Can You Capture Colors on Consecutive Nights with a Telescope?

[russ_watters]

Jezz, sorry, been so long since I ues my scope I haven't looked in this thread! There is software out there that aligns and stacks images. I use Registax. It doesn't deal well with field rotation, so it is best to do all your data from each channel in one night.

I've done colors on consecutive nights, and combining them into an RGB image works best if the camera remains attached to the scope during the few nights of imaging so there aren't any rotation issues.

For luminance, I just went two months between capturing the color data and replacing some poor luminance data with better luminance data using a hydrogen alpha filter. So nothing about the camera setup was the same - not even the magnification. But it was relatively easy to rotate and stretch the luminance image in Photoshop.

Here's the full saga:
On 6/20 I shot:
14 exposures at 30 seconds for red (7 minutes)
27 exposures at 45 seconds for blue (20 minutes)
26 exposures at 45 seconds for green (20 minutes)

The red channel is more sensitive than the other two, so I use less exposure, though the number of exposures really should be equal. Also, tracking wasn't very good that night, so I had to discard a lot of frames. Still, the overall exposure time was a little on the low side. My first attached image is the resulting RGB.

I then shot:
34 exposures at 2 min for luminance (1:08 total) the same night.

Due to my bad tracking, the stars came out egg-shaped. So the second attached image is the combined lrgb. Not terrible, but the egg-shaped stars are a dealbraker to me. Plus the exposure time seemed a little low - the detail wasn't great.

Then I had two solid months of clouds, during whcih the telescope was set up in my living room. Last night was the first good night of sky(and perfect tracking) in months, and I shot:

26 exposures at 4 min each with a hydrogen alpha filter (1:44 total).

The third image is the result of combining that luminance image with the earlier color data. It's just under 2.5 hours of data altogether. I really could have used longer subs for the color, but it is good enough I'm not going to redo it for a long time. This was the first target I ever imaged (last year) and I've spent way too much time on it trying to get a good one as I climbed the learning curve. My first attempt is here, earlier in the thread (11 months ago): https://www.physicsforums.com/showpost.php?p=1097341&postcount=148

 

[chemisttree]

...For luminance, I just went two months between capturing the color data and replacing some poor luminance data with better luminance data using a hydrogen alpha filter. So nothing about the camera setup was the same - not even the magnification. But it was relatively easy to rotate and stretch the luminance image in Photoshop...

...I shot:
26 exposures at 4 min each with a hydrogen alpha filter (1:44 total)...

Russ,

Have you ever tried to shoot the luminance shots using an IR bandpass filter instead of the H alpha? I've heard that the IR image is less subject to seeing problems.

 

[russ_watters]

All of my images are shot with a uv/ir filter, including the Ha. I do that to make them parafocal, since the Meade color filters pass uv and ir. So I have stacked filters (one on the nosepiece of the camera, and one in a rack).

 

[chemisttree]

So you don't have an IR bandpass filter? It might help with the luminance shot.

http://www.astrovid.com/technical_documents/Microsoft Word - Baader IR.pdf

http://astro.neutral.org/imagehtml/20060505_m51_near_IR.html

 

[russ_watters]

Oh, you mean one that just let's through IR, not one that blocks it - right. Misread.

It is my understanding that you want to block the IR for images of nebulas because stars shine so bright in IR that they'll drown out the nebula. The stars get bloated. That seems to fit with my experience.

For galaxies, you need all the light you can get, and imaging in IR only doesn't give much signal. The second link you provided shows that.

Actually, about the only time you even want to include the IR at all is if you are imaging only stars or planets (though even for planets, the resolution is lower in IR because of the wavelength).