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Sorry..But yet another EP question


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Please bear with me as I'm really new to all this.

I've got a Celestron NexStar127SLT. It has a f/ratio of 12 - so, according to the excellent Sticky:Eyepieces article I should be looking at 9mm 15mm 25m and 36mm EP's.

Now my 'scope came with a 9mm and 25mm - but I'm guessing that these are pretty bog standard ones - they are only branded "Celestron" - so I'm guessing that not all 9mm's are the same, so, on to the questions:

  • would a 9mm Plossl be hugely different to the Celestron one I've got
  • er - what is a plossl
  • Should I be looking at other alternatives

Secondly - and to show my ignorance further - A Barlow lens - Am I right in saying that it will increase the magnification of the EP you're using? and therefore do you use a Barlow AND your EP together or is it a totally standalone item? and are there different types of Barlow's?

Sorry to appear a real newbie - but I do want to learn!

Thanks for your patience

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Plossl eyepiece is sort of the standard. It comprises of 2 doublet lens - achromatic doublet, each being the same and arranged with the most curved faces facing in towards each other. The lens are separated by a small bit of tube.

Make sense? Probably not.

"Inexpensive" as you make a few thousand doublets all identical, drop one in the eyepiece, drop in the separating tube then drop in the second lens and then screw them down. Do that for each eyepiece focal length. If the lens are well matched then you get a good one, if not then a poor one. Sheer chance.

Ignore 36mm, nice number but you will find more 32mm's.

A 9mm plossl will (by rights) be much the same as you have but a new 9mm may be better quality so give a better image. The ones you have will be plossl's.

Bit undecided but I would have added in a 12mm as well.

9mm for when the opportunity presents itself.

12mm probably most of the time for magnification.

15mm when conditions are poor or a slightly wider view.

25mm and 32mm for wide views.

Alternatives are the planetery eyepieces, usually 6 lens in them I think in 4 groups, meaning 2 doublets and 2 singlets. These can go down to small focal lengths so give much more magnifications, but you need a good scope for ones that small.

Another alternative is something like the GSO Wide Angles.

Barlows are as you say. Put barlow in, put eyepiece into barlow and the eyepiece acts as if half the focal length. Suspect they are similar to a plossl where the first lens is half the focal length of the second. Don't own one so haven't pulled one apart.

Barlows come in numerous types based on the multiplication factor they have, most are 2x, some 2.5x, 3x, 5x others also.

Plossl's can suffer form small/short eye relief, so if you wear glasses this could be a problem. Planetery's tend to have more so are better in that respect.

Think Rother Valley do the Antares plossl's at £20, if not try Greenwitch, GSO plossl's are sold by Modern Astronomy (think thye are) - noit sure on price but close. No idea what FLO do oddly.

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Hi Sim

Generally speaking the eyepieces supplied with a scope are bog standard, there are many brands of eyepiece out there, the top end plossls being the Televues. But there are many other good makes, Meade's Series 4000 Plossls are a good make as are Skywatcher and some of the Celestrons, though I have no experience of these two makes.

A Plossl is a four element, I believe, eyepiece that gives a field of view of approximately 52 degrees.

We are all looking for alternatives no matter what we have.

A barlow increases the magnification of an eyepiece, for example a 26mm will become a 13mm eyepiece. The barlow goes into the eyepiece holder and the eyepiece pops into the top of the barlow. The most common barlow is x2, but there x3, x4 & x5 by a variety of manufacturers.

Hope this helps.

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Do remember that with barlows you are not only magnifying the object, but also the imperfections in the atmosphere. They also introduce extra glass in the light train which can also degrade the view to a minor extent. Tracking also is also impacted as it increases the speed of the object through the ep.

That said, judicious use of a well chosen good quality barlow can be very effective in both observing and photography. A good vfm budget barlow is the TAL, next step up I'd suggest the Celestron Ultima, Orion Shorty, or any of the Televue barlows. :)

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What you get will all depend on how much you want to spend. A good quality eyepiece is a sound investment. The more you spend, the less likely you'll want to change in the future.

So, for 9mm:-

Any Plössl - not really much different to what you have, better brands are better quality though. Eventually you'll want to upgrade.

Baader Orthoscopic 9mm - at £73 very sharp, clean images, much better than any Plössl but only 40° field

Vixen NLV 9mm - at £141 a large step up in image quality from a Plössl with 20mm eye relief and a 50° field

If you want to go Televue, you'll need to have 8mm - x188

Televue Plössl 8mm - £71 much better build quality than standard Plössls

Televue 8mm Radian - £174, getting expensive, but with 20mm eye relief and a 60° field

No matter what scope you have, a good quality eyepice is never wasted and will last a lifetime.

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I fully understand - as with everything - that you get what you pay for, though I am tempted to get a selection of different sized EP's and filters to experiment with what I like and then maybe save up for the higher end version of what I like - I can always sell the other ones - that's me - champagne taste with a lemonade budget!

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Er... nobody's mentioned the TMB clones, so...

How about the TMB clones (for the 9mm slot at least)? I have 2 branded as TS Planetaries from Modern Astronomy for £49 and they are very nice - 16mm eye relief and 60 degree field of view. You can get them cheaper from other suppliers as well.

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