30 replies to this topic

[Borodog]

I haven't used my old Celestron Minus-V filter onb our refractor yet. The color hasn't been all of that objectionable. However, in the next month or so we are hoping to use a QHY camera to image Mars and Jupiter through the Clark. Will the image be better than a larger SC or modern APO refractor...no probably not. But it would be historic!

Serious response. If you are going to have a go at imaging with it, the best thing you can do is simply throw out the poorly corrected blue channel, or don't capture it at all if you are planning on using a mono camera and filters. If you are going to use an OSC (color) camera, use a minus violet type filter (even a simple #8 pale yellow is adequate) to prevent the de-focused blue light from affecting the green and red channels via color bleed. Throw out the blue channel, and reconstruct it from red and green:

 

B_synthetic = 2G - R

 

This is an astonishingly good approximation. See some examples here.

 

This can be done live in SharpCap (color cameras only), by the way, which also supports live stacking and sharpening of planetary images. PM me if you are interested in discussing how to use either feature.

Edited by Borodog, 30 January 2025 - 05:15 PM.

[phxbird]

One of the big issues that has hindered high power viewing as well as imaging, is the poor tracking. After much trial and error I figured out that it needed a small weight added near the objective on the west side of the tube. An add on 2" focuser was placed in 2000 and made this slightly tail heavy. I went to Harbor Freight and picked up 2 chrome covered magnets (it's an iron tube). Adding one to the west objective holder seems to have solved the problem. We have 3 weight holders but sometimes the scope tracked well and sometimes it didn't. Hopefully this will suffice to give us better tracking until we can rebalance the whole tube.

[RichA]

I wonder what the focal point difference is on the scope between the blue and red ends of the spectrum?  I think I read the 36 inch Lick difference was about 80mm!!

[deSitter]

Serious response. If you are going to have a go at imaging with it, the best thing you can do is simply throw out the poorly corrected blue channel, or don't capture it at all if you are planning on using a mono camera and filters. If you are going to use an OSC (color) camera, use a minus violet type filter (even a simple #8 pale yellow is adequate) to prevent the de-focused blue light from affecting the green and red channels via color bleed. Throw out the blue channel, and reconstruct it from red and green:

 

B_synthetic = 2G - R

 

This is an astonishingly good approximation. See some examples here.

 

This can be done live in SharpCap (color cameras only), by the way, which also supports live stacking and sharpening of planetary images. PM me if you are interested in discussing how to use either feature.

I love to read something and think "This dude knows his shizzle". I was reminded of the early Technicolor film process, where 2 colors were made to simulate 3. Martin Scorcese paid homage to this groundbreaking technique in his film "The Aviator".

 

-drl

[deSitter]

I wonder what the focal point difference is on the scope between the blue and red ends of the spectrum?  I think I read the 36 inch Lick difference was about 80mm!!

Wow

 

Imagine using it with a humongous Plossl made from two 6" f/8 achromats!

 

-drl

[Tyson M]

I've owned a 9" superb istar achro with a matching chromacorr. Best views of Jupiter I've ever had. The 25" f5 obsession was a close second

Edited by Tyson M, 13 February 2025 - 06:39 AM.