optical diffenerence with barlow

[Sheap]

Is there at all a difference with what you see through say, a 6mm eyepiece with a 2X barlow, and a 3mm eyepiece? Im starting to think of investing more into astronomy.
Is this barlow a good quality one?
http://www.myastroshop.com/products/details.asp?id=MAS-129
It seems cheaper than a couple of the others have there, why would it cost so much less?

[ving]

well, there are fans of barlows and there of the others... i am with the others. however that said barlowing a 6mm will give you more likeley than not more eyerelief than a 3mm. more glass to look thru too so it may degrade the image, or not depending i guess on the quality of the balrow and eyepieces in question.

anyhow, somone hwo likes barlows for visual work will come along and tell you the positives :)

i use my barlow/s for imaging

[janoskiss]

I don't expect that Optex barlow to be very good at all. A cheap barlow will disappoint. A good eyepiece in a good barlow will not. E.g., a UO HD ortho in Televue barlow is hard to beat or even match for optical performance unless you sacrifice comfort (e.g., get an ortho with painfully short eye relief), or spend top dollar on a premium EP like a Pentax XW.

Orion Deluxe barlows are also worth considering. I have an unbranded version of the 2" model and it's excellent (same as UO 2" 2x barlow). The 1.25" under $100 would be a steal if it's as good as its bigger brother - with FMC vs MC lenses there's no reason why it shouldn't be.

BTW. You will not have much use for a 3mm EP in an 8" Dob, if that's what it's for. In good seeing 5mm is near ideal for that scope. 4mm will get used very rarely in exceptional seeing. 3mm virtually never, except for star testing and maybe if you're into splitting very close doubles which may require close inspection of overlapping Airy disks.

[rmcpb]

A good barlow is worth its weight in gold for "stacking" on those really exceptional nights. I often use them on the moon where there is plenty of light to go for the power. With my 8" I run out of light over 320x using a barlow on Jupiter and prefer to use unbarlowed lenses here but the tighter eye relief becomes a bit of a problem with these short lenses.

I would say that a good barlow has a place in each observing kit but should be used with care.

Some good ones are:

Orion Shorty Plus
Celestro Ultima
Meade #140


Don't go for the cheapies, they will surely disappoint.

[janoskiss]

The Meade #140 have a reputation for poor QC, which my own experience with several units confirmed. Even if you get a good one, they are not in the same league as the Televue barlow which does not cost a lot more. Superior barrel blackening and lens coatings of the TV barlow make a lot of difference.

[Sheap]

frontier optics have a University optics 2.2X Klee barlow (the site only mentions a 2.8, but when i e-mailed them they also mentioned a 2.2). On claims for the 2.8X "simply put, there is no equal." Anyone know how this stacks up against others?

[janoskiss]

It may be a very good barlow, but that claim you read on the website is of course just marketing hype from UO that you should ignore. (Televue and Meade make similar statements about their products on their websites.) From what I've read, the 2.8x klee has less clear aperture than many other 1.25" barlows, which means that it will vignette more easily (with long f.l. / large afov eps). But that won't affect its performance at high powers.

I haven't used one myself so I cannot comment on how good it is.