Quote:
Originally Posted by Pharian
Hi all,
Can anyone recommend a 1.25 to 2" correct image diagonal for my C8?
Don't want to have to trade my firstborn, but also can't take the mental gymnastics of working out mirror images of the sky while I am learning my way around up there.
Any advice?
Cheers!
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The amount of sky you will see through the eyepiece at low power can be represented by the width of a fingernail at arms length. You do not need to do any mental gymnastics as any star patterns you see with the unaided eye will not be recognisable at the eyepiece as the field of view is so small.
Quote:
Originally Posted by Wavytone
If you are really determined to use a roof-prism diagonal to give a correct upright image I would suggest you don't, and instead learn to get used to seeing a reversed image.
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I agree. Get a quality 1.25" mirror diagonal and if you want lowest possible power then add an f6.3 focal reducer or get a 2" visual back which is not very expensive and often found used (one for sale now) and add a 2" mirror diagonal and use either 1.25" (with 2"-1.25" adaptor usually supplied with diagonal) or 2" eyepieces for lowest possible power. Note using both 2" low power eyepiece and f6.3 focal reducer does not always attain focus and I recommend against the f6.3 reducer for visual if going the 2" path.
Note the Celestron 93653-A visual back has a single screw lock with no compression clamp (unless they've added a compression clamp very recently). Without the compression clamp you are relying on that single screw to lock the star diagonal. The 93653-A has a lock ring that screws onto the thread at the rear of the telescope and the idea is to unlock this when rotating the diagonal and eyepiece so you don't have to loosen the screw locking the diagonal but in actual use the small lock screw can become loose.
You can get a 2" SCT diagonal which also has the lock ring or a SCT-2" visual back that then takes a standard 2" refractor diagonal. Whichever way you go you want the visual back length to be long enough so that if you place a large body eyepiece into the diagonal you can still rotate the diagonal and eyepiece without it fouling the focus knob. The SCT-2" visual back is likely to produce a longer path than the dedicated 2" SCT diagonal and you will find most observers use the 2" visual back.
Another option is replace the focuser with an SCT Crayford style but this does not work if the SCT is fork mounted due to clearance issues.
Whatever you choose, enjoy!
