onwards and upwards

[davehunt]

I am thinking of upgrading to TV Radians primarily for planetary observation.Will the 8mm Barlow well enough (to give me a bit of flexibility) or would I be safer getting a 4mm 0r 5mm ? Or shall I flog my TV 2x Barlow?

[Moonshane]

hi there

I have an 8mm and a 10mm Radian and use them in a fast and a slow dob.

They are excellent performers, giving a nice wide (for a 'planetary' eyepiece - I am not sure I accept that they are just for planetary as they give excellent views of all objects). They do give a slightly yellowish cast (VERY minor) but this is the case for a number of TV eyepieces.

My concern with barlowing them would be that you'd increase the eye relief (which is already long at 20mm) and may have difficulty with blackouts. As you already have a good barlow, I'd buy the 8mm and see how it goes, you might be happy you might not and you can then decide what to do. 8mm would give a very usable planetary mag of 150x assuming your scope is f6? 300x would be usable more infrequently I feel. Can you get a good image with your 4.5mm?

[davehunt]

Hi-thanks for that.I get a reasonable image with the 4.5-but viewing Jupiter the other night(which was clear and steady for a change)there was a slight fuzziness I felt might have been down to optical shortcomings,and wonder if a higher quality e/p-even at lower mags-would allow the magic red spot to materialise. The cost is a real factor for me,and I am loathe to do a suck it and see exercise at £180.00 ! But I take your point about the power of 8mm,so think I might go in that direction.

[Damo636]

Hi Dave. I have the same scope as you and was observing Jupiter's GRS the other evening at 150X with my 8mm eyepiece. With the 6mm Radian at 200x it was still there but not as well defined. As Shane states, 150x is a very useful planetary mag so the 8mm would serve you well. I have barlowed my 6mm Radian and experienced no issues with the eye relief.

[davehunt]

Thanks-think it's going to be the 8mm.First search for s/h one,to try and preserve marital harmony......

[cantab]

My concern with barlowing them would be that you'd increase the eye relief (which is already long at 20mm)

I thought Barlows didn't affect the eye relief of a given eyepiece, since using a Barlow is simply like using the EP in a scope with a greater focal length.

[John]

Barlows have the effect of pushing eye relief out a bit. That can be helpful or a hinderance depending on the eye relief of the eyepiece being barlowed. The Powermates retain (more or less) the eye relief of the eyepiece.

[brantuk]

The 8mm Radian will give great planetary views at 150x in your dob (with good seeing). If you do Barlow it then the Antares 1.6x will give you 240x and works very nicely.

If you can afford to push the boat out then a Powermate will give you the best at 300x but in UK atmosphere you won't use that combo often - my highest power is the 5mm Radian and it only comes out to play once in a blue moon lol

[davehunt]

Thanks guys