Testing the MPCC mk III

[Uranium235]

Last week I received the new MPCC from FLO - which I had decided to get in order to achieve better flattening and zero reflections - both are areas where my other two correctors leave a bit to be desired.

The SW corrector, though good (suffers very few reflections) it never seemed to deliver a flat enough in all four corners field despite endless collimation - always the same end result, a tipped field. Ive checked the focuser is not sagging becuase the direction of the tipping never changes with movement of the telescope and mount (if it were sag, it would move about as the scope does).

The mk II MPCC was good at delivering a flat field, but flippin' awful for internal reflections and stray UV/IR with my camera. So, this is where the mk III steps in with its improved coatings.

Does it work?

Yes!

But... I still had imperfect correction (yep, tipped again). So to work around that, I focused with a bright star in the most affected part of the field. Took a test shot.... and bingo! A considerable improvement in flatness. Ive shot all the data in 2x2 binning, 3.4" p/p isnt so bad but the speed boost is very welcome indeed (x2.23), especially when on limited time (took just 2hr 15min). Anyway, I might have to bite the bullet at some point and properly square the focuser as I believe that to be the source of the tilt.

6x450 (Ha) x3 panes

130pds, Atik 383L+, NEQ6, Baader MPCC mkIII

Thanks for looking!

Rob

 

Fullsize for pixel peeping:

http://farm4.staticflickr.com/3764/11934828685_f5874b823b_o.jpg

[sologuitarist61]

What a great and interesting way to show this remarkable subject - well done!

[Astroscot2]

Excellent image, just shows what these little Newts can do,  - Picked up a lot of nebulosity.

Mark

[andyo]

Nice shot Rob lovely contrast and very smooth

[lensman57]

Lovely capture, would you recommend the Baader over the SW coma corrector? I too had heard and seen a test comparison showing the t reflections with the SW coma corrector.

Regards,

A.G

[Skyline]

Hi

Strange, I think the skywatcher coma corrector does a good job in correction of coma but due to the focuser having only two thumbscrews tilt appears on a corner, On my 130P DS i have just introduced a third thumbscrew on the collar to expel that problem

The MK II Baader (Made in Japan), gives a better flat field & colour correction compared to the skywatcher. The MKIII I do not have so cannot comment, but the link below puts the MKII & MKIII on a Interferogram. An interesting read.

http://interferometrie.blogspot.co.at/2012/08/130650-skywatcher-und-mpcc.html

Chrome does a good job in translating.

Al

[lensman57]

Hi

Strange, I think the skywatcher coma corrector does a good job in correction of coma but due to the focuser having only two thumbscrews tilt appears on a corner, On my 130P DS i have just introduced a third thumbscrew on the collar to expel that problem

The MK II Baader (Made in Japan), gives a better flat field & colour correction compared to the skywatcher. The MKIII I do not have so cannot comment, but the link below puts the MKII & MKIII on a Interferogram. An interesting read.

http://interferometrie.blogspot.co.at/2012/08/130650-skywatcher-und-mpcc.html

Chrome does a good job in translating.

Al

Hi Al,

Thank you for your reply, the two thumb screw system is a well known old way of securing  a cylinder in a piston type fixture, it is all old engineering but the fitting tolerance between the barrel and the cylinder , as in an eyepiece and the visual back should be about 0.001"  ( it should pop when taken out of the barrel ) inclusive for this to be of reasonable accuarcy for centering. My experience of the tolerance of the Chinese made stuff is that they are about 0.2 mm inclusive or about 10 times the allowable tolerance, much cheaper to machine and no QC required. Even your excellent idea of  adding a third screw will not  always work as you have 0.2 mm of play to correct on either side. The problem with the ghost images and secondary reflections  has more to do with lens coatings than the position of the barrel in the holder.

Regards,

A.G

[Uranium235]

lensman57, on 14 Jan 2014 - 8:43 PM, said:

Lovely capture, would you recommend the Baader over the SW coma corrector? I too had heard and seen a test comparison showing the t reflections with the SW coma corrector.

Regards,

A.G

It depends on what camera and filters you have I guess.

If you have a large chip (8300 and upwards) and only 1.25" filters, then I would choose the Mk III Baader and run at native f5 (which is fast enough already!). It delivers a good field and has a choice of either T2 or M48 connections, which comes in handy if you have the threaded connection adapter for the SW crayford focuser (which requires an M48 thread for internal mounting). Using the SW corrector @f4.5 really cuts into the light cone with my filters, almost unfixable - even with flats.

If you have a smaller chip then the SW corrector will be fine. I know I could just crop my images, but thats no good for mosaics (which I like doing) where the overlapping panes need a fairly flat(ish) field to make stitching together easier. I know my tilting issue isnt related to the acutal connection of the camera as I have tried it with threads and thumbscrews but its still tilted - so it can only be the focuser.

Oh, and with the Mk III  -  the error introduced by the tipped focuser mainfests itself as outwards coma (unlike the rotational error I get with the SW), but like I mentioned earlier - focusing on the more affected side of the image balances the whole field a lot better. That is one of the benefits of staying at f5, the field of focus is a bit deeper so you can get away with tricking the focus a bit - which I shouldnt have to do, so its either square that focuser or buy a tilt adapter.

Once this bloomin rain and moon clears off I will point it at M45 and see whats what - If it can handle 10min of that binned 2x2 without reflections, it can handle anything. But it seems to have behaved on Alnitak so far.

As you mentioned, with the Mk II the problem is in the lens coatings - which seems to be a common problem for those using modded DSLRs or CCD/FW (just google "MPCC internal reflections"). This can be demonstrated by holding up the MPCC to a bright light then tilting it very slightly while looking through it - you will notice a red off-axis reflection. Do the same test with the Mk III, and there is no reflection whatsoever.

[lensman57]

It depends on what camera and filters you have I guess.

If you have a large chip (8300 and upwards) and only 1.25" filters, then I would choose the Mk III Baader and run at native f5 (which is fast enough already!). It delivers a good field and has a choice of either T2 or M48 connections, which comes in handy if you have the threaded connection adapter for the SW crayford focuser (which requires an M48 thread for internal mounting). Using the SW corrector @f4.5 really cuts into the light cone with my filters, almost unfixable - even with flats.

If you have a smaller chip then the SW corrector will be fine. I know I could just crop my images, but thats no good for mosaics (which I like doing) where the overlapping panes need a fairly flat(ish) field to make stitching together easier. I know my tilting issue isnt related to the acutal connection of the camera as I have tried it with threads and thumbscrews but its still tilted - so it can only be the focuser.

Oh, and with the Mk III  -  the error introduced by the tipped focuser mainfests itself as outwards coma (unlike the rotational error I get with the SW), but like I mentioned earlier - focusing on the more affected side of the image balances the whole field a lot better. That is one of the benefits of staying at f5, the field of focus is a bit deeper so you can get away with tricking the focus a bit - which I shouldnt have to do, so its either square that focuser or buy a tilt adapter.

Once this bloomin rain and moon clears off I will point it at M45 and see whats what - If it can handle 10min of that binned 2x2 without reflections, it can handle anything. But it seems to have behaved on Alnitak so far.

As you mentioned, with the Mk II the problem is in the lens coatings - which seems to be a common problem for those using modded DSLRs or CCD/FW (just google "MPCC internal reflections"). This can be demonstrated by holding up the MPCC to a bright light then tilting it very slightly while looking through it - you will notice a red off-axis reflection. Do the same test with the Mk III, and there is no reflection whatsoever.

Thank you for your detailed reply, SW CC is now in its 2nd generation, the first provided better correction of coma and star shapes than the MPCC MKii, but it was prone to having secondary reflections as much as the MPCC MKii, the newer ones are less prone to this "ghosting" but they also correct marginally less than the MKi. It is all a trade off I guess but if one can live with F5 then the MPCC MkIII is perhaps a better choice overal. There is also the   ASA 0.73 FF/FR at about  849.00  Euros; LOL.

Regards,

A.G

[Skyline]

 The problem with the ghost images and secondary reflections  has more to do with lens coatings than the position of the barrel in the holder.

Regards,

A.G

Oh Absolutely ! Two different problems, I was only explaining the tilt problem. The reflections is another thing !

[Skyline]

As you mentioned, with the Mk II the problem is in the lens coatings - which seems to be a common problem for those using modded DSLRs or CCD/FW (just google "MPCC internal reflections"). This can be demonstrated by holding up the MPCC to a bright light then tilting it very slightly while looking through it - you will notice a red off-axis reflection. Do the same test with the Mk III, and there is no reflection whatsoever.

Thanks for the link, interesting info.

I think it depends on what you can live with, as I said I am quite happy with the Results of the MPCC MKII at f/5 & theirs plenty of images out there where people have used the same Corrector showing good results.

[Uranium235]

Thanks for the link, interesting info.

I think it depends on what you can live with, as I said I am quite happy with the Results of the MPCC MKII at f/5 & theirs plenty of images out there where people have used the same Corrector showing good results.

It may have affected a certain batch then? Because I purchaced the Mk II a few years ago when I had the 150P - and it did exactly the same thing, even after I had squared the focuser. I ended up virtually giving that telescope away when I sold my old mount mount because i didnt think that the corrector could be to blame (doh!).

[jgs001]

It sounds like you had a bit of a challenge, but you've ended up with a great result.

[RobH]

That's a super bit of work Rob. Great to see what can be done with affordable kit in the hands of someone with an obvious talent.

Very inspirational.

[Uranium235]

Thanks Rob, Im pretty sure I can get more out of the 130pds once the focuser is sorted out. Reflections or stray light is no longer the issue, its now just a case of tweaking it until the field is as flat as possibe. The severe lack of clear sky isnt helping, but hopefully I can get it all perfected before SGL9 where it should do well under dark skies.