planetary eyepiece dilemma.

[great_bear]

You may find 8mm is pushing an F13 scope a little too far - it's certainly pushing past the edge of maximum resolution.

[Donkeiller]

I'd also give a look at the Celestron Xcel-Lx 9 and 7mm.

I sold my BST 8mm in their favour.

Not that their was any obvious optical difference, the Xcels are just that bit better made IMO.

[johnnyp]

@great bear. Could you give me idea of what would be suitable?

[ghostdance]

You may find 8mm is pushing an F13 scope a little too far - it's certainly pushing past the edge of maximum resolution.

*Completely* off topic but....Hi neighbour!

I'm just over the Lea Bridge Road

[great_bear]

You may be one of the few that have a genuine TMB eyepiece as design intended, there were a lot of very poor ones hit the market after the design was first launched, many QA prolems, some by all accounts are cheap clones marketed after the sad death of the designer T M Back.

Alan

That's not quite right.

There are no "cheap clones" - this style of eyepieces all come from the original manufacturer.

The dispute was over who had the right to sell, and under what branding. Since none of us are party to what was agreed in the contract in terms of minimum order size, penalties, redress, etc. etc., it's not our place to judge in absence of facts, but what we do know, is that additional focal lengths were added independently by the manufacturer.

For the "inbetween" new lengths at the shorter end of the scale, these are likely to be fine (as these are neg-pos designs, 0.5mm - 1.0mm difference can probably be subtracted simply by lengthening the barrel, with no lens modifications and no adverse optical effects). Scaling the design above 9mm however is a little dubious...

EdZ on cloudynights asserted that in resolution tests, the eyepieces scored very favourably. People's subjective experiences of these eyepieces however, vary considerably. 

[great_bear]

*Completely* off topic but....Hi neighbour!

I'm just over the Lea Bridge Road

Ah yes - where all my light pollution comes from 

[ghostdance]

Ah yes - where all my light pollution comes from 

Nah, we borrow it from Stratford.... Then chuck it your way

[great_bear]

@great bear. Could you give me idea of what would be suitable?

Well, the nice thing about an F13 scope on a motorised mount is that any respectable simple-design eyepiece will give you top-class results on the planets.

For planetary use in such a scope I'd avoid TMBs / BSTs, and at F13 Meade 4000 Plossls will give results indistinguishable from Tele Vues at minimal cost. I'd take both the 9.7 and 12.4mm Series 4000 plossls over any one BST eyepiece for use in your scope (I've owned a Sky-Watcher 90mm before).

But preferences vary of course... :-)

[johnnyp]

Thanks great bear. I'll give the televue a whirl and see how I get on with it. I believe it will sell on pretty easily if its not suitable. And also keep in mind the 4000 series plossls.

[johnnyp]

Received the televue plossl today. Looks like a solid bit of kit. Can't wait to try it!