From: "Jeff Anderson-Lee" 
To: "Vladimir Galogaza" ,
"ATM shore"
        
Reply-To: "Jeff Anderson-Lee" 


Sorry for the slow response.

> >With the zoom lens I can easily frame and focus the image
> >of the mirror to fill the picture.
>
> You probably noticed that I am obsessed with this "focusing" problem
> in Foucault camera assisted test.
>
> Now since you are at it and apart from adjusting the size of the
> " mirror image" to fit CCD by zooming, my question is how do you
> FOCUS. What is your focusing criterion.

Well, I'm just starting at this.  My first images were on Saturday.  What I
did to focus was to place something with some amount of detail at the plane
where a Couder mask would go and focus on that.  I looked for focal
positions inside and outside of focus where it started to look obviously
blurred, and averaged those two positions to estimate the position of best
focus.

In the future I plan to use a lined card along with some software to help
estimate the best focus point, but I'm still learing how to access the
camera programatically at this point.  The plan is to write a small program
to integrate (average) some number of images at capture time and then draw
(in real time) an illumination profile graph for a selected horizontal
slice.  Given a known image pattern (vertical stripes), I should be able to
quantify the degree of focus to help find the best focus position.

Cary has suggested that I also add dark frame and flat field capabilities
to improve the overall image quality.

> In normal camera use this is
> sharpness of the image or maximum contrast in autofocus mode, but in your
> case the " mirror image" should be of equal sharpness or contrast
> at any zoom setting ( I presume).

That's why I introduce something else with a known pattern to focus on
before imaging the mirror.

> If it will be not to much work can you please take two pictures
> one well "focused" according to your criteria and another out of focus
> according to the same criteria and post it to me (or list).

I will do this eventually, but since I need to take over the kitchen to do
my imaging at this point, I will wait until I get my next camera setup
working first.  I'm not satisfied with the level of noise I'm seeing with
the Creative Webcam Pro.  I plan to try a different camera (Quickcam Pro
4000) to see if I can reduce the amount of noise in the images.

> If you are at it you can make third image by removing the lens and
> let the lensless camera came so close to the KE that CCD will
> be filled with light and make another shot and post it as well.

I think James has covered this excellently at this point.

Jeff Anderson-Lee
Sacramento, CA

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