High power eyepiece for 10" Dob

I am looking for a bit more magnification out of my 10" f4.9 GSO dob. At present, I have a 9mm plossl from TS in Germany (140x) which is ok, but I think higher power would be useful - splitting doubles is becoming addictable, and I presume the planets can take a bit more than this. I have a 2x barlow, but the barlowed 9mm plossl has been unusable in the 2 months since I have had the scope.

So how much magnification can I use regularly (emphasis on regularly, not 3 nights a year)? 6mm gives me 210x, 7mm gives me 180x. Is it worth getting anything shorter?

Considering getting a Planetary HR from Germany, seem to get great reviews. Also the hyperions, but they are a bit more expensive.

Opinions welcome!

Thanks,
Tom

Hello Tom,

You could try a 7mm or a 5mm, make sure they are good quality. It is worth paying more a good eyepiece, even if you change telescope you still have them.

I am surprised 4.5mm was always "Unusable" (about 277x). Is you scope collimated? Can the seeing be that bad for you in the last few months.

John

The problem I've found with high power eyepieces is that they generally don't get as much use as medium to low power EPs, because the dob is not equatorially mounted when the magnification gets very high the image quickly passes through the field of view and the scope needs a little nudge to keep it centered, nudge it too far and it's gone. Not many deep-sky objects require magnifications of 300X, not even doubles or the planets.

As for the Hyperions, I can testify that they are excellent EPs and well worth the investment.

Tom --

I should think you'd find 210x (6mm) usable on most all nights.

That being said, I'm also surprised that you haven't been able to make use of 277x at all. I would have guessed that at least 1/4 of the nights would have supported that.

What is your observing locale like? Do you view out over roof-tops or a parking lot? Heat from the day rising off of man-made surfaces can disturb local seeing. Scope cool-down might also be an issue....

-- Jeff.

Using the barlowed 9mm (277x), I can't get a nicely focused star, just get a squirling blob. Tried it on the moon last night, it looked like I was looking at pebbles on the bottom of a stream. I assumed that this was down to too much magnification for the conditions.

I'll be the first to admit that I could be wrong about this, pretty new to astronomy. My collimating skills are getting better, I use a Cheshire sight tube combination thing, but I don't think collimation is too far out. I managed to get glimpses of Trapezium F component last night, which I have never seen before.

I am lucky in that I am viewing over nice dark grass fields. Scope is usually pretty well cooled down, it lives in a lean-to on the side of the house.

I will try a bit harder with the barlow next time I am out observing.

Tom

Tom --

Yeah, to some extent I think it depends on what you're looking at. At higher powers bright stars are always going to be a bit squirrelish (at least under Irish skies). But if you're looking at small galaxies, or in particular planetary nebulae, you can use a lot more magnification without seeing any blobiness. Saturn and to a lesser extent Jupiter also take magnification well. For some reason Mars tends not to.

If your squirreley blobs are reasonably circular and uniform, then your collimation is probably fine. If they flare out more to one side or the other, then your collimation could use touching up.

Cheers,
-- Jeff.