Resolved what is focal length of cctv lens included in original STI guider kit?

Discussion in 'Specialty Cameras SG-4, AllSky, ST-I' started by Pieter Strauss, Jan 16, 2020.

  1. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    I have an original STI guider camera which I use both with the OAG and the original STI guider kit -- a cctv lens and mounting bracket.
    My question is, what is the focal length of the cctv lens? On the outside it says 100mm -- however, I note that the focus positions stamped on the lens are incorrect, due, I assume, to the adapter used to attach the lens to the STI. My focus point is closer to 20' than the infinity mark.
    PHD2 would like to know the focal length of the guiding telescope (here the cctv lens), and I'd like to get it right from the start.
    Any clues appreciated.

    Pieter
     
  2. Colin Haig

    Colin Haig Staff Member

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    Pieter, the lens is indeed 100mm, and the focus positions are correct when that lens is used with a CCTV security camera with standard C-mount spacing flange focal distance of 0.69 inches, or approx 17.5mm.
    The ST-I has a slightly different flange focal distance, and yours probably has an intermediate adapter ring to convert from C-mount to ST-I.
    There have been some variations in manufacturing over the years.
    The best way to resolve this is to grab an image with the ST-I of a busy star field, use MaxIm DL's Analyse -> PinPoint Astrometry and plate solve the field.
    That will give you a very accurate set of optical parameters.
     
  3. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    Thanks, Colin. I had come to a similar conclusion, but now have managed to confused myself on how to do this. Currently, my maxmdl thinks that the 8300m is camera one, with the FW5 filterwheel. I tried accessing just the STI as camera one, and it got wrapped around the axle not seeing the FW5. So: can I use the STI as camera 2, and image using camera 2?
    Or do I start from scratch, blow away the 8300 configuration, do a new configuration of the STI as camera 1, get the image, plate solve, then go back and reconfigure the 8300 plus FW5 as camera 1?
    Sorry to be clueless, but it is much better if I figure out what I should do in the warmth of my house, than to try to think on the fly at dark o'clock, with the temp below freezing and the wind blowing.

    --Pieter
     
  4. Colin Haig

    Colin Haig Staff Member

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    This is simple.
    Just use ST-I as Camera 2. You can Expose from the Guider tab.

    Alternatively, you can go to the Expose tab and select Camera 2, and expose there, but why complicate your life?
     
  5. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    Many many thanks, Colin! Now if I could get a clear sky and winds below 75 mph (no kidding), I'd be good to go!

    --Pieter
     
  6. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    I got the clear sky and fairly non-windy conditions, but received the following error: Couldn't connect to camera error 27.
    To get some imaging done, I assumed 100 mm, and guided with PHD2 and the STI, so it is working.
    Note -- in September of 2018 I was able to connect the 8300 as Camera 1 and STI as camera 2 in an attempt to guide with MaximDL.
    Next day I went out and did the following: downloaded latest Driverchecker, updated drivers (so I got the latest dll from 2019), updated MaximDL to latest (6.20), repeated attempt: setup camera 1 for the 8300, and camera 2 for the STI, got the same error: error 27. Set camera 2 to no camera, then was able to connect to 8300 as camera 1.

    What to do?
     
  7. Colin Haig

    Colin Haig Staff Member

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    Error 27 is Device Not Found.
    What happens if you disconnect the 8300 and try to connect to the ST-I by itself?
    Check the Windows device manager for both cameras when they are both connected.
     
  8. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    I believe this was the first thing I tried some days ago, however I did not check with device manager. What I remember is that I tried to connect STI as camera 1 and it got upset that it didn't have a filter wheel. Will do next time I can get out to observatory.
     
  9. Doug

    Doug Staff Member

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    If you connect the ST-I as Camera 1 then make sure Camera 1's filter wheel is set to No Filters.
     
  10. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    Problem solved! The joke's on me, I will probably win the bone-headed user award of the day.
    When setting up Camera 2 I had cleverly neglected to click on the dropdown which defaulted to "Parallel 378". When I did this, ST-i was one of the choices.
    Discovered this during daytime work, so didn't get to test out taking an image with ST-i, perhaps tonight.
    Many thanks for your patience!

    --Pieter
     
  11. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    Oops! Problem not solved. I got MaximDL to recognize my St-i with no difficulty, and took an image of ngc2112.
    However, I had problems getting Pinpoint to platesolve the image for me. Setting the pixel scale using either 7.4 microns or 5.4 microns and 100mm, and then clicking on Process gives me a failure message: the picture is too big. If I then click on Search Sky Online, it chugs away for a while, finds the center, then says to click Process, which I do, and I get the 507mm etc. result.
    1. What is the pixel size of the ST-i? The FITS header window for the image says 5.4 microns. The manual says 7.4 microns. My ST-i is one of the earliest ones to come out. I did send it back to have a defective shutter repaired within a short time, but believe I got the same one back.
    2. However, whether I use the set pixel function to determine the arc sec per pixel with 5.4 or 7.4, I end up with what seems to me to be an outlandish result: FL 507.8 mm, 2.19"/Pixel

    It seems clear that the adapter ring connecting the ST-i to the CCTV lens will alter the stated 100mm. But I can't see how I would end up with a result of 507.8mm focal length and 2.19 arcsec per pixel.

    Help please!

    --Pieter
     
  12. Colin Haig

    Colin Haig Staff Member

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    Hi Pieter,
    The specifications for the ST-I in the manual are correct.
    648 x 486 total pixels; 640 x 480 active pixels, 7.40 um in size.
    Length 4.8 mm x width 3.6 mm, diagonal 6.0 mm known as 1/3 inch size (vidicon scale).
    QE 500 nm 54% , well depth e- 20000-25000
    Send me a FITS file and I will have a look.
    Are you sure it isn't picking up the dimensions from the main camera's sensor or that you haven't selected the right option?
     
  13. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    Thanks Colin!
    I will upload the file and hope you can decipher my problem. At the time the image was acquired, I had MaximDL 6 attached to the 8300 M as Camera 1, then picked ST-i from the drop down list for Camera 2. If there was any further configuration of Camera to do, I am unaware of it (but happy to learn!) Yes, it does look as thought info from other equipment managed to flow to the control block for the ST-i.
    The attached file, ngc2112, is the unaltered image file. It is not the saved copy after the plate solve. I can provide that too if you want.
    In all this, what I am looking for is the correct focal length of the CCTV lens as attached to the ST-i. I will say, my PHD2 profile currently is running adequately (but not well!) with the nominal 100mm value, but I'd like to correct it.

    --Pieter
     

    Attached Files:

  14. Colin Haig

    Colin Haig Staff Member

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    Pieter,
    An essential thing to do:
    File... Settings... Site and Optics tab.
    Set the parameters of your main telescope.
    Then set the parameters of the guide scope.
    Check the latitude, longitude, and altitude.

    File... Settings... FITS Header tab.
    You might want to put in the details for those FITS fields.

    Then take an image with Camera 2 - and save and attach here.
     
  15. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    Aha! Will do, it will be a few days before weather clears again.

    --Pieter

    PS I alternate between imaging through the LX200 and through a piggybacked TMB80SS. The ST-i is the guide camera in each cast, but focal length etc. will change because I am alternating between the OAG and the ST-i kit. I assume I would have to go back and reinform MaximDL each time I switch?
     
  16. Colin Haig

    Colin Haig Staff Member

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    MaxIm has a feature called "Configurations". You can save the whole setup for one arrangement such as "My_LX200_STI" or "Pieter_TMB80SS_OAG".
    Then you can easily switch between them.
    Have a look at this section in the manual.
     
  17. Pieter Strauss

    Pieter Strauss Cyanogen Customer

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    Aha! There's always something to learn! Many thanks!

    --P
     

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