CaK – 23rd July

[LTHB]

Blue skies here yesterday, but Meteoblue predicted a seeing worse than 2 arcseconds, so I decided to do some testing and tinkering with my CaK setup. After setting up, however, seeing turned out to be much better, with some moments around 0.8“ and better. Unfortunately I had taken out my 90mm scope only. After 1.5x drizzle the best image of the AR was this:



Full size here: https://live.staticflickr.com/65535/483 ... 58da_o.jpg

One result of the testing that might be of interest for others doing CaK imaging: Like some people I used to put a Baader blue CCD filter as a kind of ERF in front of the CaK filter stack. My copy of the Baader blue filter only transmits roughly 35% of the K line. I replaced it now with a blue filter from Chroma which has much better transmission in the K line (more than 90%).

Regards,

Frank

[Montana]

That is super pin sharp clarity with your CaK, a very nice image

Alexandra

[MAURITS]

Really nice image Frank.

[marktownley]

Very good! Do you have a link to the Chroma filter please?

[xn44]

Super image!

[LTHB]

Thanks, folks!

Mark, I bought the Chroma filter here: https://optcorp.com/products/chroma-blue-filters
The transmission graph shows that the filter opens around 360nm and is definitely wide open at 390nm.

The same graph can be found in Chroma's flyer (p.4): https://www.chroma.com/sites/default/fi ... 2015.1.pdf
Unfortunately, when I looked in the shop on the Chroma website a minute ago there is a different graph: https://www.chroma.com/products/parts/blue

I hope the latter is some sort of error or misprint and they didn't change the specifications of their blue filter...

[marktownley]

Hmmm, 2 totally different transmission curves there, one to keep an eye on...

[MapleRidge]

Very sharp CaK image...nice work!!!

Brian

[Carbon60]

Nice CaK image, Frank. Interesting blue filter.

Stu.

[eroel]

Frank:
Nice and clean CaK shot.
Regards,
Eric.