Hello I'm light pollution ! - Page 2

h0ughy (David) · #21 11-10-2005, 09:06 PM

Wow, Dr itchy has fixed it.. another one scratched

gaa_ian (Ian) · #22 11-10-2005, 09:08 PM

You Guys are legends !
Ving ... you have a special talent there

atalas · #23 11-10-2005, 09:17 PM

Very good save Tony ! I can see the DDP effect around one a star I think correct me If I'm wrong Tony ,You've done a hell of a job trying to correct for servere gradients ! I wish I had those exposures from a dark site wth no moon. Those DUST MOTE ! your right there mate ,I have to clean the chip I'm sure It's coming from there. They shoot up as soon as you start streching the white point in levels . If I wasn't so lazy Tony I would learn to take and subtract FLATS ! eh , I think I would rather just clean the optical path, one of these days. Thanks for your work on this image and sharing of knowledge Tony and everyone else who had a go much appreciated.
In the first images I sent you Tony one of those green looking exposures were averaged with the others so I wonder If that was the problem in the green channel ?
It looked like the one I posted in this thread but was a 10 minute exposure .
This happend after I had saved as fits file and then when I reoppend the file to align and sum them one of them was green like the image above .
Now It happend again to another exposure I took last night a 15 minute sub which is the one I posted in this thread , any ideas whats happening here Tony ?

Cheers

Louie

Itchy · #24 11-10-2005, 09:56 PM

Quote:

Originally Posted by atalas

Very good save Tony ! I can see the DDP effect around one a star I think correct me If I'm wrong

I think you might be noticing a side effect of the star size reduction routine, rather than the DDP.

Quote:

Tony ,You've done a hell of a job trying to correct for servere gradients ! I wish I had those exposures from a dark site wth no moon.

A dark site will do wonders for your images, and I don't even bother with a moon around. Might as well go

Quote:

Those DUST MOTE ! your right there mate ,I have to clean the chip I'm sure It's coming from there. They shoot up as soon as you start streching the white point in levels . If I wasn't so lazy Tony I would learn to take and subtract FLATS ! eh , I think I would rather just clean the optical path, one of these days.

Flats are really worth the effort. A good master flat applied during calibration will correct a whole range of problems and make the stretching SO much easier to deal with. My advice: Do It!

Quote:

Thanks for your work on this image and sharing of knowledge Tony and everyone else who had a go much appreciated.

No worries, it was fun. I must be a little weird though. I enjoy the processing probably more than the aquisition. If someone feed me high quality data I could keep myself amused for weeks.

Although I must admit there is a peculiar satisfaction in doing the whole thing yourself too.

Quote:

In the first images I sent you Tony one of those green looking exposures were averaged with the others so I wonder If that was the problem in the green channel ?

Almost certainly. The colour balance was really screwed up.

Quote:

It looked like the one I posted in this thread but was a 10 minute exposure .
This happend after I had saved as fits file and then when I reoppend the file to align and sum them one of them was green like the image above .
Now It happend again to another exposure I took last night a 15 minute sub which is the one I posted in this thread , any ideas whats happening here Tony ?

Sorry Louie, someone else may be able to help. I'm clueless on that one.

Cheers

atalas · #25 11-10-2005, 10:15 PM

Ah ! so those circles aren't from DDP , I don't find them obtrusive at all Tony ....makes the stars look much better . Flats ! Flats ! and more flats ! from what I've been reading Its quite a bit of work to learn to produce a good Master Flat Tony, but I will look into It for sure mate , and maybe buying a light box would make It easier .
There is a new product out buy Starlight Express for taking flats so I'll look into that,not cheap around $650.00 US ! hey If It makes It easier to make and use flats I'm all for It.

Thanks again all for everyones input !

Cheers

Louie

Itchy · #26 11-10-2005, 10:34 PM

Louie
I find making flats to be one of the easier processes. I use the "t-shirt" method, so I can make them during the day. I just have to make sure I get the camera orientation correct and I can rattle off a dozen flats in a few minutes. A few minutes later and they are combined and desaturated ready for use.

$US650 ??

Easy

atalas · #27 11-10-2005, 11:02 PM

Tony I thought that tempreture and focuse had to be the same as when you took your images ? are you making Masters Flats for every image you take ?
Yes $650.00 for a gadget is heavy alright , It would wan't to do all the work for you at that price .

Louie

iceman (Mike) · #28 12-10-2005, 12:26 AM

Don't forget to read master Eddie's article on flats and darks, Louie!

http://www.iceinspace.com.au/index.p...63,211,0,0,1,0

And a very nice reprocess Tony!

Itchy · #29 12-10-2005, 06:08 AM

Quote:

Originally Posted by atalas

Tony I thought that tempreture and focuse had to be the same as when you took your images ? are you making Masters Flats for every image you take ?
Yes $650.00 for a gadget is heavy alright , It would wan't to do all the work for you at that price .

Louie

Focus has to be close. I can judge that on my scope by the focus tube position. Temperature would only be important if it greatly mucked up your focus (unlikely).

I have several master flats for different camera orientations that I use regularly. I also makes flats for my piggy backs and they are cataloged by f ratio and focal length.

Some people take flats for each new image as dust motes can change. I haven't had dust motes yet, so that hasn't been a problem.

cheers

Striker (Tony) · #30 12-10-2005, 12:25 PM

call me stupid but i still dont understand the principal's behind Flats and how to do them with a t'shirt.

Everyone says their easy???

So all I have to do is to throw a white t'shirt over the end of my scope and take some shots..firstly for how long and what settings...what do I do with each shot after this?????? and how do apply them to my images.??

ving (David) · #31 12-10-2005, 01:11 PM

Quote:

Originally Posted by atalas

Gee thats really great David ! you've got the hang of It now mate

Louie

I learned from the best, ken

atalas · #32 12-10-2005, 01:48 PM

Tony I wish I could help you but I've never tried any myself , what I can say is that they
take an image of your optical system and thats why they can be used to remove dust and vignetting from your image. You also are supposed to take bias frames and combined
them with you flats as well . Can't remember what a bias frame image is,something to do
whith amp glow I thin,could be wrong.

David, your a funny guy

Louie

ving (David) · #33 12-10-2005, 01:50 PM

Itchy · #34 12-10-2005, 03:57 PM

Quote:

Originally Posted by Striker

call me stupid but i still dont understand the principal's behind Flats and how to do them with a t'shirt.

Everyone says their easy???

So all I have to do is to throw a white t'shirt over the end of my scope and take some shots..firstly for how long and what settings...what do I do with each shot after this?????? and how do apply them to my images.??

Can I really call you stupid?

OK here goes. This is what I do: (for my DSLR)

Set up the scope with the same optical train including focus and camera orientation. I usually use a naturally lit room with the scope pointing at the ceiling. Stretch a white cloth over the objective. Choose a low ISO and adjust shutter speed so as to get a histogram spike 1/3 to 1/2 way along the x axis (when viewed on the cameras LCD). I then take about 15 shots, rotating the tube as I go to account for any uneven illumination in the room. These are then converted, average combined and desaturated. The master flat is now ready for use. It is a picture of the optical defects in your system and it is used to correct those defects in your light frames.

You then need to use software designed for astro image processing to apply the flat to your light frames. The actual process is something like this: An average pixel value of the flat frame is calculated. Then each pixel in the light frame is divided by the corresponding pixel in the flat frame and then multiplied by the average value. In effect, each pixel in the light frame is multiplied by a value close to one. If the pixel in the flat is darker than the average flat pixel, this value will be larger than one, resulting in a brightening of the pixel in the light frame. If the pixel in the flat is lighter than the average this value is less than one, resulting in a darkening of the pixel in the light frame. What you end up with is an evenly illuminated light frame.

This process can be "simulated" in Photoshop, but photoshop doesn't actually do the same "division" described above. There are various packages that will do it correctly such as ImagesPlus, IRIS (free), Keiths image stacker etc.

Hope this helps.

atalas · #35 12-10-2005, 04:05 PM

Good info Tony , hey did you get that Tony ! no the other Tony

I have now got an Itch that needs scratching

Thanks

Louie

Striker (Tony) · #36 12-10-2005, 04:43 PM

Thanks Tony....I understood about 60% of what you said.

I lost you here.

Quote:

The actual process is something like this: An average pixel value of the flat frame is calculated. Then each pixel in the light frame is divided by the corresponding pixel in the flat frame and then multiplied by the average value. In effect, each pixel in the light frame is multiplied by a value close to one. If the pixel in the flat is darker than the average flat pixel, this value will be larger than one, resulting in a brightening of the pixel in the light frame. If the pixel in the flat is lighter than the average this value is less than one, resulting in a darkening of the pixel in the light frame. What you end up with is an evenly illuminated light frame.

I will first take some shots then work out how to use them later on....expect some Pm's...hehehe

[1ponders] (Paul) · #37 12-10-2005, 07:52 PM

Tony (Strike) pop up the coast here one weekend and I'll show you how its done. It's not that difficult. If you're anything like me you can read and read and read about it and it slowly sinks in. But get it shown to you once and you've got it.

Striker (Tony) · #38 12-10-2005, 08:50 PM

Thanks Paul,

Sounds good...book me in.

atalas · #39 12-10-2005, 09:05 PM

Gee I wish I could just pop in Paul ! some people have all the luck

All jokes aside thats great Paul good onya mate !

Cheers

Louie

Itchy · #40 12-10-2005, 09:31 PM

Quote:

Originally Posted by Striker

Thanks Tony....I understood about 60% of what you said.

Hey that's OK. It took me a while to understand the process myself, and I teach Mathematics!!

The good news is that you don't really need to understand how the calculation happens. You got the important bit. ie how to take and make a master flat. In a program like ImagesPlus the rest is automatic. You just tell the program where the flat is and it does everything else for you.

Cheers