Does it work out with bias and flat frames only?

[Nigel G]

I did copy and re name 2 times  

Its a master bias .tiff which I copied twice and renamed dark and darkflat for convenience.

[Nigel G]

Ok I have tried several different ways with the same result, I'm obviously doing something wrong as everytime I get a blank image.

I tried using the master bias as a darkflat and dark frame. I have tried stacking without bias frames, with dark flats without dark flats, with dark and without dark.

The only way I can get an image is without using the borrowed master bias frame.

Any ideas ?

Nige.

[davew]

If I may suggest ..... Use the Bias as a Bias. 

The Bias frames are stacked into a master Bias.

The master bias is subtracted from each flat and then the flats are made into a master flat.

The bias is then subtracted from each light.

The master flat is divided into each light.

The calibrated lights are then stacked into a finished image.

Using a bias as anything other than a bias has to be the most confusing thing a beginner doesn't need.

Dave.

 

 

[emyliano2000]

I don't know if it makes any difference but I didn't make copies and didn't rename the master bias and instead I created a master dark and a master dark flat using a single raw image and then used the master dark and dark flat created with that single image on the exposures that I wanted to stack.

I just didn't know if dss is using a different method of creating the master bias and creating the master dark and master dark flat and that's why I thought I should do it this way.

Emil

[happy-kat]

35 minutes ago, davew said:

Using a bias as anything other than a bias has to be the most confusing thing a beginner doesn't need.

Dave.

 

 

Members can read what they like and either decide to try something new regardless of experience level. You don't learn unless you experiment.

In this case the approach greatly improved the background noise on my image so glad I did try it, nothing lost having a go and I will try it for the next set of image files I take.

[spillage]

I found that just using flats bias and flat files work best for me. trying to use anything for darks gave issues. I just see this as a way of not only not using darks in dss but actually more importantly freeing up more time on taking lights when I would be taking darks.

[alacant]

4 hours ago, davew said:

Bias as a Bias.

Hi. That's fine, but I think the gist here is toward pushing boundaries a little. A good example of not following the instructions is when I ditched all my dark frames; instant noise reduction. Please let's keep the experimentation factor alive:) 

[davew]

30 minutes ago, alacant said:

Hi. That's fine, but I think the gist here is toward pushing boundaries a little. A good example of not following the instructions is when I ditched all my dark frames; instant noise reduction. Please let's keep the experimentation factor alive:) 

I'm very pleased when people say that they experiment. That's just what I do. 

But lets say we were to do things properly with these flats. Surely the bias signal is subtracted from the flat dark as a way for the software to match the dark to the flat. If we subtract a bias from a bias that's been renamed then all we end up with is an injection of noise ? If I am wrong please explain it to me as I'd like to know.

Dark frames is a whole other subject when it comes to things like DSLRs and I'm not going there. This is a thread about bias and flats. I use dithering and a hot pixel map and have done so for years. Not the correct way I know.

4 hours ago, happy-kat said:

Members can read what they like and either decide to try something new regardless of experience level. You don't learn unless you experiment.

In this case the approach greatly improved the background noise on my image so glad I did try it, nothing lost having a go and I will try it for the next set of image files I take.

That's the nicest way I've been told to shut up for years. 

If I use software that reads Fits headers, should I re write them ? Bit complicated but I can try.

At the end of the day just do whatever works for you. It may not work for everyone so the odd ( Very odd ) dissenting voice does at least give people the chance to think about what they're doing. Let's not get too evangelical in either direction.

Dave.

[swag72]

17 hours ago, alacant said:

Hi. That's fine, but I think the gist here is toward pushing boundaries a little. A good example of not following the instructions is when I ditched all my dark frames; instant noise reduction. Please let's keep the experimentation factor alive:) 

I am all for experimentation, but I also think that having a solid knowledge base with which to base your experimentation on is a sound idea. Absolutely let's push boundaries, let's try new things, but let's also hope that we have a bit of an idea how to do it right before we start experimenting and 'breaking the rules'  

I'm all for simple explanations too...... Is a bias a bias then?   I certainly thought that it was....... 

[ollypenrice]

A bias is a bias but it is also a perfectly good 'dark flat.' I have found shooting 'genuine' dark flats to be a total waste of time. The question is, if you just load up a bias into DSS once, will it apply it as a dark flat? I don't know.

I like AstroArt because I can put my calibration files exactly where I want them and I know what it will do with them. So I put one iteration of bias in the 'darks for flats' box. I put a second iteration into my 'darks for images' box because I don't like darks. Then I have a bad pixel map which goes in its own box. This is based on experiment. It is not the conventional approach, though it is one many imagers use. For me it gives far better results than I obtained using normal dark subtraction and it is significantly quicker.

Olly

Edit: this is not to disagree with Sara. On the contrary, it is to agree with her. You need to understand what your various calibration files are going to do.

[Nigel G]

I have finished a little experimenting with using a master bias as other options, here's my findings of 5 different stacks.

Everyone's results would probably be different from mine.

1 Normal stack - Lights, proper darks, flats and bias.

2 Lights, flats & bias.

3 Lights, master bias as a dark, flats & master bias as a dark flat.

4 Lights, master bias as a dark, flats and bias.

5 Lights, master bias as a dark, flats, master bias as a dark flat & bias.

Any stack that had bias stacked with a copy of the master bias I got a blank image except for number 4 where I had only the brightest stars visible after full stretch.

Number 1-2 & 3 stacks all produced a good image which I think number 1 being very slightly better maybe.

Number 3 stack DSS suggested not to have the black point set to 0. I tried both and setting the black point to 0 worked.. Unchecking the black point to 0 tab produced no image.

I know I'm not hurting my images with darks and I can get away with no darks, but I could not better my images by using a master bias as another calibration frame.

3 images #1 L-D-F-B      #2 L-F-B       #3 L-MBd-F-MBdf. All background extracted and auto stretched only in PixInsight.

Nige.

[happy-kat]

The idea for suggesting this didn't work all 3 images have banding :-( but nothing ventured nothing gained. It's surprising how identical those 3 are.

[tooth_dr]

Ive read this thread twice now and my head hurts more than it did when I woke up !

 

Is anyone using any of these methods successfully?

[happy-kat]

For me L + F + B + MBasMD does as it fits the time I have available where darks would otherwise add noise.

[Stub Mandrel]

I tried 'master bias as dark' in DSS. I'm not sure what went wrong, but this is how M32 came out (stretched...):

I freely admit I have obviously got something wrong, but I couldn't figure out what, so it clearly isn't 100% straightforward.

<edit> Reading @Nigel G's post I did exactly the same as his number 4 which appears to have given the same result. I'm not sure I understand your No.5 though Nige...

This is the same data stretched without darks (cooled DSLR used), so yes you can get away with no darks with a cooled DSLR. I've found that darks DO improve uncooled images with my DSLR but I kept my darks in three groups for warm, cool and cold nights:

[Nigel G]

 

5 hours ago, tooth_dr said:

Ive read this thread twice now and my head hurts more than it did when I woke up !

 

Is anyone using any of these methods successfully?

After a year or 2 playing around with images this is my findings,

I get my best results from Lights, flats & bias, no darks.

To get this result I must dither every 3 or 4 subs, Some might say you need to dither every sub but every 3-4 works.

Second best result is with darks and dithering. ( unnecessary to do this one )

3rd with darks no dither.

With a DSLR darks can often make the image worse.

To properly take darks with a DSLR you need to take a dark after every sub and that's just too much messing around.

To be honest when I use darks I use them from a dark data base I made with noted outside temps, as most of my imaging is ISO800 and 120 or 240s I don't need many in stock.

Best option is to try 1 image with and without darks, see the difference in processing.

Then try dithering - by far the best option, no need for dark frames and a cleaner image.

Nige.

[tooth_dr]

9 minutes ago, Nigel G said:

 

After a year or 2 playing around with images this is my findings,

I get my best results from Lights, flats & bias, no darks.

To get this result I must dither every 3 or 4 subs, Some might say you need to dither every sub but every 3-4 works.

Second best result is with darks and dithering. ( unnecessary to do this one )

3rd with darks no dither.

With a DSLR darks can often make the image worse.

To properly take darks with a DSLR you need to take a dark after every sub and that's just too much messing around.

To be honest when I use darks I use them from a dark data base I made with noted outside temps, as most of my imaging is ISO800 and 120 or 240s I don't need many in stock.

Best option is to try 1 image with and without darks, see the difference in processing.

Then try dithering - by far the best option, no need for dark frames and a cleaner image.

Nige.

Cheers Nigel. I'm currently dithering and not using darks, just flats and bias as normal in DSS. My images seem quite noise free. In fact I don't think they could be much better so that's I was wondering what others were doing.

[alacant]

1 hour ago, Nigel G said:

 

I get my best results from Lights, flats & bias, no darks

+1. If you can dither and then use median or k-sigma stacking, better still. Dark frames on the canon cameras I've used, 700d and 1200d, introduce more noise. HTH.

[tooth_dr]

25 minutes ago, alacant said:

+1. If you can dither and then use median or k-sigma stacking, better still. Dark frames on the canon cameras I've used, 700d and 1200d, introduce more noise. HTH.

Thanks. It was the streaks of noise that finally were the last straw. I had 8 hours of subs on the bubble neb and it still looked [removed word]. Since then I've done half that time, without darks, but used dithering and the difference was incomparable. I'll just continue to use lights flats and bias only, in their respective sections in DSS

[ollypenrice]

If you want a stacking programme which makes all the experimenting with combinations quick and easy, try AstroArt.

Olly

[alacant]

13 hours ago, tooth_dr said:

Since then I've done half that time, without darks

Hi. You could still use the previous 8 hours and the new set by putting each into a DSS group with their own flat frames. It will then combine both sets. Just don't include the dark frames. HTH

[tooth_dr]

3 hours ago, alacant said:

Hi. You could still use the previous 8 hours and the new set by putting each into a DSS group with their own flat frames. It will then combine both sets. Just don't include the dark frames. HTH

I kinda just had written them off, due to the way they were recorded without dithering.  I took a few subs last night, dont think it dithered enough though.

[Stub Mandrel]

I'm becoming increasingly unconvinced.

This is the effect of using duplicating the master bias as a dark flat frame. Those elleptical bands are NOT artefacts from compression.:

[alacant]

8 hours ago, tooth_dr said:

dont think it dithered enough though

A random dither in both RA and DEC of up to 15px works well on my 700d. I find I need to have 20 or more snaps to get the best noise reduction. HTH

[Nigel G]

4 hours ago, Stub Mandrel said:

I'm becoming increasingly unconvinced.

This is the effect of using duplicating the master bias as a dark flat frame. Those elleptical bands are NOT artefacts from compression.:

 

It never worked for me either.