How many frames?

[Calzune]

Hi

2 days ago I photographed M31. 

I took around 60 lights, 50 dark, 50 lights and 50 Bias. 

When i Processed the files in deepskystacker and edited it in photoshop I couldnt really get a good image.. The left side of my image was to bright so I i couldnt really see andromeda details very good...

The moon was at 95%. Did the moon ruin the image, or did I take to many flat, Darks, Bias? 

 

Is it possible to take too many frames so the image is ruined (flat Darks and bias)? 

I have heard that Darks are good the more you take 

And same with Bias? 

How about Flats? 

[scitmon]

how long was the exposure of each light frame and what ISO setting?  A bright moon will adversley effect the image.  Perhaps if you post one of the frames to help us?

[Calzune]

ISO 1600, 60 (or 90) sec exposures. 

 

I can post an image on friday when im at my pc😄 

[don4l]

How do the individual frames look before you calibrate them?

[Calzune]

1 minute ago, don4l said:

How do the individual frames look before you calibrate them?

What do you mean? The light frames? 

 

[don4l]

3 minutes ago, Calzune said:

What do you mean? The light frames? 

 

Yes.  If you can look at one of the images as it came out of the camera, then you will have a better idea.

Perhaps deepskystacker allows you to look at the images before you process them???

If they are in Raw, then it should be possible to convert one to a jpg.  Depending on the settings in your camera, you might have the jpegs already.

If the moon caused the problem, then you should be able to see it in a single image.

To be honest,  the moon was quite bright two nights ago, so you wouldn't have been able to get anything great without narrowband filters.

[Calzune]

I use deepskystacker and its possible to look at all images before process. 

And I shoot in both raw and jpeg. 

And yea, maybe the moon is the problem.. I will try a different object next time and hopefully i will get better results... 

 

But how about the amount of images? Is it possible to take to many Darks, Bias and Flats? 

 

[cjdawson]

You are not limited to the number of images (known as "sub frames" or "subs" for short) that you take.    However there are diminishing returns for the amount that you take.

What I mean is that if you take 1 sub.  Taking 2 subs will 1/2 the amount of noise in the image.  Taking 4 will 1/2 it again, and so the sequence goes on, 8, 16, 32, 64, 128 at this point if you want to 1/2 the noise you'd need to take another 128 images.

However the longer that you expose, the more detail you can bring out of an image.   The exposure time of each sub frame is what determines the overall brightness of the image.  The trick is to make sure that you capture as much light as possible without over exposing the image (same rule as daytime photography)   How long you can expose for really depends on your camera and the settings.   As you are talking about ISO 1600, I'm going to assume that it's a DSLR, so you would be better taking lots of short exposures,  I'm talking maybe 15 seconds a sub frame, but the important thing here is to look at the histogram of your first image.  It's best to make sure that the big spike of data has been lifted off the left hand side of the chart, that means that you are capturing more data.   But most of all, make sure that you don't over let data get all the way to the right as that will overexpose the stars.

 

The rule of thumb is that the more subs you take, the less noise in the final image, and the more that you can process it afterwards.    It doesn't matter if you take 1 image with a 60 minute exposure , 60 images with a 1 minute exposure or 3600 images with a 1 second exposure.  You'll still end up with 1 hours worth of integration time after the stacking has completed, and when you stretch the histogram of the final combined frame they should all look the same.    (That's the theory, there are many caveats, but I want to keep things simple)

[Calzune]

2 hours ago, cjdawson said:

You are not limited to the number of images (known as "sub frames" or "subs" for short) that you take.    However there are diminishing returns for the amount that you take.

What I mean is that if you take 1 sub.  Taking 2 subs will 1/2 the amount of noise in the image.  Taking 4 will 1/2 it again, and so the sequence goes on, 8, 16, 32, 64, 128 at this point if you want to 1/2 the noise you'd need to take another 128 images.

However the longer that you expose, the more detail you can bring out of an image.   The exposure time of each sub frame is what determines the overall brightness of the image.  The trick is to make sure that you capture as much light as possible without over exposing the image (same rule as daytime photography)   How long you can expose for really depends on your camera and the settings.   As you are talking about ISO 1600, I'm going to assume that it's a DSLR, so you would be better taking lots of short exposures,  I'm talking maybe 15 seconds a sub frame, but the important thing here is to look at the histogram of your first image.  It's best to make sure that the big spike of data has been lifted off the left hand side of the chart, that means that you are capturing more data.   But most of all, make sure that you don't over let data get all the way to the right as that will overexpose the stars.

 

The rule of thumb is that the more subs you take, the less noise in the final image, and the more that you can process it afterwards.    It doesn't matter if you take 1 image with a 60 minute exposure , 60 images with a 1 minute exposure or 3600 images with a 1 second exposure.  You'll still end up with 1 hours worth of integration time after the stacking has completed, and when you stretch the histogram of the final combined frame they should all look the same.    (That's the theory, there are many caveats, but I want to keep things simple)

Thank you for the info!