Pentax XF 8.5mm vs Radian 8mm and 10mm

[michael.h.f.wilkinson]

Yesterday I finally got to compare the new XF 8.5 mm with the Radian 8 and 10 mm in my C8. As I reported here, I used all three EPs on Jupiter, and the XF 8.5 was the winner. Even though the seeing was patchy, as I first noted in the 10mm Radian, the GRS and associated festoon in the SEB was visible, with pretty good contrast in moments of good seeing. I then swapped in the 8.5mm, not expecting much under these conditions. I was wrong. The festoons in the SEB and the lighter edge to the GRS stood out far more clearly. Now I thought I had hit a still patch in seeing, but the difference in brightness of the image was striking. At 239x you expect a dimmer image than at 203x, but the impression was of a brighter image in the XF 8.5 vs the Radian 10. In direct comparison, the Radian showed a slightly warmer, yellowish tint compared to a more neutral tone in the Pentax XF.

The Radian 8mm showed the same warmish tint as the 10mm, and had slightly less contrast and sharpness than the XF 8.5mm (might be due to magnification, although the difference is slight: 239x vs 254x). In terms of comfort, the EPs are equal. I had no problem in seeing the whole FOV and no problems with kidney beaning. Build quality is similar too, with the Pentax being slightly lighter.

In summary, the EPs are quite closely matched, with the Pentax nosing ahead to steal the win, in particular in terms of brightness and colour neutrality, and slightly less so in terms of the crispness of the image. I hope to have another shootout on some lunar observing tonight. The Trapezium might be another test for throughput.

[AndyH]

Nice report.

Might be only two eyepieces in the XF range, but superbly priced compared to Radians. Especially with the confirmation of optical quality.

'Superbly priced' and 'Pentax', in the same sentence? The world is going mad

Andy.

ps: 'throughput' report will be of interest.

pps: There may only be 2 eyepieces(8.5 & 12mm), but they are a good FL for those with scopes in the 1200mm and higher range, looking for sharp, higher power eyepieces. In my humble opinion.

ppps: If anyone had a 9 or 12/12.5mm ortho, to go up against these XF's, that would make for a further interesting comparison.

[michael.h.f.wilkinson]

Nice report.

Might be only two eyepieces in the XF range, but superbly priced compared to Radians. Especially with the confirmation of optical quality.

'Superbly priced' and 'Pentax', in the same sentence? The world is going mad

Andy.

They are the bait in the trap to get you to buy XWs!! Run while you can! It is too late for me, but you might still escape!

[AndyH]

I added some ps, pps and ppps's to my post. Sorry about that.

If I were to suddenly find money under the bed, the Pentax range is one I'd take a serious look at. I like a 70 degree eyepiece. Very pleasing to the eye. I have a Nikon 10mm, 72 degree eyepiece which is simply stunning. Meant for the birding scopes, but if an adapter is made, they work beautifully in astro scopes. I believe this range is what the new Nikon NAV SW(not to be confused with the monumentally expensive HW's) is based on.

Back on topic. These XF's sound very, very nice indeed. Look forward to any further reports you post.

Cheers,

Andy.

[Flyingpig]

Nice report just a little thought - is there any chance the radians quality could have been slightly tarnished for example by fingerprint grease or some other surface film so that the radians are less than prime. If the radians are pure then that review is very favourable of the Pentax. In contrast I have found the Celestron Ultima LX and Axiom LX to be other Radian beaters so to speak.

[michael.h.f.wilkinson]

Nice report just a little thought - is there any chance the radians quality could have been slightly tarnished for example by fingerprint grease or some other surface film so that the radians are less than prime. If the radians are pure then that review is very favourable of the Pentax. In contrast I have found the Celestron Ultima LX and Axiom LX to be other Radian beaters so to speak.

An important point. I always take great care not to get any grease on the optics. Though not new, I would say these Radians are as new. The odd speck of dust may be present, but the same holds for the Pentax.

[Tinker1947]

I'm pleased my my XF 8.5mm.

[michael.h.f.wilkinson]

Part II of the test (well, actually I did briefly test them in my 80mm before) was carried out yesterday. All three EPs showed great detail around the Straight Wall on the moon, with the Radians showing a subtly warmer tone than the Pentax (not a real problem though). The Pentax did seem to have the edge in terms of contrast, with the black in the shadows of the craters appearing just that bit blacker. Subtle details in the plains appeared just that more prominently. Again, the differences are subtle. All three are great EPs. On this occasion the Radian 8 showed a bit of kidney beaning from time to time, which was completely absent in the Pentax XF 8.5.

I then swung towards Orion, and I carefully focused on the Trapezium. In the 8mm Radian I could of course spot A-D, but E remained elusive. Occasionally there was a suggestion in averted vision, but nothing solid. The XF 8.5 gave a slightly sharper view of A-D, and E was spotted fitfully in averted vision. It was not a solid observation (which I have made under better skies even at lower magnification), but there was a definite hint, whereas the 8mm it was really to faint to be sure. I did not try the 10mm.

I then turned to Jupiter, and compared the Radian 8 to XF 8.5mm again. The moons were consistently sharper in the XF 8.5, and the bands showed a bit more contrast than in the 8mm. Of course 254x requires a touch better seeing than 239x, but I feel the XF has the edge, albeit by a small margin.

I should compare the two in a faster scope (faster than F/10 and F/6 I have used so far), to give a final verdict, but I think the space for the 8mm Radian in my EP case will be occupied by the Pentax XF 8.5 instead. Getting an XW 10 to replace the Radian 10, and then adding an XW 7 to replace the 14mm UWA + 2x TeleXtender combo for those perfect nights seems a nice option too. Anybody know a good place to sell EPs?

[Damo636]

Nice report Michael. I am leaning towards a 10mm XW myself as i feel i need something in the 150x mag with the 12" scope.

I used to know of a really good place to sell eyepieces but sadly the powers that be removed it!!!

[Flyingpig]

Interesting; we noticed the same warmer subtle yelowish tone in the Radian when compared with a Celestron Ultima LX which we found also had a crisper Brighter contrast than the Radian.

I would be interested to see a comparison of the Pentax XF and Celestron Ultima LX. What price are the XF retailing for at present?

I also wonder if the Pentax XF and the Ultima share the same optics?

[michael.h.f.wilkinson]

Interesting; we noticed the same warmer subtle yelowish tone in the Radian when compared with a Celestron Ultima LX which we found also had a crisper Brighter contrast than the Radian.

I would be interested to see a comparison of the Pentax XF and Celestron Ultima LX. What price are the XF retailing for at present?

Mine cost EUR 159.

[Flyingpig]

The Celestron Ultima retails at a similar price, (although sometimes can be found on eBay for less £70 at present shipped from the USA!)

Could be the same optics I guess...

[michael.h.f.wilkinson]

The Celestron Ultima retails at a similar price, (although sometimes can be found on eBay for less £70 at present shipped from the USA!)

Could be the same optics I guess...

Probably not, but I am not going to look at yet another 8-ish mm EP for a while. The Ultima LX series boasts 70 deg FOV, not 60, and the focal lengths differ (8 vs 8.5mm, 13 vs 12.5mm), and eye relief is shorter (16mm for the 8mm vs 18mm for the XF8.5).

[Flyingpig]

Maybe, but I am not going to look at yet another 8-ish mm EP for a while.

No I'm with you there, its not really necessary if you've just bought one...

[michael.h.f.wilkinson]

No I'm with you there, its not really necessary if you've just bought one...

Even better, I got given one, just for staying on board of this planet for 50 rides round the sun

[faulksy]

Nice report.

Might be only two eyepieces in the XF range, but superbly priced compared to Radians. Especially with the confirmation of optical quality.

'Superbly priced' and 'Pentax', in the same sentence? The world is going mad

Andy.

ps: 'throughput' report will be of interest.

pps: There may only be 2 eyepieces(8.5 & 12mm), but they are a good FL for those with scopes in the 1200mm and higher range, looking for sharp, higher power eyepieces. In my humble opinion.

ppps: If anyone had a 9 or 12/12.5mm ortho, to go up against these XF's, that would make for a further interesting comparison.

that would be good

[andrew63]

They will be completely different optically as the Pentax are made in Japan.

[Flyingpig]

The Ultima LX series boasts 70 deg FOV, not 60, and the focal lengths differ (8 vs 8.5mm, 13 vs 12.5mm), and eye relief is shorter (16mm for the 8mm vs 18mm for the XF8.5)

Must confess I didn't look at those obvious differences...

[E621Keith]

Pentax's SMC coating is also suppose to be something special. Even if they copy the glass, it would be very difficult to copy the coatings.

Thanks for the review

[RikM]

The XW's are lovely but I find they black out quite easily on bright objects...well the moon.