Saturn

[Fay]

Did my first planet for a couple of years, last night. Skywatcher Mak. Cass. 6", DMK 04M camera.

I am quite happy for a first attempt, but a palaver getting on chip & focusing etc. Clouds were coming & going & every time I put the barlow on, I had to take it off put eyepiece in, centre it, put camera in without barlow, centre it, put barlow in search for it!!!!!

[RobertM]

Fay, that looks fantastic, and the focus looks spot on.

Sounds like you need a flip mirror, wasn't Chris is selling one the other day ?

[Fay]

What's a flip mirror?

[mickw]

About £50 

http://forum.orpington-astronomy.org.uk/index.php?topic=3258.0

[MarkS]

Well done Fay.  I did get the telescope out last night but the conditions weren't as good as Tuesday so I gave up.

But you got a decent image!

What "shutter" speed were you using?  How many frames did you stack?

One tip: when you put the Barlow in, use the eyepiece to centre Saturn then swap the eyepiece for the camera as the final step.

[Fay]

Mark, I must confess, I was concentrating on technique & forgot to notice how many frames were used etc. All I know is they were captured at 30 fps.

Will take notice next time.

[JohnP]

Very nice Fay - came out very well. Looks like it needs some more frames to reduce noise & you have to do colour next time Good to see you are making use of the 6-inch at last....

John

[Fay]

Yes, I was quite pleased as it was the first, but know more of what to do next time.

[Carole]

Please could some-one explain "noise", (what it is and what it does to your images).  I thought it created hot spots and interference etc on the background sky, but I can't see any problems with Fay's, so I obviously don't know what to look for.

Thanks
Carole

[Ian]

noise in a general term for anything that shouldn't be there. In Fay's image, the disc of Saturn is a little grainy, and we know from hi-res observations that that grain is not actually there on the disc. Therefore it's reasonable to call it noise.

Noise can also be used to describe other artifacts, including diffraction spikes and so on.

If you can tell what's noise and what's not, an absolute measure of the quality of the data (image) is the ratio, SNR or Signal to Noise Ratio. The higher the better as that indicates lots of signal to not much noise.

Granted SNR is not often talked about regarding astro imaging, but you may have come across it in other applications, including how good a tv signal you're getting. Alot of digital TV tuners show the quality of the signal as the SNR.

[JohnP]

Hi Carole - there are loads of webpages on the net that help with this... here is one:

http://photo.net/learn/dark_noise/

Basically - noise makes an image look grainy - the background on Fay's image is fine but if you look at the globe it has a 'mottled' appearance - Don't get me wrong Fay's image is great but if she took & stacked more exposures the signal would increase & noise diminish so globe would have a much smoother appearance..

As an example have a look at this old image I took from 2003 (not a very good one)... you can see just a single image of Saturn & a stack of 250 - notice how smoother the stacked image is - The final image is still noisey but a lot better than just a single image..

http://homepage.ntlworld.com/john.punnett/graphics/archive%20images/saturn/saturn_2.html

HTH, John

[Fay]

Perhaps I went heavy on the wavelets.

[JohnP]

Fay - Could you explain wavelets for me please 

[Fay]

Don't be cheeky.

Saturn was 720 frames. Quality 85%.

I have just merged two AVI's total of 1263 frames 90% quality, but looks similar to me.

Should it be a lot more?

[Fay]

Does Registax tell you how many frames it has taken? I could not see it, only the total of what it was starting with.