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 > ----- > _______________________________________________ > Seesat-l mailing list > http://mailman.satobs.org/mailman/listinfo/seesat-l > _______________________________________________ Seesat-l mailing list http://mailman.satobs.org/mailman/listinfo/seesat-l
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