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Refractor objective lens

Started by Nightviewer, 08/03/2022 02:06AM
Posted 08/03/2022 02:06AM Opening Post
Could I put a 127mm 1200mm focal lens achromatic doublet objective lens in a refractor that currently uses a 127mm 1180mm F9.3 doublet objective lens.  How would the 20mm affect draw tube focus if it could be done?  Thanks for your advice.

Jim Koerth
kfamtl@verizon.net
Posted 08/15/2022 01:39AM #1
Originally Posted by James Koerth
Could I put a 127mm 1200mm focal lens achromatic doublet objective lens in a refractor that currently uses a 127mm 1180mm F9.3 doublet objective lens.  How would the 20mm affect draw tube focus if it could be done?  Thanks for your advice.

Jim Koerth
kfamtl@verizon.net

If my brain is following you correctly it sounds like you may be able to get away with it by using a 20mm extension in front of the EP......assuming you can find such an animal and also assuming it being shorter by 20mm to the front of the draw tube inside the scope doesnt interfere with the light path.....there is a word for that which escapes me at the moment. lol

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Monroe GA
Posted 08/15/2022 02:18AM | Edited 08/15/2022 02:19AM #2
I concur with Greg:

This should work with the 20mm extension. Or there might be enough focuser travel to not need that extension.

It might possibly vignette a little (Is that the word Greg ?), but that would be minor.

Ed (aka eblanken) Blankenship