Coma Correctors??

[Paul73]

Hi Guys

I have a 16" f4 Dob. As you can imagine, the coma can be a little intrusive. Principally, I use the Delos range of eyepieces and a 24mm Panoptic.

As long as I stick to sub 75° eyepieces, things are not too bad. The problem is that 'not too bad' isn't really good enough.

The SIPS system is great, but eyewateringly expensive. I have a Paracorr (mk1), but really can't be doing with fumbling around with screws and the turntable top when I change eyepieces. How come the clever chaps at Starlight Intruments can make the benchmark corrector without the need for adjustment between eyepieces, and Televue can't?

And, what are the options / recommendations for lower cost alternatives to Starlight's SIPS system?

Thanks in advance

Paul

 

[Louis D]

Parfocalize your eyepieces.  SIPS works by keeping the CC to primary distance constant.

[scarp15]

When I use my paracorr (mk2) I only use two settings H and A, which is an easy adjustment from end to end, 31 and 21mm on the A setting and 13, 8mm at H each are a two inch format eyepiece. Occasionally I might use a 10mm delos, which will be pre fitted into the 1.25 inch adapter ready for use and requires a middle, D setting.

On Tele Vue's recommended turnable top positions, Delos 12 to 3.5 and 17.3 and 14mm also Nagler 24mm are all on the D setting. This applies to the type 2 paracorr do not know if the type 1 is fundamentally much different?

[Paul73]

Thanks guys.

Re. The Paracorr - I believe that some additional in travel was needed to cater for the whole Ethos range. Hence the Mk2. This is a bit odd as the 21mm Ethos is parfocal with the 17.3mm Delos.

Re. Sips - Does this mean that I can only use parfocal eyepieces??

Paul

[Louis D]

All coma correctors require a constant separation between the primary and the CC optics to achieve best correction.  SIPS places the optics in a fixed location below the focuser.  The focuser moves the eyepiece to the proper position above it to focus it.  In a tunable top CC, constant separation is achieved by manually parfocalizing each eyepiece each time you use it by rotating the top as a focuser so the CC optics section remains at the same separation distance from the primary for each different eyepiece's focal position.  You can also use a tunable top CC by setting it for a known eyepiece, focusing it, and then never touching the focuser again.  Focus all other unknown eyepieces by only using the tunable top.  You've created a virtual SIPS in effect by doing this.

I have a GSO CC with a fixed distance.  Once I figured out the optimal distance from the optics section to the eyepiece holder's shoulder for the vast majority of my eyepieces that focus at the shoulder, I parfocalized the rest by adding rubber O-rings to lift them out further.  If I had any that required them to be closer in to focus, I'd have to rethink my parfocalization scheme.  Luckily, I don't have any eyepieces focusing above the shoulder.