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Daz1969

Shortening an OTA?

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Hi all, Bit of an odd question but i have a 60mm x 900mm refractor that i plan to use for guiding and was wondering if i can lob a few inches of the length?

It is currently mounted on top of a C8 via rings but is seriously long compared to the C8.

In effect if i cut it shorter will i be making it a shorter focal length?

Cheers.

Daz.

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You won't change the focal length by cutting the tube, the focal length is governed by the lens, not the tube. If you want to lob a couple of inches off the end just make sure you have those inches spare by seeing how far the focuser is racked out when the guide camera is in focus. If its racked out a few inches then you can safely cut off a little less than that from the tube (assuming guiding is all you intend doing with the scope).

Edited by GazOC

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Shortening the tube will result in the scope not reaching focus. The focal length is a product of the objective lens. Basically when an eyepiece is placed 900mm from it, focus is achieved. The tube is a means to hold the objective and the eyepiece at the right distance apart.

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