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Which eyepiece is best for me?


Simonw

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I suggest a 2x Barlow.

Yours is an f/4.7 telescope. Budget eyepieces tend to work best on slower telescopes (above f/7).

With a 2x Barlow, your scope will be sowed down to f/9.4 and its focal length doubled to 2400 mm. You then have two extra magnifications from your existing eyepiecs. Barlowed, your 10 mm will  give you 240x and your 25 mm 96x magnification. 

For around £70 you can buy a good Barlow (see here).

(You can get an even wider choice of magnifications if you take off the Barlow lens of its tube and attach it directly to the 25 or the 10mm. The Barlow's power will be reduced this way, probably to around 1.5x. Whether you can do this and what the new power will be depends on the Barlow and eyepiece. Ask before you buy.)

 

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14 minutes ago, Simonw said:

Any reason why a 2x Barlow and not say a 3,4 or 5? 

There's nothing wrong with high quality 3, 4, or 5mm eyepieces such as Morpheus, Pentax XWs, Delos, Naglers, and Ethos that are designed to work well at f4.7.  They will all show great images and have very good eye relief.  You could also go with the BST/Starguiders in that range as well for much less money.  Not quite as sharp or wide, but still more than serviceable.  There are orthoscopics in some of that range, but the eye relief is vanishingly small, so you have to practically glue your eyeball to the eye lens of the eyepiece to take in the entire field of view.  That, and they weren't designed to work very well below about f/7 or so.  As a result, only the on-axis image will be sharp, degrading considerable by 50% to the edge.

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It would give you focal lengths of 40mm, 20mm, 17mm and 8.5mm. You would be covered OK for deep sky objects but there is room for something like a 6mm or 5mm for higher magnifications to use on the moon, planets or double stars. You might also find that you want something mid power at around 12mm. Sorry if that messes the plan up !

A barlowed 40mm eyepiece is not great to use in all honesty though - the already long eye relief is extended by the barlow lens to the extent that finding an effective eye position is tricky - you have to "hover" your eye off the top of the eyepiece which is not really relaxing.

Edit: just to further mess the plan up, I'd not really recommend a 40mm eyepiece with an F/4.7 scope. 30-32mm would work better as a longest focal length. A 32mm in the 1.25" size shows just as much sky as a 40mm anyway. Sorry to introduce more variables !

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Plossls will work well. The ones branded "Revelation" can be picked up for a low cost (around £20 used) and are pretty decent in quality. Avoid the temptation to buy an eyepiece set though - quite a few of the things included in them won't be used much so this undermines their value.

If you can afford a little more, the BST Explorer eyepieces at a bit less than £50 each are very good indeed in my opinion.

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I still use Plossls in my F12 127mm Mak - Skywatcher and Televue Plossls .

I would recommend BST Starguiders for your Dob though as they are nearly the same price as 50 degree Plossls ( 42 degree at 40 mm ) but BSTs are an extra 10 degress at 60 degrees ?

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It happens all the time. An F4-5 telescope without budget for premium eyepieces and/or coma corrector. The eyepiece, IMO, is just as important as the telescope. Better have a slightly smaller telescope with good eyepieces. BUT... eyepieces can be bought afterwards at a slow pace. It's better then I think to get ONE good ep; let's say a premium mid-magnification eyepiece and slowly go from there. Like getting a 15-20mm 82-100° eyepiece (APM, ES...) and just enjoying that view until budget allows for what you want next most of all; more magnification or less magnification, more apparent/true field or less, more eye-relief or less, more or less exit pupil (what's your sky quality, how are your eyes doing...).

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