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#1 StarTrooper

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Posted 05 July 2020 - 08:09 AM

When I had my Meade 10" Starfinder f4.5 I was able to point it at an object 100 yards away, focus that object in, and align my right angle correct image finderscope. With my present scope a Meade 12" f5 Lightbridge I am unable to find a point of focus. I must wait until night time, pick out a star, focus it in, then align my finderscope. This makes it extremely difficult to do. Why is this?



#2 lee14

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Posted 05 July 2020 - 08:17 AM

The longer the focal length, the further away an object must be for the scope to achieve focus.

 

Lee



#3 kathyastro

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Posted 05 July 2020 - 08:20 AM

The focal point for nearby objects is farther out than the focal point for objects at infinity.  100 yards is very close for an astronomical telescope.  If you are trying to align your finder in the daytime, you may need to pull the eyepiece out a bit from its normal position.  Alternatively, find a more distant target, one that is several miles away.



#4 Couder

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Posted 05 July 2020 - 08:27 AM

Hardware or plumbing stores sell an extension for sink drains, it is exactly 1.25". One end fits in 1-1/4" focuser or adapter, other end accepts an 1-1/4" eyepiece. I have several of these cut to different lengths which let me focus on closer objects to at least get my finder in the ballpark. Later on I can fine tune the finder.


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#5 StarTrooper

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Posted 05 July 2020 - 08:36 AM

The longer the focal length, the further away an object must be for the scope to achieve focus.

 

Lee

I am doing things backwards! I first find the star in the telescopes focuser then try to locate it in the finder scope and center it in. Being a truss type each time I setup this is the scenario.
 



#6 lee14

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Posted 05 July 2020 - 09:32 AM

I am doing things backwards! I first find the star in the telescopes focuser then try to locate it in the finder scope and center it in. Being a truss type each time I setup this is the scenario.
 

That's the correct procedure, always center the object in the main scope first, and then adjust the finder to match the scope's FOV. It doesn't matter if it's perfectly focused in the scope or not, as long as it's centered. The target object should be reasonably distant, so that parallax between the scope and finder is negligible though.

 

Lee


Edited by lee14, 05 July 2020 - 09:35 AM.



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