Introduction

• An ELP IR Night WebCam ('ObsCam') was installed in the observatory on 2021-02-16 for the purposes of general 24x7 monitoring of the Observatory's interior and for recording the movements of the telescope and cables during live sessions (see ObsCam - New Camera for monitoring Observatory/Telescope, 2021-02-16).   
   
  The 'ObsCam' proved its usefulness at the end of session S884 (2021-04-13) when its live picture, automatically uploaded to the Observatory Status web page, showed that the observatory's shutter was still partially open (~20% open) despite the fact that the Dome System / Device Hub were saying that the Shutter was closed. This information allowed a user intervention to be made to ensure that the observatory was safe & secure.
   
• One concern about using an IR Night WebCam however is that light from the Camera's IR (infrared) LEDs might somehow get reflected back into the telescope's OTA or otherwise enter the imaging train and degrade images taken with the sensitive CCD Camera.  
   
  (typical observatory practice would be to turn off the IR lights during main exposures and then turn them back on when exposures had been completed.   Unfortunately there doesn't seem to be any easy way to turn off/turn on the LED lights on my particular make of NightCam using a computer command. This might eventually necessitate getting a different (more expensive) IP controlled camera rather than a USB camera, or get some form of IP controlled USB Hub to turn the camera off.
   
• The intention had been to run some tests to quantify the amount of IR leakage and whether it is in anyway acceptable or not, and then decide if the ELP Night WebCam was going to be suitable in the long term or whether it would need to be changed out for a different model. 
   
  I didn't get round to doing these tests in Feb/Mar as hoped, however a quicklook examination and rough comparison of images taken with the NightCam since its installation showed that it was somewhat unclear if the IR Lights caused any degradation to CCD Images taken with the LX200 Main Scope or CMOS Images taken with TS80 Secondary Scope.  For CCD images with the telescope pointing to the east or to the west and CMOS Images taken in any orientation it seems that the IR Lights were having no significant effect at all.  For other images problems were initially put down to stray light entering the telescope from a bright moon.   However as Moon reduced in phase the evidence gradually accumulated to show that CCD Images taken with the telescope pointing to the south had some extra light showing one one one side or one corner and  images taken at certain telescope positions were particularly bad,  showing quite a pronounched but uneven light gradient that couldn't be successfully removed by simple 4 corner point (tilt) correction.
  

Session S885 Test for IR Leakage (2021-04-14)

• Whilst monitoring session S885 remotely (2021-04-14) it was noticed that one particular target  (UGC 5760 w/SN2020zoq) lying at Az 186 / Alt 46 had a noticeable light gradient and pattern that was a firm candidate for having IR leakage from the Observatory's NightCam - there being no moon, light pollution or cloud at the time that could otherwise explain the anomaly.  Seeing the opportunity of making a definitive test for IR leakage an opaque cover was placed in front of the USB NightCam completely blocking it's IR light sources (a cover was used rather than pulling out the USB cable in order to prevent any in-session issue with the connected computer).
   
  Raw CCD Images with and without the IR Source are shown below. The difference is clear !
   
  The first image (taken with IR Source on) shows a clear anomaly involving a significant background gradient. 
  
  
  The second image (with IR source blocked off) is darker and shows a normal vignetting pattern without the significant background gradient.
  
  
  The following ObsCam image shows a view of the observatory at around the time of the above two images with the telescope pointing to Az 186/Alt 46.  
  The edges of the open shutter are indicated by superimposed yellow lines.  With telescope on this position the NightCam's IR lights point directly towards the back of the imaging train, and produces the  greatest roof illumination on either side of the dome slit and thus. closest to where the scope is pointing.
  
  
  Seeing the degradation in image quality the blocking cover was left on for the remainder of the S885 session pending further tests the following night.
  

Session S886 Tests for IR Leakage (2021-04-15)

• Part way into session S886 (2021-04-15) the telescope was slewed close to Az 186/Alt 46 and the cover in front of the NightCam taken away in order to perform a series of specific tests that were designed to identify the nature of the IR leakage path. 
  
  
  • Test 1.  180s image with IR Light fully blocked at source
    (Av ADU 2243)
    Aim : Provide baseline image.  
    
     
  • Test 2.  180s image with IR Light on and unblocked
    (Av ADU 4230.  IR Excess 1987 (4230-2243) )
    Aim: Confirm IR leakage as seen in previous Session, and characterise leak pattern.
    Notes : IR leakage is clearly present. 
    The somewhat linear left-to-right features near the bottom of image are believed to correspond to reflection & shadow effects in SBIG ST-10XE Camera caused by the boundary between the main CCD chip and the directly adjacent 45 deg mirror used for the smaller guide chip. This is a pattern that has in part been noticed before on bright flats.
    
     
    
  • Test 3.  180s image with IR Light on and partially blocked by a 12" Telescope Cap held at back of CCD Camera
    (Av ADU 2265, Max IR Excess? 22 (2265-2243) )
    Aim: Test for IR leakage coming onto CCD Chip via OTA (i.e. IR light reflected back into telescope)
    Notes:  No obvious IR leakage. Test seems to show that IR leakage isn't from IR light reflected back into telescope through the OTA
    
     
  • Test 4.  180s image with IR Light on and 12" Telescope Cap placed attached at front of telescope (ie a Dark Frame)
    (Av ADU 1628,  but excludes sky background,  IR Excess 1445 (1628-183) )
    Aim: Test for IR leakage that is entering via rear of CCD Camera or between Camera and OTA
    Notes: IR Leakage is clearly present.   No stars, so the leakage is clearly not via the OTA and must be through rear of camera/rear part of imaging train.
    
     
    
  • Test 5.  180s image with IR Light on and CCD Camera Shutter closed (i.e. Dark Frame) 
    (Av ADU 183)
    Aim: Test for IR leakage that is entering via rear of CCD Camera
    Notes: No IR Leakage    (IR leakage path would seem to be entering the imaging train between Camera and OTA,  through the TCF-S focuser prehaps ?)
    
     
  • Test 6.  180s image with IR Light on and a jumper wrapped around TCF-S Focuser & Camera Adapter 
    (Av ADU 2295, Max IR Excess? 52 (2295-2243) )
    Aim: Test for IR leakage that is entering via imaging train between Camera and OTA  (i.e. through Camera Adapter  or TCF-S focuser)
    Notes: No obvious  IR Leakage  (Jumper appears to have blocked the IR leakage path )
    
     
  • Test 7.  180s image with IR Light on and unblocked (check frame)
    (Av ADU 2817.  IR Excess 574  (2817-2243) )
    Aim: Confirm IR leakage is still present and hasn't disappeared due to change in position of the telescope in the 41 mins of tracking since Test 2
    Notes : IR leakage is clearly still present, but has changed slightly in character and decreased somewhat. 
     This is consistent with earlier observations that the extent of IR leakage effect varies quite a bit with the telescope position / pointing.
    
     
    
  • Test 8.  180s image with IR Light on and a jumper wrapped around TCF-S Focuser & Camera Adapter 
     (and with scope returned back to Az 186/Alt 46)
    (Av ADU 2295, Max IR Excess? 52 (2295-2243) )
    Aim: Test for IR leakage that is entering via imaging train between Camera and OTA  (i.e. through Camera Adapter  or TCF-S focuser)
    Notes: No obvious  IR Leakage  (Jumper appears to have blocked the IR leakage path )
    
     

Solution for Short-Medium Term

• Picture below shows jumper/jersey tied around the telescope's TCF-S Focuser / Camera Adapter. This was shown to effectively block IR light from the NightCam from entering the Imaging Train and reaching the SBIG Camera's CCD chip.   (although the jumper is dark coloured it shows up as white in the IR illuminated NightVision image. The remainder of the S886 session was run with the IR blocking jumper in place. There were no problems caused by this setup and the session returned good quality images without any sign of IR Leakage.
  
  
   
  
• A daytime examination will be conducted to see if the precise IR leakage path through the camera adapter and /or TCF-S focuser can be found and see if an alternate / smaller method of blocking the IR light can be found (using black tape for example)
   
• A longer term solution will depend of finding a means to turn off/turn on the IR lights on existing NightCam using computer control or swapping the NightCam for a new model/type than has this control feature.  ELP (the manufacturer of the IR NightCam camera used) have been contacted for assistance.  It is suspected however that there simply isn't a way of doing this using this particular NightCam model.  The cost/benefit of a new NightCam or other technical solution (computer controlled USB Hub/Power etc) will have to be weighed up against the 'jumper' bushfix which is cost-free and permits observatory monitoring to continue during imaging.
   
  

• Update 2021-10-23

• A facility has been developed in the AstroObsCam program to turn the ObsCam On/Off using a new Pegasus Astro USB Control Hub and ASCOM Switch. (2021-10-16)
   
  
• A new set of tests were conducted which confirmed that IR light was still leaking to the CCD Camera when scope was pointing at certain positions (see Daytime Tests  - Examination of IR Leakage from Observatory WebCam, 2021-10-23) 
   
• A new facility has been incorporate into AstroMain 3.45 to turn the ObsCam On/Off  during job queue execution in order to make the webcam's IR lights become turned off during target imaging.  (2021-10-23 , AstroMain 3.45) . This was successfully used for the first time during session S927 (2021-10-24).