Mars 10th Dec

Well tonight was some night!
After all the bad weather we were treated to some fantastic moonless skies
with excellent seeing.
I managed to get in a couple of hours observing and imaging.
Mars was nice and high at 12 midnight so I gave it a go once again.







ETX-125, Spc900 webcam, IR filter, 2xBarlow, 2min AVI at 30fps, Registax & Photoshop.

Absolutely beautiful Barberskum!!

Can I ask you what your view through the eyepiece was like though? I am still just seeing a white disc at any mag in my 12in Dob. I am pretty sure the scope is reasonably well collimated. Scope is now stored outside in a shed so cool down can't be anything to do with it. I even made myself an offset apeture mask giving me about 5in unobstructed. This did cut the brightness a good bit but I was now just seeing a dimmer 'white disc. I am seeing absolutely no detail or colour at all. Dave L was saying he could only see the white polar cap and not much elese the last time he looked at mars. Its hard to see a white polar cap when the rest of the disc is white too!! :lol:

Ditto with saturn. The seeing was so much better than last night though. The rings were just protrusions last night. I was saying to myself, "never mind seeing the cassini division, I'd just like to see the gap between the rings and the planet itself" !! :lol: Prayers answered tongiht. I Much much sharper and I could see the gap and the shadow of the rings. Still no cassini division and the disc itself was as white and featureless as mars.

What am I doing wrong!!

Frank that's absolutely superb - a first class effort.

That weather is supposed to come up here for this evening so it's finger crossed!

Frank - that's a cracking image! The wind never really died down here in Bray so the 20" stayed firmly put indoors!

Calibos - You should be able to make out detail on Mars wit your 12" scope. The most likely culpret is the collimation, as cool-down shouldn't be the
problem for you. If you're not certain about the collimation there's a quick, rough'n'ready way to test if it's ok or not:

Put a bright star in the centre of the field of view - Polaris will do nicely, as it won't try to do a runner on you while you test. Now crank up the magnification with a short focal-length eyepiece and focus until it is as sharp as possible. What do you see? Is it a sharp round point of light or a soft blurry disk?

Now de-focus it slightly so that the star becomes a very small disk. If the seeing is steady enough and the magnification is high enough (use a Barlow lens if necessary) you should see that the star becomes a series of concentric bright and dark rings, very close together. These are called diffraction rings. Are the rings perfectly concentric or are they slightly eccentric (not centred exactly one inside the next)? Is the ring pattern perfectly circular or is it oval or even roughly triangular?

If the rings are perfectly circular *and* concentric then your collimation is ok and the problem may lie elsewhere.

If the rings are not perfectly concentric then you have a problem with collimation.

If the rings are not perfectly circular then you have a problem with the way your mirror is mounted in its cell - probably it is being warped by it in some way.

If the ring pattern is not *exactly* the same inside and outside of focus then the quality of the mirror *may* be suspect and warrants more testing.

This is called the Star Test - look it up on Google for more details and pictures of what to expect in the eyepiece and how to interpret the ring patterns. If all is not well with your scope or mirror then hopefully we can sort it out on-line. If not then you're welcome to call round to me if you are anywhere near Bray over Christmas.

Do the test and let us know the results.

Phil.

PS - What is the focal length or f/ratio of your scope?

Bejaysus Frank, that is one heck of an image for an amateur! Sweet mother, the detail you got on that disc is stunning... :shock:

:shock: :shock: :shock:
Holy ........... :shock:
Thats an incredible shot Frank. I had no idea a 5" scope could produce superb images like that. You will have to give me some imaging tips next time we are all out in Boher.