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Post by mikey cee on Oct 5, 2011 23:38:47 GMT -5
Hi Jim....Sure wish I had my own shop and metal fabricating equipment. I'm so fortunate in other ways tho'. I'd like to powdercoat things too but it's just too much at this stage. With portable stuff it's definitely the only way to go. But I think tidepool green and smoke gray powdercoat would be the cat's meow. ;D ;D Can't wait for you to finish and give us a report on that lens. How close was your focal length to the purported 72"? Later Mike
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Post by jimcurry on Oct 10, 2011 9:50:08 GMT -5
The tube/dewshield will be the same deep blue as my 4" I built earlier this year. I stripped down the 4" and I'm having cell, backplate, etc. black anodized, 6" too. With any luck I'll get all parts this week with an assembly session this weekend.
Jim
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Post by mikey cee on Oct 10, 2011 13:34:39 GMT -5
Oooohhh like cool daddio! Mike
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Post by Watcher3 on Oct 10, 2011 15:08:39 GMT -5
Sounds like a real looker!
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Post by jimcurry on Oct 10, 2011 17:29:41 GMT -5
Mikey:
I didn't really measure the focal length, I just rig up a board to support the lens at one end and the focuser/turret at the other end. Once I have some tree tops about 1/4 mile distant in focus I measure the flange to flange distance and I know how long to cut the tube. With my somewhat standardized design using AP focusers it's 14" less than the stated focal length. I figure the focal distance is within about 1/4" from those tree tops to infinity. With 4" of travel I set the focuser at the midpoint and I'm confident I'll have plenty of travel available for any eyepiece I drop in.
Jim
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Post by jimcurry on Nov 9, 2013 7:00:13 GMT -5
Well, I never did finish this thread. I've not taken any photos until recently and here's one a buddy took of me and the scope. The lens is shockingly wonderful. On a steady night this instrument is loafing at 300x on double stars. My 80mm Unitron and 4" Istar can discern some pockets along Hadley's Rille, with this scope I can trace the full extent as well as great detail of the craters and sink holes along its length. The views with an f/12 scope are so steady. Set the focus and forget about it. I try to use eyepieces in sets in my turret. That way they're parfocal so little adjustment is needed. These Astro Physics focusers, once I degrease and regrease them, are buttery smooth and the 3" knobs provide precise adjustments. I like 1:3 ratio on the dewshields of my scopes. No dewing issues even when rivulets are running down the OTA. I have a few smaller Zeiss and Jaegers lens sets to build OTA's for. I have some time to think about which Istar lens will be next :>). In the meantime, Jupiter is getting closer to being an evening showcase in early 2014. Can't wait! Jim Attachments:
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Post by boomboom on Nov 9, 2013 19:11:30 GMT -5
Oh drool....inspirational Jim. Like the 3:1 dew shield too. I have just found the Moonraker site..... Back to the shed to finish mine. Matt
P.S. Any painting tips?
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Post by jimcurry on Nov 11, 2013 7:49:11 GMT -5
Oh drool....inspirational Jim. Like the 3:1 dew shield too. I have just found the Moonraker site..... Back to the shed to finish mine. Matt P.S. Any painting tips? Painting tips? Yup, powder coating! Rugged, glossy, deep color. Jim
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Post by astromanuk on Nov 11, 2013 8:44:29 GMT -5
That is one beautiful instrument Jim! If it Performs half as good as it looks it will be a real gem.
Can't wait for observing reports.
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Post by jimcurry on Nov 14, 2013 7:44:19 GMT -5
That is one beautiful instrument Jim! If it Performs half as good as it looks it will be a real gem. Can't wait for observing reports. Ian: I've had some fantastic nights with this scope. Last autumn I was out observing double stars with it. I forget which star it was in Cassiopeia but it was a tight one. I took the scope up to 300x with a 6mm eyepiece. I was comparing views between different eyepieces. The scope was in perfect collimation and showed perfect rings with a rock steady views. The secondary lay just outside the first diffraction ring and was like the tiniest of jewels hanging there. This past weekend I had a chance to do some evening lunar observing. Saturday wasn't much fun, 120x and the atmosphere got wobbly. Sunday I swear the atmosphere over St. Louis stopped moving. I was observing the moon for about 1-1/2 hours from sunset on. I was up to 360x and still revealing more detail! As time wore on I did have to dial it back moving from 5mm to 6mm to 7mm as the atmosphere cooled but it was an evening for the record books. I woke up for a midnight session on Jupiter but was disappointed with a mediocre 150x useable mag and no real details revealed. But, the short story is when the atmosphere permits, this lens performs! It has a great Strehl for an achromat and myself and anyone else who looks through it is impressed. Jim
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Post by astromanuk on Nov 15, 2013 6:52:15 GMT -5
Hi Jim, your observations remind me of my first 6" f15 which I was using three decades ago. It was almost a year after installing it in my observatory that I had my best view ever of Jupiter through that telescope. That image is etched in my mind together with the view of Saturn I had through Patrick Moore's 5" Cooke refractor when I was 14. Long focus refractors have been in my life for a long time. It is lovely to see them having a revival through the work of Istar and enthusiasts like you who are out there observing with them.
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