Random defocus?

[Manok101]

Sorry if I misspelled it, but I was looking at Jupiter last night, and there were points for a few minutes where my telescope would just appear to defocus. What causes this effect? I'd wait a few minutes, and it'd be fine again.

[Capricorn]

2 thoughts come to mind.

First is that it was one of the more turbulant of the several atmospheric layers getting between you and Jupiter and so the light simply got refracted all over the place.

The other is your eyes. Find that mine need a change of focus and a rest when viewing. They suddenly decide that nothing will be sharp until I have a break, look round and let them get back to normal.

[brianb]

I was looking at Jupiter last night, and there were points for a few minutes where my telescope would just appear to defocus

You had GOOD seeing .... normally you get long periods of blur with, if you're lucky, occasional flashes of sharpness!

My guess is that your intervals of bad seeing were when a heat plume (perhaps from a distant domestic boiler) got between your scope and Jupiter.

[Moonshane]

I'm with Brian, planetary observation depends on patience and persistence due to atmosphere. this is the case with the moon too. it goes something like fuzzy, fuzzy, fuzzy, less fuzzy, WOW that's awesome, fuzzy, less fuzzy etc .

the key is not messing with your focus when you have got to the stage where the sharpness does appear at that setting. keep watching and you'll build a mental picture.

good luck.

[Tim]

Yes, it is possible to have perfect focus, but still have a blurry image at the eyepiece.

Although your optical system may be adjusted properly, there is a lot of junk in the atmosphere between you and your target, which acts almost like an extra piece of glass or lens. This atmosphere is moving all the time, and contains varying amounts of moisture, dust and heat currents, all of which can spoil the views when they get in the way.