Eta Car, help needed.

[White Rabbit]

Hi Guys.

Here is my Eta Car from last night, there are multiple things wrong with it, least of all my PS skills. The red is out of control and I couldnt find the curve that I used to back it off.

Besides the really bad tracking (I really need to get my guiding sorted out I still cant get it right), there is a darkening in the corners of the image. What is causing this?

Here is the details.

Camera Model Name
Canon EOS 1000D
Shooting Date/Time
7/05/2009 22:31:10
Tv(Shutter Speed)
300Sec.
Av(Aperture Value)
F0.0
Metering Modes
Evaluative metering
Exposure Compensation
0
ISO Speed
400
No flats used as I'm not really sure what they are lol, and NR was done in the camera.

I live in really light polouted skies so the blue tint to everything is my CLS filter plugged into the dslr.

Thanks guys

Sandy

[desler]

Sandy,

First off, nice pic. The red is caused by mis-alignment of the colours in the histogram. I'm not sure with PS cause I use Gimp, but with the raw of tiff images, you can individually look at the histogram for each coulour, red green and blue.

As explained to me, all the histogram values should be about the same, in other words you shouldn't be able to see all three colours separately in the histogram.

There are some great on line tutorials to help explain PS, other than that, just keep playing around. The undo button is my best friend!

Check for a thread from me, actually showing eta carina, with the title "Red in Images" RB, one of the moderators explained it a lot better than I just did to you! Good Luck!

Darren

[White Rabbit]

Thanks, the whole photoshop thing is something that will come in time I'm sure. I dont think that PS has a histograme like you suggested, the canon appliction does though so maybe I'll try the colour correction there before I open in photoshop.

Any idea what is causing the darkness around the edges?

Thanks
Sandy

[Bolts_Tweed]

Gday Sandy

Some answers that may be of use. Firstly I am pretty sure that NR in Canons is a good approximation of dark frame subtraction (I am not a DSLR man tho)

IN CS2 try image->adjustments->color balance and play around with the sliders to see what they all do. Dropping the red makes a big difference in your image (I just did it) especially in mid tones and highlights - just click on the radio button to change them then move sliders

The darkened edges are probably some form of vignetting due to the combination of otics and camera (As I said I am not a DSLR guy but this is what I would say it is - I am ducking here in case I am wrong but I am pretty sure DSLRs suffer fom this as CCDs do). Flat Frames will fix it if it is vignetting. unfortunately I have no idea about Canon S/ware and what it is capable of - others may be able help. Google flat frames and you get an absolute mile of info on how to do it.

Anyway this may be some starting points for you

MB

[TheDecepticon]

Try dragging your image into PS and then select from the top line of FILE, EDIT, IMAGE etc, the button that says WINDOW. Select Histogram from the drop down menu. Now that you can see your histogram, select Image, Adjustments, Levels. In your levels box at the top, you will see RGB in a drop down box. Click on this box and select red. you will see your other colours there too. Now grab the black slider(you should see 3, from left is black, middle is grey and right is white) and move the slider to the foot of the histogram. You should see the red in your image fade off a bit. Click ok. Now go to Images, Adjustments, Curves and select. Same as in levels, you can select your different colours. Select the blue channel and grab it in the middle of the curves line and gently pull it around while watching your histogram. Try to make one mountain out of the histogram with as much as possible smooth slopes each side. That should drain a bit more red out of the image. Now you have your colours more or less aligned. You will suffer clipping in the image due to the nature of the problem, you cant help it. Now go to Images, Adjustments, Hue/Saturation and drag the Saturation slider back to the left a bit to suit your taste, probably try a value of -25.
Hope that helps a bit!!!:)

PS:I have posted your image with the steps outlined above so you get some idea. This is the only reason I adjusted the image and reposted it. Sorry if this has offended anyone!

[Alchemy]

to get as below.

open in photoshop

images-adjustments- levels, click middle eyedropper and click in area known to be middle gray( this will adjust color balance).

images-adjustments-saturation select red channel and drop it 30 or so

you can continue as you wish from there

[jjjnettie]

You captured some really nice detail!

You'll need to set your black points.
In CS3, go to curves, click on the left hand eyedropper and then point and click on an area of the image you know to be black.
This will darken your back ground. If it's too dark, adjust the curves.
Adjusting the Saturation will improve the colour heaps.

[Alchemy]

RE DARK BACKGROUND

a common mistake in astro processing is people expect the sky to be black.... it isnt , logically if you consider even the hubble deep sky image there is many sources of light which your scope cannot resolve behind it.

The test is as follows, once you have callibrated your images (this means darks and flats for most people) you have an image which essentially contains all the light data, given you are using a DSLR and dont have to deal with the deep well issue of CD cameras, this is probably the point at which you will do your color balance. As described in my last post.

300 sec @ iso 400 should not give you a black sky IMHO . so from here have a look at IMAGES-ADJUSTMENTS-LEVELS there will be a histogram with 3 sliders underneath it, ( note when color balance is out you will often see a double hump, but at this point i assume you have done that), What you need to see is a bell shaped hump, check to see if there is a small tail to the left, this can be due to possibly alignment during stacking process , check edges of image to see that no black or underexposed area at edges exists if so crop out. it should only be couple of pixels wide.
Move the slider to the end of the tail if it still exists, you have now opened up your data to maximise its range.

IF YOU GO PAST THE TAIL AND INTO THE CURVE AS YOU HAVE ON YOUR POSTED IMAGE THEN YOU LOSE DATA, I CANNOT STRESS THIS ENOUGH.

the faintest detail exists at this end that is things like outer halos of galaxys .

At this point in your "career " it may not be obvious but as you progress it will be. your eyes are great , but the histogram NEVER lies.

hope this explains a few issues



a cheery regards

CLIVE

[White Rabbit]

Thanks for the detailed responses and comments. I'll try them all and post the results.

Thanks again.

Sandy