Quote:
Originally Posted by adebear
Hi,
This is my first post here :-)
I have just recently purchased a ED80 + EQ5 mount and love them.. I have taken a few shots of jupiter (shown as my avatar) and it came out fairly well, if not small.. it did get me thinking though.
these cheap achro telescopes ie 150mm skywatcher's ..
if your taking shots with a B&W with colour filters and use a micro-focuser..
the fact that the different wavelengths don't focus at the same place wouldn't be an issue if you re-focus between each filter.. is that right or is there something I am missing..
just looks like if you spend the money on a good B&W and a good micro-focuser you wouldn't have to fork out $1000's for a really good scope?
really good forum BTW...
thanks,
Adrian
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I agree that it should be possible to refocus the scope to get around the achro image but I have tried it with mixed results. I have a 120 x 600mm achro as a guide scope but have tried to image through it. See
http://www.iceinspace.com.au/forum/s...ad.php?t=20710
As you can see, I was still unable to get the blue image to come to sharp focus. Having read some more since these images were taken I think the problem is that the filters leak somewhat into the violet and near UV. The camera is not very sensitive at those wavelengths but still enough to give you some ghosting. I havent tried yet but adding on of the minus voilet type filters should help but this is adding further glass to produce reflections ets.
If you use narrow band filters then there should be no problem but they are expensive and I don't own any.
With Jupiter you also need to be pretty quick taking the separate colour exposures as Jupiter rotates pretty fast. I don't own a filter wheel and have to manually change the filters. This would take too long.
The way around it of course is not to use a refractor but a scope with mirrors for your imaging.