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Some thoughts on Springfield mounts.

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10 replies to this topic

#1 bmwscopeguy

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Posted 03 February 2019 - 11:55 AM

What if you could set up once, and after that, simply sit in your seat and observe? And if this telescope mount was GOTO, then even better. Even if you had to set up only once per observing session, it would be beguiling, but if you had an observatory, where everything was as you left it last session, it would be nirvana…

Click here to view the article

#2 ShaulaB

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Posted 03 February 2019 - 12:03 PM

Yes, it is.

 

Our club'sC14, housed in an observatory, uses a mount with a "last align" command to use a previous 2-star alignment. Rock and roll!


Edited by ShaulaB, 03 February 2019 - 12:04 PM.


#3 jtsenghas

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Posted 03 February 2019 - 12:12 PM

Very interesting, and a nice writeup! I had realized quickly that such a mount would require a high f/number when I saw the original at Stellafane. It hadn't occurred to me to adapt such a mount to a SCT.  This has major implications for the physically handicapped, not just the aging, since the eyepiece is fixed and more space is available UNDER the scope.

 

Well done! 



#4 petert913

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Posted 03 February 2019 - 01:15 PM

How Funny.  I just started a thread in my local astronomy club asking why Springfield telescopes aren't more popular.  Great minds think alike.



#5 bmwscopeguy

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Posted 03 February 2019 - 03:19 PM

I think the answer to the vignetting issue (which I have since verified, but not quantified) would be a relay lens. This would allows the SCT focus to remain close to factory specs for infinity, but project the image further down the optical path.

 

As stated, I am not an optical engineer. I have read that an achromat of X focal length, mounted at 2X from the image plane, will 'relay' the image without enlargement or reduction a further 2X beyond the relay lens... If I need about 6" of additional back focus, this would suggest a really lens of about 38mm FL mounted about 75mm away from the image plane. For the inner diameter of my housing, this would mean a lens with an F1 focal ratio.....!! 

 

So I'm not really sure where I am at this point..

 

Malcolm



#6 woodscavenger

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Posted 03 February 2019 - 11:53 PM

Just for kicks.  A local guy I know really well loves Springfield’s.  He has what may be the largest one in the nation.  It is a 12”.....possibly f5.  Currently he is building a 17.5”.  He is an amazing engineer.  He loves the design.  When he brings this to our star party he invites many friends.  It takes about 3-6 hours to set up.  I know he has had this one and a baby brother 8” setup in his backyard for months at a time with a tarp for protection.  His is push-to with SLO-mo controls.  It is fun just to sit and follow things along.  It tracks very well and has amazing views.  I can’t wait until he finishes his 17.5!!!  Now that he is retired he might get it done quicker. 

 

Here is a link from many years ago.  I wish I would have documented the setup.

 

https://www.cloudyni...ingfield-mount/

 

https://www.cloudyni...ingfield-mount/



#7 sixtysomething

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Posted 04 February 2019 - 10:16 AM

Nice out of the box thinking, that is begging for a relay lens setup to get the image past that DEC bearing.

 

Or perhaps eyepiece projection. 

 

https://www.cloudyni...ece-projection/



#8 Jeff Morgan

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Posted 04 February 2019 - 11:06 AM

I think the answer to the vignetting issue (which I have since verified, but not quantified) would be a relay lens. This would allows the SCT focus to remain close to factory specs for infinity, but project the image further down the optical path.

 

As stated, I am not an optical engineer. I have read that an achromat of X focal length, mounted at 2X from the image plane, will 'relay' the image without enlargement or reduction a further 2X beyond the relay lens... If I need about 6" of additional back focus, this would suggest a really lens of about 38mm FL mounted about 75mm away from the image plane. For the inner diameter of my housing, this would mean a lens with an F1 focal ratio.....!! 

 

So I'm not really sure where I am at this point..

 

Malcolm

 

50mm binocular objectives are plentiful and low cost ...



#9 bmwscopeguy

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Posted 04 February 2019 - 12:43 PM

Hi Jeff,

 

I think that bino objectives are typically around 150-200mm focal length. 

 

To use one as a relay lens, I would need to mount one 300-400mm from the standard SCT focal plane, and then the image would be relayed a further 300-400mm beyond that to the new fiscal plane.. That would provide additional back focus of 600-800mm - much more than is required.

 

Don't know if I'm missing anything in this whole equation..

 

Cheers

Malcolm 



#10 bmwscopeguy

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Posted 04 February 2019 - 12:53 PM

Eyepiece projection would probably work (without knowing what the spacing requirements would be however), but it sound like you'd essentially be magnifying the image along the way.

 

If using a standard F10 SCT - this means you'd have a native F20 system....



#11 sixtysomething

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Posted 04 February 2019 - 02:49 PM

I think the idea was to follow a barlow with a focal reducer, with a 2" reducer you could have wide field of view on a 1.25 eyepiece.


Edited by sixtysomething, 04 February 2019 - 02:59 PM.



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