Baader Multipurpose Coma Corrector (MPCC)

[steppenwolf]

This particular problem is a really thorny one and I had a couple of stabs at the design because if you are not careful you end up with too little outwards focus!!

There is a 'down and dirty' solution if the above or a low profile focuser don't appeal and that is to drill and tap the screw in collar that attaches directly to the silver focus tube with three holes to hold the MPCC 'suspended' in the middle of the focus tube but I don't like this option because even though you could fill the light gap around it, you would not have any facing plates to ensure the correct alignment. I love adapters, I have even written an article about them - so many uses!

[Erwin Kats]

Here a pic made with the MPCC in place.

specs:

Vixen R200SS 8'' F4 newton

canon eos 40D unmod

baader mpcc

300s (5 minute ) ISO 1000 exposure of Mizar and Alcor.

+a crop of the left upper corner.

[Erwin Kats]

and this pic was a crop from a pic i made without the MPCC

[Neil I]

Thats a huge improvement Erwin

I've recently bought a MPCC for my 8' f4.5 and it really has transformed the scope. The FOV is now coma free (well at leat 95% ). This really is an essential item for any uncorrected fast refelector and well worth the money.

Cheers

Neil

[irishbloke]

I have got a skywatcher skyliner 250px. Has anyone heard how this scope works with the mpcc? Also do my eyepeices need to be up to a standard to benefit from it? I have a 32mm panaview and 8mm and 17mm hyperions.

[Ben Ritchie]

Can't comment on the 250px, but have a 300p and the MPCC is excellent with it - a great improvement to the edge performance of my 28mm UWAN. That's generally the only eyepiece I use it with though, I don't find the visible coma too bad with the 13mm Ethos or anything shorter.

With eyepieces, i'd guess that it's not going to help if the eyepiece itself is showing aberrations due to being used in a fast dob - that's an issue with the eyepiece itself, rather than the coma inherent in the Newtonian design. But otherwise I don't think the eyepiece itself is an issue.

[athlon]

i bought an MPCC for my 12" Skywatcher dob, and am having some issues with it.

Firstly, the back focus issue. I couldnt get the scope to focus with the MPCC 1.25 assembly fitted. the work around with the slide it half way in and secure it. not fantastic, but it seems stable enough, and i like the qaulity of the adapter, and big knurled thumbscrews, certainly better than standard.

Secondly, and this is where i get flamed, i can see absolutely no difference. I have tested it on a few eyepieces, Meade 4000 plossl at 40, 32, and 26 and could see absolutely no difference. i then tried a GSO eyepiece i had handly, only as it was a 15mm 'ultrawide' and i know ultrawide sometimes just means 'coma' again, no discernable difference.

i have checked and i am pretty certain i am setting up the adapter correctly, the 2-1.25 adapter, the 14mm spacer, and then the MPCC itself on the bottom, and that should be it for general usage of 1.25 eyepieces.

its a shame, i really wanted this to make a difference.

can anyone help?

[John]

I've read that it's only when you use really high quality and well corrected wide field eyepieces that you notice the coma inherrant in the short focal ratio newtonian design. Otherwise what you are seeing is astigmatism introduced by the eyepiece itself which a Coma Corrector cannot help with.

John

[albedo0.39]

Hey people - correct me if I'm wrong, but isn't a coma corrector effectively a 0.25X Barlow ? i.e. a good barlow has the same effect ?

I've read all about them, and from studying seems to make sense...

[johninderby]

The Televue Parracorr has a small barlow effect but that's just there to change the amount of outfocus. The Baader MPCC has no barlow effect at all and doesn't alter focal length. The higher the magnification the less obvious coma is so a barlow will reduce noticeable coma a bit but it's not actually correcting the coma.

To second the comments in earlier replies you need good quality eyepieces with a coma corrector to get good results. What a lot of people mistake for coma is actually caused by the eyepiece so there's not much point in curing coma if that only allows you to see the defects in your eyepiece.

John

[Doc]

I know this is an old thread but I have a question. This is the equipment I have....

2" to 11/4" adapter thread for 2" filters.

2" O111 filter

A selection of 1 1/4" eyepieces.

Can the MPCC be threaded onto the bottom of the adapter and then the filter screwed onto the Mpcc then the whole lot could be innserted into the focuser and the eyepiece placed into it.

Is this possible. Or is it the filter fits between the mpcc and adapter.

A little confused.

[GazOC]

The end of MPPC is threaded for 2" filters but it also needs to be a given distance from the eyepiece its used with.

[terryf]

I've got an MPCC and from what I remember from the manual that I downloaded, the MPCC has to be 55 mm in front of the focal plane - the detector in the case of a camera or the field-stop position for a lens - so getting the right spacing might be tricky. Also, the MPCC has a T-thread on one end (42 mm?), so I doubt that would screw onto the bottom of the adapter and you would need a stepper ring.

Terry

[joselin]

Hi Terry,

Sorry for late reply but not been on SGL much recently and missed this post! I have designed and had made an adapter to allow me to use the MPCC with my SW 10" Reflector and SXVF-M25C but in answer to another person's query re using this with a DSLR, I designed this alternative:-

hi steve

do know anywhere that would sell that kind of adaptor ? i found this site but i dont think they sell exactly the same thing but maybe one of them could be adapted ?

kind regards

J

[albedo0.39]

Found this link describing Coma - shows some interesting results (that seem to match the images from Erwin )

[adamsp123]

I know mine works a treat on my 200mm GSO F/4 newt, without it I get very obvious coma, with it my images show little if any coma right up to the edge of the frame just like Erwin pics show.