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

From: Petter Aslaksen (
Date: Fri Dec 14 2012 - 12:04:49 UTC

  • Next message: Gavin Eadie: "Re: Using a DSLR (was Re: North Korea satellite observed)"

    I have a follow up question here, making my comeback on the mailing list
    after about 10 years
    I am stuck with my 18-200mm 3.5-5.6f for now, I have a 50mm 1.4f at home,
    which I guess would be a good lens for this.
    I want to shoot satellites tonight. What should I do, zoom in all the way
    and keep it at 5.6f, or should I zoom out and have it at 3.5? Any ISO
    suggestions for 30 sec exposures.
    By pure accident I photographed Lacrosse 4 two days ago when I tried to
    shoot Geminid meteorites. Coincidentally, Lacrosse 4 passed through the
    Geminid radiant, and at first I thought it was a meteorite.
    On Fri, Dec 14, 2012 at 12:11 PM, Marco Langbroek <
    > wrote:
    > 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:
    > 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:
    > Twitter: @Marco_Langbroek
    > -----
    > _______________________________________________
    > Seesat-l mailing list
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