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Barlow Lenses

Alf Fraser

By Alf Fraser
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Alf Fraser

Alf Fraser

Posted
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Hi, I'm a newcomer. I've been reading posts as a visitor but I've taken the plunge and bought a 'scope.

I have a Celestron 8Se with the 25mm eyepiece that came with it and a Celestron 7mm x-cel. Was observing Jupiter last night and was impressed with th 25mm lens so switched to the 7mm. Not very good, but I think that the seeing was difficult and also it's the 1st time I've used the telescope properly.

I'm now thinking, should I get an intermediate lens, say 12mm for nights like last night or should I consider a barlow first as a stop-gap. If I was to get a barlow, what are my options. If I was sticking with the brand, what are the advantages of the X-cel barlow over the standard plossl? Is a 3x Barlow worth considering?

Is a 12mm suitable for 'deep space?

Does anyone have any views?

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JamesM

JamesM

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Hi Alf, It might be worthwhile you reading the sticky on "eyepieces - the very least you need" which you can view here for some understanding on how they work within different scopes. Your particular scope has a focal length of 2032mm which is a figure which when divided by the focal length of a given eyepiece, will provide you with a level of magnification that it can generate. No matter what scope you have, under normal circumstances the maximum amount of magnification that we as observers can use is around x180 - x200. There are exceptional nights where you can push the magnification past x250 but here you are talking about maybe one or two nights a year. The seeing and transparency conditions generated by our atmosphere are what stands between us and the object being viewed and can be best seen by the scintillation or twinkling of stars.

Coming back to your question, a 25mm eyepiece in your scope will produce x81 magnification, whereas a 12mm eyepiece will provide you with x169 magnification and 11mm will give you x184. Of course different manufacturers produce different focal lengths are available to you and so referencing the above sticky will help you with other considerations that eyepieces can offer such as field of view. The general consensus is to buy the eyepiece required rather than a barlow as this will introduce more glass between you and the object, although it is fair to say that not all barlows are created the same, as the a Televue Powermates (£265 :eek: ) have a 98% light put through and can do it without altering an eyepiece's eye relief (see above sticky). The TAL barlow was great value for money but alas they don't seem to be available anymore but perhaps the X-cel might be great too but I have no experience with them. If you do decide to go the barlow route I wouldn't go above x2 barlow.

Clear skies

James

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swamp thing

swamp thing

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Hi and Welcome to the SGL.

The idea that Barlow lenses somehow detract from the view when compared to an eyepiece alone is wrong. Modern Barlows add nothing but power the extra glass has zero detrimental effects on views. Remember a lot of modern eyepieces (like Naglers, UWANS, Nirvana's ) have inbuilt Barlow elements in them and I don't hear anyone saying they aren't as good as BST's. ;)

Sent from my iPad using Tapatalk

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wookie1965

wookie1965

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Posted

Hi and Welcome to the SGL.

The idea that Barlow lenses somehow detract from the view when compared to an eyepiece alone is wrong. Modern Barlows add nothing but power the extra glass has zero detrimental effects on views. Remember a lot of modern eyepieces (like Naglers, UWANS, Nirvana's ) have inbuilt Barlow elements in them and I don't hear anyone saying they aren't as good as BST's. ;)

Sent from my iPad using Tapatalk

Well im glad i learned that i read on this site about the glass http://physics.stackexchange.com/questions/26252/what-are-the-differences-in-using-an-eyepiece-with-a-barlow-instead-of-a-shorter ive since done some more research thank you.
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Mr Spock

Mr Spock

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Hi, welcome to SGL :)

A 7mm is probably a bit over-powered for your scope. Aim for something around 10mm - the new Baader Classic Ortho 10mm would make a fantastic planetary eyepiece and it's not too expensive.

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rwilkey

rwilkey

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Hi Alf, and welcome from me too. A barlow with the 8SE would be too much magnifications for most nights. I think the focal length of your scope is 2032mm, you just don't need a Barlow in any circumstances in my view. Go for a 12mm eyepiece, say the BST Explorer/StarGuider, for example, it will serve you well. Shown here: http://www.ebay.co.uk/sch/i.html?_trksid=p5197.m570.l1313&_nkw=bst+explorer&_sacat=0&_from=R40

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Alf Fraser

Alf Fraser

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Thanks everyone for the welcomes and the useful feedback - much appreciated.

I'll just stick with what I've got for now until I've had a bit of 'scope time under my belt. I was very suprised to see as much detail on Jupiter as I could with the 25mm. As planet watching seems to be a bit restricted for a while, I think I need to concentrate on alighment so I can get to see some nebulae. I had the alignment OK so that I could slew to bright stars the other night but I couldn't seem get accurate enough to find e.g. the Orion nebula. Seeing as how this was the 1st time I'd looked through a 'scope for many years, it's probably down to the eyes......Pun was not intended by the way. Better learn how to find them before I start buying any more eyepieces.

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