[Aavso-photometry] RE: Rope Light Illumination for Flats

[Donn Starkey]

Wolfgang:

After the two images were divided, the image was trimmed to eliminate the
outer 50 rows and columns of the image before performing the statistics.  The
values that I posted were copied and pasted from the screen data provided in
Maxim DL's 'Information' window.  No chance for error in data transfer.  I am
not sure where the possible rotation in part of the image might have come
from.  The images were taken about 24 hours apart.  If I had rotated the
camera the first night, it should not have made any difference.  The camera
rotator homes back to the same spot after each imaging session and is accurate
to a few arcsec according to the manufacturer [RC Optical Systems].  The
camera as well as the filter wheel is rotated as a unit.  I would not expect
to see any dust-donuts from the primary or secondary.

Donn

==============================================
The price of freedom is constant vigilance.
Donn Starkey
starkey73 at mchsi.com
http://www.starkey.ws
AAVSO Observer SDB  -  CBA Indiana
VSNET Observing Team  -  MPC Code H63
==============================================


~ ------------------------------
~
~ Message: 4
~ Date: Fri, 14 Jan 2005 17:17:11 +0100
~ From: "Wolfgang Renz" <w_renz at onlinehome.de>
~ Subject: [Aavso-photometry] Re: Rope Light Illumination for Flats
~ To: <starkey73 at mchsi.com>
~ Cc: AAVSO-PHOTOMETRY <aavso-photometry at mira.aavso.org>
~ Message-ID: <018401c4fa54$8175e2c0$0b01a8c0 at 168.1.1>
~ Content-Type: text/plain;	charset="Windows-1252"
~
~ Hello Donn
~
~ Nice new building, dome and RC.
~
~ At which f number did you take the flats ? 8.4 ?
~ It shouldn't be very high, as the total and partial shadow of the guiding
~ chip mirror is visible in both flats !?
~
~ Did you cut out the edges and the area that is affected by the guiding
~ chip mirror before you made your statistics ?
~
~
~ I played a bit with CCDops for Win and the two flats using the Rainbow
~ color table to enhance the details. I matched the contrast of the flats
~ according to the color in the lower right quadrant to show about the same
~ background details:
~ - Sky flat:    Contrast: Back 15630, Range 800 & Processing Smooth
~ - Screen flat: Contrast: Back 18395, Range 870 & Processing Smooth
~ If you blink the sky flat against the screen flat with these
~ settings you will
~ notice a rotation of ~ 70 in the "background" of the flats.
~ * Did you rotate the camera between the two flat series ?
~
~ If you flatfield the screen flat by the sky flat and set the
~ Contrast to Back
~ 18600, Range 480 & Processing Smooth you will see a gradient from
~ buttom to top. The blue and red patches in the buttom part outside the
~ corners are due to the rotated background.
~ * Are the rope lights evenly spaced around the ring?
~
~ Looks like the begin overlap with the end by ~ 300.
~ * Is this the cause for the gradient to the sky flat ?
~
~ You will also see easily two "donuts" in the upper left quadrant
~ (the single,
~ faint donut with a diameter of ~ 630 pixel and one of the seven ~ 150
~ pixel donuts) and also slightly the center left ~ 150 pixel donut due to
~ the above mentionen rotation.
~ The other five of the seven ~ 150 pixel and the numerious ~ 22 pixel
~ donuts are not highlighted and seem not to be rotated.
~ Its a bit strange that two of the ~ 150 pixel donuts are rotated and the
~ other five are not.
~
~
~
~ Clear skies
~   Wolfgang
~
~ --
~ Wolfgang Renz, Karlsruhe, Germany
~ Rz.BAV = WRe.vsnet = RWG.AAVSO
~