Flats for DSLRs

[Doug]

Paul, you are wrong in your reasoning re light frame artifacts because even if the artifact stays in a fixed position relative to the imaging sensor, they will cerainly not remain fixed relative to the image. When 2 or more points (stars) are aligned any pixel that is at odds with those belonging to the image will be outlier pixels and hence eliminated. This will apply in small part to vignetting, but is not as good as a flat field would be.....admittedly.
Can we keep this thread on topic please?

Doug

[[1ponders] (Paul)]

Sure.

[mostschaedel (Gerald)]

Originally Posted by Doug

Gerald, when you say "The Masterflat gets anyhow monochrome ", are you referring to the fact that you are applying the flats before colour conversion, or are you converting the flats to monochrome, ie. removing the Bayer matrix coded data? Sorry, just not sure of what you mean.

cheers,

Doug

Hi Doug!
I am using IMAGEPLUS for the flatfieldcalculation. Imageplus automatically
converts the flatfield before division to monochrome. Using bluesky
flatfields without conversion to monochrome would create uncorrectable
color errors!

Concerning camera rotation:
Camera rotation alone DOES NOT MAKE SENSE.
I do Camera rotation together with the OPTIC to reduce the minimal gradient
which could be there in the blue sky 90 degree away from the sun.

[Doug]

Aha!! Thank you Gerald! A bit of light begins to dawn. A lot of people use Images Plus, whereas I do not. If Images Plus converts the flat fields to Gray-scale, that would explain why nobody is plagued with colour variability from Flat series to Flat series. MaxDslr does not do this as far as I can understand Canadian English. Leaving the Flat Field frame with the colour encoding will make the calibrated image influenced by the colour balance of the Flat. Now I begin to understand why people are having trouble understanding where I'm coming from here.

I have tried to grey scale a flat, but found that the process reduces the effectiveness of the flattening. I will need to re expose some flats at a higher density, so that after grayscaling they will have a 30%-50% intensity.
Nevertheless, I think the ideal will be to get a light source that will give a fairly constant colour temperature or spend money on Images plus....I think a steady lightsource will be cheaper. I agree with your comments on rotating camera only.
cheers,
Doug

Paul I will try to reply to you tomorrownight

[JohnG (John)]

Originally Posted by Doug

Aha!! Thank you Gerald! A bit of light begins to dawn. A lot of people use Images Plus, whereas I do not. If Images Plus converts the flat fields to Gray-scale, that would explain why nobody is plagued with colour variability from Flat series to Flat series. MaxDslr does not do this as far as I can understand Canadian English. Leaving the Flat Field frame with the colour encoding will make the calibrated image influenced by the colour balance of the Flat. Now I begin to understand why people are having trouble understanding where I'm coming from here.

I have tried to grey scale a flat, but found that the process reduces the effectiveness of the flattening. I will need to re expose some flats at a higher density, so that after grayscaling they will have a 30%-50% intensity.
Nevertheless, I think the ideal will be to get a light source that will give a fairly constant colour temperature or spend money on Images plus....I think a steady lightsource will be cheaper. I agree with your comments on rotating camera only.
cheers,
Doug

Paul I will try to reply to you tomorrownight

I suppose I should have said I have been using ImagesPlus for quite some years now for all my DSLR work.

Just to be clear, I do not rotate the camera or advocate rotating the camera when taking Flats.

Cheers

[Phil]

This is what i made to make my flats. It has 4xwhite LEDs that can be dimed inside. The LEDs are defussed with the white defusser that goes in front of the telescope. This works great and is very cheap to make.
Phil

[Doug]

What processing program do you use Phil?

[Doug]

I picked up a worthwhile idea from Chile the other night.
http://www.astrosurf.com/antilhue/li..._ccd_flats.htm

Daniel Verschatse is a very accomplished Astro-imager with considerable experience and many fine images to his credit.
I intend using some white LEDs an combo with some yellower tungsten lights, though for the DSLR work any light will do as long as I can get constant colour temperature for use with MaxDslr.

cheers,
Doug

[Phil]

Originally Posted by Doug

What processing program do you use Phil?

I use Maxlm DL for all my camera control and and processing my darks flat etc. Then i use photoshop.
Phil