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lukebl

Skywatcher Coma Corrector and Low-Profile Crayford focuser

19 posts in this topic

Hi,

Just acquired both a Skywatcher 2" Low-Profile Crayford focuser and a Skywatcher Coma Corrector for my old-style blue Skywatcher 200P. Just a couple words of caution for anyone with one of these scopes.

Firstly, I originally intended just getting the Coma Corrector, but found that it couldn't come to focus with my DSLR using the stock Rack and Pinion focuser, even though the DSLR focussed OK without it.

So, Caution 1 is that even though the CC is intended for f/5 200mm Skywatchers, it doesn't necessarily work for all of them if they've got an old-style focuser.

Secondly, I therefore subsequently had to invest in a Skywatcher Low-Profile Crayford to enable the DSLR to focus. The instructions indicate (and some postings here confirm that some people have been lucky) that the four fixing bolts are in the same position as the original ones, so will fit the original tube without drilling new holes. Not so with mine! I had to drill new holes about 6mm either side of the original ones.

So, Caution 2 is that you may need to drill new holes even if the instructions indicate otherwise.

So I'm now more than a hundred quid lighter than I was expecting to be. Ouch! But that's par for the course with this game.

Anyway, I'm now the lucky owner of a georgeous shiny new Low-profile Crayford focuser and Coma Corrector. Hopefully a first light report to follow.

And many thanks to FLO again for their superb and speedy service. It's amazing to order something at lunchtime and receive it at 8.30 next morning!

Edited by lukebl

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Nice warnings mate, some people aren't so lucky to spend more.

Good luck with the new kit and looking forward to the DSLR images from the scope.

Cat

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Cheers Luke! Just in time since I'm contemplating getting low profile crayford.. My question is, how's the focus for visual, if you have tried it? Since when I measured the focus travel for some of my EP's on Sun today, I've noticed they were all pretty much over 10cm, which, IIRC, is the max for SW dual crayford?

Cheers

Marius

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Cheers Luke! Just in time since I'm contemplating getting low profile crayford.. My question is, how's the focus for visual, if you have tried it? Since when I measured the focus travel for some of my EP's on Sun today, I've noticed they were all pretty much over 10cm, which, IIRC, is the max for SW dual crayford?

Cheers

Marius

I am no imager but I think that in focus is the key problem rather than out. you can always add extension but you cannot go further in than you can go with any specific focuser.:)

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Thanks all.

Yes, it's the IN focus that was a problem. I do seem to have the opposite problem now with eyepieces, but have simply used an old Barlow with the lens removed to provide an extension.

Can't say I could afford the extra expense, but the alternative was just sending the Coma Corrector back, and then I would still be at square one! The kids'll just have to go without shoes for another year.

Edited by lukebl

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I am no imager but I think that in focus is the key problem rather than out. you can always add extension but you cannot go further in than you can go with any specific focuser.:D

The IN focus may be an issue for astro photography, yes. And yes, you can add the extension tubes for EP's to come to focus (though even more £££), but as the SW crayford already comes with built-in extender, I kinda hoped that would suffice.. that was my main reason for asking.. Seams it's not quite as simple.. again :)

Cheers

Marius

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Hi Marius. Just been checking again, and the focus tube definitely won't go out far enough to focus with EPs. However, as I said, I am using a cheap and unloved old Barlow with the lens removed to act as an extension tube. So no new cost there.

I must admit, the Crayford is a joy to use, with a really smooth action and no movement of the view.

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Luke, have you found the built-in focus extender?

Just checking :)

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I am using a cheap and unloved old Barlow with the lens removed to act as an extension tube. So no new cost there.

I'd need more out-focus for my 2" as well, so unfortunately can't go this way.. Decisions decisions.. :):D Nice to get things made clear though! Thanks Luke

Marius

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Luke, have you found the built-in focus extender?

Thanks Steve. Yes, that's including the built-in extender.

Marius, your scope might be different. It seems that the older blue Skywatchers aren't necessarily all the same. Anyway, a simple extension tube isn't expensive.

Edited by lukebl

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I wonder how the Baader mpcc would have compared, I think it's designed to bring the focus out another 10-20mm. I'm suprised Skywatcher have designed one for their own scopes that make it not possible to achieve focus with a DSLR that did focus without their coma corrector.

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I wonder how the Baader mpcc would have compared, I think it's designed to bring the focus out another 10-20mm. I'm suprised Skywatcher have designed one for their own scopes that make it not possible to achieve focus with a DSLR that did focus without their coma corrector.

In fairness to Skywatcher, I guess it's intended for the new generation of Newtonians (i.e. the Black ones with different focusers), and not for the older-style ones like mine. Mind you, it's less than two years old, so it's hardly old!

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The new Skywatcher Explorer DS series have secondary mirrors positioned closer to the primary mirror for more convenient prime-focus photography. Interestingly the product description on Skywatcher's UK website suggests the Skywatcher coma corrector is compatible with the earlier f5 Explorer series. I have sent the importers a link to this thread and updated the product description on our website.

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I don't actually think they would work with the "older" black tube versions with the single speed crayford - which I have. There is a lip inside the focusser (just under 2" in diameter - bad design!) which stops it accepting 2" accessories without the 2" eyepiece extension. With the extension there is no way mine would come close to focus with a DSLR. Spoiled a very nice telescope:confused: The DS version got it sorted - have better focussers which allow 2" accessories without extensions - I think?

Mark

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Some interesting thoughts and heads up here.

I have just got the Skywatcher 250P DS and already found that there isnt enough inward travel for prime focus! What I haven't tried yet is my Baader MPCC to see if that solves the issue. Maybe If I get time and can figure all the attachments out for the MPCC ill give it a try tonight.

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An update: I've only had one serious attempt so far using my new Skywatcher Coma Corrector and Low-profile Crayford (see here), but I'm fairly pleased so far. I can now achieve focus with the DSLR with the CC attached, which I couldn't do before, and focussing is so easy with the Crayford and a Bahtinov mask. There seems to be some chromatic aberration when you look closely, but that may be partly because I have ramped up the saturation in Photoshop to emphasise the star colours. Just need some darker nights to test it properly.

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Sorry to hear you had to fork out for a new focuser, but you'll be more than happy with the upgrade.

I've got a SW coma corrector on it's way right now. I'd like to use it with a CCD.

It seems that Baader isn't making the MPCC any more although there are rumours of an updated model coming soon.

Do you happen to know what the correct distance to sensor should be ? I see reports of 55mm and reports of 53mm but with all the different adapters around I'm still lost as to the correct spacings for it and where the distance starts from, i.e. coma corrector glass or coma corrector threads.

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