NavList:

   

Reply

As a check do a statistical pixels per degree measurement of the Sun
when it is high in the sky. For a terrestrial check try photographing
distant horizontal angles and comparing them with horizontal sextant
angles. I found that each of my 50mm lenses have different pixels per
degree calibrations and I suspect even a same make and brand would not
have identical calibrations.

On Aug 21, 11:26�am, Greg Rudzinski  wrote:
> Marcel,
>
> I agree with George's comments and would like to add that my Canon
> DSLR Rebel camera produces reliable images when way under exposed in
> black and white. Try using no filtering with settings of f22, 1/4000,
> ISO 100 and then increase the amount of light incrementally until the
> horizon is just visible as a reference. Also try a pair of opposing
> circular polarizers held out in front of the camera lens and adjusted
> to produce a faint image of the sun with a bright horizon beneath it.
> Experiment to find the best combinations for your particular camera
> and lenses.
>
> Greg
>
> On Aug 21, 4:49�am, Marcel Tschudin 
> wrote:
>
> > For investigating the refraction near the horizon I perform systematic
> > observations by photographing sunsets. So far I used the horizontal
> > diameter of the sun as a reference scale (pixel per degree) for
> > measuring the sun's position above the apparent horizon.
>
> > Recently I compared this scale to one derived from pictures of
> > landscapes and found to my surprise that they differ by around 8%; the
> > sun is systematically slightly larger.
>
> > The scale in landscape photos has been measured with distinct features
> > and the distances measured with Google Earth. The scale for (not
> > overexposed) sun photos has been calculated with the angular size of
> > the sun for the corresponding days; this size is based on the sun's
> > diameter (of the photosphere) and the earth's distance.
>
> > The difference is not related to refraction since the measurements are
> > made in horizontal direction. �Any idea, why those two scales differ?
> > It is known that some CCDs have a leak in the IR, also the one in my
> > camera. Could this be responsible for it? Does anyone know more on
> > this?
>
> > Marcel
--~--~---------~--~----~------------~-------~--~----~
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply