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

Fri Jan 14 11:17:11 EST 2005

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 ~ 7° 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 ~ 30°.
* 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.

A ring illumination doesn't guarantee an evenly illuminated field. Especially
if the spacing was picked miserably (too small) or if the light source emits
directed light & there is no secondary diffusor (see ray overlap in e.g.
http://www.visionelements.co.uk/illumination/images/flat-ring-ray-diag.jpg).
In machine vision they sometimes even an on-axis ilumination via a a half
mirror to overcome this for special applications.

See e.g.:
Firstsight Vision Inc
Illumination Products - LED lighting for machine vision applications
http://www.visionelements.co.uk/illumination/led_home.html

'Shower' Illumination:
http://www.visionelements.co.uk/illumination/shower.html
http://www.visionelements.co.uk/illumination/images/shower.jpg
http://www.visionelements.co.uk/illumination/images/shw-lum.gif

Flat Ring Illumination:
http://www.visionelements.co.uk/illumination/flat-ring.html
http://www.visionelements.co.uk/illumination/images/flat-ring-ray-diag.jpg
http://www.visionelements.co.uk/illumination/images/flat-ring-lum.gif

Dome Illumination:
http://www.visionelements.co.uk/illumination/dome.html
http://www.visionelements.co.uk/illumination/images/LDM-ray.jpg
http://www.visionelements.co.uk/illumination/images/dome-lum.jpg

On-Axis Illumination:
http://www.visionelements.co.uk/illumination/co-axial.html
http://www.visionelements.co.uk/illumination/images/co-ax-ray.jpg
http://www.visionelements.co.uk/illumination/images/co-ax-lum.gif
http://www.visionelements.co.uk/illumination/doal.html
http://www.visionelements.co.uk/illumination/images/doal-ray-col.jpg

Dome + On-Axis llumination
http://www.visionelements.co.uk/illumination/cdi.html
http://www.visionelements.co.uk/illumination/images/c-d-i-ray-col.jpg

Clear skies
  Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO

----- Original Message ----- 
From: "Donn Starkey" <starkey73 at mchsi.com>
To: "Brady, Steve" <sbrady at kerkmotion.com>; <aavso-photometry at mira.aavso.org>
Sent: Thursday, January 13, 2005 11:51 PM
Subject: RE: [Aavso-photometry] Rope Light Illumination for Flats

> Steve:
> 
> I took 5 B band flats using twilight illumination and 5 B band flats using the
> light ring illumination on the dome screen. I averaged each set of flats and
> then created a new frame that was composed of one set of flats divided by the
> other. The brighter of the two flats was scaled down to equal the average
> pixel intensity of the darker of the two flat before creating the new frame.
> This action offsets the differences in inherent brightness of the two frames.
> Each frame was in the 17,000 range for average pixel brightness.
> 
> The new differential frame had the following values:
> Maximum      1.142
> Minimum      0.763
> Average      0.938
> Std Dev      0.005
> 
> The two averaged frames are available at:
> http://starkey.ws/FTP%20Page/Bu%20Flat%20Frame%20Set.ZIP
> 
> On the Blanc Fixe coating, my company can supply it in quart containers.
> Anyone that wants to purchase it should contact me off-list for details.
> 
> "Talent", to paraphrase Rush Limbaugh, "is only on load from God."
> 
> 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
> ==============================================
> 
> 
> 
> ~ -----Original Message-----
> ~ From: Brady, Steve [mailto:sbrady at kerkmotion.com]
> ~ Sent: Thursday, January 13, 2005 10:07 AM
> ~ To: starkey73 at mchsi.com; aavso-photometry at mira.aavso.org
> ~ Subject: RE: [Aavso-photometry] Rope Light Illumination for Flats
> ~
> ~ Donn--
> ~
> ~ Thank you for your description - I am stimulated to duplicate your
> ~ setup!! I can check with Lumetron on availability of the coating
> ~ but wonder if this is something that could be purchased through you
> ~ / your company in quantities (cost??) that are appropriate for an
> ~ amateur needs. Out of curiosity, have you compared your domes flats
> ~ to twilight flats?
> ~
> ~ I very much enjoyed browsing your web site - your a man of many talents.
> ~
> ~ Clear skies,
> ~ Steve