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Old 27-02-2008, 03:08 AM
Its only a column of dust

žAB is offline
Join Date: Aug 2007
Location: New Iceland
Posts: 761
12 inch dob first light

Ok I found a great deal on a used 12" Abell muncher so I bought it. The scope is truss and has a hand figured mirror. The mirror is 304mm and focal length is 1415mm making it F4.65. The finder is actually a 50mm binocular objective fitted with a 1.25" diagnal with interchangable eyepiece capability, how cool you can change the finder's mag! Now I've got a use for my 25mm Kellner The finder has an old 30mm Celestron plossl in it, and its views are pretty good I must say! Physically, the scope is beast! Although its mirror is only 2" larger than my 10", the thing is basically twice the size!!! The collimation springs are about as big as your 4WD suspensions

This is my first experience with a truss scope so its all a learning process. Ofcourse, being the first time out I did a few clumsy things, which I learned from. After 5-10 uses, I'll feel right at home.

I messed with the collimation in the dark, so I'm not sure if I got it right, but with the views I got I'm assuming I did something right! When I dropped the 22mm LVW in, I was shocked that it would not come to focus. I tried my other EPs, no focus. I then moved the primary as far forward on its collimation screws as possible, then voila! The 22mm JUST reaches focus while the remaining EP / Barlows are comfortably within focus range. I also tried shifting the secondary closer to the focuser (might've been too far off, dunno) to move the focal point further out and get comfortably within focus range. I'll have to experiment with collimation later and get a feel for it. Unfortunately, I discovered that the collimation shifts slightly when the scope is moved towards the zenith. For instance, the primary center ring moves away from the cheshire dot once you get above around 60-70║ altitude. That;s something I'll have to follow up.

First views, very encouraging. Especially considering my collimation attempt!

I suspected that the nebula actually appeared more textured than with the 10". This was at 108x, and all 6 trap stars were easy. One thing that struck me was 3 faint stars at the limit of visibility in the 10" were quite bright in this 12".

Eta Carinae
Moon was just rising, but I do believe the star count in this region has increased somewhat over what is visible in the 10". The nebula appeared similar, but the keyhole was slightly more obvious. Actually I was surprised by how well the nebula was visible in moonlight.

Homunculus Nebula
Damn, its a different object in this thing! Using powers of 217 to 272x, The structure was crazy....I could see a tiny star right next to Eta Carina which I've never seen before. There were two spikes shooting out from Eta Carinae perpendicular to the main lobes. Haven't ever seen these either. The difference between the 10 and 12 here is pretty big

Very nice views at 217x, sharp but seeing wasn't fantastic. Cassini division easy, extending beyond the ring tips. Crepe ring easy aswell, some banding visible on the globe. IMO, the view in the 12" was virtually the same as in the 10".

Physically, the scope is more demanding than the 10" solid tube GSO. The size means I have to dismantle it with each trip in n out which takes a bit of effort, but the views are so worth it This puppy will be saved for those moonless all nighters, rather than casual observing. Frankly, my 10" dob is MUCH more easily deployed and packed away and hence will definately continue to see good use
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