First Light on the First Night: A Custom Eyepiece, and More About the FlexTube 250P

Though the weather forecast was not very hopeful, I stayed up late so I could peek through sucker-holes in the clouds, intent on feeding my new ten inch telescope some astronomical photons.

I was surprised to find that it wasn't too difficult to just lift the whole telescope up and take it outside all at once. What the telescope gains in weight it makes up for with having easy to use handles. I wouldn't carry it up or down stairs or anything, but it will go sideways just fine. Maybe I gained a bit of muscle mass by carrying the DT6 in and out all at once the past month.

 

The seeing was really bad, the cloud cover was really bad, and the conditions did not provide an opportunity to really test the performance of this telescope, but the one thing I did notice was that it was bright as hell. I've seen the nearly full Moon at the same magnification, and at the same surface brightness, but combining the two concepts together puts a bright disk of energy shining into my eye.

Mars was never better than a blurry orange ball, and though I think seeing conditions were the main cause of this, I also think the scope was not collimated well when I got it outside. (I had collimated it already, but when I first collimated it for practice I hadn't been sure to push the struts up to fully extend it)

I saw a peek of Orion, and knew I had to turn the scope on the Great Nebula (M42). Though the transparency and moon prevented me from appreciating anything other than the brightest part of the nebula, I was struck by just... how much brighter the stars in the field seemed to be.

It's tough to describe just how different the experience of using this scope, even in poor conditions, is compared to using the 6" (either 6" f/5 or 6" f/8) and smaller apertures.

I also had the opportunity to finally try my custom-made eyepiece. A few weeks ago I was wondering what kind of 2" eyepiece I would get to take advantage of the 2" focuser in the 250P. I was going to go for a svbony 35mm model which normally goes for $100 but I could find for $70 used. I wanted something that would provide an appreciably wider field of view than what you can get in the 6" f/8 dob with a 1.25" focuser. As a lark I e-mailed Gary Russel of Russel Machine & Optics, asking what kind of custom options there were. Expecting to have to pay one or two hundred dollars for such a thing, I was mostly doing it out of curiosity. Then he made an offer to build me an eyepiece for $55 (including shipping & handling). The eyepiece in question is a stock Meade 32mm Plossl, which has been given a newly machined barrel and the field stop has been opened up as far as it'll go. In an f/5 newtonian I never expected it to perform well, just well enough to be used for wide field scanning and finding objects, and Russel did warn not to expect good performance at the edges from essentially a stock Plossl optics. But his option seemed like the best deal, and I didn't have a lot of money, so I bought it, and I actually got it maybe a week later, long before I got the dob.

 

I only tried it out on the Moon, and it worked fine on-axis. Seeing did not permit a proper test, but I did in fact notice how much more claustrophobic the 32mm 1.25" plossl seemed afterwards.

The 10mm Plossl performs fine, no false color or anything, but good lord the eye relief might as well be 0.

I found that, especially at high power, the telescope's motions were pretty awful. But it can be fixed. The azimuth axis was too tight, so today I took the mount off and loosened the azimuth axis. Would really be nice if it could have been designed with a tension adjustment knob, because using two wrenches at the same time, lifting the whole thing up on its side, is a bit of a pain. I'm happy with the az motion now. The altitude motion is still meh. The tension knobs help alleviate this somewhat, but the scope is definitely front-heavy, so I will need to get some kind of counterweight.

I love love love the 8x50 finderscope. It's actually technically NOT a RACI, the diagonal seems to be an ordinary mirror diagonal, so it gives a mirrored image. But it's so much more usable than the straight-thru unit, and I can even use it while standing up. Though I AM in fact missing having some sort of straight-thru finder (a red dot for example) for the initial aiming. That was a problem I'd often have at the observatory with the 8" FlexTubes--just getting in the right ballpark initially wasn't super easy, whereas despite the ergonomic disaster of straight-thru finding, it does allow you to point your telescope to a specific spot on the sky at a glance. I really might get a Telrad.

It looks like it's supposed to be clear skies tonight, though the transparency will be mediocre, the Moon will be bright, and the seeing will be awful, so I still won't get a very good idea of what the telescope can really do. When I have something more useful to report regarding the actual optical quality and capability of the scope, I will.

I think I might take both the DT6 and the 250P out tonight to compare them side by side. (Otherwise I risk being disappointed on the 250P's performance on DSOs in the slightly opaque moonlit skies)