Delos nudges Pentax, Nagler

I recently received a Stellarvue SV80-ED for use as a light travel scope alternative (the doublet with the FPL-51). I’ll want the option of using on a camera tripod, so want to keep it light.

With a focal length of 560mm, I wanted an eyepiece that would give me about 150x, so settled on a 3.5mm, which will give me 160x, or about 50x/ inch.

But, which eyepiece? I have a Pentax 7mm XW, a Delos 6mm, and a Nagler 5mm, and all are offered as a 3.5mm.

I decided to try all three in a daylight shoot-out to see which would be the best choice for my 3.5mm. (Of course, since I’ve got the scope, it’s been cloudy at night.) Target was the top of a 50’ cedar tree, about 150 yards away. This is not quite at infinity focus.
Going into the competition, I expected the winner to the the Nagler T6: At night, in my 10” Newt, I really like the Nager T6 9mm especially: it is compact size and weight (222g), I find the 12mm eye relief comfortable, and I like the 82 º AFOV. For a small scope where size and weight were an issue, it seemed to be a slam-dunk.
But, I was surprised by the amount of Chromatic Aberration in the 5 mm Nagler T6 – quite a bit of yellow outlining of the branches. To be sure it wasn’t the telescope objective, I also checked with the 5mm setting of a Nagler 3-6 zoom – no CA in the zoom, so it wasn’t the scope.

Next up was the Pentax 7 XW – significantly lighter than the Delos (388g), legendary optics and, at about 70º AFOV, still pretty good field for high power eyepiece. I’ve had this eyepiece for a while, and thought I knew it well, but I was surprised, in the day-light, how much blackout I was experiencing at the edges of the field, no matter how I adjusted the cup. I guess I just hadn’t been noticing this at night. No CA, bright, sharp image.

Finally, the Delos 6mm – very nice – I could adjust the eye-cup to remove any blackout, which made observing much more relaxing. A very bright, crisp image, with no CA. The tripod and focuser seemed to handle it fine, so the weight of 469 g may not be an issue after all.

So, the Delos, despite its larger size, wins the right to represent the 3.5mm class in my eyepiece case – Congratulations, Mr. Delos!

David, congratulations on the Stellarvue.
Good report on the eyepieces.
Strange about the c/a in the Nagler.
Have you ever seen c/a in the Nagler when using it at night?

Steve

I hadn't noticed the CA at night, but I haven't tried the Nagler 5mm on bright targets. I expect I'll be using the 80mm on mainly bright targets, like Moon and planets, where the CA may be more of an issue.
So, I'll have to give that a try.
(Who would have thought a measly 80mm scope would bring an end to a record-setting string of clear nights? This new scope curse is without mercy!
)

Who would have thought a measly 80mm scope would bring an end to a record-setting string of clear nights? This new scope curse is without mercy!
)

Yes..... Who would have thought....
Thanks for that..... !@#$%

If you bring it to the Merritt Star party you will have to be careful. I've heard they sacrifice the smallest scope to the cloud gods...

The Delos 6mm is a great choice but I am surprised you couldn't adjust the eyecup satisfactorily on the XW 7. It is very easily adjustable to exactly the right height and even many Delos-lovers have conceded that the XWs have the Delos beat in this regard. Also, I would be concerned that you picked another eyepiece over the XW 7 based solely on daytime tests but since you chose a Delos, an eyepiece in the same 'class' as the XW 7, you should be fine.

The Delos 6mm is a great choice but I am surprised you couldn't adjust the eyecup satisfactorily on the XW 7. It is very easily adjustable to exactly the right height and even many Delos-lovers have conceded that the XWs have the Delos beat in this regard. Also, I would be concerned that you picked another eyepiece over the XW 7 based solely on daytime tests but since you chose a Delos, an eyepiece in the same 'class' as the XW 7, you should be fine.

+1

The Pentax eyecup is mechanism is much simpler than the Delos, and probably contributes to its lighter weight; but, I was unable to find a suitable position throughout the range of its adjustment. I'm sure YMMV.

Same experience here, I have the Delos 6mm and to my eye (good eyesight, no glasses) it's less prone to beaning/blackouts compared to the Pentax 7mm (which I used to own). Definitely YMMV. Also have the Nagler 5mm T6 and I'm keeping it because of the expansive 82-deg FOV.

Best,

Tried this shoot-out again this morning. A cloudy background, instead of the bright, blue, sunny day of yesterday.

No yellow fringing with the Nagler (5 or 9), so perhaps the CA I saw yesterday was due to the exceptionally bright light of the background (not a problem at night!).

I spent more time with the Pentax, adjusted at various positions, but still found unstable beaning/ blackouts, while the Delos was rock-solid.

My eyesight is quite poor (-5.25), but I observe without glasses. Perhaps this has an effect on the where the focused exit pupil image is presented for me, and the Pentax does not control this as well for me as it does for others. Whatever the reason, there seems to be a subjective difference here.

... which illustrates really well the what's and why's we should all be thankful for- that there exists some excellent gear out there that almost ANYone can find that works *best* for them, their eyes, their face, their viewing preferences.

I've got 3 T6s used for mostly HA and some lunar-planetary all of which have very good lateral color correction. For night viewing I prefer my 2 Delos and 2 XWs over the T6s, for HA they're different but equal. For me the Delos and XWs are close in ease of use though the Pentax are more sensitive to eye position being off when it comes to lateral color. I put 2" eyecups on my T6s which made for much improved ease of use but they still lag behind the big boys in this reguard. The XWs are more prone to blackout when barlowing. A plus for the Pentax is their eyecups adjust higher so the extra ER when barlowing is easier to deal with. David

If you bring it to the Merritt Star party you will have to be careful. I've heard they sacrifice the smallest scope to the cloud gods...

I'll gladly contribute a straight-through stock finderscope to the sacrifice!

So, I got the Delos. It didn't hurt that it was on sale for $315.00, so less than the $325.00 for the T6 (not that $10.00 makes any difference in the long haul.)

Interesingly, the Delos 3.5 is yet another 100g heavier than the Delos 6, at 488g, over 388 g.

But, I did have a slight impression that the Delos 6 was a tad sharper than the T6, (which also seems to the weight of opinion on CN) and, like all us obsessive astro-neurotics, would have had the niggling doubt with the T6 that it wasn't giving me the best image.

So, bring on the clear skies!