Telescope problem?

[nutbarjo]

Having only looked at some objects in the daylight and once at the moon to practice finding and focussing with my new telescope I at last experienced a clearish sky last night. With excitement I ventured out into the garden to look at some stars. Being a beginner it took me a while to actually find a star with the telescope, when I eventually did find one I got a white circle with a shadow or image of the stuff inside the telescope blocking most of the image. This doesn't appear when I look at anything else. I could see the moon nice and clear with no obstruction and indeed anything else I looked at. Am I doing something wrong? Please help!!

[arad85]

Sounds like it was out of focus.... Did you try changing the focus when you got your white circle with (I guess) a cross on it...

[nutbarjo]

Hi, It was in focus as it was crisp but had the shape of the internal of the telescope (i.e. what you see when you look into the tube - like a cross of plastic with the secondary mirror fitted behind this).

[arad85]

How big was the white circle. All my stars are single points of light. The only time I get the problem you are describing is when it is very out of focus... This is what an out of focus star looks like: http://www.backyardvoyager.com/Tutorials/Focus/collimationthumb2.gif

An in focus star is a point of light....

[nutbarjo]

Maybe it was out of focus then! I could see what is in your attached image but with a white circle behind it! It was quite a large circle. Maybe I need to use less magnification? Very bizarre...

Definitely need more practice I think!

[yeti monster]

Does it need collimating? There's plenty of advice about this on the forum (somewhere).

[nutbarjo]

I have no idea! I have heard the word and read that it should be out of the box but I don't know how to check. I have viewed other objects with no problem.

[The Warthog]

Collimation isn't the problem. If you could see the craters on the Moon clearly, you should not have had to adjust the focus unless you changed eyepieces or put in a Barlow. What you are d escribing is exactly what you see when the telescope is very out of focus. This could occur if you change eps, and the solution is to rack the focuser out and in until you find the focal point for that ep.

If you cannot get to focus at either end of the focus travel, then you have a mechanical problem that you should talk to us about some more, but I doubt this will happen.

[arad85]

Maybe it was out of focus then! I could see what is in your attached image but with a white circle behind it! It was quite a large circle. Maybe I need to use less magnification? Very bizarre...

Definitely need more practice I think!

Sounds like you were WAY out of focus then. Collimation errors look like the star is one sided, but still a pinprick of light. I'd try playing with the focuser and see what happens

[nutbarjo]

I'll have another go tonight - provided it isn't cloudy. Thanks for the help much appreciated!

[resonator77]

Arad85

My Nexstar SE has that spot on the objects when I look at through the eyepiece. Do you think I need to collimate mine too? The spot I believe from the secondary mirror in Schmidt - caasagrain.

Any Advice appreciated.

[arad85]

Huh.. never had that spot on my 6SE. Again, are you sure you have the thing focused. ALL stars are pinpoints of light. The only things that have any discernible area are the planets, the moon and some DSOs

[resonator77]

focus, you mean turn the knob underneath the eyepiece?

then yes, still could see secondary mirror spot on planets and stars

[arad85]

Knob underneath eyepiece - yup. Stars should be pinpricks of light with no area. You have something wrong if they are anything other than that. I suspect you haven't focussed enough - keep going - there's a LOT of focus travel.

[resonator77]

Arad85

I thought schmidt-cassagrain does not need much collimation...;-(

what about gas storms on jupiter, should I use filter to see them? and what filter would you suggest?

[arad85]

Big circles for stars = out of focus, not a collimation problem. SCTs should be checked (I check mine almost every time I'm out). Miscollimation will show as a one-sided pinprick of light (have a look in the manual for the 6SE)

Cas storms - depends what you're expecting to see - I can see between 2 and 4 bands plus an area that is the great red spot. I have a feeling from your other comments elsewhere that you may not be able to see anything due to focus being out. Anyway, as to filters - take a look here: SkyandTelescope.com - Planets - A Jupiter Observing Guide

[resonator77]

Arad85

by focus you mean the same knob underneath the eyepiece?

When I went out last night I could see M52 and polaris well sharp. Do you still think I need to focus or collimate?

Thank you for your help

[arad85]

Yes, the focus knob is the one on the back and to the side/below of the eyepiece.

How big were the stars in the eyepiece? If they are in focus and sharp, stars are not big enough to see the secondary shadow...

[The Warthog]

You probably don't need to collimate. You will need to focus at the start of your sessioin, and any time you change eps.

[ashenlight]

I was a bit thrown by this 'out of focus' star image when I first started observing. It looked like something was wrong! But it really isn't - it's perfectly normal. Just remember to twiddle with the focus knob when you change eyepieces and even when moving on to a different object to get the sharpest image you can.

Best of luck

[resonator77]

Arad85,

pretty big, but polaris looked to me the same as Jupiter that night. although I turned the knob of focus several time to get the most focus. do think I need to collimate my telescope?

[arad85]

You are WAY out of focus - and that's why you can't see any of Jupiters belts too.... Keep turning the knob - SCTs have a huge focus range.... Also, until you get focus, you don't know if you need to collimate.

[resonator77]

Arad85

will check this out tonight if the weather stay good.

What do you use for astrophotography, camera with a laptop or DSLR camera?

[John]

You are WAY out of focus - and that's why you can't see any of Jupiters belts too.... Keep turning the knob - SCTs have a huge focus range.... Also, until you get focus, you don't know if you need to collimate.

I agree entirely with this diagnosis - the scope is not in focus. Even just shortway of focus will show stars looking like ring doghnuts with the "hole" being the shadow of the secondary mirror.

Keep turning that focus knob !.

John

[arad85]

Both a webcam (planets) and DSLR with auto shutter release timer (DSOs). The few DSOs I've done have been done with a shorter focal length scope for wider field views.