View Full Version here: : Which eyepieces to get for an old old C8?
15-07-2011, 10:38 AM
I have brought my 20yr old C8 back from the dead, and it has the obligatory celestron 25mm eyepiece, I bought a long eye relief 9mm eyepiece for it way back then as well, but am still looking in the shed for it :)
To get the most out of the scope, and to cater for the kids, and my own parents (who wear glasses) which eyepiece purchase would people recommend?
I have dark skies out near Mudgee, and the kids and folks like to see the planets. Any recommendations appreciated, am more than happy to purchase 2nd hand too.
15-07-2011, 11:25 AM
there are 3 very good EP's that won't break the bank in the 1.25" format:
GSO 32mm super plossl & GSO 15mm Superview, both avialable from Bintel & Andrews.
Also a 9mm TMB Planetary Type II from Sylvain in the EP's classifides section here in IIS.
I've got an old, old C8 too, & use these EP's with it very successfully.
15-07-2011, 12:14 PM
Thanks, that is exactly the info I was after.
I found the other eyepiece ,it is a 50 degree LV10mm long eye relief (20mm) fully multicoated.
I'll try it out tonight.
I wonder how it compares to the 9mm TMB?
Is there any use in going to anything smaller than a 10mm or is the magnification just too much for this scope?
15-07-2011, 10:11 PM
The TMB has a FOV of 60*. I've not tried an LV10mm. Give it a go however. If your C8 has a drive in it like mine, this won't be a problem. I'm not a fanatic when it comes to alignment of my EQ mount as I don't do imaging, but on occasions, I manage to fluke a good alignment that sees a planet stay in the FOV for over three hours and not need to touch the Dec or RA controls.
Either a 10mm or 9mm will give you 200X (give or take with the 9). This is well within the theoretical limits of the C8's aperture diameter. The max. magnification for a given diameter is 50X per inch of aperture. So, for the C8 that's 400X. The limiting factor is actually the atmosphere, which rarely allows even 200X to be used regularly. Anything higher magnification wise is a very rare bird.
As an example, my big dob is 17.5", and has the exact same focal length as my C8. I just don't use the 6mm in the big dob. Not that it doesn't work, but the occasions that the atmosphere good enough to use it, I can count on one hand the number of times in 2 years. 333X is not really an option for me. The same goes for the C8. I would need to be up higher in elevation to be able to use it more often.
Actually, you're out Mudgee way, you may be able to get more use out of a 6mm than me in your C8. You'd be around the 1000m mark in elevation. Something to consider then. Would make for some kick-arse Lunar sketching! (well, that's my thing anyways).
What I do like about the C8 over my big dob, is that its slower focal ratio make it a better planetary scope! The image in the big dob of the planets is just too bright without using filters.
One scope my 6mm TMB excells in is my C5. And guess what? This scope/EP combo also gives me 200X, :lol: !
21-07-2011, 10:16 AM
I actually got a clear sky last night for a few hours, put the 10mm in, and the view was quite good for a few seconds at a time, but the atmosphere got in the way.
I live on the side of a mountain, so decided to trek it up to the top.
View was much clearer up there, the 10mm gave quite sharp moon views, I think if I can get a 6mm for $50 I might try it out, I'd love to get a better look at Saturn and Pluto, but I think you are right, the amount of times I'd get the atmosphere not roiling away ruining the view would be rare.
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