Hi all, I currently have a Celestron SE6, and a Meade 5" refractor (LXD55, I think, but I haven't used it for a long time). Due to light pollution, I'm a bit limited, but I do enjoy planets, doubles, the moon and those sorts of things. Would around a 4" refractor be good for this? My issue with my 5-incher is it's huge, the mount is heavy and cumbersome, and it's just a paint to set up. It's just not a very grab n' go scope.
It seems like a 4" refractor isn't going to be much better in that regard, but I see they also make short tube, fast refractors. This sort of thing seems more to my liking, BUT I've also read these type of fast scopes aren't good for planetary viewing.
So in short, I'd like a lightweight, somewhat small scope with a GoTo mount. Maybe I already have the answer, and it's my 6SE. If not, any suggestions? It would be a huge bonus if I could use the refractor with my 6SE mount, but I'm not sure that would work due to tube length (it might hit the mount when pointing towards zenith?).
You want a fast refractor for planets....that is cold fire and hot ice. Let us say you get the very short AT 92 (f/5.5). You would need a 5 or 6 mm ocular just to get to 92x which is not a lot on planets....better than nothing, but not a lot. But to get to 184x you're going to need a 3mm (or a little less) eyepiece and you're going to be observing at 0.5 mm exit pupil.
Those oculars exist, you can do it. But you're stretching the capacity of the scope and your eye if you want to do this for a long time. You might also discover what is in the "attic of your eyeball" which is to say all the dust and grime in there that you didn't know about and don't want to know about.
I have had different experiences with small aperture viewing. First of all I think if you're going to get a small refractor you might be better with a longer one like the Vixen ED81s which is now marketed as the SD81. Because it's f/7.7. Now you're looking at a 4 mm to get to 160x and that may not sound like much but at the high end these small increments matter. This is a popular scope on CN, I bought it because of the rave reviews and because people were snarking that I shoudn't knock 80mm viewing till I tried it. So I tried it, and they're right, you can see quite a bit in 80 mm. And in fact you can see quite a bit if you use the dustcover (it has a hole with a removable cap) to make a 40 mm telescope. Amazing what you can see in 40 mm. And even though the SD81 is f/7.7 it *might* be short enough for your mount. You would need to get the measurement.
Again, on behalf of small aperture viewing, I always have a refractor on top of my SCT and the other night was viewing Jupiter in the 92mm f/6.9 and the C14. First point: A friend and I agreed it was a terrific view. I said I couldn't believe it was only 128x (my 5mm ocular). And I realized reaching into the box that it WASN'T 128x, it was 180x, because I had grabbed the 3.5 instead of the 5 mm. So I was at peak power and the view was razor sharp. And at 0.5 mm exit pupil. And you could see things. You couldn't see what you see in the C14, but there was enough there to view.
But on the other hand the C14 was rendering MUCH more at 224x or 1.6 mm exit pupil. This is a much more comfortable viewing range and I was getting much more detail and color rendition--the blessings of aperture.
But I was fascinated by the view in the smaller scope and kept going back to it until this long semi transparent filament placed itself between me and Jupiter. I tried looking left and right, jumping up and down, but it insisted on staying right there covering jupiter from N to S.
There was no filament at all when I looked in the C14. When I went back to the refractor, there it was again. (No it was not on the ocular)
So the point about observing planets in a fast refractor is that you will want to push the magnification below 1 mm exit pupil and below 1 mm ex pupil all sorts of eyeball critters can make themselves known, at a time and place of their choosing. They're called floaters.
On an unrelated matter if you *do* get a fast refractor for high power viewing of planets make sure you get the best one you can afford. Because fast optics tend to stretch the limits of design and execution.
Edited by gnowellsct, 29 July 2020 - 01:20 PM.