black dot?

[Benwyvis]

hi guys, happy new year to you all,just about made it throught the party season unscathed!.anyway, our 102mm mak arrived and the kids and i have had a ball observing the waxing moon. jupiter looked pretty good also, but for a black spot in the centre of the image which is not there in daylight or while observing the moon. have 10 and 25mm eyepieces and a 2x barlow, the spot is present with both 10 and 25mm eyepieces.i think this is a focusing issue question is if i get a 6.5mm eyepiece will this eliminate the spot.focal lenght of the tube is 1300.or am i way of track here.any advice wuold be greatly appreciated.thanks ben.

[jamespels]

You've seen 2001, right?

[Ags]

Was Jupiter in focus? Out of focus, a Mak always shows a black dot in the middle of the out-of-focus fuzzball. Sorry if I am stating the obvious.

[jamespels]

Apologies - I mean 2010, of course. I presume the black spot is growing?

[Benwyvis]

lol, no not seen 2010.and yeah jupiter itself was in focus could make out cloud bands but spot is centred on it.

[Starblazer]

Could well be the shadow of one of it's moons

[lukebl]

Could well be the shadow of one of it's moons

Nope. There weren't any transits this evening.

[Starblazer]

Then that rules that out lol

[jamespels]

Nope. There weren't any transits this evening.

Not even of moons the size of Neptune? May not be known to science yet

As you can see, I have nothing at all productive to add to this thread and I'm afraid I can shed no real light (or shade...) on the cause of this spot - I'll get me coat.

[Benwyvis]

lol,hell yeah, i think i am gonna like this place.its something to do with scope for sure cos if i look at a star and focus on it the spots on them as well.

[lukebl]

If it's doing it on stars too, then it's clearly not focussed. A star should only ever appear as a point, and not a disc.

[BazMark]

Are you allowing all your equipment to cool down sufficiently before using it?

I have the 127 Mak and I get a similar problem when I don't allow my eyepieces to cool down enough before using them. If I take them outside and start to use them straight away, they fog up a little and the secondary mirror (at least I think that's what it is) cast's it's shadow on the fogged lens in the eyepiece. It is definitely more noticeable when viewing stars or planets as opposed to the moon. It's the only explanation I've come up with. Of course it might not be the correct one but the problem seems to disappear if I allow everything to cool down for at least half an hour before viewing.

[GazOC]

Its got be a focusing issue. Are the stars pin points or is the black dot in the middle?