Burgess Optical / TMB Planetary Eyepiece

[jaspa]

Are these any good for use with an 8'' DOB ?

Also what size eyepiece to start with.

Thanks

Mark

[Andrew*]

Mark,

what's the focal length? If it's 1200mm, then a 6mm is as high powered that I would go for. If it's 800mm, you could get a 4mm one. I presume you are wanting a high-powered eyepiece for observing planets? The lengths I've mentioned will give you a reasonable compromise of getting a high power, but still being able to track the object with the dob.

And yes, I believe the TMB's are a superb choice.

HTH

Andrew

[iancandler]

I've just got two to use with my ZS66 .. theyre cracking eyepieces and not so little.

The quality of build on them is really good, far in excess of the price.

I read a lot of reviews and comparisons before going for them and feel sure I made the right choice.

My scopes have focal lengths off 1250mm and 389mm, working on a max of 200-250X magnification I decided to play safe and not push it to far so went for a 14mm radian plus 9mm and 6mm BO/TMB

PS you may have problems finding a 6mm as burgess havent released any of the new batch yet but.. a funny thing happened with these.

Apparently the firm that was making them for burgess pulled out or was binned by burgess and had produced the same eyepieces for teleskope services who are currently selling them via ebay for £50.30 a piece.

Ordinarily I wouldnt advocate this route but due to the fact that you just cant get a 6mm original burgess for love nor money, its worth bearing in mind.

[beamish]

My 8" is 1200mm and I still get use out of the 4mm ! Though in fairness a 5 or 6mm would be ideal. Ade Ashford reckons my scope could cope with a 3.2 if the skies are dark enough and the seeing good. I'm just waiting for the new batch (includes the 5 & 6mm) to come in some time after xmas.

[blinky]

3.2mm thats X375 My 8" is 1000mm and the most I use is a 5mm Ortho in it.

[beamish]

I know ! but only when conditions are right, hence my reluctance to buy one , but the 4mm does get used .

[mhc]

I thought that the "rule of thumb" for max usable magnification was aperture (inches) x 50, do an 8" would have a max usable magnification of x400.

Have I missed something? :?

[James]

Thats more of a theoretical figure. Whilst the scopes optics may be perfectly capable of delivering a magnification of 400x the reality is that seeing is usually the limiting factor and usually restricts the higest magnification you can get, and still have a good view, to around 250 - 300x at the most. I've only once had conditions good enough to get 400x out of my scope, most the time its 240x tops. Any more than that usually leaves me with a mushy poor quality image.

James

[Andrew*]

I got 333x out of my scope on the moon (stunning) the other day and the seeing was actually just good enough to accommodate that; however, I wouldn't buy a £50 eyepiece specifically for the very rare occasions when this kind of mag is useable.

This rule of thumb also doesn't apply to every scope. For example, the theoretical limit for the ED80 is (2x80=) 160x, but I've used it at 200x no probs.

Cheers

Andrew

[beamish]

No mhc, I don't think you've missed anything, the 50x rule of thumb is just that a "rule of thumb". Bare in mind theoretical max depends on conditions. When conditions are perfect(rare) then you ought to be able to use max' magnification available.

[beamish]

Beaten to it !

[mhc]

Thanks folks. So I should stick to my 9mm Burgess/TMB as my shortest fl ep with Barlows (Vixen DX (x2?) and Tele Vue x3) for my C8N?

Actually, no you haven't. It's just going to be diverted to the next item on the wish list. 8)

[jaspa]

Thanks for all the replies, reckon i may have to order one.

Mark

[Whippy]

Thanks folks. So I should stick to my 9mm Burgess/TMB as my shortest fl ep with Barlows (Vixen DX (x2?) and Tele Vue x3) for my C8N?

Actually, no you haven't. It's just going to be diverted to the next item on the wish list. 8)

Could do, but I've found the shorter the length of the EP, the more useless a Barlow is. I've found that anything under about 10mm Barlowed, the image gets darkened almost to the point of uselessnes image-wise. Just my 2p's worth...

Tony..

[Sam]

I've got a 6mm with my 8" and find it quite useful when looking at splitting double stars - and for trying to find some surface detail on Mars. I even use it sometimes with my 2 X barlow and it still can be quite useful, though I'm not expected great results at 400X.