Longer focal length - suggestions please!

[Skipper Billy]

My current setup is ....

Takahashi 106 EDX IV

Atik filter wheel with 2" Antlia Pro filters LRGBHaSiiOiii

Atik 16200 mono CCD camera

All perched on a Mesu mount in a home built micro observatory.

I have been thrilled with the performance of this outfit but it is a very wide field of view and I have pretty much 'done to death' the big targets that are available to me and are a sensible fit in the frame. See attached for an idea of my current FOV. (Uncropped M31)

For next season I am thinking about a significantly longer focal length but ideally re-using my exisiting filter wheel and filters and hopefully the same camera.

I know CCD is now pretty much a thing of the past but it performs extremely well but nothing is off the table and budget isnt an issue.

The Mesu will take 100kgs so weight isnt an issue either.

I want to be able to image the smaller targets like the Cats Eye Nebula and the Fireworks Galaxy, Bubble neb, Coccoon neb etc etc.

I have been burned with a Ritchey Chretien in the past but I am all ears.

Any suggestions welcomed !!! 

 

 

 

[TiffsAndAstro]

Can't offer advice but that is a fantastic pic of m31

[woldsman]

CCDs are not a thing of the past especially if you need large pixels for mono imaging. Your camera isn’t going to create over sampling problems paired with a longer FL scope. Plus you can probably guide with a guide scope at 6 micron pixels.

Your mount can take a large reflector so I guess the question is why go for a longer focal length  design? They are lighter and less bulky but otherwise not as straightforward.

I did go for one after it came up for sale. I wanted an open tube (shorter cool down) design. The scope is a Vixen VC200L which is an eccentric though plausible design. I’m learning with it - it’s fine as the price was just a few £ hundred. Experimenting at this level keeps it fun.

My advice is to make sure the 2” focuser on the scope you get can take the weight of the camera & filter wheel. You also want it aligned so that removes a degree of freedom from collimation. Buy from someone reliable if it’s not factory new. Likewise check the focal length hasn’t been altered by (eg) removing the secondary & not resetting correctly. That takes care of another degree of freedom. You also want to make sure the scope comes with a reducer ready for use.

Assuming the focuser & focal length are sorted, that just leaves the secondary & the primary to collimate. You can’t rely on daytime collimation & have to check star collimation. So the scope has to hold collimation to avoid becoming a pain.  Opinion seems divided on this whatever model you go for. For example, some owners of my scope say it held collimation well - others say the opposite. As you have an observatory, keeping collimation should be easier.

Anyway, I think your choice rests between a Ritchey-Chretien or a Classical Cassegrain if you are not simply going to try a large reflector. A fast reflector would need accurate collimation but is easier in the sense that you can get closer in daytime with the right tools.

 

[Louis D]

I'm not an imager, but how about a Planewave Instruments CDK12.5?  They seem like a well made imaging scope with a longer focal length.  They even show up second hand on CN classifieds for about $8000 on a somewhat regular basis.