Posted 26 July 2013 - 06:30 PM
Posted 26 July 2013 - 07:32 PM
1X/2X/3X eyepieces - Click on the "Extended Information" tab.
You normally want a low, medium and high power eyepiece.
Some of those eyepieces that you got in the kit might be uncomfortable to use due to short eye relief. If they are plossls, the 6 and the 4 will be tough.
With my 8" dob, I find my 24mm gives good low power views, my 10 gives good medium power, and the 6 gives good high power. Sure there's a big gap between the 24 and the 10, I'm thinking of getting a 16 to fill that.
I would say a 20 would be a good one for you. I would also look into getting a more comfortable to use eyepiece in the 12-10 and 6-5 range. You should look for ones with a wider apparent field of view so the object you are looking at stays in view longer.
The astrotech paradigms are supposed to be good eyepieces. You should check them out. Link
Posted 26 July 2013 - 07:39 PM
Assuming 1200mm FL, the 30mm gives you 40x and depending on what its Apparent FOV is, ~1.7 to 2deg true FOV.
The Cel 15, likely a Plossl, will do 80x and ~0.65deg TFOV.
So, if you're looking for another Plossl, go for something that gives close to 1deg TFOV, yes that means about a 20mm ep. An alternative would be to replace the 15mm with a 16-17mm 82deg ep, that also gives just over 1deg TFOV with a bit more magnification.
[edited to correct TFOV of 15mm Plossl, sorry]
Posted 26 July 2013 - 07:58 PM
Posted 26 July 2013 - 08:19 PM
Posted 27 July 2013 - 08:36 AM
Posted 27 July 2013 - 09:40 AM
Posted 27 July 2013 - 06:16 PM
I have a 20mm EP for my 8" scope and I like the 2mm exit pupil it delivers. For me it provides a nice balance of darker sky, but large enough exit pupil to make a lot of DSOs stand out a little better than other focal length EPs.
Posted 28 July 2013 - 05:23 AM
30 to 15mm is NOT a big jump. In my scope I go right from a low power 30-32mm eyepiece to an 11mm Nagler and almost never use anything in between.
Hmm, I sort of both agree and disagree.
On the one hand, I do think it's a pretty big jump. On the other hand, I find this particular gap less of a problem than most.
I'm assuming this is a typical 8-inch f/6 Dob. In that case, the 32-mm eyepiece gives a 5-mm exit pupil -- a nice, low magnification, great for wide-field viewing. The 15-mm eyepiece gives a 2.5-mm exit pupil, which is about where I start when I want to view deep-sky objects in detail.
From 2 or 2.5 mm on to 0.5 mm exit puils, it's really useful to have a good range of eyepieces, generally in increments of around 1.4X. So one might have a 15-mm, 10-mm, 7-mm, 5-mm, and 3-mm. Or more likely a 2X Barlow.
Intermediate powers, exit pupils between 3 and 4.5 mm, are somewhat less useful because they hardly ever offer the best detailed views, nor do they offer the widest possible field of view. However, you do occasionally find objects where these exit pupils turn out to be the ideal compromise. More to the point, they're often the best choice in conjunction with aggressive filters like the O III or H Beta.
On an f/10 scope, the considerations are totally different.