To Barlow or not to Barlow?

[phil125]

I've been pondering this for a while... if I already have 20mm and 15mm eyepieces, which route would be a better option for planetary viewing;

a) buy shorter f/l eyepieces at say 8mm & 5mm

buy a x3 barlow, or even a x2 and x3 barlow, and use with current eyepieces

Does anyone know if there are drawbacks of using a longer f/l eyepiece with a barlow compared with a shorter f/l eyepiece - other than putting more glass in the way? I think a barlow may even give you better eye-relief, so would be better?

Nb: in my case I am thinking Televue Plossl's and Barlow, in case it differs for more expensive kit. 

[Charic]

Can you provide your telescope details please. 

Also if you consider the Tele Vue Plossl, as good as they are brand wise, their eye relief is mighty short on their shortest focal length, the 8mm, I just can't get used to it. I have the 11mm and it feels the same.

So check this out! why does my 9mm £15 Revelation [GSO] Plossl feel better and more comfortable in use, and with an extra  2° affective field of view,  over the Tele Vue,  and the same eye relief too, last time I checked?

Tele Vue are good, very good, if they fit your needs?  I'll be frank, or charic! I'm OCD when it comes to an eyepiece set, I like to have the whole set, i.e. Starguiders, and my Plossl set will be based on either these cheap but extremely effective Revelations over my Meade 4000 Japan oculars, giving the Tele Vue Plossl's amiss! 

If your not fussed, just buy whatever mm focal lengths you desire in whatever brand you choose, knowing to yourself, that you have maybe selected the best of each brand, like the Hi-Fi enthusiasts of yesteryear, but the best, as separates, rather than one branded system.

I have obtained what should be a good eyepiece for my needs, a Tele Vue 6mm Delos, and the weather has been pants since ownership, so not tested yet, but with more eye-relief than my Starguiders, and more afov, they should be good, but then they might be too much?

Only testing will decide the outcome, just waiting for the best night and some free time?

[John]

The eye relief of plossls and orthoscopics does get rather "tight" as the focal length reduces. It's intrinsic to the designs although there is some small variation brand to brand.

Tele Vue don't help the case of the 11mm and 8mm plossls by employing a rubber eyecup that is rather inflexible making it hard to nestle the eyepiece into the eye socket. Optically they are very good though.

You are correct that a barlow lens does increase the eye relief so it can be a good way to get the shorter focal lengths while retaining reasonable eye relief. This is the same for Tele Vue as it is for other brands. It can be too much of a good thing with longer focal length eyepieces though (ie: 25mm, 32mm etc) as the eye relief can get too long for comfort !

Charic is correct that knowing what scope you will be using will help make more specific recommendations.

[jsmoraes]

I would prefer barlow because it will maintain the FOV of eyepiece. But... you will need a good barlow. I always tell about the spherical distortion of barlows. A cheap one will destroy the quality of image.
See here, http://astronomia-e-astrofotos.1069742.n5.nabble.com/file/n1342/distor%C3%A7%C3%A3o_esfericahubble.jpg , what that distortion did with images from Hubble before of its maintenance.

[phil125]

I have a ED80 and Europa 250 f4.8 - was thinking for use with the 250 newt for visual planetary viewing.

[MarsG76]

For viewing I use eyepieces more then eyepieces & barlow combos, particularly 5mm and 7mm for highest power. Occasionally I'll add a barlow or power mate on particularly clear nights.

On the other hand, if you want to image planets then barlows/powermates are the way to go... that said if you want to image and observe and only have one option, the Televue barlows/powermates are excellent quality and the difference to short fl eyepieces is negligible.

[pipnina]

The eye relief of plossls and orthoscopics does get rather "tight" as the focal length reduces. It's intrinsic to the designs although there is some small variation brand to brand.

Tele Vue don't help the case of the 11mm and 8mm plossls by employing a rubber eyecup that is rather inflexible making it hard to nestle the eyepiece into the eye socket. Optically they are very good though.

You are correct that a barlow lens does increase the eye relief so it can be a good way to get the shorter focal lengths while retaining reasonable eye relief. This is the same for Tele Vue as it is for other brands. It can be too much of a good thing with longer focal length eyepieces though (ie: 25mm, 32mm etc) as the eye relief can get too long for comfort !

Charic is correct that knowing what scope you will be using will help make more specific recommendations.

Yet to encounter an eye relief that's "Too long"

Every eyepiece I've EVER looked through has been short of getting past my glasses by some way. Even in my 25mm skywatcher plossl i have to take my glasses off and move my eye far far closer to the EP the see the whole FOV.

phil125, if you decide to use a barlow to make a 15mm EP into a 7.5mm or a 5mm... It could be a very sensible decision if the barlow you choose is good. The freebies you get with scopes generally aren't that good (can vouch).

[John]

Yet to encounter an eye relief that's "Too long"

By too long I mean that the eye relief is pushed out to a point where it's well above the top of the eyepiece and the eyecup. You then need to "hover" your eye at the right point without the benefit of the eyecup as a guide. This is tireing after a while, it lacks precision as you have to re-find your spot each time and it lets ambient light in between your eye and the top lens of the eyepiece, which creates unwanted reflections and reduces contrast.

Thats why it's not recommded to barlow longer focal length eyepieces such as 32mm plossls etc.

[Charic]

I have a ED80 and Europa 250 f4.8 - was thinking for use with the 250 newt for visual planetary viewing.

For the faster f/4.8, Tele Vue are tested to f/4, so there's a starting point.

On the faster scopes, coma aberration can be more noticeable towards the field edge (caused by the telescope alone), so a coma corrector or a premium eyepiece, like a TV may be what your after. It all depends on how much the  coma bothers your, if at all?

I'm sure some of  my Starguiders would still work(not tested) to some degree, but a Tele Vue is tested at f/4.

[YKSE]

For the faster f/4.8,

.............................................

I'm sure some of  my Starguiders would still work(not tested) to some degree, 

There're many charateristics in eyepieces need to be considered, astigamatism correction, spherical aberration correction, internal reflections control, stray light control, transmission, etc. some of these get worse fast with faster mirrors.

BST Starguiders are one of the most popular beginners upgrade for years, and 10" SW dob is a quite popular scope upgrade too, yet we've not read any review for this combo, and we do have seen many EP upgrades for that scope. Here is a mini comparo of some EPs including a BST

http://stargazerslounge.com/topic/257642-why-buy-new-eyepieces/?p=2816214

Putting these pieces together, How sure are you?

[Charic]

If I could continue with my BSTs on a faster scope, I`d gladly keep the Starguiders.

I know AndyWB has a 250PX and  some Starguiders, and they  seem to work fine for his needs, though they might not work for everyone, remember, its all down to the individual.

I still think a TV might be the better option? It was my intention to have three Delos EP's to work in my new 300P for the same reason, faster focal ratio!

And whilst on the subject of Tele Vue, My scope (200P) is out just now, I wan't to test my 6mm Delos, see if it works for my needs?

[YKSE]

I still think a TV might be the better option? It was my intention to have three Delos EP's to work in my new 300P for the same reason, faster focal ratio!

Only three   Delos? Congratulations, looks like your OCD for set has been cured

Sorry to OP for been off topic, I have two barlows, so I'd recommend a good barlow, especially combined with a good zoom, you get a lot focal range covered, with noticeable less cost than fix focal eyepieces for comparable optical performance, very quick to find most suitable magnifications for vary seeing conditions, much less time for switching eyepieces, which means more time for observing.

[bingevader]

I have the 8mm TV plossl and get on with the ER fine, but I wouldn't want to go any shorter.

I like a barlow too though, especially on the moon (and on holiday).

[rockystar]

YKSE, I've seen you post on "Show me your eyepiece case" I think you've got most focal lengths covered ;-)

[phil125]

Just bought a TV 32mm and 15mm Plossl second hand, should arrive tomorrow. Lets see which gives the best view of the clouds!

[YKSE]

Good luck with the weather, looking forward to your comparo. My guess is that you'll have quite different experiences about using 15mm to barlowing 32mm.

[mikeDnight]

Many modern eyepieces such as Naglers and XWs use an integral barlow in their design and they are excellent, so a quality Barlow used with a good quality plossl or similar simple eyepiece design should not degrade the image. Buy a good one though, as a scope is only as good as its weakest link.

Mike