DM-6 vs Stellarvue M7
Posted 03 May 2010 - 12:35 AM
Posted 03 May 2010 - 12:59 AM
I had constant vertical balance issues with the M7. I talked to SV several times, got some excellent advice, made several different adjustments in the tension mechanism, but from the standpoint of balance, the DM-6 was far superior. Balance your scope at the beginning and forget about it. The M7 is a different kind of mount than the DM-6 - the M7 relies on an external knob to control vertical tension and is much more sensitive to vertical balance than the DM-6.
At different times I had a TV102, a TMB130, a C9.25, an Antares 6 inch refractor, and an Antares F15 four inch refractor on it in various combinations. The horizontal axis was very smooth, as was the vertical, but scope balances had to constantly be adjusted. The vertical tension knob controlled it well when the balance was close, but if not, the tension needed to hold the scopes was usually so much that the vertical motion became stiff.
I liked the design and appearance of the mount, but after an evening of observing, I usually felt like I had been wrestling with it most of the night.
Having said that, I bought mine about a year and a half ago. I see the current version looks a bit different, so there may have been some performance improvements as well.
Posted 03 May 2010 - 05:12 PM
Thanks for the feedback on the M7. I know other than the Disc Mounts most Alt-Az mounts have the problem of shifting center of gravity and therefore balance point when the scopes move in altitude. Since the DM-6 won't hold two scopes I need to look for other alternatives. Would you say the M7 works similar to others that you've had experience with? It looks like the Max-load doesn't have encoders and I'm not sure ioptron would handle a substantial load.
Posted 03 May 2010 - 08:15 PM
I've never used the Max-load - would really love to, but haven't had the chance.
But in answer to your question, I would say yes, the M7 works similar to other mounts of that type. I had an older Giro that had the same problem with vertical tension. That one could get away from you quickly, and did several times.
I now have the new Giro III, which has much better vertical tension control. When I increase the vertical tension by tightening the knob, the vertical motion remains smooth. However, I've noticed that if the balance is too far off, even with the vertical tension tightened as far as it will go, the scopes will tend to move anyway - but it's a gradual movement, not a rapid swing, like the older Giro. The M7 did that a couple of times also (the rapid swing). In those cases, obviously you have to rebalance the scopes.
So, if you're looking for encoders, the M7 may be the best way to go. JMI does makes some encoders for the Giro III, but I haven't tried them, so I can't help there.
Universal Astronomics offers the Double-Star for handling two scopes, which I haven't used, but I've been told that vertical balance is not an issue for it. I don't know if it will accept encoders.
Between the two mounts - the M7 and the Giro III - I would have to say I prefer the Giro at this point, mainly because the vertical tension is better controlled, and because with the tension tightened, the vertical motion is smoother. I had a six inch Antares F6.5 and a Celestron 9.25 on it the other day and it handled the weight with no problem, and motion on both vertical and horizontal was smooth.
But as I've said, the new M7 may have some improvements to it now. And I've only used the one, so it's tough to generalize based on just one sample.
Since you're in Napa, you might consider calling Stellarvue and see if they have an M7 available that you can try out with a couple of scopes on it. Might be well worth the trip up there to find out.
Posted 03 May 2010 - 10:43 PM
I'll give Vic at Stellarvue a call tomorrow. I've been to see him several times. Last time I was there he didn't have an M7 in stock. I'll post a follow up if I find out anything exciting.