More MPCC MkIII Testing - flatness & bright stars

[Uranium235]

Last night it was clear enough to do more testing with the Baader MPCC MkIII. Two objectives, firstly to achieve the correct spacing for my setup (which turns out to be 57mm) - and secondly to throw a bunch of bright stars at it to test for reflections in Lum.

There are still some mechanical issues with the focuser as im still detecting some tilt or movement of the optical train as I point the scope at different parts of the sky, therefore I have to "trick" the focus point every time I move to a different part of the sky - a bit of a faff really. Which im soon hoping to address, either by finding a replacement focuer (easier said than done with a 5" scope), or taking the focuser apart. I'd prefer the first option, but something tells me there isnt anything available to replace it (smallest ive found is for a 6").

Focuser aside, the MkIII had me doing a celebratory jig as the first few subs rolled in - lots of round stars to the corners!

First object required a good starfield, what better place to start than the Cocoon nebula:

10x240 (L) 2x2 bin

3.4" p/p

No cropping

 

As you can see, not bad!

Next, a bunch of bright stars - M45 usually does a good job of generating reflections in my other correctors - lets see how the MkIII gets on:

5x300 (L) 2x2bin

No cropping

 

No reflections whatsoever!

Quite pleased with it now

[lensman57]

Thank you for posting, I had already oredered the MPCC for my newly aquired and desparately in need of colimation 150 PDS, l also totally agree with with regards to the focuser, it will have to do untill  something better is found. I quite liked the idea of a Baader steel track but it only has a focus range of 30mm, I am not sure if this is enough, then there is the TS one.

Regards,

A.G

[ollypenrice]

Great result. Super.

Olly

[tich]

That's great to know as I've recently brought one of these. Thanks for posting.

[Uranium235]

Thank you for posting, I had already oredered the MPCC for my newly aquired and desparately in need of colimation 150 PDS, l also totally agree with with regards to the focuser, it will have to do untill  something better is found. I quite liked the idea of a Baader steel track but it only has a focus range of 30mm, I am not sure if this is enough, then there is the TS one.

Regards,

A.G

Dont get too hung up on the collimation, or it will drive you nuts! Ive found the MPCC to be more forgiving of slightly-off collimation than the SW is.

Your focuser travel will depend on whether you are ever going to use it for visual (short ones are intended for imaging), but im pretty sure you can get extension tubes for the steeltrack if you need them.

Ive since made  changes again in regard to the optical train attachment. For the above images (and previous HH test image), I had switched back to the stock thumbscrew arrangement as there had been a little problem with the M54-T2 adaptor (I broke it!). But, with the help of some PTFE tape ive been able to bring it back from the dead - so its back to an internally mounted corrector. This came about when I was checking the thumbscrew arrangement for slop - what i did was to insert a 2" barlow (with no safety undercut), tighten up the screws, then grab the barlow and basically wobble it with a little force to see if it rocks in the focuser  tube - which it did (the focuser tube remained still).

[Mr Spock]

Looks like you have a winner.

[sologuitarist61]

It is certainly working for you - those are great images!

[Sam]

Great result, I think I need more spaces.

[Uranium235]

Great result, I think I need more spaces.

Cheers Sam, mine turned out to be 57mm because of the thickness of the filters and CCD window - calculated as an extra 1mm over the normal spacing, plus a bit more to get those corners right on 22mm diagonal chip.

And for info:

Standard spacing from bottom of T2 thread = 55mm

Standard spacing from bottom of M48 thread = 57.5mm

[laser_jock99]

Nice result- can you clarify what size CCD you are using? Are these any good for the APS-C size and up?

[Uranium235]

Nice result- can you clarify what size CCD you are using? Are these any good for the APS-C size and up?

Its the kodak 8300 sensor, its about 25% smaller than APS-C.

To figure out whether its good enough for APS-C you need to find MPCC spec for the corrected field, then compare it with the diagonal measurement of you sensor. I should think that you will need a few mm headroom to be sure of getting round stars to the corners.

Ive just looked up some info and it says it can deliver across 35mm full frame - whether that can be believed is another thing, but the bigger the sensor - the more critical the spacing becomes so you probably wont nail it in one night (it took me three attempts).

[tich]

I'm hoping to use mine using a DSLR & 250P if these pesky clouds will go away, I hope I get stars that look as good as yours.

[Uranium235]

Good luck with that, it should be a bit simpler for you to set up as its a case of screwing the corrector into your T adapter.

There are some clear patches developing, so perhaps I might get out for an hour or two later on

[Uranium235]

I did get out last night, and a very short session it was!

It turns out that the MkIII cannot be mounted internally as there simply isnt enough out travel to reach focus. Fortunately the MkIII does have very generous scope side threads, so ive mounted it directly to the focuser with the M48 filter thread. Feels like a bit of a tenuous connection though, so I might employ some saftey measures.