Short But Sweet (the session, not the telescope)

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Short But Sweet (the session, not the telescope)

Unread post by Rotorhead »

Brian put out a very tempting invite to his place last night, but I needed to stay home and do some 'work' tuning up Mark's old 4" f14 refractor that is on loan to me. This scope has a main objective from a submarine periscope, and has given me some excellent views in the past. Set up, this telescope is over five feet long, which, with a 4" aperture, makes it resemble nothing so much as a WWII bazooka. Mark brought it to my place in December, for installation of a new 10:1 Crayford focuser, a clean-up (it's been sitting unused for a while), and a new retaining ring on the main objective. The holidays, then the arrival of grandkid #10, preoccupied me for too long, and I've only recently done my part to restore this nice refractor. For perspective, note that the finder scope on this photo is a fairly large 10x50 Orion.


Last week, I finally star tested the scope and found it to have a 'soft' focus, and an internal reflection of some sort, which made it impossible to observe anything. But on the other hand, during the evening's attempts, I found the old retaining ring, which had gotten loose somehow, and was stuck at the mid-point inside the dew shield, where it couldn't be seen from either end. A few minutes on my drill press the next morning had the retaining ring tapped for hold-down screws and installed where it belongs... Of course, this being New England, I had to wait three days for another clear evening to see if the retaining ring had improved the view through the scope.

When Mark heard I was going to take the scope out for another test run last night, he kindly offered to come over and apply his experienced eye to the objective to see if he could figure out the problem(s). We decided to keep the scope here, rather than test it at Brian's, since Mark was fairly certain that we would need to disassemble the objectives at some point, and we wanted my tools and workbench handy.

I set the scope out to cool at 1815, and went in to supper. At 1900, I set the scope on Polaris, and found the same internal reflection as before. A flashlight showed that there was no moisture on or between the elements, and a star test showed a spectacular set of diffraction rings, so the collimation was not suspect. Mark showed up shortly afterward, and he checked Polaris, M45, and M42, and saw the same problem as I had. Nonetheless, we could see 4 stars in the Trapezium with little difficulty, even at a fairly low magnification, so we knew the problem must be minor. Mark suspected that one of the elements of the objective had gotten reversed during the time the retaining ring was 'missing' and only a cardboard aperture mask was holding the objective in place. :shock: As soon as the objective was disassembled, the culprit was obvious, and Mark gave me some instructions on how to reassemble the objectives properly and without leaving fingerprints all over them. If you watch him, you can tell he's done this before... :)

Rushing outside to test the scope, we found the internal reflection gone, the collimation still good, and the views to be spectacular. My subdivision is more correctly described as semi-urban, rather than suburban, with a distinct sky glow from Fall River, two streetlights abutting my house lot, and several neighbors who feel that porch lights add ambiance to the night. Because this was an 'equipment testing night' rather than an 'observing session' per se, we were working on my driveway, which is the worst spot in my yard to observe. And then my son's cat kept tripping the garage light sensor, which didn't help, but he's such a friendly cat that it's hard to complain. He's become a faithful companion on cold nights when I'm observing alone in the yard. Except that he has tried to get inside my big dob on several occasions... while I'm observing :(

Given the light situation here, we still ran several targets, with the Trapezium showing five stars at 166x, the Cassini Division on Saturn (along with about four or five moons), and some nice views of M45. We tried several filters on M42, and found that this little scope gets some fairly decent details within the nebula. We tried to pull in some galaxies, to no avail, and Mars was too high to view with such a long scope, which nearly drags the eyepiece on the ground when aimed at zenith. We spent some time trying to find the Flame Nebula, also without success, and we tried but failed to split the Pup from Sirius. As the night had progressed, the sky was deteriorating, and we had developed some serious 'boiling' in the field of view at high powers.

The rest of the evening was occupied with diffraction ring and Airy disk tests, which revealed that this little wonder is back in action, and ready for some dark skies. By 2200, we both had frozen toes and sagging enthusiasm, so we called it a night. A short night, surely, but sweet nonetheless. I had wanted to get this scope working for the Mars opposition, but sat on my thumbs for too long. So now it will get a workout on Saturn and Jupiter as springtime moves along. This is also an excellent tool for double stars and galaxies (under a dark sky!), and I hope to give it a good workout in the coming months.
Last edited by Rotorhead on Tue Feb 26, 2008 8:44 pm, edited 1 time in total.
Bob M
15" f5 Starsplitter Dob/80mm Finder
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"He numbers all the stars, and calls each one by name." Ps 147:4
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Unread post by Bruce D »

Sounds like a successful night for you guys, hows the color on that periscope objective?
Bruce D
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Unread post by Mark G »


Nice report. 8) Reading it I felt like I was there! ... err wait I WAS! :lol:

Too bad I'm so experienced with refractor objectines that I dropped it off to you with the front element reversed. :shock: :lol:

Luke's cat added a nice flavor to the EP time we shared. A young "coon cat" that is very friendly was a real joy for me. As my son is allergic to pet dander Sandy & i had to find new homes for our 2 cats. :( Now hearing he wants inside the dob when you are using it is a HOOT! :lol: I'm not surprised at all though as a cat wants to sit on the newspaper when you are reading it. :lol:

Brian, I'll make it to your next observing invite I hope you & Joe had a good night too! :D

Bob if you can email me the image you took last night I'll get it so you can post it here.

Bruce at 166x Saturn had only the slightest hint of deep blue that honestly I had the hardest time seeing. Sirius at 300x+ was a different story. Not horrendous but noticable.
Clear skies,


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Unread post by Pete »

Thanks for sharing Bob. With a detailed report like this, and knowing you guys, it's like being there.
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Unread post by Galactus »

Another report in which I feel I'm looking over the poster's shoulder! I am starting to get the bug to get a couple of scopes beyond my SCT, and a refractor or newtonian have been getting my notice...your report, Bob, kinda gives me a hankerin' for a refractor. Great report! :)
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Unread post by WCGucfa »

Hey George,

There's nothin' like a good ol' (new) refractor. ED of course, if you can swing it.

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