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Attempting to Observe Jupiter/Venus

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5 years 5 months ago #92740 by Calibos
Calibos replied the topic: Re: Attempting to Observe Jupiter/Venus
Just to clarify. The Photo is a grossly out of focus image with the siloutte of the secondary mirror and spider vanes. Bright pinpoint stars with 4 bright spikes is cause by the spider vanes but its not the same thing as the photo earlier in the thread.

The only way to be sure focus is not a problem would be to focus on the moon. You'll know you are in focus when you see the larger craters in sharp detail. Then move to Jupiter without changing focus. Whatever Jupiter looks like whether you think it looks right or not or whether you cant believe its that small, well thats Jupiter in focus whether one likes it or not.

One wonders are you pointing at a star instead of Jupiter and are actually defocusing the star until you think its as big as you imagine Jupiter should be.

I don't think you should buy anything until we figure this out or you meet a fellow astronomer who can sort things out for you.

Keith D.

16" Meade Lightbridge Truss Dobsonian with Servocat Tracking/GOTO
Ethos 3.7sx,6,8,10,13,17,21mm
Nagler 31mm

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5 years 4 months ago #93373 by renglish
renglish replied the topic: Re: Attempting to Observe Jupiter/Venus
You might see something like this if your primary mirror or mirror cell was somehow moved further down the telescope tube (away from the diagonal mirror). If you cannot achieve focus, then something has changed in the geometry of the optical path. Somehow the eyepiece OR the primary mirror have moved either farther away or closer to their optimal position. Perhaps you have inserted something into the optica path--a barlow or spacer of some kind? The distance that something has moved is not a great distance--12mm inside or outside of focus would give such a result. If you are seeing the moon in focus, then you should be able to see all the planets and start in focus. The moon is a quarter million miles away, which is, for all practical purposes, infinity in terms of focusing your scope. BUT...is you move you scope from a high position in the sky to a lower one (to see the planets) and the focus changes, then something is loose, and shifting and changing your focus, and in that case, I would look at the primary mirror cell or the focuser.
Hope this helps.

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