Eyepiece for Mars

[koputai (Jason)]

Hi Folks,
What with Mars this month being at it's best for years, I'm contemplating getting an eyepiece for the occasion. I have an f6 8" Dob, fL=1200mm.
I'm thinking something around 6mm, in a 60 to 68 degree. Candidates at the moment are:
1) Televue Radian 6mm
2) Orion Stratus 5mm
3) Burgess/TMB 6mm

All will give about the same FOV, but the Stratus will give 240x versus 200 for the other two.
I already have a Nagler 13mm and 2x Barlow, so is it actually worth getting a 6mm eyepiece?
If so, how do the three above compare? Should I throw a Nagler 5mm into the mix, giving 240x with a bigger FOV? (21' vs 18')

Thanks,
Jason.

[ving (David)]

i have the same scope... celestron ultima 7.5mm is great. 5mm is getting too high. dont get fixated on fov...

or a 31mm nagler

[Astro78]

Highly recommend throwing a 2nd hand Pentax XL into the mix, or even the newer XW if you can swing it.

Beware there are some Pentax models which are cheaper new but really only for
land viewing.

[ausastronomer (John Bambury)]

Originally Posted by Astro78

Beware there are some Pentax models which are cheaper new but really only for land viewing.

Are you referring to the 8.5mm and 12mm Pentax XF eyepieces ?

Cheers,
John B

[Astro78]

Yes I think that's them. They're similar but with no lanthinum and half the weight and cost.

[rmcpb (Rob)]

I would second Dave's advice about the celestron ultima 7.5mm. I have one and its a beauty and on those really special nights you can still barlow it.

[ausastronomer (John Bambury)]

Originally Posted by Astro78

Yes I think that's them. They're similar but with no lanthinum and half the weight and cost.

If they are in fact what you are referring to, I can re assure you that the Pentax XF's while designed as a terrestrial spotting scope eyepiece, work superbly for astronomical use. I own the 8.5mm Pentax XF in addition to a boxfull of other premium eyepieces. It is not inferior in any way apart from it's slightly narrower FOV @ 60 deg. Being designed for terrestrial spotting scope use does not detract from its ability as an astronomical eyepiece in any way shape or form. Historically, 80% of eyepieces that see extensive use in astronomical telescopes today, were designed with other purposes in mind. For instance, both plossl and orthoscopic eyepieces which are today the most highly regarded of planetary eyepieces, were designed in the 19th century for use in microscopes.

Pentax do not make "ANY" fixed focal length eyepieces that are not excellent performers for astronomy.

Cheers,
John B

[Astro78]

Well wouldn't disagree with you there John. I certainly found a great review of one below:

http://www.cloudynights.com/item.php?item_id=1438

Actually John, after reading further seems they use "special ED Glass" not specified as Lanthanum (as done in the XL or XW), assuming to keep costs down. This must effect something in some shape or way as you say. It's amazing how much extra weight and cost goes into the extra 5 or 10 degrees field (XL or XW) you must admit.

[PeteMo (Pete)]

Of the eyepeices you short listed, I use the Radian 6 and it is an excellent eyepiece giving 20mm of eye relief and a 60 degree AFoV. I've used it on Mars a few nights and like it. My scope is a 10" f1200 dob and feel that this is on the edge of useability as it gives 200 x magnification in both our scopes so some nights images are blurry when the seeing conditions aren't good, so I end up falling back to my Hyperion 8mm.

Ditto the advice to back off the magnification a little and go for something around the 8mm focal length. Apparently the Pentax XF 8.5 and say the Burgess TMB Planetary series ie 9mm and 7mm are very popular and excellent value for money too. Daniel at Frontier Optics can supply you with both Pentax and Burgess eyepieces.

Pete

[koputai (Jason)]

My Burgess/TMB 5mm arrived today (thanks Phil). This one came up here for sale so I thought I'd grab it to see what they're like. Will probably shelve the 6mm idea for a while and get something in 8 or 9mm. (That is, after the 31Nag or 35Pan)

Cheers,
Jason.

[chunkylad (David)]

I think you'll like you Burgess TMB 5mm.

I got a half hour between the clouds at Mars last night with Burgess/TMB 9mm, 7mm, and 5mm (I even pushed my luck with the 2.5mm, not successfully I might add). The extra afov afforded by these eps comes into its own when you have a non-tracking mount like a dob. It's so good to see your target float through the (large) fov crisp and clean from edge to edge.

I can't fault any of mine. Perfect choice for this and every planetary opposition IMHO.

Cheers