200P focusing tube

[DaveGarland]

Hi all. When focusing all the way in last night, looking for "airy rings" I noticed a rectangular part of the image missing! I checked and re-checked the collimation and all seemed fine. Eventually though I found out what was causing this. The focusing tube actually moves into the OTA and blocks part of the primary mirror!

Surely this can't be right? Has anyone else noticed this? Is this normal? And how much does this interfere with the image. And also is there anything that can be done about this???

Thanks for any of your input.

Dave.

[NGC 1502]

Hi Dave. I once had a very low power eyepiece that needed much more in focus than normal, and this put the focus tube into the light path. But if when you are in focus, and the focus tube is not in the light path, then there's no problem. Even if the focus tube protruded into the light path when in focus, any problem with the quality of the view is likely to be very minor.

Your scope is probably set up to allow a wide range of eyepieces to come to focus, some need more in focus, some need more out focus.

Regards, Ed.

[Stephen]

The tube does extend into the OTA (mine does,) but it's never caused me an issue.

I thought to check the airy disc, you only want to be "just" out of focus as opposed to all the way in?