barlow vs straight focal length

[gooseholla]

So, some people dislike barlows. I find them quite useful - 1.5 and 2x has come in useful many times.

However, when it comes to it, I have an 8mm TMB designed eyepiece. Is it better to use this on the planets barlowed to a 4mm and 5.3 mm, or would a straight 4 and 5mm give better, crisper views?

Still thinking through different options for my high powered needs!! Zooms, barlows, new eyepiece range below 8mm... so many options!!!

[Dipper]

Barlow adds additional layer(s) of glass. Some light is absorbed by glass, some scattered and some reaches the eye. From that point of view barlow isn't a bonus but I'm not sure on what scale.

[gooseholla]

I think, and this is just my experience, that with a 25 or 20mm, or even a 15mm, a barlow has worked quite well for me. I'm not convinced, however, when it comes to finer detail (which mid powers don't exactly need when looking at star clusters, or a less detailed view of a planet), that a barlow will be the best economy, and spending £100, or £150 on some good eyepieces or zoom will be better.

But maybe it is just the cheapskate in me hoping that my wallet can remain padlocked and a barlow will suffice!!

[Naemeth]

A barlow can fill in the gaps of a collection that isn't yet complete. For example: You have a set of eyepieces that compromises a 2x Barlow, a 25mm, a 18mm and a 8mm/10mm. Which gives you another 3 focal lengths, 12.5mm, 9mm and 4mm/5mm.

If however, you already have a 25mm, a 18mm, a 12mm, a 9mm and a 4mm/5mm, you have no need for the barlow for visual use.

At best a Barlow only adds eye relief and changes eye placement slightly, and at worst can degrade the image because of the extra glass. A Powermate adds no eye relief, but is a high price for many to pay, compared to the cost of individual eyepieces (of course, if you are Powermating a Nagler or Ethos, a Powermate is cheap!).

This is all for visual, but for imaging, where I believe you have a fixed focal length for planetary work, you have to use Barlows/Powermates to increase magnification.

[E621Keith]

It depends on how much you want to spend.

The sky in UK is usually seeing limited, so a high power eyepiece may not get much use, so a barlow can be a better investment. However, barlow adds additional glass in the optical path which will degrade image quality. The amount it degrades depend on the individual barlow, and usually the more you spend the better it performs.

[alan potts]

I have a powermate which is like an up market barlow. Having said that I do not use it that often. Maybe it will get used now I have a couple of Ethos eyepieces.

Alan.

[John]

I've used some good barlows, a telextender and a powermate in the past and had satisfying performance with them. Of these I felt the Powermate was the only such device that I truly felt added absolutely nothing other than the magnification. As Alan says they are expensive though, unless you are using one to expand your range with otherwise very expensive eyepieces.

[gooseholla]

So an average barlow for the average viewer would be fine. For the more discerning, an expensive barlow for expensive eyepieces. For me, probably get a couple of eyepieces, then if I want absolute best quality for visual work / recording results via sketching?

[Stu]

Unless you are going to get a powermate, I would probably go for one or two dedicated high power ep's to get the sharpest results.

Stu

[Moonshane]

I have always preferred more eyepieces than a barlow. one reason perhaps peculiar to me, is the extension of the eyepiece out of the focuser with a barlow gets ridiculous sometimes. e.g. (silly example but illustrates my point) 26mm Nagler with 2" barlow vs 12.5mm BGO. I have cracked my face more than once in the past using barlows/powermates.

[Damo636]

Al Nagler had this to say regarding the use of barlows...

Quote..

Concept: I originally designed the Tele Vue Barlow line to complement the high performance of our eyepieces. Only 2 elements of high index glass were required to reduce all aberrations to well below the airy disc in an f/4 system. It has taken a good 15 years, but I think we're finally laying to rest the popular myth of the "degrading Barlow." In a 1997 Sky & Telescope review, Terrence Dickenson wrote "...Technology has erased the old objections. A modern Barlow will not degrade your telescope's optics. Anyone telling you otherwise is using outdated information. Moreover, the highly regarded Nagler eyepieces and their clones have built-in Barlows - ample evidence that the lens is not some detrimental intruder." Thanks Terry, I couldn't agree more. — Al Nagler

If its good enough for Al, its good enough for me :-)

[Stu]

True enough, but you're talking about Televue barlows. There are many barlows out there of lesser quality, and some very cheap/bad ones which really do degrade the image.

Stu

[michael.h.f.wilkinson]

My only objection to using Barlows is the hassle switching Barlows is more than just switching EPs. I have three "Barlows": two TeleXtenders, and one PowerMate. All three excellent pieces of kit, and really only used in planetary AP.

[Damo636]

True enough, but you're talking about Televue barlows. There are many barlows out there of lesser quality, and some very cheap/bad ones which really do degrade the image.

Stu

Agreed.

[Tinker1947]

My thoughts on a good use for a Cheap Barlow, take the lens out and use it a a 1.25 tube extension....never thought to use one, i will eventually get a full range of EP to my liking..

[Moonshane]

I have to say that only the very cheapest barlows are in my experience optically problematic. it's the hassle factor for me. I have a generic GSO barlow and it performs superbly well in my school astro club 200mm dob with a cheap 15mm Meade plossl. I think if looking to reduce kit e.g. for a travel scope then they make for a great addition to kit.

[crazyjedi]

I only have experience of one barlow and it came with my scope. Truth be told I hardly ever use it. I think (just from a personal perspective) I would rather have a range of EP's. One of my EP's (the Radian) is a 12mm EP with a built in barlow so barlows can't be all bad eh?