Focus on a Celestron 11"SCT

[bloodhound31]

Hi all,

I seem to be having quite a problem with focus on the Nexstar 11" SCT.

I have a 2x barlow (good quality) on the visual back of my celestron, and a modified ToUCam attached to it.

My optics are clean, the seeing is good. I am displaying the planet Jupiter on screen using IRIS and have a nice big bright planet. After adjusting the brightness, gamma, frame rate etc, I can get atmospheric banding, but absolutely NO detail. No matter how much I fiddle with focus on the SCT, I can't seem to get even close to seeing the big red spot, much less any other cloud feature.

Even after a 180 second AVI at 10FPS, stacked and optimised in Registax, there is still nothing to work with.


Any suggestions?

Baz

[RB (Andrew)]

Hi Barry,

Sorry for this basic question but just in case:
Is the GRS suppose to be visable at the time when you're view Jupiter, or is it around the other side?

I would have thought you'd see something with a 11" when the GRS is facing us.
I remember I could pick it up with the 12" and the Toucam ( a long time ago now ).

[bloodhound31]

Originally Posted by RB

Hi Barry,

Sorry for this basic question but just in case:
Is the GRS suppose to be visable at the time when you're view Jupiter, or is it around the other side?

I would have thought you'd see something with a 11" when the GRS is facing us.
I remember I could pick it up with the 12" and the Toucam ( a long time ago now ).

Hi RB,

I don't know if the GRS would have been visible last night at the particular time I was viewing. My point is, I can't seem to get ANY kind of detail, GRS or not.

I see other people getting good details with land based telescopes and think to myself, "Surely 11 inches of aperture is enough?" I have to think it is a focal length issue. Perhaps the optics on the SCT are just not geared for planetary work?

Would a 11 inch Newtonian be better than a 11 inch SCT because of different focal length?

Baz.

[RB (Andrew)]

How long did you leave the scope to cool?
The SCT's are notorious for long cool down times.
Tube currents will greatly affect detail and contrast.

[Matty P (Matt)]

I have never personally used a Toucam or an 11" SCT but one thing is for sure is that 11 inches of aperture for planetary work would be perfect. I use an 8" SCT for planetary work and when the seeing is good, I can make out fine details.

How often do you collimate your SCT? Good collimation is critical for high magnification planetary work.

[Dennis]

Hi Baz

Sorry to hear of your problem.

I’ve got the C9.25 and from memory, when Jupiter was low and the seeing was quite poor, all I can recollect distinguishing was least a couple of equatorial bands, using an x2 Barlow.

Good seeing and altitude are paramount when it comes to seeing fine detail and even then, it can pop into and out of visibility depending on the conditions.

Cheers

Dennis

[Robert_T]

Hi Baz, looks like the others below have pretty well covered it. Your SCT is fine for planetary views and especially for imaging. I'd stress what a couple have already mentioned. 1) cooling... doesn't matter if the seeing is 9/10, if you haven't got your scope fully cooled you wont see much detail at all. This can take hours for a scope your size in a place like canberra... this is why people use fan coolers. 2) collimation... you have to work to get this right. Get your self some "Bob's Knobs" if you don't have 'em already and tweak your collimation. If you centre a bright star at high power - 200-300x and defocus the image it should show as a series of concentric rings of light... if these aren't perfectly concentric (when star is centred) then your collimation is out and you'll never get a decent image until it's fixed. While these factors aren't so important for low power viewing of deep sky objects, they're pretty well essential to get even half decent views of planets. Seeing is still the biggest factor, but there's not much you can do about that. cheers, Rob