High power eyepiece for 10" Dob

Hi Tom,
I'd bet your scope hasn't cooled down adequately and thats why 270x is not giving you results, on a good night I use a 7mm eyepeice to give me 357x, its super on globular clusters and helps with the now difficult cassini division around saturn.

Like heebyjebby, and a complete novice - I have tried my 9mm with Barlow x2 on my 10" dob, I know Collimation needs to be tweaked, but comment about squirrelish star is a little reassuring for me. caus I am experiencing same problem - although moon views were sharp and awe inspiring - when I looked at trapezium It seemed slightly blurred

I put it down to experience on my part...and as I have mentioned before...my annoying habit of breathing on my eyepieces with the excitement of it all.

"Captain Slog Star Date 140208.90"

I did a little test with my barlow this evening. I have a 20mm plossl, so when barlowed it is 10mm (125X), not too far away from the 9mm (138x). The unbarlowed 9mm gave much sharper images than the barlowed 20mm on the trapezium, castor, saturn... I was looking at sigma Orionis and I could only barely make out the faintest 4th star with the barlowed 10mm, but it was very obvious with the 9mm. Barlowing results in squirling squidgy stars, whereas they are sharp points using unbarlowed eyepieces

Saying all that, I barlowed the 9mm and put it on the moon (with a filter). The view was better than last night, quite impressive, but it wasn't tack sharp at all. I spent a while making minute adjustments to focuser, but it never snapped in to a nice focus.

Maybe the barlow is low quality? Didn't cost a huge amount (€30), possibly a false economy.

Assuming a 250mm/1250mm GSO Dob (I've never seen a specification for a GSO with OD in inches) your scope should be good for up to 500x in perfect seeing but as pointed out above that kind of magnification is impractical for a Dob because things drift across the FOV too quickly. 5mm would give 250x, which is manageable if the weather suits.

I have a hoard of eyepieces that start at 2.5 mm and go all the way up to 40mm, but I only ever use the shortest infrequently in my Scopos 66 ED wide field.

Does sound a bit like your Barlow may be dodgy.

Where-abouts are you located? I've got a decent quality 2.8x (a UO Klee) that I'm not currently using that you could borrow to see what it's like.

Cheers,
-- Jeff.

Thanks for the kind offer of a loan of a decent barlow. I'm down the other end of the country in Kilkenny so probably not too practical!

Might try and hook up with the Waterford club sometime, it's a bit difficult knowing what's good and what's bad if you have no experience.