Baader MPCC / Skywatcher Coma Corrector

[ribuck]

Hi All,

I'm just wondering how critical the spacing is for the Baader & Skywatcher Coma Correctors.

I believe each corrector requires around 56mm spacing from the surface of the ccd and just wondered how critical this spacing is if i'm 1 or 2mm out ?

Regards,

Rich.

[ribuck]

[steppenwolf]

1 or 2 mm is not a problem as there is this discrepancy between Canon and many other cameras anyway (Canon is about 1mm shorter than other makes) but any more and you will be out of the 'sweet spot'.

[Euan]

Your best to measure it to see, download the demo of CCD Inspector and you have 30 days to get it spot on, that's if you can get the correct spacing combo

Welcome to CCDWare - CCDInspector

I'm considering having custom adaptors made for this in the future, it would be so worth it

[ribuck]

Hi Steve,

Thanks for the swift reply. Can i just ask what your undertsnding is for the spacing requirement.

Some, have said 55mm, some 56mm, but FLO said they were told by Skywatcher that it was 52mm which if that is the case, it's way off.

Also can anyone out there tell me the depth of the thread on the Baader MPCC, as it's 3mm on the Skywatcher and i'm trying to fit it into a TS-OAG which is only 1mm thread depth so i'm loosing 2mm straight away.

One option would be to grind down the thread to 1mm which would get me perfectly to 56mm (if that is the correct spacing)

Rich.

[steppenwolf]

I can only speak for the MPCC that I use - the spacing of the rear mounting face of the MPCC to the sensor face is 55mm +/- 1mm according to Baader. The male 'T' thread depth is 5mm (just measured it). For the MPCC that I use on my SW 250 and 200 Reflectors with R & P focus mechanisms, I had to design and make my own custom adapter to obtain focus with my CCD although the same applies to my DSLR.

If you look at the bottom of this page on my website you will find details of my custom adapter.

[ribuck]

Hi Steve,

Thanks for that. Out of interest where did you get your custom adapters made ??

I think i might grind down the Skywatcher thread. Since i only want about 1mm thread, i figured that i might see if i have a 1mm spacer ring then screw in onto the thread and then grind so i'm flush with the spacer ring leaving me a perfectly even 1mm thread on the skywatcher coma corrector, perfect for threading into the TS-OAG and also giving me the right spacing.

Rich.

[ribuck]

Sorry for all the questions, but i have one last one.

When measuring the spacing for coma corrector, where do you measure from on the coma corrector.

Do you measure from point A before the lip or Point B after the lip.

The reaosn i ask is becasue the lip is about 2-3mm thick and just need to know if ths needs to be taken into consideration ?

thanks,

Rich.

[steppenwolf]

You measure from point 'A' - the mounting face itself.

I got Chris Livingstone to make mine to my spec. Please bear in mind that my adapter as shown on my website is specific to the SXVF range of CCDs and my SW Reflectors but the basic principles are the same for any CCD camera - just make very careful measurements from a known good focus point.

[ribuck]

Thanks Steve,

that's good news as i'm about 57mm at the moment whch means i just need to shave 2mm off the thread to get it perfect.

Rich.

[steppenwolf]

2mm off the thread to get it perfect.

Unless I am missing something, I am not sure how this helps as when you screw the components together, the two facing plates will touch irrespective of the thread length - unless you are saying that the thread is 'bottoming'?

[ribuck]

Hi Steve,

The Coma corrector screws directly into the TS-OAG, but the OAG itself but is limited to about 2-3mm thrad depth.

So when screwing in the Coma Corrector, I can screw in the first 2-3mm of thread, after that it can't go any further, thus leaving about a 2mm of thread on the coma corrector sticking out.

At the moment i'm around 2mm off the perfect sweet spot (57mm), so considering grinding down the coma corrector threat to get it perfect.

Rich.

[steppenwolf]

That's fine, answers my query perfectly!

[ribuck]

Would just be nice to get an official answer from Skywatcher as to the spacing, as FLO saying they had an email from them stating 52mm worries me a bit.

Rich.

[ribuck]

Would just be nice to get an official answer from Skywatcher as to the spacing, as FLO saying they had an email from them stating a 52mm spacing requirement, which worries me a bit.

Rich.

[lukebl]

I've read this thread with interest, as I have a Skywatcher 200 (older style blue one, with older-style rack & pinion focusser) and have finally splashed out on a Skywatcher Coma Corrector for my DSLR imaging. I was also well aware that focussing at prime focus is an issue with these Newtonians (although mine is fine at the moment with my DSLR), and was assured that being made by Skywatchers for Skywatchers it would be absolutely fine.

Needless to say that, despite being designed for Skywatcher f/5 Newtonians, it is simply impossible to bring it to focus with my scope. It is at least 40mm too far out. There really ought to be warning on these that they WILL NOT FIT all Skywatcher Newtonians.

In the absence of an alternative, and not really wanting to send it back, I'll need to see if I can get an adapter made, along the lines the one Steve mentions on his website. Alternatvely, perhaps I could get a stepper ring to fit the 55mm thread of the D200-A00-02 ring directly into the 59mm thread of the focusser tube (see pic below). Any idea where I could get one, or any other ideas short of returning the item and putting up with the coma?

[ribuck]

Hi Luke,

I Also have the old style Blue Skywatcher 200P, I'm hoping for a clear night tonight so i can get First light with the Coma corrector / TS-OAG combination.

The old rack and pinion focuser is a massive beast, so i replaced mine with a moonlite to get tons of extra focus travel.

In your image, you show an adapter which comes with the Skywatcher coma corrector and you have 55mm next to it. What does that represent as the threat is only 10mm on that.

Are you saying you want some a similar adapter made with a 55mm thread. Bare in mind you need to account for the distance from the surface of the camera chip to the edge of the camera housing so you will need to factor this in as well.

Rich.

[lukebl]

Hi Luke,

I Also have the old style Blue Skywatcher 200P, I'm hoping for a clear night tonight so i can get girst light with the Coma corrector / TS-OAG combination.

The old rack and pinion focuser is a massive beast, so i replaced mine with a moonlite to get tons of extra focus travel.

In your image, you show an adapter which comes with the Skywatcher coma corrector and you have 55mm next to it. What does that represent as the threat is only 10mm on that.

Are you saying you want some asimilar adapter made with a 55mm thread. Bear in mind you need to account for the distance from the surface of the camera chip to the edge of the camera housing so you will need to factor this in as well.

Rich.

By 55mm, I mean the outer diameter of the thread.

Basically, the instructions indicate that it should be inserted into the 2" holder, which I could tell would make it too far out. So, I thought that I need to bypass the 2" focusser completely and gain that extra length.

However it looks like I need to buy a new low-slung focusser, and judging by the threads here they don't even fit properly sometimes! Disappointed mainly about the misleading sales pitch for the coma corrector. You really shouldn't have to buy additional kit or adapers to fit what is claimed to be made for the scope.

[ribuck]

Hi Like,

Not sure if you realized, but on your rack and pinion focuser, the existing 2" eyepiece holder can be unscrewed directly from the focuser drawtube and then replaced with the low profile one in your pic that comes with Coma corrector.

This alone will give you close to the 40mm you need. I just measured and looks to be approx 39mm

Rich.

[lukebl]

Hi Like,

Not sure if you realized, but on your rack and pinion focuser, the existing 2" eyepiece holder can be unscrewed directly from the focuser drawtube and then replaced with the low profile one in your pic that comes with Coma corrector.

This alone will give you close to the 40mm you need. I just measured and looks to be approx 39mm

Rich.

I think I tried that combination, and it didn't work.

Will have another go when there's something to focus on. Only the sun available right now, and don't think it's a good idea to have a go on that.

If you're right, then I will feel somewhat sheepish, but very grateful for the advice and glad not to need to splash out on more kit!

[ribuck]

Luke,

I think you will be fine for several reasons.

• The Focuser on the Skywatcher has been specifically designed to attach DSLR's directly.
  

• The Coma corrector seems to have been predominantly designed for using DSLR with the Skywatcher.
  

• The Coma Corrector has been designed specifically for F5 Skywatcher scopes which you have.
  

This is why they supply the coma corrector with low profile drawtube adapter, to replace the exsting one. If you look closely at your existing cumbersome eyepiece holder, you'll see that it actually comes in 2 parts. it's basically a threaded version of the low profile that comes with the coma corrector but with an extenstion tube screwed in.

Rich.

[lukebl]

Luke,

I think you will be fine for several reasons.

• The Focuser on the Skywatcher has been specifically designed to attach DSLR's directly.
  

• The Coma corrector seems to have been predominantly designed for using DSLR with the Skywatcher.
  

• The Coma Corrector has been designed specifically for F5 Skywatcher scopes which you have.
  

This is why they supply the coma corrector with low profile drawtube adapter, to replace the exsting one. If you look closely at your existing cumbersome eyepiece holder, you'll see that it actually comes in 2 parts. it's basically a threaded version of the low profile that comes with the coma corrector but with an extenstion tube screwed in.

Rich.

Nope. I was right first time. Just tried it on the moon and no combination of bits gets it close enough to focus.

Here is the setup:

And here's how it looks at closest focus:

It clearly seems to be designed for the new Skywatchers or those with low-profile focussers, not the older-style ones. Its return to the shop, or fork out more cash for a low-profile focusser.

Any chance of a pic of your setup, to see how it's done?

[ribuck]

Unfortunately it is a very expensve hobbie, I've found out this for myself.

I guess it's a simple choice of weather or not you really want to persue astrophotography, if you do you will have to bite the bullet of buying a low profile focuser like a moonlite. Then you have to consider guiding and how to achieve this.

Out of interested, the baader & skywatcher need around 55mm distance from surface of chip when using a ccd. I would assume the same would be for DSLR.

I dont use DSLR, but does the pinciple not hold the same for DSLR ? How far is the ccd to camera adapter ?

Rich.

[lukebl]

Unfortunately it is a very expensve hobbie, I've found out this for myself.

I guess it's a simple choice of weather or not you really want to persue astrophotography, if you do you will have to bite the bullet of buying a low profile focuser like a moonlite. Then you have to consider guiding and how to achieve this.

Out of interested, the baader & skywatcher need around 55mm distance from surface of chip when using a ccd. I would assume the same would be for DSLR.

I dont use DSLR, but does the pinciple not hold the same for DSLR ? How far is the ccd to camera adapter ?

Rich.

Not sure about the ccd distance. Yes, I already know it's an expensive hobby after imaging with a DSLR for over a year now. Had very good results but thought it was time to sort out the coma.

Just more than a bit irked that it isn't made clear that these won't fit the standard focuser. Might be cheaper in the long run to get a better scope with less coma issues. I mean, £120 for the coma corrector, another £150 for a focuser....?. All for a scope that's not even worth £200!

[steppenwolf]

The principle is the same for both a CCD and a DSLR camera - we are only interested in the mounting face of the coma corrector to the sensor irrespective of the type of camera.

Each make of CCD is different (although sometimes only by a small amount) - Starlight Xpress, for example, have their sensors 17.5mm from their front mounting face. Don't forget as well that the Baader assumes that if you are using a DSLR camera then a 'T' adapter will be in line and these are nominally 10mm deep. A Canon DSLR has a sensor to lens mounting face spacing of 44.5mm. So, 44.5mm + 10.0mm for the 'T' adapter = 54.5mm which is within tolerance of the 55mm required by the Baader MPCC.