Resolved FW7-STX loose filters

Discussion in 'Filter Wheels' started by Niall MacNeill, Jul 29, 2019.

  1. Niall MacNeill

    Niall MacNeill Standard User

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    I recently purchased an SBIG 16803, with FW7-STX filter wheel and STX Autoguider. To go with it I bought the Astronomik 50mm square filters.....LRGB Ha, OII & SII. I carefully followed the supplied instructions for their installation. As an aside, the instructions say to remove one screw and swing the sensor out of the way so as not to damage it. The computer card design has however, been changed such that it is wider where the sensor is to be swung out of the way. Therefore it is no longer possible to do this. The instructions need to be updated to reflect that. I ended up removing both screws and carefully lifted the entire sensor out of the way.
    In any case, per the instructions I careful slid the filters around the carousel into their positions. The instructions then say:
    "Attach the press plate and tighten it down enough that all filters are held in place, but not so much that you risk cracking a filter. Only light pressure is needed to prevent the glass from rattling. They do not need to be clamped tightly."
    I did this, however there did not seem to be any mechanism for retaining the filters rigidly in place. Sure enough after assembly I could hear them rattling around when I moved the camera. I disassembled the FW and redid the steps to make sure I had done it properly. I tightened the press plate as far as it would go and it seemed clear to me it was making no contact whatsoever with the filters. Again they are still rattling around when I move the camera.
    Surely this is not right. I would have thought the press plate should have a rubber gasket around the outside of each square hole to mate against the filters to hold them in place.
    Please advise.
     
  2. Colin Haig

    Colin Haig Staff Member

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    Hi Niall,
    That doesn't sound right.
    How thick are these filters? The usual size is 3mm, and in some cases 2mm.
    This sounds like they are undersized. Where did you get them?
    Let us know, and then we'll see if there's an easy fix.
     
  3. Niall MacNeill

    Niall MacNeill Standard User

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    Hi Colin,

    The Astronomik filters are 1.0mm thick. No wonder they are rattling around. I didn't see anything in the FW7-STX manual that suggests there is a minimum filter thickness.

    I purchased the camera and the filters through Bintel in Sydney, NSW, Australia. We discussed a number of suppliers and settled on Astronomik for quality and value. They were unaware that the filters will not fit the filter wheel as supplied.

    Can you advise what I should do from here?

    Kind regards,

    Niall
     
  4. Colin Haig

    Colin Haig Staff Member

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    Hi Niall, ok, now we know why the rattle. I'll have a chat will colleagues and see if they have some ideas.
     
  5. Colin Haig

    Colin Haig Staff Member

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    Hi Niall,
    Here's what we've come up with as a possible solution. It may not be ideal, but would be an alternative to replacing the filters with 2mm ones.

    Camera Light Seal Foam is an option we think may work for you. It is commonly used around film camera optics, and is made of polyeurathane, so not likely to degrade very much over time.
    Here's one possible source:
    https://www.amazon.com/Camera-Light-Seal-Form-1-0mm/dp/B0014Z09D8
    If you were to obtain some of this self-adhesive 1.0mm foam, and make a few thin strips, you could likely use this to stop the filters from rattling around.

    The filter wheel was designed for 2mm filters, and will hold 3mm ones if the cover plate is not screwed down tightly.
    There is nothing we can do for 1mm filters on that wheel.

    Good luck and let us know how you make out.
    Cheers
    Colin
     
  6. Niall MacNeill

    Niall MacNeill Standard User

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    Hi Colin, thanks for this suggestion, however, I think I have a solution. I contacted Astronomik and described my issue. They offered to make me laser cut plastic gaskets to fit onto the filters, basically in line with what you have described above. I presume they will fit around the outside under the press plate and won't impinge on the light path. They will do this for free and mail them to me, so I could have them in a few days. I only have to pay for the postage.

    If for some reason this falls through I will follow up with your suggestion above.

    May I suggest you update the FW7-STX manual to make it clear that filters less than 2mm thickness will require an additional retention mechanism. Frankly I would probably have bought different filters had I known this.
     
  7. Colin Haig

    Colin Haig Staff Member

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    Ok, let us know how this works out.
     
  8. Niall MacNeill

    Niall MacNeill Standard User

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    A further update on this issue. Astronomik have laser cut soft plastic spacers which have the same external dimension as the filters and an internal dimension of 47.5mm. I checked this agains the square holes in the press plate which are ~ 46.4mm wide. Therefore the spacers should hold the filters all the way around and not protrude into the light path.
    Astronomik provided these for free and I only had today the 18.5 Euro postage.
    I will update further when they arrive.
     
  9. Colin Haig

    Colin Haig Staff Member

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    Thanks Niall - we'll note this for future customers!
     
  10. Niall MacNeill

    Niall MacNeill Standard User

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    Thanks Colin. I am really surprised to be the first with this issue.
     
  11. Niall MacNeill

    Niall MacNeill Standard User

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    Here is an update on the spacers which I received this week from Astronomik.

    They worked like a charm and after installation the filters are being properly retained in their holders. i.e. I could not detect any rattling when the camera was moved. They provide this retention without impinging on the light path as you can see in the images.

    I would like to thank Astronomik for their exemplary customer service. They laser cut the spacers and supplied them to me for free. I only paid for the postage to Australia.

    As an aside, please notice that I removed the sensor completely, contrary to the instructions which suggested it be swung out of the way by removing one screw. In fact the dog leg that is now a feature of the computer card precludes this approach and it is necessary to carefully remove the sensor completely before removing the press plate or the carousel.

    IMG_0845.jpg


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    IMG_0849.jpg
     

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