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Adding a 6mm eyepiece


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My daughter and I have been using a cheap secondhand Celestron Astromaster telescope with an altaz mount (80mm aperture, FL 910mm, FR 11.3). I didn't want to spend too much money in case she lost interest, and having a cheap telescope also means I'm able to let her largely handle it herself without fear of damage!

It came with 20mm and 10mm eyepieces, which we've largely confined to planetary viewing. We've been really pleased with what we've seen so far, but I'm keen to see if we can push the magnification further and pick up slightly more detail.

It looks as though we could notionally use a 6mm eyepiece with this scope, though we'd need one with decent eye relief as I wear glasses while observing. I'm keen for opinions from seasoned observers on:

Whether getting a 6mm EP is worth doing with this scope?

Any relatively low-cost EPs to consider if so (In the long-term, if the hobby sticks, I'd like to upgrade the scope. I'm therefore keen to limit expenditure on this one, or make sure anything we do buy will be equally useful if we do go for a larger reflector at some point.)

Whether I should instead consider getting a barlow lens and using it with the 10mm EP? 

Thank you for reading.

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With a 6mm it may appear that your closer to the target, but you may well see less detail?

I think your scope has a focal ratio of f/11. Your 10mm almost equates to the limit of the telescope, by matching the focal ratio to eyepiece.
Any eyepiece with a smaller focal length will be asking for a lot from the telescope, which is the limiting factor here.

My scope has an f/6, and excepting the Moon, I'm normally between 8 -12mm which produces a better more detailed image.

I would look for an eyepiece around the 12mm mark for more detail, but with a smaller image than your 10 will provide. Theres no simple solution, trial and error. You could Barlow the 20mm which would be pointless, as it would equate to using the 10mm, but a 12mm would possibly give more detail than the 10mm but if you have a Barlow with the scope, you could Barlow the 12mm to equate to using a 6mm.

A 6mm alone maybe too much, a 12mm could be more useful. As a recommend, BST have a 12mm Starguider, good enough for your scope, and mine, but my scope has the bigger aperture, like I said, aperture limits the ability of the scope. The BST 12mm also has a decent apparent field of view of 60° and decent eye-relief.

I also use the Revelation Astro (GSO) Plossl's. Their cheap as chips with about 52°afov from Astro-boot. My 4mm is sat in the sorting office as I type this text,  I was out working and postie could not squeeze it through the door, yet they manage with other large  items?  but to be honest, not sure how useful it will be on my scope, but it completes the set, whatever the outcome?

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Hi, a 6mm will give you 151x, which is stretching to the limit of the scope of 160x.  If you really want to try it I can only suggest one ep with good eye relief, that is the William Optics SPL 6mm, a little expensive but you will not get good views or good eye relief with anything else.   This ep will fit well with any future upgrades.

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I think you would be better served with a 8mm eyepiece, it would have better eye relief. It would give a magnification of about 114X which would not tax the mount too much and be enough power for a decent view of the planets which are currently rather low this year. If you buy a decent quality eyepiece you can always retain it for use with an upgraded telescope in due course.  :icon_biggrin:

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I took Robins advice some  Years ago and bought the very same eyepiece, only because I could not and cannot get the Starguider in 6mm format, as they do not produce them! but as stated the WO SPL 6mm is a great eyepiece.
Im sure the 12mm Starguider is slightly cheaper, more eye-relief and afov, and can be Barlowed.
Not only that I took Robins advice on the Starguiders, and have no regrets whatsoever.

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For a 6mm you could try the Altair Lightwave 6mm, it is the one at £55. Think they have 2 called Lightwave and both can be 6mm, so if you went for one check you have the right one, the other is over £100 if I recall.

I would suggest an 8mm BST Starguider as a more usable item. Skies the Limit at £49. Slight increase in magnification over the 10mm but I would hope the view is a lot better. I half suspectthe 6mm will be a bit too much for the scope and so the image not as good. It is a fine line when performance is concerned.

The catch is that 8mm to 6mm seems small but the reality is a 25% change, so the magnification jumps accordingly.

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I would go for a 7 or 8mm personally. The Vixen NPL 8mm is good, if you do not mind the short eye relief (i.e. if you do not wear glasses while observing, like I have to do). Otherwise the TS HR planetary 8mm would be a good option:

  http://www.teleskop-express.de/shop/product_info.php/language/en/info/p158_TS-Optics-Optics-8-mm-Planetary-HR----1-25--Okular--58---voll-multiverguetet.html

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A 2x barlow would work, and you would retain if not increase the eye-relief of the 10mm whilst so barlowed, and for an effective 5mm(180x).  The barlow would also be useful for the typical reflector to be chosen as an upgrade in future, whether an f/5 or f/6, or even an f/8 as a 150mm Dobsonian...

http://www.rothervalleyoptics.co.uk/antares-x2-achro-barlow-lens-125.html

I wouldn't expect too much out of the 10mm, but you can certainly try, then strive for an aforementioned 12mm if it doesn't pan out.

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I tend to agree that a 7 or 8mm would be best. That gives you magnifications around  x1 per mm of aperture which is nicely within the capabilities of the scope and will give a good image under suitable seeing conditions.

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