nFA Observing Report September 24 and 25, 2022

[notFritzArgelander]

This series of observations was suggested by the thread viewtopic.php?t=26828&hilit=starbase+nFA

There was a suggestion from @Lady Fraktor to compare the performance of the Starbase Orthoscopics (long focal lengths are Kellner and shorter are true Plössl, perhaps after Clave’), particularly in fast f5 scopes. So, here’s the report(s).

September 24

I was visiting the grandkids in SLC so OTAs include:

AWB 130mm f5 Newtonian on a tabletop Dobsonian mount
Orion ST 80mm refractor on the Orion StarSeeker IV go to mount.

The eyepieces selected were the GSO SV 20mm with a 68 degree AFOV as a finder only. The BCOs, the Starbase Orthos, and the KK Fujiyama Orthos (after Abbe’) as a standard. However I preferred the GSO 20mm SV to the BCO Plössl 32mm since the smaller exit pupil would give better contrast at the cost of a slightly smaller TFOV even though there would be seagulls at the edges. The full sets weren’t used as I concentrated on using the eyepieces giving an relatively even spacing in exit pupil. The performance parameters of the eyepieces used in the OTAS are:

The AWB:

type / format f AFOV stop relief M TFOV pupil
GSO SV 1.25 20 68 23.735 18 32.50 2.09 4.00
BCO Abbe’ 1.25” 10 52 9.075 10 65.00 0.80 2.00
BCO Abbe’ 1.25” 6 52 5.445 4.5 108.33 0.48 1.20
KK Ortho 1.25" 25 42 17.4 22.2 26.00 1.62 5.00
KK Ortho 1.25" 9 42 6.3 7.6 72.22 0.58 1.80
KK Ortho 1.25" 5 42 3.4 4 130.00 0.32 1.00
Starbase KE 25 45 19.634 18 26.00 1.73 5.00
Starbase KE 20 45 15.707 14 32.50 1.38 4.00
Starbase Plössl 14 45 10.995 12 46.43 0.97 2.80
Starbase Plössl 9 45 7.0681 7 72.22 0.62 1.80
Starbase Plössl 6 45 4.712 4 108.33 0.42 1.20

The Orion ST80:

type / format f AFOV stop relief M TFOV pupil
GSO SV 1.25 20 68 23.735 18 20.00 3.40 4.00
BCO Abbe’ 1.25” 10 52 9.075 10 40.00 1.00 2.00
BCO Abbe’ 1.25” 6 52 5.445 4.5 66.67 0.60 1.20
KK Ortho 1.25" 25 42 17.4 22.2 16.00 2.63 5.00
KK Ortho 1.25" 9 42 6.3 7.6 44.44 0.95 1.80
KK Ortho 1.25" 5 42 3.4 4 80.00 0.53 1.00
Starbase KE 25 45 19.634 18 16.00 2.81 5.00
Starbase KE 20 45 15.707 14 20.00 2.25 4.00
Starbase Plössl 14 45 10.995 12 28.57 1.58 2.80
Starbase Plössl 9 45 7.0681 7 44.44 1.01 1.80
Starbase Plössl 6 45 4.712 4 66.67 0.68 1.20

Accompanied by a grandson we set up the Orion ST80 on the SSIV and did an alignment. Part of this was instructional. Living in SLC under heavy light pollution a goto mount is a good idea. He is quite good at using SkySafari but I am seeing an upgraded mount in his future. Unlike previous sessions where we used a heavy metal picnic table to support the tabletop dob, he set up the AWB on a light TV table. I regarded that as another teaching opportunity.

Conditions were clear and transparent with poor seeing condition trending to average later.

After aligning the ST80 we tried to do a few DSOs while waiting for the winds to calm and the seeing to improve. We aimed at M11 and the seeing was still poor. Only the brightest handful of stars could be resolved from the milky background of unresolved stars. I had forgotten my diagonal, so I asked to borrow one and got the Orion prism diagonal on loan which I don’t like with the ST80 it introduces lateral color. So, OK, I discount the observations we made of Jupiter comparing the KKs and Starbase eps. I will redo this when at home with a diagonal I like with the ST80.

We switched to the AWB and as I suspected the table was insufficient support. Jupiter was in focus as a doughnut rapidly orbiting the center of vibration.

On September 25 we fared considerably better. The seeing was better than the night before. Lower wind speeds and average trending to above average as the evening progressed.

We detached the AWB from the tabletop dob mount and used the SSIV. My grandson successfully accomplished the alignment with almost no cues from me.

First up was again M11. Using the KK 25 and 9 and the Starbase 20 and 9 the cluster was fully resolved and a magnificent sight. There was no discernible difference in the views. Hoping for a partial resolution of the outer members we next turned to M13 but we did not achieve resolution.
Our first planetary target was Saturn. The KK and Starbase 9mm gave equally excellent views and cloud bands were noted. Several of the moons were available too but I did not do an identification. There were five candidates. Titan was obvious. No Cassini Division but the cloud bands were quite distinct at moments of best seeing. The 5mm KK and 6mm Starbase were atmosphere limited.

We turned to Jupiter next. The Galilean moons presented nicely and prompted a discussion of orbital dynamics. Again, we concentrated on comparing the eyepieces at the 2mm exit pupil and found the 10mm BCO, 9mm KK and 9mm Starbase to be indistinguishable in performance. At moments of best seeing four bands were discernible, which was a bit of a surprise. There was no discernible difference in the quality of the view. Equal contrast and no color differences were noted. To get all four of the available bands to show all you had to do was wait a little.

Highly satisfied with the observing session thus far, (my grandson demanded his parents share in the observations), he retired for the evening. I kept on chasing summer nebulae with the Altair Astro 1.25” Tri-band filter with little joy to be had. To finish I turned the AWB with the KK 25mm towards the Double Cluster.

No hard conclusions since this was a shared experience and I did not have the usual time for careful intercomparison that mark solo observing sessions. But the experience I had in this session hints that there isn’t a dimes worth of difference between the Starbase and KK orthos at f5. This differs from my earlier comparison of them in the VMC110L at ~f10. Perhaps the slower scope gave the KKs and edge that they don’t have at f5? The higher transmission of the Starbase KEs has also been noted before in observations of DSOs at f10.

Anyway, I’m intrigued and will research further. To make a more direct comparison I hear a rumor that an AWB is on its way to me.

[Lady Fraktor]

Good evenings with the grandson nFA.
Some interesting findings so far, I use Kellners but usually at slower than f/8.
So far I am leaning towards a set of these eyepieces before the price rises.

I am looking forward to any more observations with these!

[notFritzArgelander]

Good evenings with the grandson nFA.
Some interesting findings so far, I use Kellners but usually at slower than f/8.
So far I am leaning towards a set of these eyepieces before the price rises.

I am looking forward to any more observations with these!

I'm surprised at how well these Kellner's do. More and more measured observations will follow. I did not look hard at astigmatism at the edge of field of the Kellner's. That's up first on my to do list. The ST80 should be good for that with a suitable diagonal.

[Lady Fraktor]

Well Dai-ichi Kogaku have been making eyepieces for almost 70 years now so I did expect them to be decent eyepieces but your findings so far are surprising.

[notFritzArgelander]

Well Dai-ichi Kogaku have been making eyepieces for almost 70 years now so I did expect them to be decent eyepieces but your findings so far are surprising.

Indeed they are surprising. I'm so surprised I need to redo this under more controlled and relaxed conditions.

[Lady Fraktor]

I am just fascinated that a Kellner is playing nice with a fast mirror...
The 130mm AWB is a great telescope in that size and Kellner are good eyepieces with the right scope, but fast mirror + Kellner....

[notFritzArgelander]

I am just fascinated that a Kellner is playing nice with a fast mirror...
The 130mm AWB is a great telescope in that size and Kellner are good eyepieces with the right scope, but fast mirror + Kellner....

Yes, that's something that needs replication. I did not spend much time with the Kellner eps so please don't make too much of it. On the planetary observations I did not use them at all and concentrated on the Abbe' and Plössl designs among the KK, Starbase and BCO series. I only used the KEs on DSOs and the most that can be said with certainty is that they suffered much less from edge of field distortion than the GSO SV.

[helicon]

Very interesting report and useful eyepiece comparison. I also am a bit surprised at the Kellners performance in a fast optical system. Then again my old Edmund RKE (circa 1979) performs pretty well in the f/6.5 scope. Congrats also on the VROD award for the day notFritz (9-30-2022).

[notFritzArgelander]

Very interesting report and useful eyepiece comparison. I also am a bit surprised at the Kellners performance in a fast optical system. Then again my old Edmund RKE (circa 1979) performs pretty well in the f/6.5 scope. Congrats also on the VROD award for the day notFritz (9-30-2022).

How very kind! Thanks for the VROD!

[notFritzArgelander]

Very interesting report and useful eyepiece comparison. I also am a bit surprised at the Kellners performance in a fast optical system. Then again my old Edmund RKE (circa 1979) performs pretty well in the f/6.5 scope. Congrats also on the VROD award for the day notFritz (9-30-2022).

I revisited the question of what is the fastest scope in which these eyepieces are supposed to work using the reference at the top of this thread: viewtopic.php?t=4250 The GSO, 5 elements in 3 groups, is likely an Erfle II and allegedly good down to f4. The Kellner and RKE designs are allegedly good to f6 as is the Abbe' heritage. The Plössl is good to f4. So perhaps, I'm thinking, the really big surprise is the relatively poor showing of the GSO SV. Perhaps I have a lemon?

[Bigzmey]

Great to hear that your grandson is sharing your passion for astronomy, nFA. I have a long way to go to get there.

Congrats on the hectic by enjoyable session with family and VROD!

[notFritzArgelander]

Great to hear that your grandson is sharing your passion for astronomy, nFA. I have a long way to go to get there.

Congrats on the hectic by enjoyable session with family and VROD!

Thanks. I've fallen a bit in love with the AWB as a grab and go device.
This grandson might have a future in quantitative pursuits but I think his favorite sciences are biological. The other grandson is wordier and definitely more lawyerly. He'll take a look if something special is in the offing but is not interested in learning the ropes of it. That's OK. Kids often define themselves by their differences.

[kt4hx]

Well done nFA and despite not having the field to yourself for a deep dive comparison, the joys of sharing with a willing participant is very enjoyable. Glad to see the Starbase KE played that well at f/5, though I am surprised. Congrats on the VROD as well.

[Unitron48]

Excellent sessions and reporting, nFA! Congrats on the VROD. Best part was grandson time!!

Dave

[John Baars]

Congratulations on the VROD!

[Makuser]

Hi nFA. I knew that for many years the Kellner eyepieces were in popular use for binoculars, however you have displayed that they be used in short focal length refractor telescopes with success. It looks like you had a great time performing your telescope/eyepiece comparisons and also had fun with your grandson. Thanks for a great observing report nFA and congratulations on receiving the TSS VROD Award.

[terrynak]

Very nice observing sessions with the ST80 and the AWB OneSky, NFA!

My version of the AWB OneSky was branded as the Bushnell Ares 5, which I got in 2011 and was discontinued by 2012. The AWB OneSky became available by late 2013. However, in Canada and the UK it was always available as the Skywatcher Heritage 130p. You probably knew about the history of this scope, but just in case there are readers who didn't...

Hope you get your AWB OneSky soon, if not already! Can't wait to get mine out on the next clear night.