What I'm seeing thru a 100mm ed

Hi,
I'm pretty sure my scope is fine (very pleasing views at225x consistantle)but
is anyone familiar with the following;is it normal to see a ring around brighter stars (no color) at low powers? The diameter of the ring is about the same diameter as the moon So it's not fringing the star but surrounding it at a little distance.It may be my ep as the sirius 25mm that I have is not a very good sample.
Around planets the planet is surrounded by a black background and then a little further out it is sort of like a whitish tinged background this is more visible at higher powers as I have seen this effect thru my etx 105 as well I assume that it's normal but would just like to make sure.
Thanx

What you are describing sounds like the first diffration ring. This is common for a refractor is it not? I mean, I have seen this and people are stating that this shows that the scope has good optics. Am I off base here?
A quote from a review.
The refractor showed a classic Airy disk with only one bright diffraction ring on stars of 4th magnitude or less.

Itz,
I've read through most of the replies to your post and don't recall anyone suggesting to stop down the aperture. If the problem is not the EPs then you could have a bad edge or SA. Try masking the objective down to 80mm or so and see if the problem persists. Here are a couple helpful star test links.

http://aberrator.astronomy.net/html/turned_down_edge.html

http://www.mindspring.com/~jeffpo/startest.htm

Does the turned down edge image (1st link) depict what you are seeing?

Bob

Itz,

I've followed your thread for the last week or so and was hoping someone here could help you but I think it's very difficult for us to understand the problem without actually seeing what you are seeing. I've made a quick sketch, as best I can at monitor resolution, and hope it may be something close to what you are experiencing.

On the left is what I might see in my 102mm ED refractor when looking at a bright star with medium to moderately high power. The diffraction rings are much smaller using low power but you can certainly still see them (Sorry, I cannot illustrate a smaller star at 72dpi).

The eyepiece view on the right is what I would expect to see if I had an internal reflection. If this is what you are seeing then I would suspect, like others here, that you have a shiny diagonal nosepiece, or something else reflective in or close to your lightpath.

It's a long shot, but is this what you are seeing? :S

Jerry

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