ST-i
Planet Cam and Autoguider


 

 
 

ST-i PLANET CAM AND AUTOGUIDER

The ST-i Planet Cam and Autoguider adds features unavailable elsewhere in a camera of this size and price.  A high performance compact camera that is an excellent guider and very capable Planet Camera.  The body is light weight, no larger than many 1.25" eyepieces. In fact, it is 1.25" in diameter, 3.5" long and weighs only 2.2 ounces.  The camera receives both control signals and power from the USB port of your computer, so only one thin USB cable is required for using the camera as an imager.  For guiding, a standard, opto-isolated, autoguider output port is located in the back panel (see below).

KODAK KAI-340 CCD - Mono or Color

Rather than using a low cost CMOS sensor (with high noise), the ST-i uses a high quality, low noise, Kodak CCD.  The KAI-340 CCD has a measured read noise of only 9e- in the ST-i camera.  This is the same CCD used as the guiding sensor in the new STX series cameras and the AllSky-340 cameras.  The array is 648 x 484 pixels at 7.4 microns square.  Anti-blooming is standard.  We use only the Class 1 version of this CCD with 0 column defects, 0 cluster defects, 0 dead pixels, and 0 saturated pixels, all according to Kodak specifications.  On-chip binning is available for 14.8u pixels if desired, and various sub-frame modes may be used to speed-up the focus and download rates.  A full frame high res image will update at the rate of approximately 5 frames per second.  In addition to full-frame, half-frame and quarter-frame modes, the user may select a sub-frame region of interest (ROI) of any size located anywhere on the CCD.  In focus mode, using a 20 x 20 pixel box the update rate is greater than 20 frames per second.  This sensor is available in monochrome or color.

Kodak describes the performance of this CCD:  "Designed for demanding imaging applications, this sensor has additional features including electronic shuttering, peak QE (quantum efficiency) of 55%, extremely low noise and low dark current. These features give this sensor exceptional sensitivity and make it ideal for machine vision, scientific, surveillance, and other computer input applications."

ELECTRONIC AND MECHANICAL SHUTTERS

This sensor has an electronic shutter allowing exposure times as short as 0.001 seconds.  Most other eyepiece sized cameras rely on this type of "global" shutter alone due to the difficulty and cost of building an additional mechanical shutter into the camera body.  However, in the ST-i camera we have also included a mechanical shutter enabling the camera to automatically take dark frames.  This feature alone dramatically improves the performance of the ST-i, particularly when used as an autoguider.  Cooling of the CCD to reduce dark current is unnecessary at the short exposure times common to planetary imaging and autoguiding, but there remains the possibility of bright pixels in an image that can raise the threshold of brightness required for the most sensitive guiding performance.  The ability to automatically take and subtract a dark frame results in a very smooth background against which detection of dim stars is more reliable.  Finally, while some inexpensive guiders save cost by using low cost 8 bit or 10 bit electronics, the ST-i camera uses a high quality 16-bit A/D for superior resolution of the full dynamic range of the CCD, greater than 70 dB.

16-bit frame rates using prototype camera and desktop computer
         
Focus Mode Full Frame Half Frame Quarter Frame 20 x 20
High Res 1x1 5.8 fps 10.6 fps 16 fps 21 fps
Medium Res 2x2 10.6 fps 16 fps 21 fps 21.fps
         
Autograb mode Full Frame Half Frame Quarter Frame 20 x 20
High Res 1x1 4.6 fps 7.4 fps 9.7 fps n/a
Medium Res 2x2 7.3 fps 9.9 fps 11.9 fps n/a
         
  Focus = recorded using 0.001s exposure as reported by CCDOPS
  Autograb = Ave. of 100 uncompressed frames saved to disk using 0.001s exposure

STANDARD ACCESSORIES:

OPTIONAL ACCESSORIES:

PLANETARY IMAGING

Planet Master Commands in CCDOPS

The Planet Master command is used to take the sharpest images of planets or other objects.  It takes a sequence of images, grading them for sharpness and keeps the sharpest one.  Typically you would take short exposures, knowing that throughout the sequence a stable period of seeing will give a clear image.

The simulation below demonstrates how it works:  

moon_sharp.gif (529302 bytes)

This animation contains a series of 14 images that simulate the change in sharpness from moment to
moment caused atmospheric turbulence.  In "Best Sharp" mode, PlanetMaster software will continuously
update the image on the left and calculate a Figure of Merit (FOM) based on the sharpness of the image.
The image on the right hand side is updated only when an image appears on the left that has a Figure of
Merit greater than the last best image stored in memory and displayed on the right.  


The Grade Image By Sharpness command in the Utility menu allows grading a set of already acquired images.  It's like an Off-Line version of the Planet Master command. Many planetary imagers like to average several of their best exposures.  This requires taking a large number of images in a short time and then examining each image for the best of the lot of the best few of the lot.  In this case the imager might prefer to use the Autograb function of CCDOPS to capture as many images in as short a period of time as possible.  (Planets rotate!)   PlanetMaster software may then be used to automatically examine a series of images and assign a Figure of Merit for sharpness to each one.  Then only the best of the lot can be selected for averaging. 

GUIDING SENSITIVITY

A sample 1 second dark minus dark frame is shown below followed by a 1 second light minus dark frame of the Orion Nebula region.  The 1 second light frame, taken with an 60mm guide scope, shows numerous potential guide stars fainter than 11th magnitude, and many more 10th magnitude or brighter.

 

1 second dark minus dark frame at room temperature (+25 C)


 

1 second light minus dark frame through 60mm scope showing numerous stars fainter than 11th Mag.

 

 

ST-i compared to typical 1.25" eyepiece

Rear Panel

USB and Guiding Cables Attached

 

Specifications
CCD   Kodak KAI-340 Mono or Color
Class  Class 1 (0 column, cluster or dead pixels)
Array  648 x 484
Pixel Size  7.4 microns
A/D  16 bits
Read noise  9 e-
Dynamic Range  > 70 dB
Download  5 - 21 frames per second @ 16 bits
Mechanical shutter  Yes (internal)
Electronic shutter  Yes
On-chip binning modes  1x1, 2x2, 1xN, 2xN
Sub-frame modes  Any size
Power and Interface  USB 2.0
Guide port  Opto-isolated, ST-4 Standard
Weight  2.2 oz  (68.4 grams)
Size  1.25" D x 3.5" L (31.75 x 88.9 mm)
Guiding sensitivity  11th Mag / 2 sec / 60mm
Software  CCDOPS and CCDSoftV5 included
OS Requirements  All Windows versions supporting USB
 2.0 including Win 7, Mac, 3rd Party Linux
Drivers  32 bit and 64 bit

 

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