strange halo in moon photos?

[Astronutjob]

Hello does anyone have any idea why i get this white dougnut appearing in my moon photos, it only appears when using a barlow lens? Im using an lx90, 450d and revelation astro X2 barlow. iv tried using a different barlow X3 but it is still there. Its not a prob without the barlow, but i dont get the magnification without. It almost appears as glare, Has anyone had anything similar? Any ideas how to get rid of it, or an explanation would be greatfull.

[Earl]

it looks like a reflection of the primary mirror to me

[LukeSkywatcher]

Agreed.

[yeti monster]

Unless you lost a polo mint down the OTA, then I'd say it's you primary reflecting and showing the shadow of your secondary.

[michael.h.f.wilkinson]

The extra surfaces of the barlow in the optical path can cause this. I do not get similar effects with mine, but they were very expensive ones, and officially they are not really barlows (Meade TeleXtenders, which are more like TV Powermates). The difference in design (and possibly better coatings) may explain the differences.