor do I necessarily want to, given the imaging effect).

[Andy Resnick]

Regarding dust removal, astrophotography software always has algorithms to remove any irregularities. Astrophotographers take what are called "Flat frames" (ten or twenty) with a white diffuser over the lens. The programs use these frames (averaged together) to adjust all the real frames (the "light frames"). These are very well developed standard procedures in astrophotography. The same process also automatically corrects soft vignetting.

Well, this is a whole other topic. I also do astrophotography using a 400/2.8 lens (w/ or w/o a 2x tele), but I stopped using flat field correction several years ago. Lots of reasons why... bottom line, flat field correction caused me more problems than it solved. Sensor dust (for me) is not an issue here b/c the slight amount of (long term) drift is sufficient to average out the dust during alignment and stacking.

[Lou Jost]

...flat field correction caused me more problems than it solved. Sensor dust (for me) is not an issue here b/c the slight amount of (long term) drift is sufficient to average out the dust during alignment and stacking.

But for the common problem in microphotography mentioned by the poster, it is the perfect solution.