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lets imagine I wasn't to see a nice DSO about 15' size and I think it should look good nicely framed with a 1 deg field of view in the EP..
Which would give the better (or higher probability of seeing anything at all ) view from a semi urban light polluted home site (e.g Bortle 6)?
a) an 100mm f/6 refractor (fl 600mm) and a 10mm EP (60 deg afov, gain 60x = fov pf 1 deg)
(and exit pupil of 100mm / 60 = 1.6mm)
b) a 200mm SCT with focal reducer to give f/6 (fl 1200mm) and a 20mm EP (60 deg afov, gain 60x = fov of 1 deg)
(and exit pupil of 200 / 60 = 3.3mm)
My gut feeling is that the SCT should give a better view just based upon its 2xaperture - but Im not sure I understand fully the maths why.
Is the larger exit pupil going to result in a better / brighter / more successful view?
Or will the view be 'roughly' the same ?
Or have I got it all wrong.....
I am only a few weeks into astronomy and started off with a Celestron 9.25" Evo on the standard AZ mount. I guess with hindsight this wasn't the best place to start and also with hindsight I would have done better to have bought a GEM mount. Anyway, lesson learned and at 71 years old I have to speed up the learning process compared to younger enthusiasts I have 2 issues. 1/ Its a pain dragging the scope out into the garden and setting it up every time I think the fickled weather might be obliging. 2/ I now know that the mount I have is useless for long exposures and a wedge is fiddly to get polar aligned.
My question is, though I gather wedges are a PITA to setup etc is if I was to build or buy a pier for the backyard and use my existing mount + a wedge is this a reasonable way to go? Though it's fiddly to set the thing up once set I could leave the mount, wedge, etc covered up and would just need to drop the OTA on when I wanted to use it. Is this reasonable or am I missing something fundamental down near the bottom end of my learning curve
Any advice much appreciated and don't feel you have to spare my feelings
By Cosmic Geoff
I recently acquired a used CPC800 SCT. I thought a 'First Light' report might be of interest.
First impressions: the tripod is a heavy duty affair with thick legs, a folding lower spreader and a big cast alloy eyepiece tray/steady. The OTA/fork assembly (not separable) is very heavy (21Kg/44lbs) but has a couple of grab handles. You need to be fit to handle this. ? (I was seriously tempted not to go ahead with the purchase after trying the weight.)
With the legs retracted it is just possible to pass the tripod through a standard doorway, but it is just as easy to pull up the lower spreader and carry it folded. It is much heavier than a C8SE tripod but more comparable with a EQ5 tripod in weight. Once in position, I checked the level with the handy built-in bubble level and left it. I forgot to screw up the eyepiece tray/upper spreader but I don't think this made any difference.
Scope stored on a table with faceplate down and rear handle uppermost. Took the weight with my left arm, elbow fully bent, forearm vertical. Got it on the tripod which took the weight till I got the base to drop over the centre pin, spun it till something clicked into place and then did up the three thumbscrews. I would not try this with an equatorial wedge unless I had a helper. Celestron also sell a CPC 9.25 and CPC1100 - if I had one of those I'd need a sheerlegs or a brawny assistant.?
Fitted the visual back (same as C8 SE), prism diagonal (same as C8 SE), straight-thru 50mm finder, handset (Nexstar+) and handset bracket which holds it facing rearwards (a handy feature not implemented on the C8 SE). Fitted a 25mm X-Cel LX that came as an extra.
Connected my new lithium powertank and its DC cable, and powered up. It comes ready (CPC Ready) very quickly. Selected 2-star auto align - it whizzed past a time display showing the time ahead of my watch by 1 hour - more on this later. Aimed at Arcturus and afjusted the finder aim. Selected Capella - it nearly got there and then blackout! The cable had snagged and pulled on the plug. I ran the cable through the side handle on the fork and tried again. (It appears that the CPC's supplied cable has a locking ring and the other end has a cigarette lighter style plug.) Capella ... Arcturus .. aligned. Told it to find Mizar (named star menu). It did.
Also found M48, the Ghost of Jupiter planetary, Gamma Leo (split ), 54 leo, 88 Leo, 90Leo. The scope appears to be collimated and resolution OK. GoTo is just accurate enough to drop doubles into the bottom of 9mm X-Cel Lx field. Even at 200x and a gusty night the view is rock steady. A pier mount could hardly be stiffer than this! And no obvious backlash in use (unlike C8 SE).
Fiddled with the menu, found the GPS is obviously working, and the time set for daylight saving. Corrected it to standard time. GoTo still works.
Teardown: tube horizontal, power off, tube cap on, diagonal off, handset and bracket off, left visual back on and capped it, loosened clutch to point tube straight down. Got OTA/fork assembly off and back indoors on table, twirled it into position. Folded up tripod and carried it indoors. I would not try carrying the tripod and scope together.
Verdict: Very solid mount should be good for planetary imaging. Some nice features not on C8 SE, otherwise same optical performance. Alarming weight.