Must subs be the same ??

[Bizibilder]

SImple question really: Must all subs in a set be exactly the same length?

I took around 80 x 1min last night and a few were 61 - 65 seconds long - due to me operating the shutter manually. Can I stack all of them together or must I reject the "non standard" ones?

(All my darks are 60 secs)

Thank you!!

[Psychobilly]

no go for it...

[RobH]

Like Peter says....stick them all together.

Cheers

Rob

[LukeSkywatcher]

Nope. DSS will just use the good subs and disregard the rest. It does the work for you.

DSS (Deep Sky Stacker).

If you stack 200 subs it may only stack 30. You can always add more data later

[LukeSkywatcher]

My camera (Canon 450D) is set to automatically take darks the same length as exposures. I find this blumming annoying.

How do i take darks with the 450D?

[Psychobilly]

Luke ,

Disable long exposure noise reduction and hi iso noise reduction whilst your at it... both in the custom functions menu...

Then take your own darks a couple before a few more in the middle and more at the end of the session

Peter...

[RobH]

Just to be clear about the original question.

It is perfectly fine to mix subs of different exposures.

Where you will lose out is, for example, if you had 50% 20 minute subs, and 50% 5 minute subs.

What will happen then is that you will probably lose some of the fainter data from the long subs.

With the sub length you are talking about, and the fact that you don't have many shorter ones, ther is no good reason not to add them.

If a program rejects perfectly good subs just because they are a different length, then the program is either rubbish (not so with DSS as loads of people get good results with it), or the settings are wrong.

Cheers

Rob

[Psychobilly]

There are other methods to usefully use the data if the subs are substantailly different length...such as Auto Adaptive Weighted Average in DSS used to produce a higher dynamic range image. but a range of a few seconds in 60 wont be an issue...

Peter...

[LukeSkywatcher]

Luke ,

Disable long exposure noise reduction and hi iso noise reduction whilst your at it... both in the custom functions menu...

Then take your own darks a couple before a few more in the middle and more at the end of the session

Peter...

So when i disable NR and Hi NR................is the best and easiest way to take darks...............simply to put the lens cap on the camera?

[Psychobilly]

yep...

[JohnC]

If you take say 1 minute darks can these be used in future pics with sme sub lengths?

Ie can last weeks 1 min darks be used with next weeks 1 min subs?

[Psychobilly]

If you take say 1 minute darks can these be used in future pics with sme sub lengths?

Ie can last weeks 1 min darks be used with next weeks 1 min subs?

Depending on the camera... darks really need to be temperature matched to the lights... especially if the cameras noise changes dramaticallly with temperature...

Its worth doing some tests on your camera to see how it performs...

The fridge is useful for this experiment...

Peter...

[RobH]

If the darks are taken at a similar temperature to the lights, then thay can be done 6 months ago and will work fine.

Many people build up a library of darks of different lengths and at different temperatures.

Rob

[JohnC]

Thanks Peter/Rob

[Bizibilder]

Thanks all!! I guessed it was OK - its just that DSS seemed to seperate the subs by time on the summary screen before you hit "go!"

Thanks for the info about darks - its a PITA to have to take 20 x 1min after you have been doing 80 x 1min manually!!! AND at half past the early hours as well!!!

[LukeSkywatcher]

yep...

Thanks for that. I am so sick of waiting for my camera to automatically do this for me.

It doubles the time of every exposure.

So from now on as soon as i take an exposure i will put the lens cap on and take an exact same exposure and then when stacking i will add those "darks" to my "lights".

I kind of knew this was the way to do things but wasnt too sure.

Learn something new every day.

Dare i ask just what the hell bias frames are?

[LukeSkywatcher]

If the darks are taken at a similar temperature to the lights, then thay can be done 6 months ago and will work fine.

Many people build up a library of darks of different lengths and at different temperatures.

Rob

WOW..................this whole AP is rather more blumming technical then i ever imaged.

So i can take darks 6 months in advance and store them and they will work with light frames i take 6 months later assuming the outside temp is the same?

Good god my eyes are being opened tonight with regards to just how much time and effort you guys put into AP.

[Bizibilder]

:clouds1:

You could take the darks outside on cloudy nights!

[LukeSkywatcher]

:clouds1:

You could take the darks outside on cloudy nights!

But not every cloudy night is the same.

Every dark frame taken with the lens cap on will be the same.

[Dons255]

I'm hoping Bizi was referring to the temperature, as there's little else to do on a cloudy night

[martin_h]

I take darks on a cloudy cold night, because waiting for 15 - 20min darks is a pain, set it up at about 11pm or midnight and just let it rip all night.

[Psychobilly]

Luke,

You dotn need a 1:1 ratio of lights and darks... Its always better to have more lights to stack... you could try takign one dark every 3-4 lights and see how you get on...

Peter...

[LukeSkywatcher]

Thank Peter for all the info. Most helpful. Hopefully the darks i take will get rid of the LP i suffer from in my images.

[Demonperformer]

Luke

I tend to do 10 darks - batch of lights - another 10 darks, stacking each batch of lights with the 10 before and 10 after - seems to work ok

[Psychobilly]

You might find more lights and less darks works better

Depending on the camera you might evene get away with darks altogether and just let the cosmetic hot pixel routines in DSS take care of any noise... thats what i tend to do most of the time...