Odd OIII filter gradient - Why?

[opticalpath]

In my head though I'd discounted the filter wheel as the others that have posted with similar problems have different wheels. Apart from the filters themselves, THE common factor is the Atik.

Yet it's hard to ignore the fact that the Atik camera showed no gradient when the filter was mounted in a nosepiece. Ergo it can't be wholly down to the camera, or you'd see the issue with the filter mounted that way too. If you're comparing to others' experience of the same gradient problem with the Atik, it would be worth asking if their filters were in filter wheels .... which could be another common factor!

Adrian

[ChrisLX200]

Thanks all for your continued thoughts on this. I have learnt to accept it and process the out the problem although it would be better if it wasn't there in the first place!

@Adrain - A most detailed reply, thanks. In my head though I'd discounted the filter wheel as the others that have posted with similar problems have different wheels. Apart from the filters themselves, THE common factor is the Atik. But when I break down my imaging train again (if I can find something that will work as flocking material) I'll give your ideas a go.

@AG - What camera are you using when you are getting the gradient issue? The filters have all been screwed up and tested that they are flat in the carousel, I don't think it would be orthogonality with just the one filter?

@Chris - An interesting idea, I'll be sure to check that out.

Are you using an LPA filter in combination with the narrow-band filters? (i.e., effectively 2 narrow band filters in series - because the LPA has some sharp cut-offs).

ChrisH

[swag72]

Yes Adrian, all folks that have passed through with the same issue have been using a filter wheel - Albeit different types.

@Chris - No I don't use a LP filter in the imaging train with my NB filters.

[zombi]

Sara - what size of filters do you have ? Maybe it is some kind of vignetting - would it be possible to check 2" filters fit your CCD ??

[swag72]

I use 1.25" filters and don't know anyone out here in Spain with 2" filters - So won't be able to try that sadly.

[famax]

Sara, you should verify any light leakage from the filter itself :

take the filter in hand and look a light bulb filament throught it.

leakages at the edge of the filter  would act as secondary sources thus projecting shadows on the ccd edges...

this is more likely to happens with unmounted filters, but it cost nothing to check.

francois

[swag72]

Cheers Francois, it's all sorted now by a change of camera. No longer an Atik customer I can say that my OIII gradient is absolutely a thing of the past.

[FLO]

Cheers Francois, it's all sorted now by a change of camera. No longer an Atik customer I can say that my OIII gradient is absolutely a thing of the past.

Be fair Sara, you changed more than just the camera. You went from an Atik camera with a number of non-Atik accessories to another brand with integrated filter wheel. 

... it's hard to ignore the fact that the Atik camera showed no gradient when the filter was mounted in a nosepiece. Ergo it can't be wholly down to the camera, or you'd see the issue with the filter mounted that way too. 

It sounds better coming from him

Steve 

[swag72]

Be fair Sara, you changed more than just the camera. You went from an Atik camera with a number of non-Atik accessories to another brand with integrated filter wheel. 

You're right Steve of course. The comment that changing the camera has cured the problem is unfair.

[ollypenrice]

The thing about the QSI is that the filter spacing is radically different from non-integrated cameras. I strongly suspect that this will be why the problem came and went with the cameras. I doubt that there is anything inherently wrong with the Atik, or different about it. Spacings are hyper critical in anything concerning internal reflection. You never know, with a different filter the problem might be reversed. I've never had O111 gradients with Atiks or the SXVH36.

The suggestion of Francois might also explain why the QSI performed better with this filter. It will be using a more central part of the filter since it meets the light cone closer to the chip.

Olly

[famax]

all right, nice to see that the problem is solved.

I'm not surprised to see that was a kind of compatibility problems.

By the way, when issues are solved, evryone should ensure to tell it and how.

have a nice imaging (if the weather goes better...)

[lensman57]

Sara, you should verify any light leakage from the filter itself :

take the filter in hand and look a light bulb filament throught it.

leakages at the edge of the filter  would act as secondary sources thus projecting shadows on the ccd edges...

this is more likely to happens with unmounted filters, but it cost nothing to check.

francois

Hi Francois,

I too have had a lot of trouble with a Baader Oiii CCD filter ( to the extent that I have given up NB imaging ) when in use with my Atik 314L+. In my case it was the huge halos formed around bright stars no matter what scope I used, An SW 80 ED, WO 72 Megrez, Ascension 80mm ED triplet and even on a Quattro 8s. I also discovered that my filter wheel, a Zagyl motorised one had a design fault, the carousel is not large enough to cover the gap left over from the front aperture so unfilterd light gets into the imaging chamber from the top of the carousel and enters the CCD. I have solved this problem by machning an aluminium plug painted balck but even so the problem still persits, infact it was there while I was using a manual filter wheel of a different brand that was a lot thicker than the tiny Zagyl. So I don't think that it is either the wheel or the scope so the two remaining culprits are the camera, very unlikely or the filter itself, quite likely. The issue of spacing is also critical but unless a proper distance can be specifed by Baader one can not  forever change wheels to compensate for this short coming.

Regards,

A.G

[famax]

Hi Francois,

I too have had a lot of trouble with a Baader Oiii CCD filter ( to the extent that I have given up NB imaging ) when in use with my Atik 314L+. In my case it was the huge halos formed around bright stars no matter what scope I used, ....

Regards,

A.G

Hello AG, A lot of peoples complain about baader OIII filter. So i think it is a layer design problem in their filter model.

My advice is to keep all the other filter from baader and to take an OIII from astrodon.

By the way ,  generally ,OIII is a very different from Ha and SII in the way that it covers a spectrum subject to  common light pollution , moon glow, etc, etc..; so this filter

will be very sensible to stray light.

So in my opinion, it is very common to have difficulties with  the OIII filter.

But  i repeat that halo on bright stars can be avoided by a proper filter design, as astrodon  filter (cost a lot, but you now why....)

[lensman57]

Hello AG, A lot of peoples complain about baader OIII filter. So i think it is a layer design problem in their filter model.

My advice is to keep all the other filter from baader and to take an OIII from astrodon.

By the way ,  generally ,OIII is a very different from Ha and SII in the way that it covers a spectrum subject to  common light pollution , moon glow, etc, etc..; so this filter

will be very sensible to stray light.

So in my opinion, it is very common to have difficulties with  the OIII filter.

But  i repeat that halo on bright stars can be avoided by a proper filter design, as astrodon  filter (cost a lot, but you now why....)

Very True Sir. At least I ascertained that Baader Ha, Oiii and Sii filters are truely Parfocal with each other the last time I experimented with the Quattro 8s. This is not true of my other " Lens " scopes as they are not truely parfocal with all the wavelenghts, the Quattro 8s  being a mirror scope does not suffer from these short comings but the halos are still there.

Regards,

A.G

[ollypenrice]

Yes, my Baader O111 is halo prone as well, though gradient free. SInce I only add O111 to green and blue I can eliminate it by Photoshop thuggery, of course!

Olly