Saturn from Brisbane 29/01/2008 1:19am

[edwardsdj (Doug)]

Hi All,

Just sharing my image of Saturn from last night.

This is my fourth imaging run on Saturn and I think I'm getting better

I used the full 640x480 resolution of the SPC900NC this time. Feel like such an idiot for not doing this previously. I've got twice the image scale during capture now Thanks to Mike for his advice on this.

Seeing was still pretty poor but the Cassini division is much better resolved in this image. The crepe ring is visible and the detail of the rings in front of the planet is far clearer than I've been able to get it previously. The banding on the planet is more detailed also.

There is a fuzzy halo to the top of the image. It looks blue in the raw frames. Does anyone know what this might be or how I can fix it?

Celestron C8 with 2x Ultima barlow for 4000mm focal length;
Philips SPC900NC webcam at 5fps, 1/25s exposure;
Stacked 900 of 2000 frame in Registax with 1.5x resampling;
Wavelet and final processing in Registax.

Thanks for looking.

Have fun,
Doug

[iceman (Mike)]

Excellent result, well done.

The blue channel is always the worst when the seeing is bad, so it could be those effects showing in the blue channel. it's also making the background very splotchy.

You could adjust the levels to reduce the background back to black. You could also adjust the colour balance to try and make it less "yellow".

overall, a fine effort!

[edwardsdj (Doug)]

Hi Mike,

Thanks heaps for the help. I actually attempted a colour balance on that image which made it yellow. I thought I could see more detail though.

Here is a version processed in my usual way. You can clearly see the blue halo at the top of the image.

I think I need to wait for better seeing to get a much better result than this.

Have fun,
Doug

[Scooter]

Hi Doug,

Looks good to me

Couple of quick ones:-

When you are imaging with the webcam (so at short exposures) is this final image pretty much what you are observing visually or is more detail comming out due to processing (stacking images etc.)?

What mag did you capture at?

I had a few goes at Saturn last night (newbie visually) although it was earlier in the night so much lower (before 11pm) and I am trying to work out if that is how it would have looked visually for your rig and loc (where about's in Brissy are you at - i'm on the southside at Moorooka) etc. I was getting it sharp (rings and moons etc.)but no detail (maybe I need to stay up later ).

Cheers

[edwardsdj (Doug)]

Hi Scooter,

It takes experience with the planet to see the finest details visually. The Cassini division, crepe ring, shadow of the rings on the planet, shadow of the planet on the rings and some banding on the planet can all be seen visually.

While I can't see as much banding on the planet visually as is captured in the image this image is similar to the visual appearance.

I took a video of 2000 frames with my webcam and stacked the best 900. Stacking improves the signal to noise ratio of the image. I then used wavelet processing in Registax to bring out more detail.

What apeture are you using (I used an 8" SCT)? Do you collimate regularly? Good collimation is critical for observing planetary details.

The more you watch the planet, the more you will see

Have fun,
Doug

[Scooter]

You never said what the magnification was that you used for this image Doug.

I am using a 12" GSO Dob and have been checking collimation (secondary visually and last night primary with barlowed laser) but given I am a newbie who knows if I am doing it right Seems to be OK and I have been pretty anal about it as I understand the importance.

Re "the more you watch the more you will see" if you check out my questions in the beginners forum you will probably realise I haven't gotten setup for optimal viewing (not really dark adapting and viewing relatively low etc.). I realise that as well but it is early days

[edwardsdj (Doug)]

Hi Scooter,

Magnification is not very meaningful when imaging. People seem to refer to the focal length and type of imaging equipment. These two things determine the image scale which is the number of arc seconds per pixel in the image. Obviously, if you display an image on a monitor with pixels that are twice the size, the image will look twice as big.

I described the equipment I used at the start of this thread. The only magnification over the 8" SCT telescope was a 2x barlow lens.

Visually magnification makes a lot of sense. If something looks 100x bigger through the eyepiece than it would naked eye then the magnification is 100x.

What magnification are you using on Saturn?

I'd usually use eyepieces giving 133x and 200x in order to see much detail on Saturn. You can only push the magnification to 200x when the seeing is good.

Dark adaption is not that important for bright planets. It is critical to view them when high in the sky though. Don't expect to see much if the planet is lower than 30 degrees in altitude.

The main thing is patience. When I first got really into Saturn I got the telescope out every second night for a few months straight just watching the planet for a few hours every time. I'm not suggesting you need to go this far but the more you look the more you will see.

You also have to be patient for the moments of good seeing. On an average night you might get a clear view for a couple of minutes every hour. On a night of exceptional seeing (maybe about once a month) you get a clear view most of the time and can increase the magnification.

Glad to see you understand the importance of collimation. It is important to collimate pretty well in order to see planetary details.

I took this image from Jindalee in Brisbane. I have lived on the South side of town a few times in the past and have had no trouble observing bright planets. In fact one of the nights of most exceptional seeing I can recall was in a backyard in a house in Tarragindi.

Hope this helps and good luck observing.

Have fun,
Doug

[Scooter]

Ahhhhhhh.... OK, my bad

I was thinking that the camera equipment was attached to capture as per the human eye so including the magnified light where as you are saying it is just collecting the available light (off the mirror and throgh the barlow). Guess I need to read up on FL v's magnification.

Any chance I could have a single frame or for you to show a full image? Just interested to see how big Saturn is in the full megapixel image. I am guessing not much of the raw image is saturn yeah? So in effect the magnification is applied post capture via the cropping etc?

As for me, I have been using between 166 and 250x (mostly 9mm and sometimes 6mm) and they are nice and crisp (but lacking detail). Throw in the barlow then I have issues tracking (no doubt will get better in time) and the image isn't crisp.

Gotta say a few hours every second night for a few months sounds pretty hardcore

At the moment I have been mostly observing from the back deck thus the low angle (although it has certainly been easy) but I will (as you have said in the other post) start looking to plan targets and times etc. and part of that planning will be optimal positioning etc.

Fun stuff

[edwardsdj (Doug)]

Hi Scooter,

No problem, it's great that you're asking questions. I'm only just starting out at planetary imaging myself.

The field of view of my SPC900NC webcam with the 2x barlow is 2.4 by 3.2 arc minutes. The image scale is 0.29 arc seconds per pixel. Saturn is about 20 arc seconds in diameter at the moment.

I posted a raw frame in my first attempt at Saturn here: http://www.iceinspace.com.au/forum/s...ad.php?t=27531

I wasn't using the full resolution of the webcam there but the size of the planet in relation to the frame is the same.

You have to get the bulk (preferably all) of the magnification during imaging. The more image scale you can achieve during capture, the more detail you will see. I did apply a 1.5x enlargement during stacking to create the image in this thread.

You don't have to look for months. You do have to build experience with your equipment and technique though.

I have a driven equatorial mounting for my 8" SCT so I can sit in a chair for hours and watch the planet visually. I find tracking planets at high magnification with my 12" Dob really difficult too. Something I've got to get better at.

In the medium term, Saturn is getting increasingly difficult due to the rings closing up. The Cassini division is getting harder and harder to see. This is the first feature you notice visually. The rings will completely close up next year after which they will start to open up again.

In the longer term though, Saturn is getting better and better as it gets further South every year

I wouldn't bother too much with Saturn until around 11pm at the moment when it has sufficient altitude.

The magnifications provided by the eyepieces you are using seem ideal for planetary work to me. I wouldn't use the barlow much. One night you'll look, the planet will be crisp at 250x and you'll want more power. Pull the barlow out then.

At the end of the day, Jupiter provides a much more dynamic target than Saturn. It's also much bigger Gain some experience with Saturn in preparation for Jupiter which will be prominent in the middle of the year

Have fun,
Doug

[peter_4059 (Peter)]

Doug,

That's a nice Saturn. I'm looking forward to it getting a bit higher so I don't have to stay up too late!

[Scooter]

Hi Doug,

OK thats not what I was expecting at all. That frame has Saturn taking up a decent part of the frame (with no or little magnification) where as when I am looking at about 250x I get the roughly the following in my field of view (excuse the rough drawing - it shows the scale at least ). How does that work? Oh well thanks for some of the detail regarding sizes etc. I guess I am going to have to do some research on arc mins and seconds etc. and get a better understanding of the concepts

Anyway setup last night (you view Saturn at all? - if you did how was your seeing?) and dark adapted (then promptly fell asleep but my daughter woke me at about 12 so it worked out well) then spent about 45mins trying to observe Saturn. Was probably 12.15 to 1.00am so almost the highest it was gonna be. Mostly used 250x and 166x (tried the barlow to 500x briefly - it's not much bigger in the field of view (does that sound about right?) I reckon and wasn't crisp etc.). Easy to track at those mags and I was mostly putting it on the edge of the view to let it move through (as opposed to trying to keep it centered so I could concentrate on the actual image).

Now in 45mins of observering maybe, just maybe at times the image changed and there could be vague details but as the image takes up so little of the field of view (refer again to my drawing) I just found it too hard to be sure. Maybe it was just my eyes maybe there actually was a subtle change in color etc.......

Hmmmm bottom line ....not sure but I can tell you I can't wait to try Jupiter.

Cheers,

Scott

[edwardsdj (Doug)]

Hi Scooter,

You seem to be doing things better now. It's not like watching TV. It takes time and practice to see details on planets. I must confess that I haven't looked seriously at Saturn visually this apparition yet as on the few evenings when the clouds have shifted I've been taking images.

As I've been saying, quoting magnifications doesn't make a lot of sense with images. Image scale makes sense.

The view you show looks like the sort of thing you would see in a Plossl eyepiece at 250x to me. The CCD chip in my webcam is tiny so the planet takes up a lot of it. It's also a lot harder to get the planet onto the CCD than to get it into an eyepiece.

Lengths in the sky are measured in angles. From the horizon to the zenith is 90 degrees. An arc minute is 1/60 of a degree. An arc second is 1/60 of an arc minute or 1/3600 of a degree.

The Sun and Moon have a diameter of about half a degree or 30 arc minutes. Saturn at opposition has a diameter of about 25 arc seconds. Jupiter gets to around 50 arc seconds.

Midnight to 1am is an optimal time to view Saturn at the moment. Sounds like you're getting the hang of tracking with the Dob now too. I'd try to see as much as I can at 166x first. 250x will only be possible with good seeing.

I'll just point out some things to look for (in rough order of difficulty):

How many of Saturn's moons can you see?

Can you make out the Cassini division?

Can you see the shadow of the rings on the planet?

Can you see the shadow of the planet on the rings?

Can you see the crepe ring?

Can you see a band on the planet?

Hope this helps, and keep observing. Saturn is a very rewarding target!

Have fun,
Doug

[Scooter]

You know I should appoligise for hijacking your image thread so thanks for taking the time to respond

How many of Saturn's moons can you see?

Mate didn't you open my attached image and see my little moons (drawn roughly where I think they were) - Now thats attention to detail (but yeah from memory I think 4 moons were clearly visible as almost single ponits of light)

Thanks on the other detail. Could be I saw some of it (pretty sure occasionly I saw the bland line seperating the ring and sometime a slight sumdginess to the main planet) but as I said it's hard due to the size in the FOV. Practice makes perfect I guess

[edwardsdj (Doug)]

Hi Scooter,

Not a problem. I'm always happy to answer any questions I can.

I only looked at the thumbnail image when I wrote my reply, then opened it up and saw you'd drawn some moons

It's been almost a year since I spent much time with Saturn visually. I can't recall the exact number of moons. I'm usually able to see Titan (which is bright and further out) as well as three to five others. On rare occasions I've been able to pick out some more.

Using computer software to simulate the positions of the moons before a session allows you to identify them and gives you an idea of where to look for really faint ones or ones far away from the planet.

Practice will improve what you can make out. Patience to wait for good seeing will help as well. When you see the planet under good seeing conditions it trains your eye as to what to look for when the seeing isn't so good.

Have fun,
Doug

[[1ponders] (Paul)]

Nice image Doug. Glad someones making the most of the odd clearish night

Did you try to realign the blue channel in registax? Or maybe try fewer images in your final stack. Be more discriminating in your selection by manually selecting only the very best images. You might find you end up with a "cleaner" image by only using 75 - 100 manually selected images rather than letting registax select the best ones. The down size of using less images though it that you can't push the wavelets as much.

You might also want to consider using RGB splitter and PCFE as part of you processing routine and do the final colour combination in Photoshop or Astra Image (not free unfortunately). Check out Mikes planetary processing tutorial in the articles section.

[edwardsdj (Doug)]

Hi Paul,

I did try the RGB alignment in Registax. I do this every time but just use the "Estimate" button.

Thanks heaps for the advice. I've been thinking about manually selecting the frames myself. This has to be an improvement as I've noticed that using the Registax quality algorithm some poor frames end up selected and some good frames end up judged as poor quality.

Thanks also for pointing me at Mike's tutorial. I had read this in the past but now is a good time to read it again. Pre-centering the images, splitting into separate RGB channels and re-assembling/aligning them after stacking makes a lot of sense.

I don't have Photoshop, but I'm getting better at Gimp.

I'll have a go today/tomorrow and see if I can post an improved version.

I'm really hoping to capture better raw data under better condtions soon.

Thanks again,
Doug

[[1ponders] (Paul)]

I'm really hoping to capture better raw data under better condtions soon.

Nothing beats having great data to start with, that is for sure. One of the things I like about using PCFE is the way it sorts the quality of images for you. It does a pretty good job and it is much easier then to just select the first couple of hundred images and drag and drop them into registax, do an alignment and then select the best of the best for optimization. Speaking of which do you do a fully automatic optimization and stack or do you to an initial preoptimization with a reference frame and then select only the best images for stacking?

Good luck with it.

[edwardsdj (Doug)]

Hi Paul,

Thanks again for the advice

I have just been hitting the "optimize and stack" button up until now. Thanks for the advice on this. The ability to select the frames with the least difference from the reference after optimisation is awesome!

I've been using the command line version of ninox/ppmcentre. I love command line tools. I wish you could do the whole process from the command line. That way I could automate things to see preliminary results during the imaging session

Anyway, I've had a go at splitting into RGB and stacking seperately then recombining the channels using GIMP. It will take me time to get better at this but I can see already that this is the way to better results

My blue channel is really bad Need better data.

Thanks again for your advice. It has been invaluable.

Have fun,
Doug

[[1ponders] (Paul)]

yeah getting that colour balance right again is a bit of a challenge at times.