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Arcturus 3x ocs light path?

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#1 De Lorme

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Posted 11 October 2019 - 12:01 AM

Hello,

 

Does anybody here know how long the light path would be in turning a Arcturus 3x ocs into a 3x barlow and WO 2x ocs into a 2x barlow?

 

Thanks for the help.

 

Clear Skies,

 

De Lorme


Edited by De Lorme, 11 October 2019 - 12:02 AM.


#2 junomike

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Posted 11 October 2019 - 06:35 AM

IME an OCS is less powerful than a standard Barlow, by as much as 50% so a 3X OCS would act more like a 2X Barlow and visa versa, however optics are tricky in that the OTA completes the

system so an SCT would definitely act differently than a Refractor or Newt.

Trial & Error is the only way to know for sure.



#3 De Lorme

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Posted 12 October 2019 - 12:01 AM

junomike,

 

I thought that once you know that light distance through the binoviewer I could just use extension tubes to get the same distance and that would give the 3x ocs the same magnification as going through a binoviewer. Why am I wrong?



#4 junomike

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Posted 12 October 2019 - 07:27 AM

junomike,

 

I thought that once you know that light distance through the binoviewer I could just use extension tubes to get the same distance and that would give the 3x ocs the same magnification as going through a binoviewer. Why am I wrong?

That is probably correct.  I misread what you were looking for.

An Arcturus BV should have an optical path of 100mm - 110mm so using a 4" extension should yield the same

magnification for the OCS as it does the BV.

 

To get a precise measurement you can place an eyepiece in the BV and using just a Refractor (w/5" travel) focus on an object far away (day or night). Note the increments on the focuser.

Then remove the BV and place the same EP directly in in the focuser and bring to focus.  Subtract the increments from the EP reading from the BV and you have your number.

You may need an extension for the single EP so be sure to add that into the equation.



#5 Eddgie

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Posted 12 October 2019 - 08:49 AM

I believe the light path through the Arcturus is similar to the WO and Celestron, so about 96mm.

 

Obviously if you need to exact power, you would want to measure the light path, but 10mm of error is not going to substantially change things.



#6 De Lorme

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Posted 12 October 2019 - 10:55 PM

Thanks Junomike and Eddgie for confirming my thinking.

 

Clear Skies,

 

De Lorme




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