Focuser visible in stars

[RogerTheDodger]

Took some of my besta subs yet last night and came across a little problem - the end of the focusser is visible in the stars in the image... I've just spent some time looking through the Imaging section at other peoples images using the same scope (SW 200PDS) and DSLR and can't find any with the same problem.

here is a full size and a crop of the same image. Does anyone have an idea why my scope has this problem but others don't?

[RogerTheDodger]

Here is a pic looking down the focusser with it in the approximate position for having the DSLR in focus.

[ollypenrice]

Not a proper answer but could you move the primary up the tube by paying out some adjustment on the collimatioon screws? Maybe your primary is very far down the tube on its adjusters?

Olly

[RogerTheDodger]

That's about an inch of movement it would need... I'm considering cutting down the focuser tube, but I want to know why other people with the same kit don't get the same error.

[Jessun]

(I see Olly is checking out this thread too so may cross post here as I write - anyways I'd trust Olly over me)

Are you sure that it is the focuser and not a result of pinched optics? Your secondary mirror is not visible inside the star - since each star is made up from light from the whole mirror surface - so forgive me if I'm wrong but then why should this little piece be visible?

Does it remain there as you defocus on a bright star?

[RogerTheDodger]

Yes it does, it's very visible when de-focused.

[Jessun]

OK, disregard my shot in the dark :-)

[RogerTheDodger]

Any question is a good question - I have no idea why I'm seeing this and no-one else is

[RikM]

I sometimes see this effect on big bright stars but I find that if I image on both sides of he meridian, it gets lost in the stacking.

[RogerTheDodger]

Hmm, I wonder if that'd work if I rotate the camera 180 degrees halfway through the subs...

[StuW]

I get this visually with the cheap 28mm eyepiece, but not with the DSLR.

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