Skywatcher 10mm EP Low quality?

[leinad (Dan)]

I got a 17mm Plossl and 40mm to go along with the 10mm & 25mm EP's that came with my 8" Skywatcher.

Im new(only 5 nights viewing) and not sure if this is a dumb question, but the 10mm seems to be not as crisp a view as the 17mm and 25mm.
Would this be due to the quality of the supplied 10mm EP, or another factor with high zoom and limited focus?

I'm wondering if an alternate 10mm EP would be better than the one that came with the Skywatcher Dob.

[OneOfOne (Trevor)]

It could be partly due to "seeing", ie how clear the sky is, partly due to magnification, collimation and perhaps quality. The eyepieces provided with scopes are not usually the "best". Usually you would not be able to use more than about 1x magnification for every millimetre of aperture (about 200x in your case). On a really clear, crisp night you could push to 2x per mm. The 10mm gives about 120x on your scope. Also as the magnification is increased the collimation of the scope will be more important too, have you checked the collimation since you got it? They could easily get out of alignment during shipping. There are lots of articles on IIS about how to do this. Generally though the "clearest" view will be with the lowest magnification as any defects will not be magnified up.

[rmcpb (Rob)]

I agree, its probably the seeing and collimation. My 8" scope is virtually the same as yours optically and its only on the better nights that I use lenses that are shorter than 10mm.

[Starkler (Geoff)]

Almost certainly to do with the 'seeing' which is atmospheric turbulence, or a scope that has not fully cooled to ambient temperature. This effect become more visible with increasing magnification.

[leinad (Dan)]

Thanks for the responses. I guess this would make sense, as the last few nights when viewing to the south, the moon has been right behind me to the north. It also has been a little windy.(WA, Perth current conditions)

For instance, looking at the Jewel Box, the 25mm looked crisp, but when switching to the 10mm, it became a little blurrier than I expected.
I suspect the glare from the almost full moon would also contribute to not so good 'seeing' with high mag ?

Are there any good guides to expecting what are good seeing conditions, in respect to eyepieces, aperture, weather, etc.

I guess the best bet would be to search the forums (will do this when I get home from work).

[erick (Eric)]

Originally Posted by leinad

I suspect the glare from the almost full moon would also contribute to not so good 'seeing' with high mag ?

I think the problem with moonlight is the general brightening of the sky, and hence it's harder to see faint objects; 1) less dark adaption of your eyes and 2) less contrast against the sky.

Seeing the bright stars in the Jewel Box would not be affected by Moonlight (unless the Moon happened to be in the same field of view and if that happens, head for the hills, gravity has gone crazy!)

As Geoff proposed, the increased "blurriness" you saw when changing from your 25mm eyepiece to 10mm eyepiece is probably the quality of the seeing (the atmospheric turbulance) at the time, and maybe some boundary thermal layer at your primary mirror, if it was some degrees above ambient air temperature in the tube. There is also a question of whether collimation was a bit out, with performance of the shorter focal lengths more sensitive to that.

[rmcpb (Rob)]

Yep, the moon glow would just cut down the contrast the same as the light pollution does in the cities. That is why its hard to see faint fuzzies in the cities. You would have noticed the background was grey rather than black.