13mm Stratus

[Scoper (Malcolm)]

Have had a 13mm Stratus eyepiece for about two weeks now and have been observing with it every night since, my log book now has a number of new entries after a lull of a considerable length of time.
On axis --no complaints: sharp, good contrast and transmission.
Off axis--astigmatism rising sharply to the edge from about 10% from the edge. Also noticeable field curvature. The usable field is about 75%to 80%.
I was wondering if this is normal for this eyepiece in a 10" f5 scope, does anyone else have the same experience? I was under the impression that the edge-of-field performance would be better than this (though not perfect). Your comments would be much appreciated.

Cheers
Malcolm

[janoskiss (Steve H)]

Depends on what you were expecting. I would say that 100% of the field is "usable", but depends on what you want to use it for. There are aberrations as you approach the edge of field, but still those stars near the edge in the peripheral vision do make a difference to me and aberrations are obtrusive only for a few of the brightest stars. And of course you won't be able to get good views of Jupiter on the edge of the field. No EP is perfect to the edge, even the most expensive ones show some aberrations near the very edge of field. Stratus is not as good as a Nagler or a Pentax XW, but they are pretty damn good. And for the price they are superb.

What other EPs have you used?

[Scoper (Malcolm)]

Thanks Steve, I guess I was more curious than anything else as well as hoping i didn't have a one-off "under achiever".
The most important thing to me is the on-axis quality of the image, the edge of field is a secondary consideration but the "Tack sharp to the edge" advertising claims seem to be a little misleading. In all honesty though i enjoy using this eyepiece, it is very good and very comfortable to use. The image quality is surprising considering the light has to traverse 8 bits of glass.
I suppose never having owned an eyepiece like this before i didn't know what to expect.

Thanks again

[Scoper (Malcolm)]

Oh and my other eyepieces are an ancient 20mm Unitron erfle, an old 12mm Plossl, a 2x barlow and recently some GSO plossls. Have also borrowed eyepieces in the past.
I am old enough to remember the days when a "top of the range" Ramsden or Orthoscopic was all the go.
I've enjoyed astronomy since I was a boy. Am now 53 and a lot has changed.

Malcolm

[janoskiss (Steve H)]

My first quality widefield EP was a 13mm T6 Nagler, and I was disappointed with that EP's performance. Reading all the hype, like you say "sharp to the edge", "ultimate" glass, contrast sharpness to "blow your mind" etc etc , and paying top dollar I was expecting a perfect image, which I did not get. The EP was worse on planets than a simple plossl, it had false colour near the edge of field, and initially I had trouble getting used to eye placement and was getting blackouts all the time. I felt cheated at the time, but eventually I learnt that there is no such thing as the perfect EP, and every EP is a compromise of features and performance parameters.

I bought the 13mm Stratus later and spent quite a few nights comparing it with the Nagler. On axis there was not much between them, and I thought overall the Stratus was very good considering it cost just little over 1/3 the price of the Nagler, and it is also more comfortable. Sold the Nagler, kept the Stratus. The Stratus has since also seen a 14mm Meade 5000 Plossl and a 14mm Pentax XW come and go. So it's a fine EP and can mix it with the best of them.

I think the best EP for your scope is the 10mm Pentax XW. It's as close to perfect as you can get it would seem.

[ausastronomer (John Bambury)]

Originally Posted by janoskiss

I think the best EP for your scope is the 10mm Pentax XW. It's as close to perfect as you can get it would seem.

I would agree with Steve on this. I own 5 Pentax XW's and a 27mm TV Panoptic for use in my 10"/F5 newt. The 10mm Pentax XW owns at least 50% of focuser time. More than the other 5 premium eyepieces combined. While it doesn't give enough power for lunar/planetary observation it is the perfect DSO eyepiece in a 10"/F5 newtonian. It creates a 2mm exit pupil which is perfect for DSO work.

The 10mm Pentax XW is arguably the best general purpose eyepiece money can buy at the moment. It represents the pinnacle of current eyepiece design and technology currently available. It gets no better !!. Unfortunately not cheap but you get what you pay for.

CS-John B

[bytor666]

John....I just picked up a Pentax 10.5mm XL and used to own two 10mm Pentax XW's. I agree that the pentax XW is one of the finest eyepieces ever made and loved using it.
Have you found much of a difference between the Pentax 10mm XW and the Pentax 10.5mm XL?
My skies have been terrible lately and I haven't had the time to get my 8" f/6 reflector out to view with it.
--------------------------------
Mark
8" F/6 Antares Dobsonian (completely flocked and modded)
15x70 Celestron Skymasters (replacements on the way !!!)
10x50 Magnicon binos
Meade 14mm series 4000 UWA
10.5mm Pentax XL
2" Barlow
Sony Dig 4.1 Mp Camera

[Starkler (Geoff)]

Originally Posted by bytor666

Have you found much of a difference between the Pentax 10mm XW and the Pentax 10.5mm XL?

Dave47tuc and myself did a quick side by side between my 10.5XL and his 10XW.
Apart from the slightly wider field of the XW, there was next to no difference.
Dave said he couldnt see a difference, and I thought I could see a slightly darker background in the XW, but couldnt be sure. This could be due to the slightly higher magnification of the XW

FWIW, I think the XL's are excellent value on the second hand market.