Posts Made By: Greg Nowell

In addition to the UO orthos I like the RKE eyepieces from Edmund. Greg N

It depends on how fussy you are. I was going to get an inexpensive 5 inch refractor, I would get it at f/8, because the optical correction is easier to make at a longer focal length, so the inexpensive part won't compromise your quality as much. It would also have less chromatic aberration on the planets and moon if you were going to use it for that.

To my mind, when you get a refractor for dsos, it is because you like open clusters and big wide views. I think this is an acquired taste; people new to astronomy usually like bigger and brighter (meaning a larger scope).

But I think you would do better to get an f/5 dob in the eight or ten inch category. The extra aperture would do well for dsos and you would still get nice wide fields. You wouldn't have to worry about chromatic abberation,the mount is part of the package and more stable than typical inexpensive refractor mounts.

I'm not saying don't get a 5 inch refractor. I have one myself. But I think you'd be better off with an 8 inch dob. At 25x it should give you a maximum field of view of around 3 degrees, not as much as a five inch refractor, but very good, and brighter. My other choice, if you want a mount with tracking, would be an 8 inch SCT. This will give you a lot more light than a refractor and be better on dsos but you won't have a nice wide field view. The SCT, being shorter, is intrinsically more stable than a five inch refractor. The SCT also won't have color issues.

regards
Greg N

I bought the AP3600 for my c8 and found that there was a lot of vibration. So I'm in the market for something more solid. You know, you can never really be over-mounted.

Greg N

For a 16 inch GEM Newt you're going to need a massive mount similar to the AP1200 so design heavy and strong. The binoviewer is a problem because it will add a lot of weight that will be leveraged way up there. So you're either going to need real good clutches to keep the scope from moving under the weight, or you may need to re-balance the OTA every time you switch between binos and the eyepiece.

It's do-able, I would think, but I will comment that a scope of this length (I'm estimating 1700-1800mm) on a really strong equatorial mount is going to have some elevation (it will have to for the mirror side to clear the ground) and so you'll be using a ladder. This raises the question of why bother when you can put the same scope on a dob mount and get tracking for it.

You may or may not need a barlow. AP makes a nice one that is very strong. The Denks have a built in power switch which would allow you to change magnifications without affecting scope balance. Also on a long Newt you are more sensitive to wind, and while one can never exclude the possibility that a mount will be strong enough to hold against a moderate breeze, there is a tendency not to build/buy enough mount for the OTA, scrimping where one should not. Dobs are also vulnerable to wind but I think it's probably easier and more cost effective to overbuild the dob mount than the Newtonian. A member of my club uses a 16" Newt on an AP1200 and he says he considers the setup just barely adequate.

Having grown up in the era of Newtonians on GEMs I like them, but truth be told I think there is a certain engineering logic to the fact that these days 98% of the scopes on German equatorial mounts are either refractors or compound scopes like the SCTs.

good luck, it sounds like an ambitious and fascinating project.

Greg N

That was a good read and probably as good as any eyeball report is going to get, much better than my own records of these things.

My only comment is that I sold my Supermono 10 because of the tiny fov. People call these planetary eyepieces but another function is to bring in faint objects such as Pal 14. In my 14" SCT the Supermono 10 yields less than 5 arc minutes.

As it turns out, the way that you find marginal dso objects is partly by comparing the field of view where you suspect it is with the sky background. One might also jiggle the scope etc. to verify that there is indeed "something there." The problem with a tiny fov is that you don't get enough sky to give enough background to make a comparison.

In my personal comparisons between the supermono 10 and the XW10 and the RKE 8s and 12s (there are no RKE 10s) I never "got anything additional" on planets. This was mainly because over the course of over a year I never had good seeing conjoined with an available planet.

This tells me something about planetary eyepieces. The conditions in which they might make a difference are few and far between in my part of the world.

I also like being able to see Jupiter's moons and Saturn in a field of stars is its own beauty: I like having space around the planet. So it's the XWs for me as a rule.

The other thing is that at the back end of a c14 these little tiny eyepieces are a real pain in the forehead. You keep bumping the rear casting.

I've also done my mini-evaluations in an FS128 and a Vixen 102mm ED, and similarly concluded that the Supermono wasn't justifying its space in the box.

But I'm glad they're out there for them that wants 'em.

regards
Greg N

The coatings can take it but you don't want the dew to drip and then leave a run mark on the lens especially between the lenses. I find it more likely however that you had the dew not in between the lenses but on the other side of the doublet or triplet i.e. moisture in the OTA condensing on the exposed surface. It is very tricky to examine what is going on inside a doublet esp. at night etc. So my suspicion is that you *thought* it was in between the doublets, and *maybe* it was, but it is *as likely* that it was on the "far side" of the doublet on the side exposed to the air of the tube. In that case cleaning is fairly easy the whole lens assembly will typically come off without much hassle...easier to disassemble (leaving all the lenses in place in the cell) than something like a 24 Pan, for example.

On a four inch your options include:

1. adding exterior insulation
2. taking it into your car and getting it toasty in front of the heater
3. a dew strap

As an sct guy dew straps come naturally to me and it is much easier to keep my 4" and my 5" refractors dew-free than my 14" SCT. All you need is a power supply that's up to the job. I'm including a picture of my simple but works power supply; note that I installed an in-line fuse in the cord. But this is more than enough for a four inch refractor dew strap.

Greg N

Then I would have to get an extra set of ZAO IIs for the bino? What kind of Zeiss scopes are there anyhow, besides spotting scopes? Greg N

When are you going to get a REAL tripod for that Mach 1. That moonlander looks a little weak in the legs.

Greg N

Here's a shot of the lip, note the blue dribble on the left of the edge of the mirror. To me it looks more like some run off from the number on top than a deliberate orientation marker.

thanks Greg N

One solution is to get the Losmany setting circles for a G11. They are a nice wide circle. You have to get a machine shop (or be handy yourself) to put a disk of metal inside the circle so you can attach it to your axes.

Another solution is to call Don Rothman and tell him you want him to scavenge some setting circles for you from an old mount.

http://astronomy-mall.com/astro.parts.outlet/

regards
greg n