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C102 HD

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#1 droid

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Posted 25 February 2013 - 07:12 AM

I prchased this scope some years ago, used.
I used to know it true focal length, before painting it , it had a stick on its side telling me, lol.
After painting the sticker wouldnt adhere, and has since gone missing.
In any case, I had alwasy believed since that is f/8, but I keep reading the C102s were f/10
Now I know this isnt the most scientific way to measure a lenses focal length, but when it is all up, I measured from the back of the lens to the center of the diagonal, and its 36 inches, which would make it f/9.
Im totally confused now, as its neither of what I thought it was, lol.
It wont stop me from using it, as its the best refractor , optically, Ive owned.
Just had to do away with that god aweful black it was originally. lol

#2 GOLGO13

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Posted 25 February 2013 - 08:26 AM

It's a 1000 focal length...technically it's F9.8...but usually listed as F10.

#3 siriusandthepup

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Posted 25 February 2013 - 09:49 AM

The usual way to measure would be from the back of the primary lens to the focal plane. One way to do it is to aim the telescope at the moon. Remove the eyepiece/diagonal.
Using a piece of paper see where the moon image focuses on the paper. That is the focal plane. From the back of the lens to the focused moon image is your exact focal length.

I also have one of these and Golgo is correct on the specs.

#4 buddyjesus

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Posted 25 February 2013 - 09:01 PM

what golgo said

#5 Jon Isaacs

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Posted 26 February 2013 - 07:56 AM

Now I know this isnt the most scientific way to measure a lenses focal length, but when it is all up, I measured from the back of the lens to the center of the diagonal, and its 36 inches, which would make it f/9.


You need to measure from the about the middle of the objective lens to the focal plane when the scope is in focus at infinity. If the diagonal is a 2 inch model, it's optical path length is about 4 inches.

But in any event, the focal length of the 102HD is 1000mm.

Jon

#6 csrlice12

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Posted 26 February 2013 - 09:46 AM

and they are very well built scopes.

#7 droid

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Posted 26 February 2013 - 12:13 PM

Thanks everyone... and yeah this puppy is built like a tank.
It was the first small scope to show me M51 directly, in the city with poles lights everywhere.
But I got it in my head the black had to go, and I wanted classic looking.

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#8 GOLGO13

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Posted 26 February 2013 - 12:14 PM

Looks pretty cool...nice!

#9 csrlice12

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Posted 26 February 2013 - 01:44 PM

Different color scheme, but it's basically the same thing as my 102XLT OTA, Is that an EQ4/CG5 mount?






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