Is it worth taking more lights?

[batema]

Hi,

I imaged the Leo Triplet on Saturday evening and got 120 minutes of lights and 70 minutes of darks. I am having school viewing nights over the next three nights and was wondering of the benefit of taking even more lights and darks after the viewing?

I think I could get another 180 minutes over the three nights all shots being 10 minutes or am I going overboard?

Mark :D

[leon]

Mark, you are definetly not going over board with you lights, the more data the better, but mate if possibly get the darks a close as possible to the lights temp and time, ICNR is good, and some flats would be helpful as well.

leon

[batema]

Thanks Leon. It was 21c on Saturday so I will be taking darks on the night as well.

Mark

[Hagar]

Hi Mark, I just took a look at your image and do find your question an interesting one.
More lights does lift your signal to noise ration with each extra image you take. That is the amount of actual signal in the image increases while the noise level doesn't increase by quite as much.
With good processing skills you can use this extra signal to improve the clarity of the images and with dark subtraction or processing you can reduce the background noise level quite a bit. One thing to remember is that dark noise is often quite random so in most cases more darks will improve the image by quite a lot.
The use of full calibration ie. Darks, Flats and bias files will again lift your image to another level. The use of flats and bias files will remove any imperfections in your imaging train and also correct problems with the illumination of the entire imaging chip.

I would sugest that as the image is quite small in a semi widefield such as this that the use of Flats and bias and more darks will provide more improvement than more hours of lights.
It is all a learning game so experimentation is the name of the game. Take some more lights and darks and bias and flats and see where it takes you. You may be surprised with the end result by being more critical of the lights before stacking and the diference full calibration and more darks makes to the final image.

Good luck and keep at it.

[iceman]

As Doug says, proper calibration is much more important than more hours of lights.

Once you've got those other "basics" under control (including image processing), then it's time to look at other ways to take your imaging to the next level - including more lights.

[batema]

Thanks Doug and Mike. As you say it all learnig with experimentation. I'll sway towards more darks and bias frames as well as applying flats. And a couple of more lights.

Mark

[Alchemy]

i have to agree completely. Good advice !




i usually do 2-3 hrs lights each set. i have done one where i went 8 hrs but i couldnt tell any difference between the 6 hr and the 8 hr personally. there was an improvement up to 6 hrs.... as that was my only one i did that long i wouldnt declare it to be complete proof of such though.

clive

[batema]

If I could ask one more question it would be can I use a series of flats I took in Feb for an image I took 2 nights ago and if I take a number of different nights (both lights and darks) can I bung the whole lot into DSS and stack that or do I have to stack the individual nights and then somehow stack the final of each of the nights. Not sure how to do the last if required.

Mark

[avandonk]

You are wasting your time as you have no hope of matching darks to lights on one night let alone different nights. Leons advice is good, use ICNR (In Camera Noise Reduction). It gets worse if you chuck the lot in to a bit of software you will get a result. It will be nothing like as good if you sift through your images to get the best, and the sift through the darks that at least seem to match.

Bert

[Hagar]

Darks from a previous session can be used providing they were taken at near enough to the same temprature. If you are going to be critical then the darks should be taken at the same sensor temprature. This can be difficult with a DSLR as the senson temprature changes with every image taken. The answer is Darks= maybe OK but Flats are a different item to deal with. They are an illumination map and irregularity map of the entire imaging train. They assist in the removal of imperfections such as dust and dirt in the imaging train and as such MUST be the exact setup and alignment used to shoot the lights. Flats should be taken during or at the end of an imaging session before any changes have been made to focus, camera alinment and filters etc in the imaging train.

This will improve your images immencely.

Good luck with it all. It seems like a lot of work but with practice it is quite a quick and easy process.

[TrevorW]

This question has been put forward on a number of occassions and from what I can gather the consensus has been

a) the law of demishing returns applies where lights are concerned
b) darks should be taken at the same time as the lights and under the same conditions (as far as DSLR cameras are concerned)