First thing for a SCT.

[MartinB]

Paul, I had an 8" Celestron Nexstar GPS for  a couple of years.  It was the nicest scope I've ever had for observing, I loved the alt az fork arrangement.  I was always happy with the stock focuser, it was a great planetary imager and I also got a wedge for DSO imaging.  The design makes very low demands on EPs.  I often used a 30mm Moonfish UWA which gave fantastic views, cost around £80 new (not a great EP in an F5 dob though!).  A change of focuser with this scope wouldn't have been a great value for money investment at the time.

I now have and 10" LX200 ACF OTA.  The focuser on this gave lots more mirror shift and also requires use of focus locking.  The focuser is adequate for observing but was well worth the upgrade to  a motorised moonlight crayford.  It's all useless if the optics are dewed up though!

[YKSE]

I've got a FeatherTouch Crayford on mine which has the advantage of using the maximum aperture of the visual back, is as smooth as butter and it means you don't have to use the focuser that moves the mirror up and down. 

Not having issue with moving mirror is an advantage with an external focuser (none-micro), but, are you sure that you get bigger TFOV ? There're a quite a lot discusions on other site, the concensus is

Every 1mm increase in light path over about 100mm after the rear port increases the SCT focal length by 3.1mm.

The nominal SCT's focal length is calculated with the stock visual back (diagonal with SCT fitting).  An external focuser adds easily 100mm light path, that's 310mm longer focal length for SCT, which should mean narrower maximum TFOV with the same eyepiece as I understand it.

[DRT]

are you sure that you get bigger TFOV ?

That isn't what I said

I'm no technical expert but from what I understand the light cone coming out of any telescope towards the eyepiece has a fixed focal point that cannot be moved by simply adding a longer aluminium tube around it, it would require another optical glass element to do that or an adjustment to the elements that already exist. The fact that the Crayford adds distance at the back is compensated by the fact that the primary needs to be moved so that the focal point ends up where it needs to, which is in the eyepiece.

For what it is worth, the minimum length of the FeatherTouch Crayford including its mounting is 88mm. I don't know what the standard fitting is but suspect it is at least half of that distance so at most I have added about 40mm, not over the 100mm that your logic requires.

In any event, I think anyone worried about TFOV should be looking at something other than an SCT

[YKSE]

That isn't what I said

For what it is worth, the minimum length of the FeatherTouch Crayford including its mounting is 88mm. I don't know what the standard fitting is but suspect it is at least half of that distance so at most I have added about 40mm, not over the 100mm that your logic requires.

In any event, I think anyone worried about TFOV should be looking at something other than an SCT

That's great that it's only 88mm.  I'm not the what stock diagonal other SCTs get, my C8 comes with 1.25" diagonal with SCT fitting, it add only a few militers.

Another unwanted side effect is increased spherical aberration which results in less sharp stars, maybe not visible in small increase focal length, but worth knowing it IMHO.

[michael8554]

Your request was for "First Things", so I'll keep it short(ish).

You'll have noticed by now that the list depends on whether you are visual or imaging, with some overlap.

Whichever you do you will need:

Dew shield and maybe a dew heater

Bob's Knobs, you won't have to adjust collimation very often but it is extremely fiddly without them.

Visual:

2" star diagonals and eyepieces aren't SCT specific items, they depend on your preference and wallet size.

The standard focusing arrangement is prone to backlash but is useable, a Crayford focuser makes it easier.

Imaging:

Wedge

Crazy to spend all those bucks on an F10 and then have to buy an F6.3 focal reducer/coma corrector, but for DSO's it will make guided imaging possible and improve your inbuilt coma.

Conversely for planetary a Powermate image amplifier.

2D balance system 

Crayford focuser (motorised if you can afford it)

And the never-ending list of kit that any imaging system requires.

Michael

[DrRobin]

I would second 'an observatory' best investment I made after getting a large scope.

Robin