Things that have always baffled me....

[lil_coz]

Hey all.

I've got a few questions for you knowledgeable folk    I've been reading about some people's processes in imaging and some things always keep coming up, and I'm not too sure what is meant...

When people talk about DSO's, they talk about 'darks' and 'lights'. What does that mean exactly? I've also read the word 'luminescence' a few times. Again, not sure what that is.

What I've been doing so far is take 30-60s exposures with a DSLR, and that's pretty much it! With the likes of M31, I'd take 4 or 5 sets of pictures, and stack those, then fettle in Photoshop.

I also want to check up on planetary imaging. I've got a mono camera with LRGB and IR-Pass filters. My process is record 30s on each filter (for Jupiter) and use Registax to align and stack them, then in Photoshop put the RGB pictures in the RGB channels of the IR-Pass image (I hope that makes sense!). What happens to the L image?

Thanks in advanced for clearing it all up

Coss

[rob0971]

Lights are the 30-60 second pics you are taking. Darks are the exact same exposures with the lens cap on. They are used to lessen the noise in the final picture. There are also flats & bias frames as well. Get a good book such as "making every photon count" which is a bit of a bible for astrophotographers, that will explain a lot about dso imaging & is fairly up to date.

[Langy]

This YouTube video may be of interest as it covers a bit about using the Lights, Dark and Bias frames. Not in too much detail but a starting insight.

http://www.youtube.com/watch?v=e0JSTF8SGi4&list=WLpWIx6AVA0qogAX0syRenFPf3pGFWEB6K

[lil_coz]

Lights are the 30-60 second pics you are taking. Darks are the exact same exposures with the lens cap on. They are used to lessen the noise in the final picture. There are also flats & bias frames as well. Get a good book such as "making every photon count" which is a bit of a bible for astrophotographers, that will explain a lot about dso imaging & is fairly up to date.

OK, so darks are basically a black image? This might be a silly question, but what's the difference if the exposure is set to 1s or 60s if the lense cap is on?

So say you have 5 lights at 60s. would you have 5 blacks at 60s? Or use your judgement on it?

Thanks for the input

This YouTube video may be of interest as it covers a bit about using the Lights, Dark and Bias frames. Not in too much detail but a starting insight.

http://www.youtube.com/watch?v=e0JSTF8SGi4&list=WLpWIx6AVA0qogAX0syRenFPf3pGFWEB6K

Kool, I'll give it a watch. Thanks Paul!

[StuW]

OK, so darks are basically a black image? This might be a silly question, but what's the difference if the exposure is set to 1s or 60s if the lense cap is on?

So say you have 5 lights at 60s. would you have 5 blacks at 60s? Or use your judgement on it?

Thanks for the input

Kool, I'll give it a watch. Thanks Paul!

The longer the exposure the more the internal components of the camera heat up and cause interference through thermal noise.  You use the darks of same length as the lights to "subtract" the similar value of noise and therefore removing amp glow and hot pixels etc.  That's probably over simplifying but it's how i understand it.

[Langy]

It's quite clever how the software uses the three types of images to sort out the noise or dead pixels on the sensor.

As with the video I gave a link to you will see that he only covers the very basics to get you started, which is what I used.

There is a manual on the website which I suspect goes to extreme lengths.

[lil_coz]

Ah ok, I see the theory in that. So am I right in thinking that for example, if you want to use x5 30s darks, that you just take the one 30s exposure and use that 5 times? 

Thanks again for the help/advice guys!

[StuW]

Ah ok, I see the theory in that. So am I right in thinking that for example, if you want to use x5 30s darks, that you just take the one 30s exposure and use that 5 times? 

Thanks again for the help/advice guys!

That wouldn't work as you would just be multiplying the noise in the single dark frame.  I don't think there's any hard and fast rule about the number of dark frames, but I like to take one after each light frame throughout the night as the camera's temperature can change quite a bit throughout the imaging session.

[lil_coz]

Ah ok. Thanks. I'll give that video a watch and see what's what. I came across this on Amazon which I'm considering getting.

http://www.amazon.co.uk/Lessons-Masters-Astronomical-Processing-Practical/dp/1461478332/ref=sr_1_1?ie=UTF8&qid=1390740603&sr=8-1&keywords=lessons+masters+astronomical+processing

Will also look at getting Every Photon Counts.

Since I started, AP just took hold! It's too blumming addictive! lol