[Comm2011] edge reflections

[valentyn]

Hi Koen

I looked at it last night, during the only 1.5 hour we could open.
Indeed we find the effect in a narrow range but around 1.5 arcmin off the
edge.
The observations were quite time taking with  1.5 min read out due to slow
hard disk, and I used a grid of 30 arcsec, to search faster.
I did not zoom-in with finer grid, but could if you want.

I planned to work more on u sensitivity, but nights are not photometric.
At least I could get calib filter with 300 sec in u.

I'm afraid it's still very cloudy at the moment- sunday afternoon.

Good trip!

Edwin
  

On Sun, 8 May 2011 17:58:06 +0200, Konrad Kuijken
<kuijken at strw.leidenuniv.nl> wrote:
> Dear Dietrich, cc Edwin:
> 
> Mostly to record my own understanding, I made a little drawing of how
> I suspect the reflections we see at the edges of the field may be
> caused. I'm pretty sure this is what you meant as well. The pink ray
> in the drawing only occurs in case 2, when the star is not too close,
> and not too far, from the edge of the filter (blue) on the left. Only
> then do you get sufficiently inclined rays. As you pointed out, the
> fact that in reality the beams from stars in the outskirts of the
> field come in at an outward angle (see figs in user manual, for
> example) makes this inclination a little worse than you would expect
> from an f/5 beam.
> 
> If this is the explanation the prediction is clear: only bright stars
> in a narrow range of distances (between ~3-4 arcmin, at a guess)
> outside the field will cause this effect.
> 
> Happy travels,
> Konrad