Barlows

[jason.p]

Does a Barlow have any significant detrimental effect on the optics, (I've noticed one or two people prefer not to use them), by introducing another piece of glass in the light gathering system.

Mine is x4 (with 15mm, 25mm and 42mm EPs). Would I be better off with a x2 Barlow and perhaps some different EPs?

[AndyH]

I must admit to being one who doesn't use a barlow. I just use 3 or 4 eyepieces for each scope. A rough example is a range of pieces to give 50x, 100x 150x and 200x.

I wasn't a huge fan of the 4x barlow that came with my 2M.

Andy.

[glowjet]

According to our more knowledgeable experts such as Al Nagler et al, a good quality Barlow has no effect on the optics of your eye piece, however, I have read that inferior types are only useful as door stops. I think some of this is covered in the Back Yard Astronomers Guide. Barlow's are useful to reflector owners who have fast scopes and of course the imaging brigade use them stacked especially the Powermates or super Barlow's which bring all the diverging field rays parallel to aid in photography. so what it boils down to in the end is, if you want a Barlow, then buy a good quality one, it will not hurt your eye piece optics, but it might your pocket

John.

[damnut]

Hi Jason.P,

A 4x barlow is a hefty multiple. The max theoretical power for your scope is 300x (2* apperture in mm). In reality you would not use much more than 200 - 250x on a clear night with clean optics and everything collimated perfectly!.

I think your scope is F5 (750mm focal length) so your current eps yield 50x,30x and 18X.

Tal make an excellent 2X Barlow, you may be better served filling in the gaps with say an 6mm ep and a 2x barlow that would give you :-

Primes of 125x, 50x,30x, 18x using the 2x Barlow would yield 250x, 100x 60x 36x.

There is a great guide to ep's in the sticky section by Warthog.

Clear Skies

[JamesF]

I think that's a fair summary. A barlow doesn't have to be expensive to be largely un-noticeable in use (the GSO/Relevation 2x and 2.5x models are less than £50 new), but low-quality ones are worse than none at all. In particular, the 2x barlow that ships with many Skywatcher scopes (or did -- I don't know if the current one is still the same) is a crime against optics. I was quite astonished at the difference when I replaced mine with a decent model.

James

[AndyH]

As often is the case with very old(early 90's) Tal scopes, it's not always a simple 'get some new eyepieces' etc, fix.

Jason - I posted in the other thread http://stargazerslounge.com/showthread.php?t=189823&page=2 some ways around your potential problem.

Andy.

ps: The 2M is a 6" F8 (FL1200)newt.