Which mount for a 150mmf/8 refractor
Posted 07 June 2009 - 12:50 PM
At this moment I am using a EQ6 Pro (pier mounted) as a mount for my telescopes. For small telescopes this mount is rock steady.
But a 150mm f/8 refractor (12kg without acc.) is a different story. The EQ6 is not 'overloaded' but at its maximum due too the long tube.
Which mount (reasonably priced) would be needed to make this big refractor also rock steady ? Would a G11 be enough ?
Thanks for your advice.
Posted 07 June 2009 - 01:24 PM
But to answer your question I have an 152mm AR6 f/8 which I use on both a LXD650 (believe its comparable to your EQ6) and a G11 and it does fine on either. However I do use a 14" saddle and dovetail which I suspect a similar setup would benefit you also.
Posted 07 June 2009 - 01:27 PM
I've been using G11 for 6" f/8 refactor, about 20Kg fully loaded. For visual use, it is stable enough to me. I am looking for relatively portable but beefier mount, Takahashi EM-400, 10 Micron Astro Technology GM2000 for now.
I need two 21 lb counter weight to balance the scope.
Posted 07 June 2009 - 06:05 PM
What scope is that? Apo or Achro? doublet or triplet?
Posted 07 June 2009 - 06:44 PM
I never thought I would see a setup that made the G-11 look so small.
To add my answer for the OP: I feel a pier mounted Atlas could do the job. The tripod is the weakest link in that system and you have already removed that problem. My old pier-mounted Atlas easily carried gear up to its rated capacity for visual work.
A G-11 is simply "more better"
Posted 07 June 2009 - 11:58 PM
Herbert, the scope is William Optics FLT152 f/8 TMB/LZOS triplet.
Originally, I was planning to get Losmandy Titan for the scope. Someone asked mount for TEC160ED on CN. A few people mentioned that G11 is OK for visual use. So I canceled Titan and got G11 instead
Posted 08 June 2009 - 08:13 AM
Even my 6" f/8 AP seems a bit undermounted on a CGE. I use the C14 on the CGE all the time and feel that it is pretty good, but I use it with the legs all the way down.
When I put the 6" f/8 on it, I feel like the mount is not hearly as rigid with the big refractor. I think the problem is with the tripod.
For this reason and this reason alone I would perhaps recommend the Losmandy. I think that the tripod is perhaps a bit stiffer when used at higher mounting positions as required with a big refractor for compfortbale viewing at zeneith.
If you can find one, the old Meade LXD 750s are PERFECT for a big 6" f/8 refractor. Of all the mounts I have used for big refractors, it is without question the most stable (though I only use it visually).
Posted 08 June 2009 - 12:18 PM
The Vixen style dovetails can flex a lot between the tube rings. This is often the weakest link with bigger OTAs on the EQ6.
Posted 08 June 2009 - 02:33 PM
If I lowered the legs down about 1/2 way, it was MUCH better, but then I couldn't get to the eyepiece. If it was the dovetail, I would have thought that lowering the tripod would not make a difference.
Even my CGE is not all that rigid when used with a 6" refractor. It is just hard to get the mount stiff. Focusing will induce long oscillations.
The LXD 750 is the best mount I have used with a big refractor that was affordable, though the OP may not have one in his market.
Behind that, I think the Losmandy tripod is a bit stiffer than the CGE, so that would be my second choice for a big refractor.
Then the CGE.
Only as a last resort would I put a 6" f/8 on an Atlas.
But that is me. I am now used to being able to keep the tripod high enough to sit in a lowered observer's chair and focus at high powers while the telescope holds quite still. I could never get both with the Atlas.
So, to be fair, somewhat depends on how stiff you like your mount. If one can tolerate some wiggling then an Atlas might do fine. In the end was too much wiggle for me though.
Posted 08 June 2009 - 04:43 PM
That older AP scope is extremely light for a 6 inch refractor, the WO/LZOS scope could be a good 10 pounds heavier.
Posted 09 June 2009 - 08:35 AM
Recentlly finished off the "Re-model" with a new Feathertouch 3035B.
And yes, the scope is fairly light for a 6", but it all adds up. With rings, dovetail, Telrad, Feathertouch, diagonal, and 31mm Nagler, it all tips the scales at exactly 30 lbs.
And to the OPs question, because the weigth is all out there at the ends, if you start it shaking, dampening can be a bit longer than I like even on the CGE.
I think it is the CGE tripod. When I raise it, it shakes. I can use the C14 and it is pretty solid, but when I use the C14 on the mount, I use it with the legs fully retracted.
The Losmandy tripod is stiffer. I prefer the CGE folding legs for convenience (and it works well enough for the C14), but I realized that for the 6", it was not as stable as I would have liked. When I started looking for a mount, I actually was looking for a Losmandy G11, but the LXD 750 presented itself and I jumped on it. As it turns out, I get why Meade made this mount. It is perfect for the telescopes they put on it (Meade 152ED and Meade 178ED, which I think would have been pushing it for this mount).
So, TRIPOD STIFFNESS is the critical area here.
Another option would be to go to an older Astro-Physics cable-stayed pier. These things as it turns out were pretty stiff. Roland Cristen didn't make "Pretty" equipment back then, but he still made GREAT equipment.
So, my advice is because big refractors tend to be used a lot at high powers (though I use Buffy more as a "Rich Field" telescope), investing in a really ridig tripod becomes more important for really satifying use.
Posted 09 June 2009 - 08:46 AM
Posted 09 June 2009 - 09:53 AM
Great job! Never should have sold mine, best $1400 I ever spent, but it's in Australia now.
Posted 09 June 2009 - 11:01 AM
So in the end, spending another $1000 on powder coating and a new focuser seemed worth it for a scope I plan on keeping the rest of my life.
I learned from your mistake!!!
Posted 09 June 2009 - 02:17 PM
Posted 09 June 2009 - 03:02 PM
If the scope is shorter than a 6" f/8 and you keep the load light (no 31mm Naglers), and you don't mind sitting on the ground or with your observer chair fully lowered, and don't mind a bit of wiggling, or only use the scope at fairly low powers, you might get away with it.
This is because the Tripod is the weak link, and if you can use it with the legs lowered, and the scope is less than maybe 20 lbs all up, you mignt be OK.. The CG5 actually uses a tripod similar to the Atlas I think, so I could see putting a fast, light 6" refractor on it.
Again, depends on how tall you need it to be and how heavy it is overall.
As an example, I used a Vixen 140 NA on a CG5 and didn't even have the steel legs (though I had the very stiff and super-light Vixen HAL 110s on it). The Vixen 140 weighed a bit over 20 lbs. all up with rings, diagonal, Telrad, and 35mm Panoptic. Now this was not the most stable platform, but I used the Vixen 140 for its amazingly sharp wide field capabilities, and because of that, I could tolerate a bit of shake. Worked quite well for me actually. I would think that on a modern CG5 with heavy steel legs it would be a bit better. That being said, I never used this telescope over 160x, and even at that power, it was shaky.
So, a great deal depends on the scopes length and weight.
Posted 09 June 2009 - 05:58 PM
Any chance a CG-5 GT can do the job with any 6" refractor like a faster/shortest tube one? (contemplated next project). Thanks.
I have a 152mm AstroZap mounted on a CG5 for visual use. The scope along with 2" diagonal and 1# ep weighs about 25#.
I wanted to keep the legs retracted for stability and less tripping hazard in the dark, so I built an extension from 4" pvc. I had to use turnbuckles and cable to stiffen it up. Dampening time is less than 3 seconds at 200x
Posted 09 June 2009 - 09:00 PM
Posted 10 June 2009 - 12:24 AM
Eddgie, I guess I can live with some wiggles. The reason I asked is that I already have a CG-5 GT and want to utilize it fully with a C8, a 102ED and a 6" short refractor. I better start saving up for the 6.
Don, great setup you have there, nice touch on the extension tube (so I don't have to sit on the ground as Eddgie says), will follow that lead, maybe have a heavy one fabricated to help dampen the shakes. 3 seconds at 200x is very acceptable I think.
Tom, no doubts about the G-11, thanks all.
Posted 10 June 2009 - 12:28 AM
Posted 10 June 2009 - 06:52 AM
I have always been pleasantly surprised at how well the channel tripod works on my GM-8. It's much more stable than I thought it would be and carried my TMB130 with similar results.
Posted 10 June 2009 - 12:51 PM
I found that a simple weight counterpoise to the finder balanced the OTA wonderfully in all DEC orientations, which helps reduce vibration. The weight also biased the OTA forward a bit, making meridian viewing much more comfortable. Adding the "pizza pie plate" accessory holder stiffened the tripod up further. Using vibration pads on hard surfaces was icing on the vibration cake.
This combo was very satisfying to use visually and I miss it.