View Full Version here: : 40mm Pentax XL first light report

06-05-2007, 10:39 PM
Hello fellow astronomers!!! I wanted to make a first light report of a 40mm Pentax XL as seen in my 8" f/6 reflector with 1/8" mask around the edge of the mirror making it a 7/5" f/6.3
Took the scope out in my yard at 6:20 PM for cooldown until 9:35 PM.
After cooldown, I took a peek at Venus in my 7mm Pentax XL at 171x for a very pleasing view at gibbous phase
and then slapped in my 2" barlow at around 350x for a closer look. The image was shimmering a bit , so I could tell that the air was slightly unstable, but the view was still very nice after refocusing a bit.
Then I moved the scope to catch a look at M-81/ M-82 in Ursa Major. I didn't have ANY maps with me, so I looked for that "L" shaped asterism with my 10x50 binoculars that makes the "tip of the rooftop" when joining some stars in the bowl of the Ursa Major.
I scanned the area with the 40mm Pentax XL and there they were!!!...Just visible in the 40mm XL were both galaxies...so I added my 2" 2x barlow for a closer look and the contrast was much better !!!
I then tried screwing the bottom of the barlow portion right to the 40mm XL making it into a 27mm eyepiece at 44x and it threaded perfectly onto the barrel making for a slightly smaller exit pupil,(4.3mm).
Next up was a look to the east for M-13 in Hercules. I scanned the area and saw it with my binoculars and then aimed my telescope there with the telrad and 14x50 finder. I put the 40mm Pentax XL in and looked...still not enough power to see detail, I added my 2x barlow for a closer look and it was better again. I then added my extension tube for a magnification of roughly 78x and this view of M-13 was just right.
I knew I had to get up for work the next morning at 4:30 am so I packed it all up at 11:00 PM and headed in for some much needed 4 hours of sleep before work !!!

Of course, I won't forget to mention the testing I did with some stars on the eyepiece on axis and off axis.

On axis- Extremely sharp
Off axis- (about 70% of the way out)- still very sharp
Off axis- (about 80% of the way out)- still very sharp
Off Axis- (about 85% of the way out)- need to confirm if it was coma or astigmatism, but it was so slight I couldn't really tell what it was...need to test again.
Off axis- (90% out then to the extreme EOF)- same as 85%

Overall, the 40mm Pentax XL is an excellent eyepiece with great light throughput and it shows stars with natural color and excellent sharpness. I only had it out the one night so this is only a tip of the iceburg as to what can be seen.

I am now very curious as to how the 31mm Nagler would be !!! I am thinking that the 31mm Nagler would have better correction then the 40mm Pentax XL near the edges. I did however try a 35mm Panoptic before the 40mm XL and I would have to say that I like the 35mm Panoptic a bit better as it has better correction towards the edges.

Happy Observing, I hope I covered enough, but I will need more time with this under different conditions!!!

04-06-2007, 07:49 AM
thanks for the replies everyone LOL

04-06-2007, 08:24 AM

Thanks for the very thorough report, Mark.

It's only just Monday morning here in Oz, so I think the lack of replies is more the product of the time difference between the US and Australia than a lack of interest/enthusiasm;)


05-06-2007, 10:31 AM
Thanks Mark,
many people have given positive comments with this eyepiece I've noticed. Have you tried it in your Refractor yet? I wouldn't be surprised if edge correction was better in this scope. I have a 30 XW and find it pretty good even at the edge of field with scopes from 900mm FL and up. I wonder how the XW40 compares with yours?

Enjoy the views and clear skies