HELP. Celestron 14" EdgeHD changed focus

[Marsian]

Hi everyone!

I have a Celestron 14" EdgeHD tube. I have had it for 3 years and used it very little the first year. But I have moved to a darker place and have started to use it regularly. When I used it directly after i bought it I could use a diagonal and an eyepiece and watch the stars, and with a 65mm long T-adapter and my Canon 550D I got focus.

Now I can´t  get focus with an eye-piece and a diagonal, and with the camera I have to use a 20mm T-adapter to reach focus.

So the focus seems to have changed about 45mm.

I stored it in the box it came in but on a south-side glass-sealed balcony one summer, can that have affected the optics so it has changed the focal-length so much.

I have checked the mirror-lock screws and they are loose in both ends when i turn the focus knob from end to end.

I still get very flat photos  but I can´t use eye-pieces with a diagonal.

It is ment to be a telescope for astrophoto and that part works fine, but I would like to look through an eye-piece and watch Saturn for example.

What has happened?

Is there any tests I can do to determine the true focallength of the telescope?

[Plantins]

Your mirror lock screws will not be out far enough. Back them out some more, just being loose is not far enough out. 

[brantuk]

Are you using the same diagonal and eyepiece that you originally used? I doubt your storage will have affected the focal length far enough to exhibit the symptoms you describe. There is considerable throw between focusing a camera/extension and an eyepiece/diagonal.

I'd suggest you test the focus throw across it's entire length when observing. But do it slowly cos it's easy to miss the focus point if you're going too fast.

[callump]

45mm is an awful lot of difference - i don't know this scope but i'd be surprised if the mirror support allowed that much adjustments.

Did you have a visual back on before, or a focal reducer? Or added one?

/callump

[Peter Drew]

The focal plane shift in a SCT is primary movement X the amplification of the secondary squared so a change of 45mm is not very much in real terms, Probably needs the locking screw backing off more as suggested by Plantins. 

[Marsian]

Hi all and thanks for helping.

I´m using the same equipment now as when it was new.The only real facts I have at this time is:

I use an other length on the T-adapter and that i couldn´t get focus in the eyepiece with the same diagonal as I used before. I got focus with the camera and a 65mm adapter before and now i don´t get focus with that adapter anymore.

But I get focus with the camera and I have taken some photos with it.

Can I be such an idiot to forgotten the locking bolts? Probably, but when I got focus with the camera I was happy and didn´t try the eyepiece any more.

And after my eyeoperation I have some strang reflections when I watch bright obejcts on a black background.

I will have to lift her out, all her 110kg and do some testing. To bad the sky is so bright and cloudy.

Thanks all!