5mm Radian or 5mm Nagler - which would be best?

[Martin-Devon]

I have an 8" SCT Celestron CPC800, and am looking to upgrade to a high quality planetary eyepiece - Jupiter is waiting! I gather that my CPC800 (2032mm focal length) will take at best a 5mm EP for best magnification without distortion. I've been looking at the Televue Radian 5mm and the Televue Nagler 5mm EPs - both come highly recommended.

So my question is what are the main differences and the pros/cons of each. I gather that the Radian EP gives very good eye relief, and is claimed to be very good for observers with spectacles - but this is not relevant to me. Both eyepieces come in somewhere between £170-£200 - which is pricey, but I assume I'll appreciate the extra detail they will offer on my CPC800 - tell me though if this is a mis-assumption.

The other option I have is to buy a Meade Plossl 5mm EP or similar which comes in at a third the price (£63) - tell me is there a major real positive benefit by having either of the Televue EP's above and will I really see a significant difference versus the cheaper Meade EP?

Thanks for your help

[Ben Ritchie]

Ok, I wouldn't buy the Plossl as eye relief is extremely limited at 5mm focal length - but would strongly consider the TMB Planetaries which are strong performers at even less money (i've just paid £75 for two, delivered). 5mm is also quite high power for a 2000mm-FL SCT, so i'd consider buying something at a bit longer focal length as I suspect it'll get more use.

As for the original question, both eyepieces are superb in my view. The Nagler has a wider apparent field, at the cost of less eye relief (but certainly still sufficient) and slightly lower on-axis sharpness IMO. Personally i'd think about my balance of priorities between planetary and deep sky, which is why I have a couple of Radians for high powers and a Nagler for somewhat lower. Both are certainly premium options though, and i'd strongly consider the cheaper options before deciding on either.

[dweller25]

Hello Martin,

A 5mm in the 8" SCT will give x406, I think this is way too high given our seeing conditions and Jupiters current elevation.

I would suggest a 10mm eyepiece that you can always Barlow to 5mm.

As to which eyepiece - I looked at exactly the same issue as you. I wanted a premium 5mm Eyepiece for planetary. The general consensus was to buy the Pentax XW BUT all it seems to gives over a 5mm Ortho is more eye relief and a wider field of view - it will not necesarily be sharper.

I decided to buy a premium x2 Barlow and stick with my very sharp Baader Orthos. I now use a 12.5mm BGO plus a Zeiss x2 Barlow extended to x2.5 which gives me a 5mm effective eyepiece but with around 10mm eye relief.

HTH

[pbyrne]

Another question to consider is how often will I use this eyepiece? I'm assuming that your focal length is about 2000mm, this will give a magnfication of 400, there are few, if any, deep sky objects that can take that kind of magnification from an 8" scope, I could be wrong.

That leaves the moon and planets, and I agree with Ben, it might be better to go down the TMB route.

Again, as Ben said, avoid the Plossl.