Posted 17 February 2009 - 11:50 AM
Posted 17 February 2009 - 12:07 PM
Seems like a lot of scope for the porta mount,IMHO.
Posted 17 February 2009 - 12:11 PM
Posted 17 February 2009 - 12:15 PM
Posted 17 February 2009 - 12:20 PM
Posted 17 February 2009 - 12:27 PM
Posted 17 February 2009 - 12:34 PM
But...you could probably pick up a Orion short tube 80mm scope off e bay for about $100.
Posted 17 February 2009 - 01:32 PM
Posted 17 February 2009 - 01:46 PM
Posted 17 February 2009 - 04:02 PM
I'm starting to seriously think about a different mount.
Posted 18 February 2009 - 04:37 PM
Posted 18 February 2009 - 04:46 PM
Posted 18 February 2009 - 05:32 PM
Posted 18 February 2009 - 08:16 PM
My scope came with the Porta, and at first I was appalled by it's vibrations after using my previous XT dob. I did lots of experiments on damping time. Near 200x, it took between 3 and 4 seconds to dampen. Focusing at high power is still difficult.
I still have my 100ED on the Porta. Why? because it's a light setup and it's easy to use, and the slo-mo controls are so nice. I've gotten used to the shakes; they don't bother me. Here's what I did to mitigate the vibrations:
1. I observe on pavement, so I need VSPs. However, I don't like the idea of picking them up every time I move my setup, so I cut open tennis balls and stuck them on the tips of my tripod. I dunno if they work as well as VSP, but they cut settle time by around 1s.
2. I ditched the stock accessory tray. I replaced it with an aluminum pie tin. I actually don't think this helps much, but actually bolting the accessory tray to the three arms of the spreader (a la Manny Miles) seems like a good idea.
3. I keep my scope light. I use a 1.25 diagonal and EPs. I do have a 9x50 finder, with is a big help in LP, so I keep it. Extra weight hanging off your scope just makes things worse.
Wooden legs: I have a Vixen SP tripod with wooden legs. I swapped them on once, and they surely improved the mount. Focusing was much better. I took them off because they were bulky and harder to set up. Starlighter has the HO legs, he like them a whole lot.
Other 'fixes' I've heard of:
Put weight in your accessory tray, or attach weight to the tripod hub and hang it through the acc. tray (extra weight, I pass).
Use some kind of tensioning device to spread out the tripod legs. I may tinker with this one. The idea is to insert a triangular piece of wood or metal between the legs and pull up on it, so it forces the legs outward against the spreader legs. This is supposed to stiffen the tripod significantly.
Bottom line: The porta is too light for the 100ED. If your mount weighs 3x your scope, then it will be steady. The Porta weighs almost the same as the 100ED OTA. Another way to go, cobble up some way to attach the porta mount to a heavy homemade tripod or pier (4x4). I bet that works.
Posted 18 February 2009 - 10:31 PM
Its strengths are the slo-mo controls which work very well. The tripod isn't bad, appropriate I would say.
Its weaknesses are the plastic knobs, easily swapped for set screw type, and something that some of us have been focused on - some jiggling. I've tried the wooden legs. I think they may help a bit. I've switched back to see. But the real culprit in mine is the play in the azimuth bearing. It can be tightened up, but only so much before the friction gets high for slewing.
Next I'm going to check the balance of my scope and keep the az friction fairly high and see how it does but this is with an 85mm f/7.
I think 100mm is pushing the capacity a bit.
Posted 19 February 2009 - 01:26 AM
Posted 19 February 2009 - 02:22 AM
Guess what? An unexpected improvement to my porta mount was my... focuser I increased the diameter of one of my focus knobs using sections of bike inner tube. It takes a lighter touch to focus, which results in a lot less shaking. The porta almost pleasant to use! At 150x it took around 3s to dampen from a hard tap at the diagonal. I had a great time setting up Saturn with the slow motion knobs and watching it drift through the FOV for a minute at a time.
Posted 20 February 2009 - 09:19 AM
The most leverage is placed on the Az bearing due to the length of the arm. Also the staked bearing post or stud in the Az bearing will sometimes develope some movement...
Wish I had never bought mine!
Posted 20 February 2009 - 09:31 AM
I'm wondering if a thin spacer ring would help the az bearing. It would just prevent the tipping that occurs. If it worked, it could make a big difference, I think.
Anyone more mechanically inclined out there care to comment?
Posted 24 February 2009 - 12:51 PM
Hey guys, so I have a Vixen portamount, I complained about its stability so I tried the Orion Altaz, lets just say I like the slow motion controls, sure the Orion was stable but was jerky and I kept over shooting while trying to track by hand...the portamount has beautiful slow motion controls that don't make me miss having a clock drive (more altaz mounts should have em!)...problem is it is jiggly! I think the aluminum legs suck, I was thinking about getting wooden legs from Handsonoptics....has anybody tried and do they make a difference, btw the scope is a C100ED...
I had a Porta mount and had the same problems with my Vixen ED100sf (the same size as your scope). By tightening all the bolts on the Porta, using fairly high friction on both bearings, and sinking the legs well into the dirt, I could get the settle time down to about 3-4 seconds. But there was so much jiggling when trying to focus that it was nearly impossible to focus the thing.
I thought about the wood legs from HandsOn Optics, but I knew that in the long run I would never be happy with this mount. So I sold it and bought a William Optic EZ Mount with the tripod. This completely solved the problem. Incredibly stable with a settle time of 1/2 second or less. Easy to focus. I do miss the slow motion controls but with the tube well balanced on the WO mount I can keep objects in view with a light touch on the tube or diagonal, even at high power. The head is very well made and fairly small (but heavy). The tripod is a bit crude but it works well. And you can add a second telescope (or binoculars or camera) to the mount by adding an extra dovetail base on the other side). For $500 I think it is the best in this class.
Posted 24 February 2009 - 01:54 PM
Not the right mount for a 100mm, IMHO.
Posted 24 February 2009 - 02:19 PM