Re: Orion 150mm Mak
- From: "Stephen Paul" <smarshallpaul@xxxxxxxxx>
- Date: Fri, 2 Sep 2005 00:51:59 -0400
"David Nakamoto" <res07oeg@xxxxxxxxxxx> wrote in message
news:u%JRe.32279$Uz2.19709@xxxxxxxxxxx
> Hello fellow amateur astronomers !
>
> One first quarter moon ago, an informal side-by-side-by-side test was
> inadvertently arranged during a public star party, all telescopes within 5
> meters of each other, looking at the first quarter moon.
>
> In one corner, the new 150mm Mak from Orion. A slightly beefed-up version
> of the EQ-3 mount (an EQ-6?) was used and came with the scope.
>
> In another, Orion's 127mm Mak, mounted on the EQ-3 type mount it came
> with.
>
> In the third, relatively new (last 5 years?) Celestron C-8. Dual arm fork
> mount.
>
> We didn't use the same eyepiece through all three. Need to remember to do
> that next time. I'll try and stick to what I saw. The eyepieces used
> gave similar magnifications; the entire moon was visible through all
> three.
>
> Images:
> The Maks had consistently higher contrast and sharpness over the C-8, and
> both consequently showed more details. The Moon with its wealth of find
> details allowed for good comparisons of this. The C-8 was significantly
> brighter, but not overwhelmingly so. If the 150 was brighter than the
> 127, I couldn't see the difference. The 127mm Mak seemed to me to have
> SLIGHTLY better sharpness than the 150m.
Should we assume that the C8 was not critically collimated?
I had a StarMax 127 and a C8. My results were completely different. At 250x,
the 127 Mak simply didn't hold up to the critically collimated C8 in good
seeing.
I sold the StarMax 127 shortly after picking it up in a trade. Later I sold
the C8. I decided after a few years that I just didn't like the FM/Wedge
combination of my C8, so I sold it to a school teacher at a private Vermont
high school. He's now collected three Ultima 8-PECs to teach imaging to his
astronomy class.
Some time ago I started to regret losing the versatility of the C8 OTA for
general purpose astronomy. Being in need of a decent planet scope for this
years Mars opposition, yesterday I picked up a used Celestron Advanced
Series C9.25S, and added the GoTo to make it a full blown AS-C9.25GT. What a
pleasure to have GoTo in a reasonable aperture again, and the C9.25 lives up
to its reputation. I give it 1/6th wave undercorrection at the eyepiece
after assuring that it was critically collimated. The C8 that I had (the
Ultima-PEC model) also had excellent optics for an SCT.
I'm sorry, I just don't see the 127mm Synta Mak competing well with the
Celestron SCTs of 3" additional aperture. It just doesn't seem credible to
me that a 5" scope is going to best an 8" scope, unless there are conditions
around that particular test case that are inducing extraneous errors in the
C8's optics.
This is just as hard to take as reading how Joe Blow's 4" apo refractor
outperformed an 8" F6 reflector on planets. Well, I've been there and done
that test. My results were different. The 4" apo is an absolute dream scope
optically, FOR IT'S APERTURE, but there's no way in hell it's going to
provide more resolution than a scope of twice its aperture on the moon,
Saturn, Jupiter, or Mars, given decent seeing, and someone experienced at
collimation.
Never mind using the same eyepiece in all three scopes, use eyepieces of the
same design, with focal lengths that make each scope operate at the same
magnification. Try to get all three scopes as close as you can to 100x,
150x, 200x, 250x, and 300x.
Above 150x, the 8" SCT should steal the show. If it doesn't, then check the
collimation at 400x or more.
.
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