Baader MKiii CC not working

[Andy Milner]

Hi, I have purchased a Baader MKiii Coma Corrector to use with my Canon DSLR.

I've screwed it straight into my t-Ring and it's not eliminating the Coma?

Is there a spacer or something I need? I assume that it's not the right distance from DSLR to Coma corrector?

If so which space do I need?

Thanks for help.!!

Andy.

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[Thalestris24]

Hi

You shouldn't need a spacer:  http://www.firstlightoptics.com/user/Baader_MPCC_Mark-III_Coma_corrector.pdf

Have you an image to show your problem?

Louise

[Andy Milner]

Will upload sub frame later. It looks to me like coma. As the outer stars all elongate towards edges of image. But it's first time for me. So I might be wrong.

For info I connect the DSLR to a Low profile t-ring to the baader mkiii then a LP filter in the front of the mkiii.

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[markarian]

It may not be coma.

I chased what I thought was coma for ages on my 200P and DSLR. It wasn't in the end. The coma corrector did it's job OK but the camera alignment was out.

If your focuser like mine had a single lock screw, that "may" be the problem. Tightening on one side only changed the alignment. I bought a replacement adapter with 2 screws and a ring for the end of the focuser.

Mark

[Thalestris24]

Will upload sub frame later. It looks to me like coma. As the outer stars all elongate towards edges of image. But it's first time for me. So I might be wrong.

For info I connect the DSLR to a Low profile t-ring to the baader mkiii then a LP filter in the front of the mkiii.

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Hi

It might be coma. I'm not sure about the low-profile t- ring - that might mess up the spacing. You might need one of these instead:

http://www.firstlightoptics.com/adaptors/skywatcher-dslr-m48-ring-adapter.html

Louise

[Andy Milner]

Thanks Marksriam for that. I never considered the camera may not be flush. This seems very feasible. I would like to upload one of my subs so you guys can analyse it. I think it could be down to the DSLR not centered. If it is do you remember which adaptor you purchased. I have a two screw 2" focusser adaptor. Would it be wise to replace this?? Is there a self centerring 2" adaptor that will make the DSLR fit flush?

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[Andy Milner]

Thanks Louise! Considering the possibility it's the DSLR not sitting flush. It could be that the t-ring needs extra spacing too. Will upload a light frame when I get back home. I took a load of frames last night of m42.

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[markarian]

This is what I bought - has a compression ring not 2 screws. Be sure that's the problem first though.

Mark

http://www.teleskop-express.de/shop/product_info.php/info/p4018_2--adapter-with-brass-compression-ring-for-Skywatcher-Newtonians.html

[Earl]

is it posible to attach the corrector to the focuser via the thread on the focuser?

[Andy Milner]

Here you go.. What do you think it is?

This is a 120s unguided sub. PA was prety much bang on. as i spent ages on aligning the reticle and the RA axis turned perfectly.

If you look at the stars in middle, do you agree they are nice and round. The out edge stars appear to be eggy, and i have diffraction spikes leaning to one side.

[Uranium235]

Ahhh..... Unfortunately you might be going through the same experience as I did with these compression rings from TS    In the end, I just ripped out the ring with pliers - its utterly useless.

To test whether yours is the same:

1) Move your OTA so the focuser is pointing straight up

2) Insert the camera + CC into the focuser under gravity (straight down), dont tighten the thumbscrews.

3) Get the point where the MPCC meets the face of the 2" compression adaptor at eye level, and hold a bright light on the other side so you can check for light leaks around where the corrector meets the focuser. There should be no light leaks.

4) Now tighten the thumbscrews - you should notice that one side has now been "popped" out and there will be a noticeable gap if you repeat step 3.

Such was the amount of tilt that it made it virtually impossible to make a reapeatable and reliable connection, which renders useless any corrector used. The only way I could get it to work in the end was to produce my own M48 threaded connection with a tilt adaptor and internal thread for the MPCC - which is then allen screwed to the focuser. Cost about 100 quid to tool up, and here is what I ended up with:

[Thalestris24]

Here you go.. What do you think it is?

This is a 120s unguided sub. PA was prety much bang on. as i spent ages on aligning the reticle and the RA axis turned perfectly.

If you look at the stars in middle, do you agree they are nice and round. The out edge stars appear to be eggy, and i have diffraction spikes leaning to one side.

Hi

Yeah, looks like coma to me. I would check the spacing with the low-profile t-ring. It needs to be 55mm between the cc flange and the camera sensor and it's a critical spacing. If the low profile t-ring reduces the spacing, it might be causing the problem. CC's and flatteners are designed with dslrs in mind, apparently. But the only reason to have a low-profile t-ring is for when you can't achieve focus with a prime focus connection. Baader refer to using a 'standard' t-ring:

http://www.baader-planetarium.com/pdf/mpcc_e.pdf

I'm sure there must be some other dslr/mpcc users here that can confirm. I have one but it's attached to a ccd...

Hth

Louise

[markarian]

I think Louise is right. It's coma. not alignment. Work on the CC spacing.

I used a normal T-ring with Baader CC and DSLR and it worked great.

Mark

[Uranium235]

Just looked at the pic, there is a fair amount of coma which might suggest the spacing is too short. Try increments of 1mm to see if any improvement occurs. If the star distortion becomes radial, youve  gone too far.

The above mod I posted is an extreme case since my imaging train is over 1.5kg.

[Thalestris24]

Hi Andy

I think probably one of these will do the job:

http://www.firstlightoptics.com/adaptors/skywatcher-dslr-m48-ring-adapter.html

Louise

[Uranium235]

Thalestris24, on 03 Oct 2014 - 11:57 PM, said:Thalestris24, on 03 Oct 2014 - 11:57 PM, said:

Hi Andy

I think probably one of these will do the job:

http://www.firstlightoptics.com/adaptors/skywatcher-dslr-m48-ring-adapter.html

Louise

That adpaptor is for the Skywatcher corrector, it wont give the correct spacing with the Baader becuase the spacing distance from the M48 thread is 57mm.

Might be cheaper to try the existing T adaptor whith a delrin spacer to increase the spacing in gradual steps. Ive got a hunch it might be in the 56-57mm area (mine turned out to be 57mm).

Edit:

Check this thread, its in regard to flattener spacing - but exactly the same principle applies to coma correctors:

http://stargazerslounge.com/topic/225831-flattener-spacing/#entry2431515

[Thalestris24]

That adpaptor is for the Skywatcher corrector, it wont give the correct spacing with the Baader becuase the spacing distance from the M48 thread is 57mm.

Might be cheaper to try the existing T adaptor whith a delrin spacer to increase the spacing in gradual steps. Ive got a hunch it might be in the 56-57mm area (mine turned out to be 57mm).

Edit:

Check this thread, its in regard to flattener spacing - but exactly the same principle applies to coma correctors:

http://stargazerslounge.com/topic/225831-flattener-spacing/#entry2431515

Hmm...

I thought it was the same as this one: http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3631_TS-Optics-T-Ring-Adapter-von-M48-Filtergewinde-auf-Canon-EOS-Bajonett.html which lists compatibility, including mpcc. Exactly the same photo! I suppose the best thing might be to check with FLO...

Louise

[stoffe]

How big sensor do you have on your Canon camera? I got a full size sensor (36x24mm) and I do not got pinpoint stars at the edges (as excpected), I got a 4-lens GPU corrector and that is a very good corrector for the price btw. A MPCC MK-III should be very good too, but I do not know how big sensor it is optimized for. I think a Canon crop-sensor is the limit for it.

[Andy Milner]

Thanks everyone. I've found my collimation is slightly off. So I'm going to check that first. It appears it could be this and I will get the climatic spot on first. It looks like my secondary mirror is off. So I will get this sorted and order a standard DSLR t ring I could do with another one for my other camera and scope. Will test all this out as soon as I can and let you all know what the fix is. Cheers.

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[stoffe]

Also check if your mirrors are jammed. They should be free to move a little bit in their cells. When my primary mirror was jammed, I got triangle shaped stars..

[Andy Milner]

Okay scope collimation fixed with Cheshire and barlowed laser. Bang on it seems. Star tested.

I ordered a standard m48 t-ring and connected the mkiii baader to that in hope with my collination and not using a Low profile t-ring it may narrow my problem down. I Took the scope out last night and still got coma identical to what I got the other day.

So I'm thinking this..

I have a 2" focuser on my 200p Newtonian, I insert directly I to the focuser with no eyepiece holder. Is this correct? Should I be inserting the 2" eyepiece holder into the focuser first? Could this be the cause?

Another possibility is as you suggested there is a distance problem between the coma corrector and the DSLR. If by understand why as it should work?

By the way I had to remove the the m48 plastic ring as pictured here.

It is a small thin ring that allowed me to screw the mpcc into the canon T-ring.

Is there anyone else out there using a 200p and a baader mkiii ?

P.s. I am using a crop sensor and not a full frame sensor DSLR the 11100d. So there should beno issues there.

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[stoffe]

How does a bright star looks in high magnification if you are using a high power eyepiece?

[Thalestris24]

Hi

Very puzzling. "For imaging with digital SLR cameras, only the MPCC MkIII is needed - additional spacer rings are not required. (You WILL need a T-ring for your particular camera model, of course). The MPCC MkIII is designed for a nominal 55mm distance from the mounting flange to the camera sensor (55mm is the standard flange-to-sensor distance for most DSLR cameras, measured from the front of the T-ring to the image plane)." It's not at all clear why the cc isn't doing it's job as expected. No, you don't need an eyepiece holder. It's the distance between the cc and the camera sensor that's critical - 55 +/- 1mm. Can you post a photo of the camera with mpcc attached? I can only imagine there is still a spacing problem. Did you get the M48 t-ring from FLO - did you check with them that it would be ok to use with the mpcc? (Uranium235 suggested it wouldn't...)

Louise

[Andy Milner]

Hi Louise

Thank you so much fir your advice.

I spoke to FLO they say it should work with a standard 10mm m48 t-ring. I bought the t-ring from them and they say it should work.

I expecting too much? I really expected no coma in the edges of my images. Am I to accept that it won't eliminate all together?

I will post a photo later.

I'm a bit perplexed myself as the collimation looks good.

How do I increase spacing by increments of 1mm as suggested? Do I need delrin rings?

Thanks.

Andy.

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[Thalestris24]

Hi Andy

I'm sorry you're having these problems. It should all be so straightforward... I think the mpcc should eliminate coma. It does with my qhy8l which admittedly has a slightly smaller sensor. However, Baader quote 'virtually eliminates coma', presumably to give them some leeway. But the spacing is critical. However, everything should work out of the box, as it were. I take it you don't have a clip filter fitted and the camera is unmodded?

You say the problem is identical to before? Can you post a single sub again?
There must be someone here that also has a dslr + mpcc and who can advise.

Louise