QuickCam

Updated as of 2/8/00

I have needed two things to be able to autoguide my Alt/Az scope for CCD astrophotography.  The first was to solve the problem of how to deal with field rotation when using a piggyback guidescope.   That problem was solved, and I built a prototype system to use on our 32"f/4 Alt/Az mounted newtonian at Danciger, TX. (Click here for details). 

The second problem was to come up with an autoguider camera.  Ideally, an ST-4 type camera (small, self contained, and accurate).   The problem is these qualities make it popular, and popular means not inexpensive (at least for me).  Mel Bartels updated his fine scope.exe program that I use to operate the scope to accept inputs from an Accutrack Photodiode Autoguider.  This input actually works quite well, but it only guides in one axis.  This is enough if most of the motion is only in one axis, but dual axis guiding is what is required.

Then along came the QuickCam "cult" that has shown the feasibility of using these remarkable little cameras with telescopes.  They are not cooled, and so their exposure time is limited, which limits their capability for imaging deep space targets, but an autoguider does not need long exposures.  Quick images are what is needed.   Achay Doan and the team of Marty Niemi and Bob May have each developed software that provides autoguider outputs based on a Black and White QuickCam as the sensor.  While Achay's software (CamZoom) needs Windows 95/98 to operate, Marty's and Bob's software(Guider.exe) runs in a DOS environment, which is what I need since I plan on using a lowly little ZEOS subnotebook (20 mhz 386 with no math co-processor).  

Marty and Bob's software use the "standard" Cookbook interface circuit as described in the Cookbook CCD Camera  manual on page 167.   I have modified the circuit slightly to interface to Mel Bartel's motor control circuitry.  A .gif file of the circuit schematic is available by clicking HERE.  A Powerpoint version of the same file (looks a little cleaner) can be downloaded by clicking HERE. The basic information on the circuit can be found on the Cookbook website by clicking HERE.

The software that comes with the camera (after downloading the updates available from the Logitech website) work quite well to use the camera simply for imaging.

So, I purchased a b&w QuickCam thru Onsale.com for $19, and, after reading thru several of the websites on how people have modified the mounting of the camera to allow its use with a telescope, I too joined the "QuickCam Cult" <grin>

In the process of learning about QuickCams, I discovered there are a LOT of folks enjoying these amazing little cameras!!!! There is a small list of sites specializing in QuickCams at the end of this article.

To modify my camera to use 35mm camera lenses as well as being able to be mounted into a focuser as either a main imaging camera or as an autoguider,  I first disassembled the camera, using the excellent, detailed instructions I found from Hanno Muller's Website 

The pieces I did NOT use are shown in this photo:  (Click on any of the following thumbnail images for a larger view)

 

Based on Marty Niemi's approach, I used a 2" PVC Pipe Cap and a 2" PVC Pipe Plug to remount the camera:

 

The metal ring in the front of the camera in the previous image is the female  t-threaded portion of an old unused t-mount adaptor for a 35mm camera.  The following shot shows two t-mount adaptors. The ring was removed from the one on the right.  This allowed me to inset a precision set of t-threads into the face of the PVC plug, which then allows me to attach a variety of camera lenses or a 1.25" tube to allow mounting in a telescope focuser:  The t-thread ring is captured by 4 set screws.

 

A black paper mask was attached to the face of the camera's PC board with double stick tape to help cut down any stray reflections:

 

The PVC Plug was shortened to allow the distance from the CCD detector to the rear shoulder of the camera lenses to be the right distance to allow the lenses to reach focus.  The t-thread lenses require 2.125", and the Pentax threaded lenses I have require 1.8".  In addition, I wanted the chip to be as far forward in the mounting as possible, to minimize the "in" travel required by the focuser when being used at prime focus.   I used two different combinations of additional t-mount adaptors to achieve the required CCD Chip to camera lens distances.  The first combination is two adaptors stacked for the Pentax lenses: one "t to t" adaptor, and the second a "t to Pentax" adaptor.  The second configuration is three adaptors stacked for the t-thread lenses (the original 2 adaptors plus a "Pentax to t" adaptor).    Keeping the chip as far forward as possible also allows me to make a "t  to c" adaptor to use some C-Mount lenses I have that require a 0.675" distance.     The PC Board is simply clamped by the edges to the rear of the shortened PVC Pipe Plug with small brass screws.  The following shots show the front and rear views of the Pipe Plug and camera PC Board:

                    

 

 

I flattened the bottom of the pipe cap, and then drilled and tapped a 1/4-20 hole in the side of the PVC pipe cap to be able to attach the camera to a tripod mounting, and then attached the cover with two 4-40 machine screws to the pipe plug.     The assembled camera, with its rear cover and a 1.25" Prime focus adaptor (from my EP Projection adaptor) is on the left.  The center picture is the camera with a 300mm t-mount lens, and on the right shows it with a 28mm Pentax screw mount lens.

                  

 

All the various pieces are shown together below:

 

The image quality with the camera lenses is GREATLY improved over the tiny f/1.6 lens the camera comes with.  

I also recently modified the camera by adding a switch to allow me turn on or off the Anti Blooming Gate (ABG) which, when off, makes the camera susceptible to blooming, but also increases its sensitivity.  The image below shows the modification to the parallel port connector (the connector is plugged into the back of the 20mhz 386 laptop I use to run Guider.exe).:

(click on the image to see a larger view)

The modification is really quite simple ands only took about 30 minutes from the start to finish.  Dave Allmon has an excellent description of how to perform the modification at http://home.earthlink.net/~dallmon/html/abgmod.html

I have the camera and the autoguider interface circuit built and running with Guider.exe, and able to control the telescope very accurately with the camera mounted at prime focus.  With the telescope control software in "record" mode, the autoguider has provided VERY accurate guiding commands to allow recording of Periodic Error Corrections for Mel's telescope software (Scope.exe) to use to correct the approximately 4 arcsec of Periodic error that was in the system.

To be able to use the autoguider while my CB245 CCD camera is at Prime focus, I will be building a Guidescope rotator  to carry a piggyback guidescope and rotate it to eliminate translation errors that would result from the guidescope being mounted on an AltAz system.  For more info on Guidescope rotators, click HERE.

The following are links to sites that have more information on using QuickCams:  The first two are my highest recommendations for software specialized for astronomy related activity.  All the sites listed are EXCELLENT!  Visit each one to gain a little more insight into these cameras and options folks have come up with for modifying them and using them.....

 

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