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3" focuser


Tweedledee

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I got a 3" focuser to avoid the vignetting that would likely occur using large wide angle eyepieces at fast F ratios with a 2" draw tube on the 20". It would also be nice to be able to use 3" eyepieces if I could afford one.


 


When I unwrapped the focuser it was a very solid well made chunk of equipment, and although it was plenty big enough, I immediately saw that there was nothing to allow a 3" eyepiece to be clamped in the focuser. So I was straight on the phone to Germany using my best English voice, and as always they spoke fluent English back and explained that to use a 3" eyepiece I would need to buy their special adapter for another €150+shipping! Also I would need to buy yet another special expensive adapter to switch to a 2" eyepiece within the 3" adapter!!! :o


 


How silly of me to expect a 3" focuser to take a 3" eyepiece! :)


 


It is quite large... :lol:


 


focuser.gif


 


 


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I got a 3" focuser to avoid the vignetting that would likely occur using large wide angle eyepieces at fast F ratios with a 2" draw tube on the 20". It would also be nice to be able to use 3" eyepiece

Just got agreement from TS to return the focuser.   I'm exchanging it for a different, more expensive model, that comes ready kitted out to take 3" tackle straight out of the box, complete with a

Cheers Rob. That 30mm 100 degree 3" eyepiece would be a nice thing to have and would be great for my observing interests, but just ridiculously expensive even without buying more adapters. My 20

It looks the business Pete. But a 3" focuser that cannot use a 3" eyepiece without the need to spend further money is just daylight robbery, they have you over a barrel as you can't say no.


 


Btw I love your animated photo, it really shows the size of it.


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Very impressive Pete.


I love your animation .


 


Is it a definite gameplan to buy the ES 30mm ?


What F ratio are you planning for your Dob ?


 


Just thinking of the exit pupil factor, and if you're thinking of F4.5 (or slower) your going to need a ladder ?


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Very impressive Pete.

I love your animation .

 

Is it a definite gameplan to buy the ES 30mm ?

What F ratio are you planning for your Dob ?

 

Just thinking of the exit pupil factor, and if you're thinking of F4.5 (or slower) your going to need a ladder ?

Cheers Rob.

That 30mm 100 degree 3" eyepiece would be a nice thing to have and would be great for my observing interests, but just ridiculously expensive even without buying more adapters.

My 20" mirror is F4.14, so therefore the exit pupil would be a bit big. This is less of a problem with a larger aperture since there is lots of light grasp to play with. A 20" with just over a 7mm exit pupil will waste some light, but will still give as much light as a 17" scope! The main thing is that I could get over 1.5 degrees FOV, which is massive for such a large scope. I've also read lots of reports of people getting great views with fast scopes using 31mm Naglers and obviously large exit pupils without getting problems with seeing the shadow of the secondary obstruction. The 3" ES would give one heck of a 'spacewalk experience' :)

I have already calculated that I will need a 300 to 400mm step to get to the eyepiece when pointing at the zenith 'dobson's hole', and I'm 6 foot tall!

So, is the 3" ep a definite gameplan??.....

Well - I'm a step closer :)

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I think you'll be more than happy just using your ES 25 / 100


 


Bet the view through a 20" with that eyepiece will 'blow your socks off'  :)


 


You could get a very nice binoviewer system though instead !


Problem is theres no bino out there (Siebert 2" excepted) that will pass an f4.14 light cone.


I think F4.6 -F4.7 is about the limit with 1.25 " systems. Faster than that you get aperture reduction, but as you say, with a 20" not such a problem anyway.


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I think you'll be more than happy just using your ES 25 / 100

 

Bet the view through a 20" with that eyepiece will 'blow your socks off'  :)

 

You could get a very nice binoviewer system though instead !

Problem is theres no bino out there (Siebert 2" excepted) that will pass an f4.14 light cone.

I think F4.6 -F4.7 is about the limit with 1.25 " systems. Faster than that you get aperture reduction, but as you say, with a 20" not such a problem anyway.

Yes, the 25mm 100 should provide a nice big view on the 20" :thumbsup:

I love the Siebert Optics gear. Their bino-viewers are fantastic but then I'd want to double up on my big eyepieces as well - and counterbalancing :)

Perhaps I will just have to make do and manage :)

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Never doing things by halves eh Pete.  :thumbsup:

It's a bit poo they didn't tell you before buying it you couldn't use a 3" eyepiece in it, as you would have assumed just that.

 

I do have some big ideas and like to plan ahead. Hopefully I can make them work. :)

 

Trouble is that I'm now seeing the 20" project as a step up the learning curve to a 32" F3 trailer mount for my retirement. :o

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Just got agreement from TS to return the focuser.


 


I'm exchanging it for a different, more expensive model, that comes ready kitted out to take 3" tackle straight out of the box, complete with a 2" step down adapter.


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