Pentax XW 30mm

[cydonia]

Hi,

Can anyone tell me how sharp the stars are at the Edge of field in this eyepiece in f5 and f10 scopes? Which would be the better eyepiece between this one and a Televue 27mm Panoptic?

Thanks

[Starkler]

At f5 the XW absolutely trounces the panoptic. Imo its the best buy in its class of 70 degree eyepieces. At f10 it probably wouldnt matter.

The xw will cost more and imo its worth it unless you want to shell out for more field in a 31 nagler.
The nagler is good but suffers pincushion (or is it barrel) distortion, so panning around with it isnt the pleasant experience you get with a 30xw.

[ausastronomer]

Hi,

I own a 27mm TV Panoptic and a 31mm TV Nagler T5. I have also used the 30mm Pentax XW. Optically the 30mm Pentax XW is a class above the 27mm TV Panoptic, which itself is a very good eyepiece. Optically, I also rate the 30mm Pentax XW ahead of the 31mm Nagler T5. However, at this longer focal length my objective is to maximise the FOV, not contrast and light throughput (where the pentax excels). I keep the 27mm Panoptic for use as my lower power eyepiece when I use the 10" scope, which isn't very often, as the 31mm Nagler has balance issues in the 10" scope.

The 30mm Pentax XW is one of the very very best eyepieces money can buy, at any price. Highly recomended.

Cheers,
John B

[cydonia]

Hi John and Starkler,

Thanks for your replys. I'm going to go for the 30mm XW, Yes it cost more than the 27mm Pan, but it is water proof so it will keep moisture out. I've heard that this can be a problem in non water proof eyepieces.

The troubles outlined in another thread here about the 20mm XW are not present in this focal length?

Cheers

[ausastronomer]

Nope, the Pentax XW series are not a "scaled" design. Hence the lens configuration and element design is different from one focal length eyepiece to the next. Consequently they are not all identical in their performance characteristics.

The best of the XW series are the 5mm, 7mm and 10mm in 1.25" barrel and the 30mm in 2" barrel. These all exhibit a flat field in just about any telescope. Despite what you may read from many, the other focal lengths are all exceptionally good eyepieces. Whilst they may exhibit some field curvature in some telescopes, they outdo all the "widefield" competition in terms of comfort, sharpness, contrast and light throughput. Further, if your scope is a fast newtonian the field curvature issues are fixed by using a paracorr.

Cheers,
John B

[gb_astro]

Anyone done a side by side comparison of the 30XW and Nagler 26?

gb.

[Starkler]

The 26 nagler is much the same as the 31, except its getting short on eye relief, meaning I found seeing the entire field to be a challenge. I owned a 26nag and sold it for this reason. The Pentax by comparison is viewing comfort supreme (of a smaller but complete field)

[ausastronomer]

Never A/B'd them, but used them both and the 31mm Nagler. Geoff's assesment is spot on. They will give you the same TFOV, albeit the 26mm Nagler at slightly higher power. The 30mm Pentax is a lot easier and more comfortable to use allowing you to take in the full FOV more easily. I regularly use Andrew Murrell's 26mm nagler and I personally prefer the 30mm Pentax and the 31mm Nagler over it because they both have longer eye relief and greater comfort. Andrew is not fussed about the eye relief and I know his preference is for the 26mm Nagler. The Pentax is the best of the 3 in terms of contrast and light throughput, although at this level they are all outstanding. One thing I will say is that if you are likely to do a fair amount of observing from less than pristine skies (like Pony Club) the 26mm Nagler may be a better choice due to its smaller exit pupil in your F4.5 scope and resultant greater contrast because of the higher magnification. If you only ever observed from "dark" skies then the 30mm Pentax XW would be my choice. I am more than happy to let you try our 26mm and 31mm Naglers if you can wait until the June new moon, which is the next time I will be at Pony Club.

Cheers,
John B

[gb_astro]

Geoff and John, thanks or the info.

John, a chance to look through the 26 and 31 would be great.

gb.

[PhilW]

I bought Geoff's 26mm Nagler in preference to a 30mm XW, purely for reasons of exit pupil. It produces a 5.6mm exit pupil in my F/4.6 scope, whereas the 30mm produces 6.5mm. The eye relief doesn't bother me provided I fold the rubber eyecup down.

That said, the XW 30 is a great eyepiece for all the reasons mentioned below, esp contrast & comfort. They are both great choices.

Note that they are both heavy eyepieces so can cause balance problems (around 0.7kg). But the 31mm Nagler is much heavier again at 1kg.

[StarLane]

Go the Pentax. Mine is awesome in my F5.

Excellent sharpness and contrast, eye relief is perfect, (sometimes ER is overlooked when deciding on an EP) very very comfortable. After hours of use this EP will not stress your eye, and the eye cup is adjustable (twist up and down to adjust eye postion). I would choose ER over field of view any day. Build quality is amazing.

You will only see MINOR softness/streaking stars (coma) at the very edge of field at F5, only the outer 5% or so of field, this is mostly due to my mirror (most people would not notice it, I'm fussy which is why I went for the 30XW, didn't want to fork out for a Paracorr). Very well corrected EP, and no distorsion. In my F7 the EOF is perfect.

IMO, can't find a better low mag wide field EP.....:thumbsup: