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Hi, I've got a Skywatcher Heritage 130p reflector, and if i insert anything less than 10mm eyepiece, the image won't get crisp. I guess it's normal, but as I'm very new to astronomy, I'd like to know what the sharpness depends on exactly. 

Is that the focal length (how fast the telescope is? ) or the size of the mirror and how much light it gathers? Or both affect it the same way?  

Are things the same with refractors in this regard? Thanks. 

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Sharpness would depend on the quality of the optics, correct collimation, how well cooled the scope is and the state of the atmosphere. I think you can discount the first factor at 65x but I'd think about the others. Have you checked collimation? Was the scope cooled for long enough? The last factor, atmosphere, you can do nothing about but how did it look visually?

Your scope should be able to go to a 2.5mm (260x), in theory anyway, so the atmosphere is probably the limiting factor. Even so, I'd have though you'd notice if conditions were bad enough to limit you to 65x. Last night I used 70x with a smaller scope and got a sharp view.

EDIT: I forgot to say sharpness also depends on not over-magnifying but as explained, that should not be a factor in this case.

Edited by wulfrun
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A few questions just to clarify things:

Were you using just the 10mm eyepiece and no barlow lens ?

What were you trying to observe ?

Were you outside with the scope rather than inside looking though a window etc ?

Had the scope had some time to cool down to the outside temperature ?

The Heritage 130m should be able to deliver very sharp views at 65x and even twice that much, normally.

 

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Yes, outside, cooled down. Without barlow. If I insert the two times barlow (metal, not too bad quality one) with the 10mm lens, I can still focus, maybe it's the contrast that gets less and the image seems less sharp to me. 

The sky was very light polluted as well. I'm gonna experiment more when it's fully clear outside. 

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11 minutes ago, Planetarian said:

Yes, outside, cooled down. Without barlow. If I insert the two times barlow (metal, not too bad quality one) with the 10mm lens, I can still focus, maybe it's the contrast that gets less and the image seems less sharp to me. 

The sky was very light polluted as well. I'm gonna experiment more when it's fully clear outside. 

Is that the bundled 10mm EP or a better one? The bundled one doesn't have a good reputation - I have the same one and haven't bothered to use it based on opinions I saw. As you say, check again to see if you can get better results another time, that would confirm the conditions having been poor.

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Mainly the Moon. First I used the Super 10 that came with the telescope, then I tried my Ostara 10mm SWA 70 FMC which was a little better. 

Now that I'm thinking about it, it might be possible that the secondary mirror got steamed up somewhat from be breathing while observing. As the tube is extended, there's nothing between my mouth and the secondary mirror. I might try to add some kind of shield next time. 

I'm thinking to get a Bahtinov mask as well.

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