Canon 20D use

[G4YVM]

I want to do some first forrays into imaging.

I have a 20D (unmodded), I have a Skywatcher 102 refractor and a 5" newt. I am getting an EQ6 pro.

Thats it. What the heck now?? I have tried to understand flats, darks etc, but not how i get them. I gather I control my 20D from a PC? How? Does the PC take the pics as well? Ive looked at a load of different software, registax, pix r us , gimp etc or whatever and not much seems to me made for a mac, which I use.

I have looked at the imaging stickies but, unless I'm blind, I cant see a really basic overview of a typical imaging set up.

Anyone got any links to point me off to please? Im after the first basic principles.

David

[120ST]

the 20D software that came with the camera will have the ability for you to control the camera via USB port to your mac. When you take a photo the image will transfer to the PC and you can view it right away. I forgot the name of the actual utility, Canon Capture or live view....

"Dark's" this is an exposure that is identical in exposure length to the original image. But you will cover the objective to NOT allow light into the scope.

Technically it is preferred to take the Dark, right after the original image so the noise level will be about the same, so when you subtract the dark from the original, it will do a pretty good job at removing hot pixels and noise to make the Blacks "Darker".

I could be wrong, but i think the Flats are a shorter exposure using a white light exposure. I have seen people place a white bucket over the main objective and place a white light source behind it. This is to capture any dust specks on the camera sensor or anywhere in the imaging path.

Then you would use that Flat to process with the others to remove any unwanted specks.

Like I said... i might be wrong on something so dont throw rocks at me....

James

[perfrej]

Take a look at Nebulosity2 for Mac. It is dirt cheap and very functional. It will capture your series of images, aid you with focusing, help you take darks and flats and the, to top off the cake, it will batch process your files.

Basically - and this took me a long time to get right - this is the process:

1) Capture your lights. These are your images of the object in question. Usually, a few minutes of exposure on each and then take a whole bunch of them.

2) Capture your darks. 10-30 frames, same exposure and ISO as your lights, and taken at the same time (for ambient temperature correctness). Just use the cover for your telescope tube and fire away. These will contain the resident noise of your sensor.

3) Capture flats. I cover the scope with a T-shirt (clean) and point it at the clouds. Actually, the best thing is to take them with a "light-box" at the same time as the lights, but if you are careful not to disturb the optical path and camera position/focus, you can do it later or before. Exposure is as short as possible so that you get an even gray-white image with most of the pixels in the middle of the histogram. These files will contain the incorrectness of your optical path, like vignetting and uneven distribution of light.

4) Preprocess your lights by means of the darks and flats. The darks are added together to create a master dark, and the flats follow the same path into a master flat (method is usually averaging). Every light frame that you have captured gets the master dark subtracted from it, and gets divided by the master flat. The darks and flats have now done their part, and your lights have noise subtracted and unevenness of light ditribution corrected.

5) Convert your pre-processed lights to color by means of de-bayering - assuming you are working raw files, which you should. Since every pixel in a digital SLR has just one color, the software needs to create composite color pixels by ading information from neighboring pixels of different colors. The pixels are originally in a matrix with one red, two green and one blue (called RGGB configuration).

6) Let your software stack all the color versions of your lights on top of each other aligning the stars perfectly. Exposure is added making the final version, for example, one hour of exposure out of ten six-minute shots.

7) Use the transfer curve functions of your favourite image processing software to expand the somewhat narrow distribution of pixels over a larger dynamic range to lure out the details of your image and make them visible.

Complicated? Yes, but once you get going it will be a breeze.

The hard-core guys and gals capture their images with black-and-white cameras and use filters for each color, something that makes the capture process much longer as you have to capture each color separately. You can, however, get excellent results by capturing in RAW format with your Canon if you follow "The Path".

This is so much fun - you're going to have a blast!

Good luck!

/per

[RogerTheDodger]

That's a great help to me too James/Per, I'm planning to go down the DLSR route when funds allow and I was wondering how it all slotted together

[harry]

What you will need to connect to say the Skywatcher 102 is a EOS T ring which mounts to your 20D instead of a lens. To this screws a 2" inch prime Focus Camera Adaptor, I bought the William Optics version (Parts are available from FLO). The camera can then be mounted onto the telescope via the 2" Focuser, held in place with the grub srews on the focuser. Good polar alignment of the mount is required for tracking objects.

Harry

[G4YVM]

Thanks all. Excellent information.

Re the T mount, I do have one of those already, but I cant recall without looking whether its 1.25 or 2".

The first snag is that I dont have the soiftware that came with the camera. It was when the 20D was new, a long time ago and I have no idea where its gone.

In the words of Arnie: I'll be back.

D

[Psychobilly]

If at all possible avoid reducing to a 1.25" pushfit.. it will introduce a lot of vignetting... 2" will be a lot better...

[G4YVM]

I now have Neb2 seemingly up and running.

Just need to learn to use it!

D

[G4YVM]

Quick question:

With neb2 I have a maximum of 30second exposure. Do i need to sit with the camera for longer exposures with the "bulb" lead connected or do I download and use something like DSLR shutter?

David

[harry]

David, you would be better off getting a remote timer shutter release, far easier to use than running a cable to a computer and mucking around with software. They can be had for less than £20, just do a google. Just set number of shots, length of exposure anywhere from 1 second to 99 hours, and delay between exposures. Plug it in and set camera on bulb, press start and go and have a cuppa while the camera does the work.

Harry

[G4YVM]

Thanks for the heads up. Job done!

This leads me to another question: How do I know what time and aperture value to set? On a normal image, I am fully aware of what settings I want to get a given result, but if I am shooting, say, Bode's galaxies, what settings would I go for and importantly , how do I know?

David

[perfrej]

In Nebulosity, you do not HAVE TO select the time from the drop-down. You can just as well type 10000 into the box and it will do a 10000 second exposure