Sunday, June 03, 2007

 

How Do You Mount a CAT?

That is, what kind of a mounting do you want for a catadioptric telescope; especially an SCT? For years I’d have said “fork it.” Since the Orange Tube C8 hit the streets in 1970, I’ve been buying SCTs as packages complete with integral fork-mountings. Until recently. I still use the forkers, but my love affair with ‘em is definitely over.

Why is that? Well, I’ll tell ya, muchachos, it’s largely a consequence of Your Old Uncle Rod getting up there into advanced middle age. Until recently, though, I saw no reason to change my scope buying and using habits. I’ve had a Celestron Ultima C8 for years. No, it ain’t got no go-to computer gee whizzery, but for the longest time I nevertheless considered it the last word in 8-inch SCTs. The U8 integrated a stupendously good OTA with a drive base containing a sweet Byers worm set, a DC drive, and PEC. To ride on this drive base, the U8 nestled in what was probably the heaviest fork ever furnished with an 8-inch SCT.

The end came one cold November star party. I had forgotten what it was like to use a non-go-to fork scope on a wedge (for you younguns, in the old days, a non-go-to scope had to be tilted over on a “wedge” for polar alignment purposes in order to track the stars). It was cold out on that observing field and I was spending a whole lot of time either kneeling on the icy ground or with my body entwined around the wedge like the gull-derned India rubber man at the fair. My contortions became especially painful when I wanted to view far northern targets. The next morning? I was flat stove up.

My solution, as I’ve recounted here before, was to buy a Celestron CG5 German equatorial mount (GEM), snatch the Ultima 8 OTA off her fork (which I’m storing in Chaos Manor South’s Massive Equipment Vault for old time’s sake), and keep on truckin'. What was ground-breaking for me, though, was not that the CG5 worked surprisingly well, but that it opened my eyes to a forkless kind of astronomy. Yes, I still use a fork mount Nexstar 11—it’s very comfortable to work with set up in alt-az mode—but even that’s being considered for an eventual forkectomy.

What makes the GEM alternative “better”?

—Easy to tote around. Even a C14 is approachable when you can break it into OTA, mount head, weights, and tripod. Those big fork-mount Meades (like that enormous RCX 14)? At my age they scare the living daylights out of me.

—Easy to balance. Proper balance is important for good tracking performance. If you’ve used a fork mount scope, you know that’s easier said than done. What do you do? Attach fussy little weights to fork arms? Fuss with a “3D” weight system on the tube that seems to have only one purpose: preventing you from balancing in declination? A GEM? Slide the RA counterweights up and down the shaft, move the tube fore or aft in the cradle, whoops! you’re done.

—Easy to use for imaging. Part of the GEM’s efficacy as an imaging platform is no doubt due to the balance factor above. Be that as it may, I find it’s easier to get good tracking—tracking good enough for imaging—out of fairly inexpensive GEMs than it is with some pretty impressive (otherwise) forks. I’ve spent quite a few evenings with Meade LX200 scopes that really had to be messed with in order to get ‘em autoguiding reliably.

—Easy to use on a variety of scopes. Want a bigger scope? Just buy a larger aperture OTA (within the payload limits of your particular GEM, of course). You can go smaller too. Point is, you don't have to buy another whole consarned scope every time you want more capability.

—Easy to keep untangled. I rarely have to worry about cord wrap with a GEM. It just doesn’t seem to happen. A fork, especially one set up in alt-az? I’m always tangling and pinching the dew heater cables.

—Easy to polar align. Maybe it’s just me, but I have always found futzing around with fork mount polar alignment to be a pain. I much prefer a good polar bore scope on a GEM. And quite a few GEM makers have developed software-driven polar alignment routines that make alignment good enough for casual imaging a snap.
—Easy to repair/replace when broken down/obsolete. When I was a fork fan, I worried a lot about how I was gonna get Celestron (or Meade) to fix my scope when the drive electronics fried. Now, I don’t worry about it. I’ll just get me a more-better-gooder GEM and keep on keeping on. Also, many GEMs can be fitted with replacement drives/electronics, often from third party manufacturers without a hassle. Imagine the reaction if I asked Celestron to fix my 1994 Ultima 8 electronics (to be fair, they never quit working).

Now, don’t get me wrong, True Believers, sure, my heart goes pitty-pat when I see a fine C14 Orange Tube, and pittypats even more in the presence of a Blue and White C10 or C16, but for me, the fork, I’m afraid, is yesterday. Now I spend my nights dreaming of obscenely huge Losmandy Titans, monstrous AP1200s, and humongous Mountain Instruments GEMs. I mean, what more can you ask for? More adaptability (which is what we SCT users are always talkin’ about as a hallmark of our favorite scope design) coupled with the ability to spend more dollars on more toys. Don’t get much better than that, does it?

Comments:
Gawd I Wish I had Da Money!Until then,well I'll be forked dead in da -ss!!!!
 
Gawd! I wish I had da Monies!Until then ,I'll be forked,ded in da -ss!!!
 
Sorry for the repeat!
 
Dr. Brian Long brought one of Columbia State Community College's 12" Meade alt-az goto telescopes to a star party a few weeks ago. The OTA plus fork part is over 100 pounds. Grunt! That is well above my lifting capacity. I've got my C8 on a GEM and love it. That is Columbia State Community College in Columbia, Tennessee, BTW.
 
I really love your writings Uncle Rod!!! Always cool to read texts from you. Still laughting about "forkectomy"!!!!
100% Aggree with you for the GEM: I have a Vixen GP with my C8 and it's fine!!! I just put the mount/tripod on the right shoulder, the OTA bag in the left hand, the accessories back-pack on my back and I'm ready to walk 200m to the darkside of my building "public" garden! With a forksystem I would have to do 2 trips and let some expensive stuff outside.....

Clear skies from Paris!!!
 
Hey Uncle Rod, you convinced me to get a GEM mounted SCT in the future. I now realised that with a GEM, the whole assembly has a higher portability comparing to the fork mounted assembly. Do you find polar alignment time taking?
 
No, I really don't. Not with the Celestron GEMs, anyway. Aim the mount roughly at Polaris, do a normal go-to alignment, hit "polar align" in "utilities" menu, and the scope slews to where it thinks Polaris should be given a good polar alignment. You then use the mount altitude and azimuth controls to center Polaris in the eyepiece. The resulting alignment is good enough for all the CCD imaging I want to do (at short focal lengths, anyway).

Only drawback? Once you complete the polar align procedure, you do have to re-do your go-to alignment (you've moved the mount), but that's not a huge pain...

Unk Rod
 
I love my GEM (MI-250), but I will more likely always keep my first scope that I purchased after 30 years away from the hobby. My Celestron N8GPS sets up in 5 minutes for alt-az viewing. This is THE scope that I drag out for public star parties. It always puts the eyepiece in accessible locations. A kitchen stool accomodates children or adults. It will always have sentimental value for being the first scope I used to get hooked on my passion, astrophotography.
 
Hi Unk,

I have a quesiton or two that may be helpful for me and others.

How about side by side vs. piggyback mounting of an SCT and Small refractor? Which do you prefer and why? What are the pros and cons of both approaches?

Thanks,

Timm
 
What's the setup time compared to a "modern" fork mount like the Celestron CPC series for visual?

The dollars involved in *really* getting into photography are frightening. :)
 
Good post.
 
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