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dual speed focusers ?


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#1 hanksta

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Posted 08 March 2013 - 06:50 PM

ok, dual speed focusers. i have a 200p dobsonian with a standard issue focuser. as a visual observer only , would a dual speed focuser be of little bennefit ?  

 are they more designed for use in astrophotography ? 

 just trying to understand the focuser thing.

 

 thanks all.



#2 Captain Tweaky

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Posted 08 March 2013 - 10:32 PM

From my experience a dual-speed focuser is almost essential for imaging. Just the slightest tweak can be the difference between clear focus and just slightly off focus - using a Bahtinov Mask as a guide. The sort of difference this has on an image is almost undetectable to the human eye, but then for imaging the exposure may be 10 or 15 minutes and any out-of-focus becomes painfully evident with fine detail.

 

A dual-speed focuser will always help attain the fine point of focus, but this also depends on the magnification - the nearer to 180x plus, the more critical it becomes. But then other factors become relevant: the seeing; the transparency; focal ratio; the viewers eyesight; the quality of the eyepiece; collimation; chromatic aberration; visual acclimatisation and not the least - expectation.

 

So for viewing a dual speed focuser may not be the first item to consider. A high quality eyepiece and a well collimated 'scope (in good atmospheric conditions) would be better places to look for improvement - in my opinion. But then I'm an imager - so what do I know!  :D

 

Yours aye - Cap'n


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And if your head explodes with dark forbodings too; I'll see you on The Dark Side of the Moon
 
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#3 peter shah

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Posted 09 March 2013 - 08:11 AM

f/ratios have a lot to do with it, the faster the scope the more sensitive the focus....its really a luxury for a slower visual scope but once you have one you don't want anything else....its always better to have a higher quality focuser, as some of the cheap ones tend to flex knocking out collimation which is essential for a sharp image....so you can always justify an upgrade. 



#4 hanksta

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Posted 09 March 2013 - 08:54 AM

thanks for the replies . yes i  looked at  a few things i could possibly modify while all this weather holds us up. the dual focuser is amongst the list of possibilities, but its actually not a cheap modification compared to others ,and i dont really feel i struggle to get a good point of focus. so perhaps that one might sit on the back burner for a while.



#5 Zakalwe

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Posted 20 March 2013 - 08:23 PM

Moonlites are very nice, but expensive. The Baader Steeltracks are a lot cheaper and have a lovely feel to them.

 

I've not tried the Revaltion rack and pinions but I've heard that they are pretty good

http://www.telescope...on-Focuser.html



#6 DENEB

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Posted 20 March 2013 - 09:24 PM

Yep, Moonlites are very Nice, decent crayford focusers.

 

I did not like the Baaders, as I thought they were not manufactured to the standard they used to be...

 

But the Revelation R&P look good even offering the shaftlock mechanism as the Moonlites have.



#7 gasman

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Posted 22 March 2013 - 08:46 PM

Interesting topic.Hope this isn`t hijacking your post Hanksta its kinda relevant but I did have this setup C8scope-focal reducer-Crayford focuser-filter wheel-camera and found the Revelation focuser just wouldn`t budge on my C8 if in an upright position as the camera+filter wheel just seemed too heavy so I took it off and wondering if this configuration would be better or would it restrict the camera`s fov C8scope-focal reducer-filter wheel- Crayford focuser-camera. Maybe the R&P Revelation is able to cope with weight a bit better?

Regards

Steve






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