Telescope Reviews: How not to build a pier footer!

We had just amazingly good weather here in Oklahoma on Saturday. Clear sky all day, very little wind - comfortable temperatures. We also had some company coming over, so it seemed like it would be a good night to show off my observatory.

The first thing we looked at was the moon. While we were looking, I asked my brother-in-law to just walk around the room some. Sure enough - you could see the image tremble slightly. Not a good sign, but I'd planned on installing some flooring to dampen the effects of people walking around.

Well, it turns out that it is a good night after all, decent seeing (although not perfect), and I show off lots of deepsky objects to my guests. But Mars and saturn just do NOT look very good.

So I wait until much later, until Saturn is near the zenith, and try again - using a 7mm eyepiece on my 12" LX200. (~400x) Sure enough, saturn still looks BAD. It's like I can't focus the scope - it just always seems slightly "fuzzy".

At that point I notice the little space heater sitting on the floor in the dome. (My niece turned it on earlier.) This thing doesn't produce much heat, but the fan in it is kind of noisy. So I think "no way", but I turn it off anyway. 20 seconds or so later, saturn is looking pretty good. I turn it back on, and sure enough, within 30 seconds saturn goes all soft again.

I try this several more times, and with the heater on, the image is pretty soft. With the heater off, the image solidifies - but it's still not perfect. So I turn off the PC in the dome - it has a couple of small fans, afterall. And hey, without the heater or the PC running, Saturn is looking pretty crisp. So I next try rotating the dome a bit while looking. Sure enough, I can see that too.

So I think it's pretty likely that vibration is being trasferred (quite efficiently really) between the floor of the dome and the pier.

Here's a couple of pictures of the pier footer:

Now you'll notice a couple of things that I did wrong:
1. I could NOT get the guy who poured the concrete to isolate the pier footer from the foundation. He argued that it would be less stable, and anyway, he wasn't prepared to do it, and he was the only person I could find who'd even take the job out in my area. So it's one monolithic slab.

2. When he installed the conduit, he didn't run it where I asked him, so the conduit is partially in the pier footer.

Anyway, I'd hoped that with 6 yards^3 of concrete, there would be sufficient mass to dampen vibrations. But apparently that's not the case, the concrete in the foundation appears to transmit vibration extremely efficiently into my telescope. This isn't really visible at low to moderate power, but at 400x it's sledgehammer obvious.

I could cut the foundation I suppose - but you'll note that because of where the conduit is set there is absolutely no way to cut the concrete without severing the conduit. I'm sort of hesitant to do this becuase the 6" thick portion of the foundation (the thinnest part) will take fairly heavy equipment to cut, and it will be just incredibly messy.

So what I'm going to try instead is one of the vibration isolation platforms from Pier-tech. (Hopefully it will arrive around the same time as my new scope and mount.) I'm also going to try adding some rubber bushings around the j-bolts that connect the pier to the slab.

But whatever ends up finally being the solution (I'm pretty optimistic about the device from pier-tech), I wanted people to know that the common wisdom about isolating your pier seems to be absolutely correct. I have a pretty respectable mass of concrete on the ground - this seems to make no real difference. (Well, maybe it makes some, but the system doesn't end up being useable at high powers anyway.)

By the way, if people have suggestions for other things to try, feel free to post them. I'm also likely to put some flooring down on the concrete slab to help dampen vibration from anything inside the dome. (Unfortunately, that won't help with vibration induced by motion from the dome itself.)

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