Re: Using a DSLR (was Re: North Korea satellite observed)

From: Wolfgang Hamburg (W.H@mburg.org)
Date: Sat Dec 15 2012 - 10:43:19 UTC

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    Am 14.12.2012 12:11, schrieb Marco Langbroek:
    Moin Marco,
    
    some dslr cameras can read gps data directly. I use a cheap gps gadget and it
    works realy good(see http://pc-mobile.net/nikongps.htm). So the exact time and
    position is written into the EXIF headers.
    
    Best regards,
    	wolfgang
    
    > Op 13-12-2012 1:09, Mal Ninnes schreef:
    >> Hi Marco,
    >>
    >> It's a Canon 600D with EF-S 18-55 IS II lens, which I only got just recently.
    >> Still getting the hang of night-time shots, as I'm not an expert
    >> photographer. I read the messages from yourself and Greg the other day and
    >> took photos of my GPS app (on android) at the start and end of my session,
    >> also taking into account the 16 leap seconds, and I've previously checked
    >> this against the US navy time servers on the net. The Canon time was off
    >> during last nights session by 4 seconds, which I corrected for as well.
    >> Obviously with this setup, I can't get sub-second accuracy. But for a start,
    >> I'm ok with it.
    > 
    > Hi Mal,
    > 
    > It is perfectly possible to get subsecond accuracy with a DSLR (it is what I 
    > do), but it involves carefull calibration.
    > 
    > Note that the time display of a GPS device is seldom quite accurate (while GPS 
    > time in itself is very accurate, this is not the case for the time in the 
    > display on most GPS devices. Unless they are specifically build for timing 
    > accuracy, such as GPS video time inserters). The display of my Garmin GPS can be 
    > off by more than a second. This is because sending positional data to the 
    > display gets priority over time information in internal processing in these devices.
    > 
    > The best time source to use with a DSLR actually is a radio-controlled clock, at 
    > least if you avoid the Cresta brand clocks (they are inaccurate, I have found). 
    > Oregon Scientific is a good brand. Avoid too fancy clocks with many bells and 
    > whistles, as you never know how detrimental those extra bells and whistles are 
    > on the actual display accuracy. Force the radioclock to synchronise shortly 
    > before your observing session (e.g. by taking the batteries out and then put 
    > them in agan).
    > 
    > Don't bother with your camera EXIF time: use the radio-controlled clock to try 
    > to trigger your camera at an exact time and write those times down. Target a 
    > number of unclassified satellites in a controlled, not too low orbit (e.g. 
    > Iridiums) and map the offsets in delta T of your obtained positions to predicted 
    > positions (Scott Campbell's software is very useful for that). That will give 
    > you your calibration values.
    > 
    > For satellite photography, ideally you would want a fast prime (= fixed focal 
    > length) lens rather than a slow and optically mediocre zoom like your EF-S 18-55 
    > (if your lens is the kit-lens, you'd want to replace that one anyway). On the 
    > second hand market you can get a fast EF 50mm for very reasonable prices: try to 
    > get one and use it with an F settings no larger than 2.8. The larger your lens 
    > opening, the fainter objects you will be able to capture. For a given focal 
    > length, an F2.8 or F1.8 hence is advantageous over an F4.5 or F5.3: your object 
    > will appear brighter on the image.
    > 
    > I noted that your picture was slightly out of focus. The best way to focus is to 
    > put your lens on "manual", then put the "live view" of your camera display on. 
    > Point to a bright star, zoom in on it on the display (not with the lens itself! 
    > Just on the display with the "+" button) and focus manually untill the star is 
    > pinpoint. Take a test image to see whether focus is indeed sharp.
    > 
    > Hope these hints are helpful!
    > 
    > - Marco
    > 
    > -----
    > Dr Marco Langbroek  -  SatTrackCam Leiden, the Netherlands.
    > e-mail: sattrackcam@langbroek.org
    > 
    > Cospar 4353 (Leiden):   52.15412 N, 4.49081 E (WGS84), +0 m ASL
    > Cospar 4354 (De Wilck): 52.11685 N, 4.56016 E (WGS84), -2 m ASL
    > Station (b)log: http://sattrackcam.blogspot.com
    > Twitter: @Marco_Langbroek
    > -----
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