Using the new 8" dob. from meade, what lens to use to get the biggest clearest image of planets?

Question

Using the new 8" dob. from meade, what lens to use to get the biggest clearest image of planets?

Answer 1

Bear in mind that shorter and more powerful eyepieces also have a smaller field of view. The image will be larger, but will move out of the field quickly. On planets, even on a scope with tracking, I rarely go above 200X.

I think 100X is a bit pessimistic for an 8" scope. Under reasonable skies you could crank it to 300X, and more than 400X under excellent skies, but you can't look at planets for very long like that because the field is very small, and the slightest touch of the scope while trying to keep it there could actually knock it out of the field.

And as mentioned, bigger and clearer don't go together. The more powerful the EP, the greater the magnification not only of the planet, but of everything between the planet and your eye, including atmospheric movement, optical imperfections on the (probably excellent) scope, and even distant footsteps or your own heartbeat.

Answer 2

It depends on the atmospheric conditions.  With excellent seeing conditions, on a well collimated 8" scope, after it has had time to cool down to the ambient temperature, you will probably be able to get a nice sharp image all the way up to 300x.  The results will vary widely from night to night.  You just have to start with your longest length eyepiece and work your way up, for as long as you are able to get a nice clear image.  Most of the time I am happy with 100-150x or less, but I have taken it up to 450x on some extraodinarilly clear and steady nights.  .

Answer 3

An 8" scope is 200 mm.  I'd go with 200x at the most.  And, i might even go that high for the planets.

But let's say you're talking about the 8" Lightbridge.  This has a 1219mm focal length.  Divide that by 200, and you get about 6 mm for an eyepiece.

You can also divide the focal length of the scope by the focal length of the eyepiece to get the magnification - for when you're shopping.  So if you see a 7mm eyepiece, 1219 / 7 = 174x.

The SN-8 AT has a 812mm focal length.  So 200x is about 4mm for an eyepiece.  Hmm.

You know, it's really expensive to make these really short focal length eyepieces with high quality.  If you've got a nice 10mm eyepiece, it's going to be pretty good.  I do use my 10mm with a 2x barlow frequently.  And i like the results much better than my 5.1mm eyepiece.

Answer 4

'Bigger' is not better. The more magnification you use,

the more washed out the image will be.

With an 8 inch objective lens, you don't want to go above

maybe 100x. Even that is pushing it.

Stick to the eyepiece that gives you 30x to 50x. You'll

get a much sharper image.