First (poor) image of Saturn; advice needed

edwardsdj (Doug) · #1 13-01-2008, 01:19 PM

Hi all,

Matt's awesome images of Mars from Brisbane inspired me to get a SPC900NC for Christmas. My Mogg adapter arrived on Friday and this is my genuine first attempt at Saturn from last night.

Conditions were poor. Mars was absolutely swimming but Saturn was bigger so I captured about 1000 frames of AVI just before the thick cloud set in at about 1am.

The first attachment is one of the best raw frames. The second is a stack of the best 250 frames in K3CCDTools.

I can see the Cassini division (just) in some of the frames as well as a cloud band on the planet. I'm very excited to have captured anything at all

I spent about an hour and a half playing with the focus and this is as good as I was able to get it. My Celestron "Wedgepod" mounting is highly unstable and every nudge of the focus knob makes the whole image wobble for about 10 seconds

So I need to know what to do next. Maybe:

1. Wait for better seeing before deciding;
2. Build a Hartmann mask;
2. Order a "Bintel Crayford Focuser SCT 10:1 (2")" for $149 (does anyone have experience with these or know if they are good);
3. Install an IR cutoff filter.

I need to get an idea of what is going to be most effective. Any advice on cam settings/processing would also be much appreciated.

Obviously a better mount would help heaps but that is beyond the budget at the moment and I was surprised at how easy it was to track objects using my existing setup. It's only a problem when I need to touch the tube to focus.

Thanks for your help.

Have fun,
Doug

matt · #2 13-01-2008, 02:49 PM

Hi Doug. That's not nearly as poor a first image as you think. I speak from personal experience!

Is there any chance that you could let us know what settings you used to capture these AVIs?

That will give us a good starting point for any tips or pointers.

As far as capture is concerned, one of the big things is to make sure your histogram is properly exposed and that you're capturing the full dynamic range of the object.

K3CCDTools has a meter you can activate which serves OK as a guide. Try to get the reading over 200. Somewhere around 215-200 is even better, but you'll have to experiment with your exposure and other settings to get it to that point.

Can you also tell us what you're doing in your processing? Have you downloaded Registax?

Hope that's OK for a beginning bit of advice. That stuff about the histogram is important and was good advice I received when I was getting more serious about imaging. (Thanks those folks who offered that advice, BTW

)

Keep asking questions.

peter_4059 (Peter) · #3 13-01-2008, 02:56 PM

Doug,

If you can fit a motor focuser this makes focusing a lot easier as you don't have to worry about the tube wobble.

edwardsdj (Doug) · #4 13-01-2008, 03:16 PM

Thanks heaps Matt and Peter.

It's so unfortunate the SPC900NC settings are just on sliders without numeric values but the settings I used were:

Frame rate: 30 FPS
Shutter: 0% (longest)
Gain: 50%
Whitebalance: Manual until it looked OK
Brightness: 100%
All other settings on 50% (middle of the slider)

I saw the meter in K3CCDTools. It is on by default. I'll keep in mind the values you suggested.

What sort of shutter, gain, brightness settings are good?

I know the images are a bit feint but I found I could see more detail with the gain at about 50%.

I have used Registax for some full-disk images of the Moon with my D80 DSLR. It works well but I just did a quick stack in K3CCDTools to see what the results would be like. I didn't think the data was good enough quality for Registax but I will give it a go this afternoon. I have done no further processing but I'll have a go with the Registax wavelets this afternoon.

If I could motorise the focus a lot of my problems would go away. I just don't think the focus control is fine enough (even visually on planets) with the standard SCT focus mechanism though. The mirror shift is a significant problem with the small SPC900NC CCD as well.

I'm thinking that if I get a microfocuser first then tacking on a motor will seem much more practical. I'm keen to attempt to build something myself to motorise the focus.

What I'd love to know is:

1. Does an IR blocking filter make a big difference with focus for planets; and
2. Do you guys use Hartmann masks, software or another method to achieve focus?

Thanks heaps for the advice.

Have fun,
Doug

edwardsdj (Doug) · #5 13-01-2008, 03:20 PM

...and I should have mentioned that I'm using a 8" Celestron SCT with Celstron Ultima barlow for 4000mm focal length.

matt · #6 13-01-2008, 03:24 PM

Doug.

From memory...I tend to capture at 10fps (less compression), leave the shutter at 1/25 or 1/33 sec and adjust the gain to correctly expose the histogram.

I don't think you want to be fiddling with the white balance?

Set the colour balance to auto.

Try to have the brightness slider in the middle as well. Leave that alone.

Just adjust the exp and gain to correctly expose the image based on the histogram.

To your other questions: an IR blocking filter is good, especially for Mars...and I think helps a little with focus since it sharpens the image a little on the screen.

I only focus by eye. No hartmann mask or any other aid. Although I do use a MoonLite electric focuser.

Hope that helps.

Quote:

Originally Posted by edwardsdj

Thanks heaps Matt and Peter.

It's so unfortunate the SPC900NC settings are just on sliders without numeric values but the settings I used were:

Frame rate: 30 FPS
Shutter: 0% (longest)
Gain: 50%
Whitebalance: Manual until it looked OK
Brightness: 100%
All other settings on 50% (middle of the slider)

I saw the meter in K3CCDTools. It is on by default. I'll keep in mind the values you suggested.

What sort of shutter, gain, brightness settings are good?

I know the images are a bit feint but I found I could see more detail with the gain at about 50%.

I have used Registax for some full-disk images of the Moon with my D80 DSLR. It works well but I just did a quick stack in K3CCDTools to see what the results would be like. I didn't think the data was good enough quality for Registax but I will give it a go this afternoon. I have done no further processing but I'll have a go with the Registax wavelets this afternoon.

If I could motorise the focus a lot of my problems would go away. I just don't think the focus control is fine enough (even visually on planets) with the standard SCT focus mechanism though. The mirror shift is a significant problem with the small SPC900NC CCD as well.

I'm thinking that if I get a microfocuser first then tacking on a motor will seem much more practical. I'm keen to attempt to build something myself to motorise the focus.

What I'd love to know is:

1. Does an IR blocking filter make a big difference with focus for planets; and
2. Do you guys use Hartmann masks, software or another method to achieve focus?

Thanks heaps for the advice.

Have fun,
Doug

edwardsdj (Doug) · #7 13-01-2008, 03:46 PM

Thanks again Matt. That's exactly what I needed to know.

I think I'm going to bite the bullet and order the microfocuser. If I could get a smooth focus adjustment at 10x the resolution I'm seeing now without the image shift that would be a great help.

My focus knob is quite stiff and I need to shake the tube a lot to adjust it just a little (I did buy the scope in 1999). From what I saw last night, I'm sure I could find a good focus just watching the image on the screen if I had better focus control.

I won't bother with a Hartmann mask or IR filter for now.

Thanks again, particularly for the capture settings.

jjjnettie (Jeanette) · #8 13-01-2008, 06:45 PM

For a first Saturn, it's really very good.
I hope you don't mind, I've played around a bit with the .bmp that you posted. I put it through Registax, resized it and did some work with the wavelets, RGB allign, then put it through Paint Shop and worked on the histogram, shadows and highlights. I've probably processed it a bit too much.
There's lots of detail on the planet's surface.
Again, it was a good capture for a first one.

bird (Anthony Wesley) · #9 13-01-2008, 07:01 PM

Seeing is very important too, if Saturn's wobbling all over the place then it's likely that your mirror is still radiating heat and cooling down, or the air over your head isn't stable. In that case there's not al lot you can do to improve except wait...

cheers, Bird

edwardsdj (Doug) · #10 13-01-2008, 07:03 PM

Thanks heaps Jeanette

I thought the data was too rough to gain much from processing but you have shown me otherwise.

Thanks again for your time in processing this!

edwardsdj (Doug) · #11 13-01-2008, 07:12 PM

Hi Bird,

Seeing was very poor

But that is the story from Brisbane lately. The image was wobbling around all over the CCD.

The ambient temperature was around 25 degrees C in Brisbane last night and I'd had the telescope out for about three hours in total by the time I captured the AVI. It never felt cold to the touch though like it does whenever I get an amazing view. Might have to wait for those cold winter months with little dew.

Hoping for better seeing tonight

Have fun,
Doug