Baader Multipurpose Coma Corrector (MPCC)

[MartinB]

My main reason for obtaining this coma corrector was for imaging with the GSO F4 Newtonian. It came as part of an excellent package put together by Bern at Modern Astronomy. £105 buys you the basic corrector for use when imaging. £129 gets you a T2/M48 expansion ring, 14mm and 28mm spacers, and an adaptor for 1.25" EPs.

For some time I have enjoyed using a 300mm Skyliner Dob. It gives lovely views but they are affected by coma. This is particularly noticeable with wide FOV EPs esp at lower powers. To some extent the immersive quality of an 82 degree AFOV Nagler is diminished by wonky stars at the periphery. I was hoping the coma corrector would improve this.

The back of the corrector optic should be spaced 55mm from the field stop of the EP although it is likely that there is 1-2 mm tolerance either side. The MPCC screws into the T2/M48 adaptor and in turn this screws into the apporpirate spacer which then screws into the EP. The whole assembly slides into the drawer tube.

The first thing I noticed was that there were never going to be any back focus issues (ie not enough in focus). The MPCC actually increases back focus somewhat. In fact I had to pull the EPs a little way out of the draw tube to achieve focus. This is a great arrangement.

My first efforts were very hurried since the clouds were rolling in. I didn't use the spacers and the results were, not surprisingly disappointing with minimal reduction in coma. Fortunately, after a look at the info provided by Baader and other sites I was armed with the spacing info I need and had another crack.

First I tried a panoptic 27mm and then a 17mm type 4 Nagler. I did an initial check on Vega and found just a little bloating as the star moved out to the very periphery of the FOV. There was also a little blue fringing. Up until the very edge there was no change to the appearance of the star with either EP. Onto the double cluster and I was genuinely amazed at the transformation of the overall view. Obviously with a near full moon the dual spangler was never going to be at it's best but the MPCC really unleashed these high quality wide angle EPs.

To use 1.25 eps the spacer screws into an adaptor into which 1.25 EPS can be fitted. My narrow FOV orthoscopics have never suffered from coma with this scope but the wider FOV Pentax 10mm XW and 7mm XL have done out at the periphery. All this coma was abolished with no apparent deterioration in the central view and no sign of CA from the MPCC.

I also had a look at the moon and for the first time with this scope enjoyed views sharp right out to the edge. I had an enjoyable time sketching the outer edge of the Mare Crisium with the Pentax 10mm and for the first time I was able to let the mare drift from one edge of the view to the other before adjusting the scope. This made life much easier!

So, If you are using a fast newtonian, especially with wide FOV EPs the MPCC makes a great buy.

[narrowbandpaul]

great review...glad that the MPCC works well..I got fast newt...that defo needs correction

paul

[themos]

Thanks Martin. I'd be overjoyed if you could check whether the MPCC pushes prime focus out at all for use with a DSLR.

[Andrew*]

Hi Martin,

does this mean that every time you change eyepieces, you need to change spacers too? Of course, before even that you need to know how much spacing you need with every eyepiece you own.

I can only see that being more hassle than it's worth, especially on a dob.

Andrew

[GazOC]

Thats right Andrew, what I do it set it up for the lowest power eyepiece I intend using in a session and just leave it in that all night. It just tends to live in my 24mm Hyperion permanently.

[MartinB]

Thanks Martin. I'd be overjoyed if you could check whether the MPCC pushes prime focus out at all for use with a DSLR.

The spacing required is 55mm regardless of whether you are using a CCD or DSLR. 55mm just happens to be what is needed for a DSLR. A DSLR will work great with the GSO 8" F4 and, given that it actually increases back focus of the scope it should be ok with other Newts but i can't say for certain.

does this mean that every time you change eyepieces, you need to change spacers too? Of course, before even that you need to know how much spacing you need with every eyepiece you own.

I can only see that being more hassle than it's worth, especially on a dob.

I really didn't find it a great hassle Andrew. 1.25 eps are just changed as usual since the spacers and MPCC are the scope side of the 1.25 adapter (assuming you are using a similar line of EPs which should have the same spacing requirements). You do need to sort out what spacer you need but this is a one time job. With 2" EPs it is a 30 second job unscrewing the MPCC from one EP and screwing it into another.

[GazOC]

I've read elsewhere that the corrector introduces spherical aberation if used at higher magnifications, I havn't tested this out yet though.

[MartinB]

What do spherical aberations look like Gaz?

[themos]

I guess you wouldn't need to use it at high magnifications, maybe I've completely missed the point!

[bern]

Yep, the MPCC is a wide field thing.

bern

[GazOC]

What do spherical aberations look like Gaz?

If you do a star test and go either side of focus, either the inner or the outer part of the image will be out of focus depending on the type of spherical aberration.

It just something I've heard, I've no idea whether it a function of magnification or the actual length of the eyepiece used (IIRC a 13mm eyepiece in a 12" f5 which would give x115 was mentioned as showing SA) as themos said the MPCC is for low power/ widefield use so its probably a but of a non-issue for most uses.

[steppenwolf]

I'd be overjoyed if you could check whether the MPCC pushes prime focus out at all for use with a DSLR.

As Martin has confirmed (great review by the way, Martin!) the required spacing is 55mm but even with the 10mm of 'extra' inwards focus travel that the MPCC gives, this can still be an issue on *some* Newtonians, for example the 8" and 10" Skywatcher 'scopes have an issue. The issue is caused by the 2" E.P. adapter supplied by Skywatcher and the fact that the MPCC is intended to fit a 2" EP holder - using the Skywatecher supplied adapter pushes the MPCC (and camera) too far out to allow focus - however, I have desgined an adapter that will work with the MPCC and a DSLR to overcome this problem if anyone is interested. For that matter, I have also designed an adapter for the same purpose for use with the Starlight Xpress range of CCD cameras too.

[John]

Sorry to resurrect an oldish, but excellent, review but I'd like to know if the MPCC would work OK visually with a Lightbridge 12" ?.

I've noticed some coma with my Naglers and I'm debating whether to live with it or seek a cure such as a coma corrector.

John

[MartinB]

I'm sure it would be ok John, I can't really see why not. I was managing to push the coma from my mind but it struck me as ridiculous to be using £200+ EPs with distortion out at the peripheries.

[John]

I'm sure it would be ok John, I can't really see why not. I was managing to push the coma from my mind but it struck me as ridiculous to be using £200+ EPs with distortion out at the peripheries.

Thanks Martin,

Does the Tele Vue Paracorr work in the same way or is the principle different ? - I understand that the Paracorr extends the effective focal length slightly.

John

[MartinB]

I've never used one John. I understand it does increase the focal length slightly but only a small amount. Obviously works very well with TV EPs!

[terryf]

I would be interested to know what your adapter is like. I have just started imaging with a Canon 350D on my 250PX and, not surprisingly, have discovered what coma looks like! I was going to buy an MPCC but have been searching to try to find an adapter that would work with the SW. If you have a solution, I'd love to know it.

Regards

Terry

As Martin has confirmed (great review by the way, Martin!) the required spacing is 55mm but even with the 10mm of 'extra' inwards focus travel that the MPCC gives, this can still be an issue on *some* Newtonians, for example the 8" and 10" Skywatcher 'scopes have an issue. The issue is caused by the 2" E.P. adapter supplied by Skywatcher and the fact that the MPCC is intended to fit a 2" EP holder - using the Skywatecher supplied adapter pushes the MPCC (and camera) too far out to allow focus - however, I have desgined an adapter that will work with the MPCC and a DSLR to overcome this problem if anyone is interested. For that matter, I have also designed an adapter for the same purpose for use with the Starlight Xpress range of CCD cameras too.

[nitram100]

I was thinking of ordering one of these a few months back and wish i had since it's gone up to £169.00! Dammit.

[Glasspusher]

Very interesting review and quite timely as there has been much discussion on certain American forums about the usability of telescopes as fast as F3. Such telescopes are very desirable in terms of transportability and general ease of use. Intial reports are quite favourable using a paracorr with such fast systems. I made a 22 inch F3.6 for a guy in Slovenia, he has sent me very positive comments on the telescopes performance using a paracorr. Of course the paracorr is quite expensive compared to the Baader alternative so I am encouraged by these positive comments about it's performance. I would like to hear about any other experiences anyone would care to share.

Take Care

Glasspusher

[Ben Ritchie]

I was thinking of ordering one of these a few months back and wish i had since it's gone up to £169.00! Dammit.

Ditto!

[Erwin Kats]

nice review.

i use it for photographical usage and it works perfectly !

[Glasspusher]

Which telescope would that be with?

Thanks

[Erwin Kats]

Which telescope would that be with?

Thanks

i work with an VIxen r200ss 8'' F4 newton

[steppenwolf]

I would be interested to know what your adapter is like. I have just started imaging with a Canon 350D on my 250PX and, not surprisingly, have discovered what coma looks like! I was going to buy an MPCC but have been searching to try to find an adapter that would work with the SW. If you have a solution, I'd love to know it.

Regards

Terry

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:-

[terryf]

Hi Steve,

Thanks for the info - it's a long time since I did any technical drawing! I had been thinking of all sorts of odd M54 to M48 - your idea looks really good. I note with interest in a different thread the low profile twin speed crayford, which is another possibility I guess if it gives enough back focus. Nothing's ever simple with astronomy, is it?

Cheers

Terry

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:-