dslr imaging advice

[little col]

i have been imaging for about 6 months now (probably about 3 days with the uk weather)i think i am now ready to start imaging in raw mode on the 300d but as i have never used this setting i was wondering how much info am i losing in jpeg and how does imaging in raw effect stacking and processing:shrug:
thanks colin
p.s may be a weeek before this rain breaks away to even get the scope out

[rogerg]

RAW is a bit more of a pain to process because in most cases you need to do some amount of conversion, and the file sizes are so much bigger.

RAW will undoubtedly give you clearer images but the degree to which you notice that would vary.

I used to image in JPG until I got the hang of the DSRL imaging and then moved on to RAW. I now only use RAW, really just because I know it's best and so I have the best chance of getting a good result. I was never particularly dissatisfied with my JPG results due to the JPG usage but the RAW is that bit crisper.

A large benefit of RAW is the use of dark frame subtraction is much more accurate. I would expect JPG compression would tend to negate the usefulness of dark frames because the low level noise in the background might be "compressed out" by the JPG format, meaning a subtracting of a dark frame would remove some noise and introduce some more of it's own (the subtraction would not be a perfect match).

My 2c worth.

[little col]

cheers roger i think i may stick to the jpeg for a while longer as it seems that there is alot of more processing to do with raw which is very time consuming ,
colin:)

[acropolite]

Col if you are going to use RAW you must manually take dark frames, the in camera noise reduction isn't applied to RAW images.

[xelasnave]

Try deep sky stacker... it handles raw and dark frames.
I have been very happy with this program as it allows short sharp exposures even if your mount is not up to scratch for long tracking.
alex

[g__day]

Wow! Is that for certain Phil on all Canon's? I'd expect if its an included feature or RAW then it must be useful. What was you source of intelligence on that startling bit of information?

[ballaratdragons]

Alex, yourself and some others keep recommending Deep Sky Stacker.

I have not been able to get a good result from it once! All I ever get is a totally over-exposed images and a big mess. I gave up trying it after about the 20th attempt.

[leon]

The newer Canon models will take Raw and Jpeg similtaneously and also have three setting in Custom setting to allow you to set what mode of dark frame subtraction you wish to use.

This works very nicely.

Leon

[g__day]

Agreed, but is it for sure on a 400D thata RAW shot, with a dark frame automatically subtracted - isn't actually doing anything as said above - or has this been addressed? Anyone know from a definitive source for sure?

Thanks!

[leon]

To be honest with you, I really don't know if the 400D dose it but my 5D dose, and also the 30D that I use, has those functions

Leon

[RB]

Dark frame subtraction (In Cam Noise Reduction) is most certainly applied to RAW frames if switched on in the custom settings.
Here I've posted two frames, both 1 hour long exposures taken in RAW mode on the 20Da. The first has no noise reduction applied, the second has noise reduction turned on (which takes the total time for the complete frame to 2 hours).
These were both straight out of the camera and only resized for the forum.

As can be seen, the first has more noise but does not exhibit much amp glow because the amp is switch off during the exposure.

The second exhibits less noise but amp glow is more evident since the amp is used during the exposure for the in cam noise reduction algorithm.

[RB]

Hi Colin,

Ever since I switched to RAW I've never gone back to jpg. Yes it's more time consuming but the benefits far outweigh the "disadvantages".
First off you are dealing with the raw data straight out of the camera.
RAW images (in camera) are in 12 bit/channel as opposed to 8 bit for jpgs, or 4096 steps per channel as opposed to 256 steps per channel, which gives you far more room to manipulate the levels, histogram, colours etc !
Also RAW allows you to make certain adjustments that can't be made if shot in jpg (you loose information to minimise file size).

My cameras are all set to record both RAW and jpg at the same time and this is my personal preference but from memory the 300D does not have this feature, you can only save in either RAW or jpg.

[[1ponders]]

Thanks for the information about the amp glow Andrew. I didn't know about that and it explains some issues we've been having over the past fortnight.

Cheers

BTW do you need to cover the telescope/lens with using the builtin noise reduction?

[RB]

:thumbsup:

No you don't need to cover the scope/lens when using ICNReduction.
If you expose say for 2 minutes, the total time the camera takes is 4 min.
As you know the second half (2 min) is used by the camera to do the subtraction internally so no need to cover anything, but you do need to allow for this extra time if using a remote release timer or software.

EDIT: I do however recommend covering the viewfinder as stray light will interfere with the sensor when exposing. Even a red headlamp will cast internal reflections when the mirror is open/up in the camera.

[[1ponders]]

Cheers

Do you find the internal dark subtraction of use, or do you prefer to do it manually using software?

[RB]

If I am spending a whole night on one object and have time to wait for the exposures then yes it's very handy, in fact Bert swears by this method.
If I'm in a hurry I'll take just straight exposures and apply the "dark stack" later.

[luka]

If you take multiple exposures that you stack later, it would make sense to take several darks and subtract them in software later and not use camera's internal dark subtraction.

Several darks averaged together in software will be a much better noise representation than only one dark image which is used by the camera. In other words your software will be doing background subtraction of averaged, more accurate dark from each of the images than if you let the camera do the job.
In theory even with two darks you should get a better result than with camera's internal dark subtraction.

Of course this only applies if the temperature/humidity conditions do not change a lot during the exposures.

[little col]

wowzers looks like i might go for the raw methos next time , question is can you still load say 20 raw frames straight into deep sky stacker or do you need to pre process each file first , i have also had problems with ds stacker but i think it may be due to my tracking and focus in my images.
it would be good if anybody knows of a site that explains the use of deep sky stacker and its errors for future use.
:)
p.s just to clarify if i take 3 exposures in raw what is the percentage of darks to the amount of frames i need to take?
dont forget my location is very poor for clouds and l.p
not used vthe neodymium filter on imaging yet but i am assuming it would make a big difference

[Astroman]

You can use RAW in DSS. Works well. Dark frames depends on yourself really, you can take one after every image or whatever. I tend to take 2 or 3 before and 2 or 3 after my light frame exposures. I also do the Bias and flat frames after my imaging session is over, but this is purely my preference to do it. DSS has a helpful help file which guides you through, but I experimented and found out what works for me.

[acropolite]

I've been under the misconception that it wasn't applied as most of my long exposure RAW's have been very noisy, but following your example Andrew, my 20D does appear to subtract the dark from the RAW.

[Astroman]

Got me thinking now so I did a comparison on a 5minute shot in RAW @ ISO1600 on my 400D. One with in camera noise reduction, one without. 100% crop. no Processing

http://southcelestialpole.org.au/forum/index.php?action=dlattach;topic=409 0.0;attach=5965;image

[RB]

I'm not sure I follow your explanation.
The camera applies a new dark frame directly after each exposure equal to the length of that exposure at the current temp.
Hence it takes twice as long to save it to the memory card but each exposure ends up with a unique dark frame subtracted from it.

[[1ponders]]

As I understand the process, the subtraction of the single dark removes the regular and repeatable noise for may actually add noise from the irregular and non repeatable noise, hence the need for an averaged master. This will reduce the irregular and non-repeatable. I'll try to dig up the reference.

[luka]

As 1ponders said, your dark has not only hot pixels and repeatable noise but also other irregular "noise".
By averaging several darks you will be improving regular (true) noise to irregular (random) noise ratio so that you dark will be a more accurate representation of the real noise.

[little col]

, i wonder is it possible to take a dark frame and save it on file for future images as long as the imaging setup is the same?

[luka]

The noise and hence the dark frames will change, for example, with ambient temperature. Therefore it is the best to make new dark frames every time you make images.

[xelasnave]

Have you played with the result using the controls in the program? group the colours and move them one way or the other to lighten or darken get something and take it elsewhere like photo shop to play with it...

May be the program make not like the cam:shrug: ..

anyways you are doing great..its like registax I cant get it to work for me and it is a great program given the results posted by folk using it.

I just go with what works for me as should you..er works for you that is not er me... you go for it your way:) .
alex:) :) :)

[g__day]

Very interesting reading, especially in that two or more averaged dark frames out performs one real time one in most conditions. The mathematican in me will be thinking that over (fun with standard deviations and anovas).

What is amp glow by the way - I've seen that a few times on 15 minute shots sometimes.