C80ED diffraction rings question - confused!

[beamer3.6m]

Having just received the C80ED I took it out last night for its first proper outing.

The 90mm sky watcher rings worked a treat and I managed to drill the dovetail so it now attaches easily to the HEQ5 with room to adjust the balance so all was good.

The views were also good and I managed to connect the DSLR and take some shots (not attached as yet) but when I put in an eyepiece, viewed through the 45 degree erecting thingy I noticed that on either side of focus when the diffraction rings are seen the rings were clearly split down the middle by a solid black line.

When I attached the DSLR, without the 45 degree thingy I did not see these so should I assume that this is the cause and if so what is it.

When I first tried the scope I noticed the black line was about 1/8th of the way into the rings/disc and swapped to the opposite side when changing to either side of focus.

The black line was solid and went straight through the rings/disc.

Is this normal?

[Merlin66]

What ever it is, I'd have to say it's not normal!!

From your description, I'd hazard a guess and say either there's something in the erecting diagonal ( hair, thread??) or the prisms are not correctly aligned, or similar hair/ dust in the eyepiece.....

Sounds what ever it is, it's near to the focus point...

Try the eyepiece without the 45 degree adaptor.... same problem? Try a different eyepiece in the 45 degree adaptor... same problem??

[John]

Those 45 degree prisms are not that good for astro viewing - I would suspect that the problem is coming from that componant.

Try viewing straight through the scope or with a 90 degree diagonal if you have one.

John

[FLO]

I don't think its anything to worry about. When you defocus you are probably seeing the edges of the prism-block in the image-erecting prism. A more expensive IEP will have a larger prism-block with finer edges and better coating but the one supplied with the Celestron ED80 is pretty cheap/basic. If you use a regular diagonal or fit the eyepiece directly to the OTA (focus extension required) then there will be no lines when you defocus.

Try it and let us know

<edit> I see John beat me by 9 seconds

[Lady Isabella]

I don't think its anything to worry about. When you defocus you are probably seeing the edges of the prism-block in the image-erecting prism.

Try it and let us know

Yes, that is what's happening.

If you hold the diagonal in your hand and point it at a bright light source you will see a very faint line running through the prism. Both my Celestron 45 and 90 degree units produce this.

[beamer3.6m]

Phew - sounds like a normal problem then.

I did not notice it when I attached my DSLR at prime focus without the erecting prism and although I could not reach focus without the prism I could not see the problem when out of focus so I suppose that is the problem solved.

Cheers guys. I was worried I may have a dud.

Now just gotta get a better diagonal. Any recommendations.

I would like a 1.25" one as these are what my eyepieces are.

[cvc]

I noticed the same black line when I used my C80ED for the first time last night with the 45 degree prism, so it is reassuring to have an explanation for this.

Thanks to everyone,

Charles

[gary1968]

I would have noticed this if I ever get clear skies, wont worry about it now. A nice 2" dielectric I think will be nice for it.......

Gary