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Ended up with 2 CMOS Cameras. Which for my dedicated Guidescope?

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#1 Mvillegas

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Posted 21 August 2019 - 08:43 PM

Ended up buying a second 60mm guidescope on CN for my new Explore Scientific ED 127mm and now have 2 guidescope cameras and wondering which one is better suited for my new scope.  My original camera was the Altair GPCam2 130 and the 60mm came with a Starlight xpress costar.  The specs don't really mean that much to me yet as I am a newbie.  All I know is that the Starlight is more expensive but that isnt always a clear indicator.

 

The Altair specs are:

ALTAIRGP130M: APTINA AR0130 MONO CMOS sensor

  • Sensor Size: 1/3" (4.8x3.6mm)
  • Exposure duration shortest/longest:
  • 0.115ms (0.000115 secs) / 800 secs 13.33mins (trigger mode)
  • 0.115ms (0.000115 secs) / 5000ms (5 secs) (video mode)
  • Bit depth: 8bit & 12bit mode switchable
  • Pixel size microns: 3.75x3.75 um
  • Resolution in pixels: 1280x960
  • Recording System: Still Picture and Video
  • Region of Interest (ROI) support: Yes, in SharpCap & AltairCapture
  • Approx. Max frame rates (assuming computer Bus and Hard Drive operating at full bandwidth)*:
  • 8 bit mode:
  • 1280x960 - 27-30fps
  • 640x480 - 55fps ROI mode
  • 320x240 - 104fps ROI mode
  • 12 bit mode - approx 50% of above.
  • * Based on average user reports. May be revised with more data. Shorter exposure durations yield faster frame rates. An expensive PC does not guarantee a fast frame rate.
  • Sensor QE / Quantum Efficiency: Approx. 78%
  • Gain Sensitivity: 6.5V/ lux-sec
  • Dynamic Range: 82dB
  • SNR Maximum: 44dB
  • Readout: Progressive Scan
  • Shutter: Electronic Rolling Shutter

 

And the Starlight specs are: 

  • Imager type: Aptina MT9M001 mono CMOS chip with low dark current and anti-blooming.
  • Full resolution Pixel data: Pixel size: 5.2 microns square
  • Image format: 1304 x 1024 pixels
  • Image area: 6.66 mm (Horizontal) x 5.32 mm (Vertical)
  • Spectral Response: QE max at 620 nM (approx. 65-percent), 35-percent at 400 nM and 770 nM
  • Readout Noise: Less than 40 electrons RMS, typically only 20 electrons.
  • Anti-blooming: Overload margin greater than 1000x.
  • Dark current: Dark frame saturation time greater than 10 minutes Less than 1 electrons/second at more than 10-degrees C ambient temperature
  • Data format: 10-bits.
  • Computer Interface: Built-in USB 2.0 compatible interface
  • Image download time: Typically 0.1 seconds at full resolution using USB 2.0
  • Power requirements: USB powered
  • Cooling system: Ambient air cooling
  • Size: 32 x 60 mm black anodized aluminum barrel with 25 x 0.75 mm, C-mount thread at the CCD window end and input/output plugs at the rear
  • Weight: approx. 45 g (0.099-pound)

Advice welcome. Thanks!



#2 stryker66

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Posted 21 August 2019 - 10:40 PM

starlight is more sensitive, usually with bigger pixel pitch. Means more star selections



#3 james7ca

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Posted 22 August 2019 - 01:38 AM

I think it would depend upon the ratio of the guider image scale and the primary scope's image scale. I wouldn't go beyond a 5:1 ratio ( guider / primary image scales). For example, if you 60mm guide scope is an f/4 (240mm focal length) that would give the following image scale on the guider:

 

Altair with 3.75um pixels: 3.22 arc seconds per pixel

Starlight with 5.2um pixels: 4.47 arc seconds per pixel

 

You'll have to calculate the image scale for your primary imaging scope (using its focal length and the pixel size of your imaging camera) and redo the guider scale if your guider doesn't have a 240mm focal length. I use a guide ratio close to 4:1 and I've actually considered getting a guide camera with smaller pixels since with my Mach1GTO mount and on nights with good seeing I'm probably pushing what you can do even at that ratio.

 

Here is a website with an image scale calculator:  http://www.wilmslowa...formulae.htm#FR

 

That said, it looks like the Starlight would be a good choice for an OAG, but maybe not for a separate guide scope (depending upon the above guider to primary image scale ratio).


Edited by james7ca, 22 August 2019 - 02:02 AM.


#4 freestar8n

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Posted 22 August 2019 - 05:45 AM

The MT9M001 sensor is an early cmos sensor and it is much less sensitive than current cmos.  I don't know the Aptina but its stated QE of 78% is more like what is currently available.

 

With a guidescope you may not need much sensitivity - but I suspect the Aptina is lower noise also.  The Starlight says the readnoise is 20e - which is huge.  I can almost believe it is that big - and for short guide exposures that would be a big problem.

 

It should be easy to try them and compare - just make sure to set gain and exposure appropriately.

 

I suspect the Aptina would be better for both guidescope and oag - and if the sensitivity is much better as I suspect - then it would be particularly desirable for oag.

 

The only downside in either case is that it is smaller.

 

Frank



#5 Ken Sturrock

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Posted 22 August 2019 - 01:50 PM

starlight is more sensitive, usually with bigger pixel pitch. Means more star selections

 

I'd actually vote the reverse because the guide scope should throw up a fairly bright but small image and the camera with the smaller pixels (which are more efficient) should give you a better sampled guide star and more accurate centroid calculation.

 

My opinion, though, is worth every penny that you paid.



#6 Mvillegas

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Posted 23 August 2019 - 05:56 PM

Thanks all, Will try both and see which yields better results. Thanks!
 




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