Help! Barlow Lens

[Appleblossom]

I have a Celestron Travelscope & only have 2 eyepieces, the standard 10mm & 20mm, that came with it. I was advised on this site that to reach one of my goals, seeing Saturns rings, I would need to purchase a 2x barlow lens. I have a limited budget though my husband & daughter may look into purchasing one for me for Christmas, but they are not millionaires either! I said I would look into it, knowing that I could count on here for some advice, to give them some idea of what would be worth buying, or where to go, etc, etc, etc...!!! I do not have the first clue of what would be cheap or expensive. Guess you all get the idea, please can you help me? Do you need to know the model of my scope or are the fittings of the eyepieces generic? So many questions... lol

[jsmoraes]

Barlow is a lens that change the focal length of your telescope and with this you magnify the image. The main problem with theses lens is spherical distortion. A cheap one can cause blurred images. You magnify but you loose details.
This image shows you what is spherical distortion. It is from Hubble before and after correction of spherical distortion by error in its mirror.

Perhaps for your intention an eyepiece of 5 mm will work. And they are less expensive. It will work similar to barlow 2x with eyepiece of 10 mm.

[opticalpath]

I think your 10mm eyepiece should give you about x40 magnification.  This should be just enough to allow you to see Saturn's rings, though not in any detail.  Why not try that first?

A 2x barlow, giving x80, might show some more detail but the image will be fainter and less steady, and will move out of the field of view more quickly.  Only a very cheap/ poor barlow would produce abberations  as bad as the above example and reasonable examples can be bought second hand (UK Astronomy Buy & Sell, for example) for around £20-40.   Measure the diameter of your eyepiece barrel.  I think it will be 1.25 inches; that's the fitting size that you need.

I wouldn't recommend a 5mm eyepiece as it will have short eye-relief and will be more difficult to use than your 10mm + barlow.    But try the 10mm eyepiece on its own first.

Adrian

[Ampthill]

Here is a pic that I took using an ETX125, Avery cheap 2x barlow and a spc900 webcam.

Hope this gives you some hope!

       James

[Knighty2112]

I have the Celestron Travelscope 70 to use as a quick setup scope, and I use a Celestron Omni 2x Barlow. I get pretty good views when the sky is clear and steady all the way to my 6mm EP. I wouldn't push it any higher than this, so with the the 10mm EP you have with the Barlow it will becom like a 5mm EP. That might make images close to the maximum this scope can image well. The moon might hold up reasonably well here, but the planets will start to loose clarity. With the 20mm this will give you the same view as the 10mm EP you have anyway, so until you have a slightly larger EP collection you won't really benefit from any 2 X Barlow yet.

[Stub Mandrel]

MI have an X2 barlow that came with my scope. It works really well and appears to be one of these, which are £23:

http://www.firstlightoptics.com/celestron-eyepieces/celestron-2x-universal-125-barlow.html

I have no trouble seeing Saturn's rings using it with my 70mm Bresser scope which is probably more or less equivalent to your scope in terms of cost and quality teamed up with a 10mm eyepiece.

It has worked really well using it with my larger scope (Jupiter;'s red spot, shadows of moons on Jupiter).