Starmaster 11" f/4.3 ELT - who has an opinion???

Started by mirfak, 03/23/2010 08:04PM
Posted 03/23/2010 08:04PM Opening Post
Please tell me about this scope.
Thanks
John grin
Posted 03/23/2010 09:27PM #1
John,
I own the F4.55 version of the 11 inch ELT and have been very happy with it. The Zambuto mirror is superb, as you have undoubtedly heard or seen. I do think the scope could use a fan to deal with getting the mirror to the ambient air temperature and get rid of the boundary layer that can affect the qualuty of the view.

Mechanically, the scope is nice, with smooth motions but a bit of friction that allows a fairly wide variety of eyepieces to be used without any balance issues. It is balanced for a Parracor, and I have used everything from a 26 Nagler to a Nagler Zoom without having any balance problems. I have also found that the four pole structure holds collimation well as you move up and down in altitude, despite some reports of collimation shift due to the lack of a true truss structure. I kind of wish the mirror box and rocker base used nicer joinery (e.g., like a Telekit), but the scope has held up well with no sign of anything loosening or otherwise needing attention.

For me, the scope has offered outstanding optical quality in a very transportable package that is about as much scope as I want to deal with in terms of size and weight. The relatively short focal length allows for seated viewing throughout the altitude range.

I typically keep the scope assembled at home, and carry it out to my observing deck (up a hill) in two pieces, the ground board and rocker box first followed by the complete mirror box/pole/UTA assembly. For travel, I take out the poles to allow a fairly compact package that fits easily in the back seat of any car. The four-pole structure with the Moonlight connectors on both ends makes for very quick assembly.

Hope that helps.

Jeff Bennett

Posted 03/24/2010 04:32PM | Edited 03/24/2010 06:15PM #2
I've got one of the F/5.4 versions of this scope.
Overall its superb. The pieces are a managable size and
weight, and it goes together very quickly. Optics are
superb -- one of the few scopes that has ever shown
me details on Jupiters moons -- the equatorial band
on Io was very easy with this scope. And theres
enough aperture for some nice views of nebulae and
galaxies.

Mine did show considerable change in the collimation
with elevation. It was pretty easy to see on star
images at 500x -- the first Airy ring would
become strongly unbalanced as the elevation changed.
I could also see these effects on planet images at
high power. For example, Jupiter at 45 degrees
elevation would be very crisp, but Saturn overhead
would show the effects of the extra coma.
The problem can be managed in
real time by re-collimating the scope on a nearby
star prior to each planet observation.

A more permanant fix is to add some steel cables
on diagonal lines between the trusses. This is pretty
easy to do -- parts are about $40 and takes an
hour or two. I did some lab measurements of the
deflection using a laser, and it was something
like 11 millimeters without the cables -- the upper
cage was drooping by that amount as the scope
went from zenith to horizon. With the cables it went
down to about 1 mm.

Probably the collimation shift on the F/4.3 version
would be smaller (shorter trusses) -- unless you are
trying to squeeze the last ounce of performance from
it, you might just not worry about it.

I also added four fans on the mirror to cool the
scope more quickly. And some counter weights on
the back to balance heavy eyepieces and camera
equipment.

Also when I first got it, the secondary mirror
was warped due to too much pillow batting in the
holder shell. Images showed some astigmatism.
But this was also easy to fix by taking out some
of the batting. Its a fairly common problem.

Overall I would highly recommend this scope.
Mine had some issues, but they were all easily fixed
with some simple mods.
Posted 03/25/2010 10:12PM #3
john raymond said:

Please tell me about this scope.
Thanks
John grin

John,
I have owned the f/4.55 version for six years. It is a wonderful scope. Superb Zambuto mirror. Easy to set up and take down, or you can just transport it in two pieces, as another poster has decribed. I have not found any cooldown problems. I do find the scope moves from the object when I remove a heavy eyepiece but I find it immediately by zeroing the Sky Commander readings. SC is very helpful in urban skies.
I highly recommend this scope. Geoff Garehy on Yahoo Talking Telescopes group has one and loves it.
Bill Meyers