Experimenting calcium imaging with small refractors

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marktownley
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Re: Experimenting calcium imaging with small refractors

Post by marktownley » Tue Oct 30, 2018 9:06 am

george9 wrote:
Mon Oct 29, 2018 2:06 pm
I am curious to hear how the AP130 EDT works out because it has implications for my AP155 EDF. Bob, you have the f/8 I take it and not the f/8.3. The f/8.3 is the same lens as the AP155 but stopped down to 130. But even the f/8 is somewhat similar.

George
Hi George,

Frederic has done optical reports on both the 130 and the 155 on his website https://airylab.com/astronomy-test-reports/ Looking at the 130 it shows pretty much perfect spherochromatism in the blue when masked down to about 50% aperture, above about 70 things start to get worse. At full 130mm aperture I think CaK would be quite hazy.
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Bob Yoesle
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Re: Experimenting calcium imaging with small refractors

Post by Bob Yoesle » Tue Oct 30, 2018 10:57 pm

Hi George,

Not sure my results will be that informative - although I am looking forward to getting things up and running with a new CaK module. My circa 1996 130 EDT f/8 uses an oil-spaced glass combination of ZKN-7 crown sandwiching an FPL-53 center element. The later f/8.35 EDF scopes used FPL-53 and a different crown glass(es - BK-7 & ?). Later lens designs may also have gone to air-spaced. Not sure which would be better for UV @ 393 nm. A little more information here:

https://www.cloudynights.com/topic/6014 ... try8276184

Also see:

https://www.telescope-optics.net/semiap ... amples.htm
Last edited by Bob Yoesle on Wed Oct 31, 2018 2:51 am, edited 1 time in total.
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Re: Experimenting calcium imaging with small refractors

Post by krakatoa1883 » Wed Oct 31, 2018 9:59 am

The color of the coating corresponds to the color or combination of colors that is most reflected out. The CIE chromaticity diagram may help in understanding what colors pass least through a given lens. If one knows the index of refraction of the coating the %T (or the % reflectance) can be easily calculated for normal incidence as it can be assumed for sun rays. Unfortunately only rarely the characteristics of the coatings are explicitly declared by manufacturers but some assumptions can be made by using of available data, for example for a MgF2 coating, which seems not bad in the violet (Edmund Optics data, but the same can be calculated by using of the above linked page):
mgf2.jpg
mgf2.jpg (33.2 KiB) Viewed 366 times
Anyway based on the images one can see on the Internet it seems that actually most telescopes can be successfully used for calcium imaging so lens or plate or mirror coatings don't seem so critical to me. Spherical correction at short WL is much more important, I think, as this leads to huge differences between different refractors and the need to stop down the least corrected ones.
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Re: Experimenting calcium imaging with small refractors

Post by george9 » Wed Oct 31, 2018 4:16 pm

Thanks, all. I know that stopped down to 67% (4 inches), the AP155 looks very nice in my coarse R2 video camera. Thinking of getting a better camera in the spring.

George

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