Barlows

I brought my 10" dob F5 outside last night - although seeing was poor due to "white out" on account of he Moon. I thought I would just have a go at seeing what the effective maximum magnification the scope could reach.
I noticed that the Barlow X2 performed poorly, for example:

9mm eyepiece = view was sharp and features well defined
15mm eyepiece with Barlow = not as defined

Is it that the very fact of having an additional piece of optical equipment
between you and the object observed creates a problem, or would it be advisable to purchase a higher quality Barlow? - barlow is a celestron that came with box of eyepieces and filters.

Declan

As far as I understand Declan, a barlow does double (2X) or triple (3X) your magnification with whatever eyepiece you have insterted into it. But the problem is the image quality. First, you have an extra layer of glass tat the light must pass through, and if your barlow is not up to scratch, then you'll get further surface reflection and a dimmer image than if just using the original same-power eyepiece. Second, a barlow is only of any real use on higher value eyepieces if you don't have any lower ones available e.g. some scopes only come with a 32mm Ep, then with the 2X barlow, you're also getting a 16mm eyepiece.

However, that 16mm virtual image will be a little fainter, and maybe slightly fuzzier, than the actual 16mm EP view.

Seanie.

Thanks Seanie, I have 2 barlows looking very much the same. One is made by Soligor and the other celestron...can't see any difference in quality of image.....suppose you get what you pay for


Declan

Declan,

I have two barlows, both from Celestron. One is the Omni barlow - very good at the price, and I've never noticed a huge deteriotaion in the image using it, even with the cheap eyepieces that came with the scope. I upgraded to an Ultima barlow when I purchased my new scope - primarily for photography use, and this one is excellent. The Ultima is an apochromatic barlow and is more expensive, but given that your views will only be as good as the weakest link in the optical train, there is no point spending any money on expensive telescopes and eyepieces if you ruin all that with a cheap barlow.

On my 4" refractor I leave the Omni Barlow permanantly fixed (cause its such a short focal length), and have never noticed any degradation in the image.

I found the same with my 2X barlow. Dimmer images and not as crisp.

I dont really use it.

I have a 32mm,20mm,15mm,10mm,9mm,6mm,4mm EP.

So if you do the maths, you see the barlow is pretty redundant.

I mostly stick to the 32mm,20mm,15mm and 10mm EP's.


Last night i found that Saturn looks GREAT in the 32mm. TINY.........but very sharp.