HELP! Odd filter behaviour

[DJScotty (Scott)]

Hi all,

I am struggling to understand what is going on with my Orion 2" Ha filter.

It has in the past, had a similar issue, but I thought I had solved it. Alas, I am wrong...

Last night, whilst housed in the filter wheel, it was working fine. (Refer to image here http://www.iceinspace.com.au/forum/s...d.php?t=137168) Tonight, I decided to remove the FW from the imaging train. The Ha filter is now producing very distorted images, almost triple offset images.

The filter is the first part of the imaging train which enters the focuser draw tube, ie the last piece attached to the camera

I have tried the following...

• Taken the glass out of the filter mount (is that the right word?) and placed it in another Orion 2" mount - no difference
• Then replaced the glass into its original mount and left the screw in piece out - no difference
• Then gently tightened the screw in piece - no difference

No other filter (R,G, B, L, OIII [Baader], or SII [Baader])produces these distorted images - Just the Ha.
I must say, I am not an idiot, but I cannot for the life of me understand what is going on. It does not make sense. :s hrug:

Any advice would be greatly appreciated

Cheers,

DJ Scotty

[Slawomir (Suavi)]

Hi Scott,

What a mystery!

If I was hard pressed to guess, I would propose that your Ha filter, unlike other filters that you use, for some perfectly explainable reason (for example - it's a product from Orion...), is producing reflections when it is placed close to the CCD.

When this filter is placed in the filter wheel, it is at a greater distance from the CCD, and for some perfectly explainable reason (reflected light absorbed by the filter wheel and spacer/connector?), it does not generate reflections on the CCD.

Solution: keep the filter wheel in your optical train. If it works, do not try to fix it

[DJScotty (Scott)]

OK... that makes some sense, BUT, I have moved the filter further from the sensor, not closer...

ATTACHED are some photos explaining it...
(The stickytape is a marker for how far into the focuser to put the tube)

I am yet to try out the new setup, as it is daytime.

I have noticed a triple image/reflection when looking through the filter, one red, one blue and one kind of normalish, red to one side, blue to the other

Any thoughts on that?

[Slawomir (Suavi)]

The mystery continues...

May I ask, what is this sticky tape for? Maybe light is leaking through it?

I noticed that in the setup with the filter wheel, that part with sticky tape is in front of the filter, while in the setups without the wheel, sticky-tape segment is between the filter and CCD.

I still believe the patterns you mentioned are caused by some internal reflections.

EDIT: Sorry, missed the bit explain sticky tape. Here goes my theory...

Having a filter so far from the CCD is a bit unusual, I suggest bringing the filter closer to the CCD and see if that solves it.

[DJScotty (Scott)]

I now have it in between the MPCC and the CCD sensor. See what that does...

I remember the reason why I took the FW out of the imaging train - I am fairly confident that the outer case if flexing slightly from the weight of the camera...

[Slawomir (Suavi)]

Hopefully these reflections will go away.

As for tube flexing around the focuser - I am confident that two rings around the tube on each side of the focuser (and attached to the focuser) could help to eliminate/minimise it. Could be an interesting DIY project...