From: "Milton Aupperle" <milton@outcastsoft.com>

Date: July 15, 2009 11:45:41 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: I think this is my best Jupiter image so far!

Hi Terrence;

--- In Astro_IIDC@yahoogroups.com, Terrence Redding <tredding@...> wrote:

Milton, thank you for taking time to write.

For the past year I have been fairly intense in my efforts to do  

occultations.  That process involves a low light analog camera, a KIWI  

OSD time insertion device that embeds a GPS location and date/time  

stamp in the recordings.  The analog video is typically sent to  

camcorder for recording.  The video is then transferred via Firewire  

for recording to a PC and saved as a very large AVI file by Movie  

Maker.  Then the video is edited down to small manageable clips and  

imported into LiMovie where the  target is anchored to a comparison  

star and a photometric light curve is generated.

I'm curious as to what sort of +/- magnitude error LiMovie reports for the photometric magnitude measurements?

Astro IIDC allows you to use multiple "Constant" stars too, which helps reducing the error estimation.

It would be nice if I could refine the work flow and simplify it and  

use a Mac in the process.

This past week I decided to commit myself to imaging the planets and  

that endeavor has exposed me to your software.  I am keen to give your  

software a go.  I am reading through the online help file now.  It is  

very well done - an excellent read.  Thank you for taking the time to  

prepare it.

You mentioned photometric time stamp.  I wonder if there is a device  

that would allow me to use GPS time insertion?

No there isn't such a device, because it would have to capture the FW packets, decode them into a frame, add the time stamp to the image,  then re-packetize the data and re-transmit it as packets.

Astro IIDC uses the absolute time of your Mac's system clock and then the FireWire relative packet time stamp (which has a granularity  +/- 125 micro seconds or +/- 0.125 milliseconds) As long as your Mac's time clock is accurate at the start of capture, then it won't be an issue. So if you synchronize the Mac's system clock with the GPS time at the start, it will be very accurate throughout the rest of the capture.

Dave Herald just released a set of procedures to use highly accurate timing to perform  

astrometry and the occultation community has started doing just that  

prior to major event to improve the predicted location of the stars  

and asteroids for coordinated events.

I'm really curious how they account for the inherent delays with any system like that. For example, your getting NTSC fields / frames at 29.97 fps / 59.95 fields per second out of the camera, then the time stamp is applied and then the analog signal is passed to the DV Camcorder which records it. Is the time stamp being done on the first field or last field of the interlaced frame, which adds +/- 16.67 ms of variance and how long does it take to re-send the analog signal after it's done?

My guess is that your looking at roughly +/- 3 fields of accuracy with it, so it's roughly +/- 50 ms.

TTYL..

Milton Aupperle