Meade telenegative barlow 2x ? more like 2.5x I think ?

[bobafett]

Bought a Meade telenegative 2x barlow from a fellow member on here - very pleased with it, nice peice of kit.

But I did notice that compared to a standard Achromatic 2x barlow that I own, the Meade unit is more like 2.5x (maybe even a touch more).

Just an observation really - very pleased with it and quite happy that it's a different magnification to my other barlow that I have since, now, rather than being a replacement in my set-up it's an addition

Need to get my neximage into this and get some shots of saturn I reckon

[great_bear]

compared to a standard Achromatic 2x barlow that I own, the Meade unit is more like 2.5x

Barlows are very sensitive to the exact placement of the focal plane within the eyepiece.

Since most eyepiece manufacturers are usually more interested in getting the overall design of their eyepiece right, rather than getting the focal plane in a totally standard position, Barlows of different physical lengths will have different results for the same eyepiece.

It's all surprisingly rough-and-ready considering how critical other aspects of optical design are.

[brianb]

It's all surprisingly rough-and-ready considering how critical other aspects of optical design are.

Indeed. Probably accounts for why some people hate them & others don't ... also the aberrations in a barlow can reinforce or partially act against those in your favourite eyepiece.