Which Telescope Should I Buy for Astrophotography and Viewing?

[chemisttree]

So, now I've got to keep my daughter away from boys with big, er, telescopes? There oughta be a law...

 

[Saladsamurai]

So they sent me the original rack and pin focuser AND two Crayfords by mistake. Nice.

 

[turbo]

Be nice. Good things come back to reward you.

 

[Saladsamurai]

Am I supposed to be able to see the spider vanes while viewing? That sounds like a stupid question, so I am thinking "no".

I have collimated the scope (the primary, as the instructions said it is highly unlikely that the 2ndary would need adjustments) and went to use the scope and I am seeing what appears to be cross-hairs (the vanes).

Granted, I had terrible seeing conditions last nite. I am going out into the daylight now to investigate.

Any suggestions on what to look for?

EDIT: after going outside, I noticed that if I back my eye (face) away from the eyepiece I can see the vanes more clearly. I believe that this makes sense. Since I am magnifying, anything extremely close will not appear so well, while far off objects will.

This leaves me to believe that it is a collimation issue. I alligned the primary mirror's center mark with the "dot" on the collimation cap. However, I did not think to allign 2ndary.

 

[mgb_phys]

You shouldn't see the vanes (they are in the pupil plane)
you can see bright diffraction spikes caused by the vanes.

I should probably leave more detailed instructions to people with more experience of amateur scopes - if I can see the vanes I go kick the researcher in charge of the adaptive optics system!

 

[Saladsamurai]

I think I have it collimated; however, I have one question: should the focuser be all the way in or out while collimating. When I look through the sight tube (the dust cap with the hole in it) I can get the "dot" center inside og the the center mark in the primary mirror; however, if I move the focuser all the way out, it becomes slightly ou of line again. This leads me to believe that the focuser itself may need collimation.

Any ideas?

Casey

 

[chemisttree]

I think you are noticing "image shift" in your focuser. This is usually caused by some play in the focuser tube. Read a review about your telescope here where the problem is identified and a partial solution offered.

I also adjusted the focuser itself to remove most of the slop. During first light I realized how much of a problem the focuser was. The image shift at high magnifications was awful. To eliminate as much of this slop as I could, I used a small Allen screw to adjust the tension on the two small Allen screws atop the focuser. Using small adjustments and setting the screws' tension to about the same level, I was able to eliminate a great deal of the image shift. Images still shift at high magnifications, but not nearly as bad as before I made the adjustment.

http://www.cloudynights.com/item.php?item_id=882

If you are really seeing the collimation change as a function of the focuser position, you should place a low power eyepiece in the focuser and focus on a very distant image (daytime). That is the position the tube will be in most of the time. Adjust your collimation using this focuser tube position. Note that the actual collimation (primary and secondary position) will not change as a function of focusser position. After that, I would implement the suggestion that I quoted above.

Good luck.