Are Flats and Bias required?

[Jojo204]

Hey, 

so I’ve been taking some shots of M57 and didn’t take any Flats and Bias shots. I’ve read a bit about them but haven’t been sure so I didn’t risk my storage getting them. I took 32 light frames and 16 dark frames. Is this ok or do I need more darks? I took the M57 frames at a 2 second exposure, ISO 3200 and did the same for the Darks. Bias and flats I don’t really get currently and want to know how big a difference they make? 

 

Thanks

[geordie85]

Flats are very important. They get rid of dust bunnies and help fix vignetting 

[Jbro1985]

Depends on camera.  Bias isn't needed on some Cmos.  Generally though, yes both bias and flats are required if your objective is to get the cleanest image.  

Bias takes out the underlying noise in the camera (coupled with darks) and flats take out vignetting and aberrations caused by any potential dust etc.

Depending on the camera, it can become more advanced still with flat darks playing a part for some also.

[Jojo204]

3 minutes ago, Jbro1985 said:

Depends on camera.  Bias isn't needed on some Cmos.  Generally though, yes both bias and flats are required if your objective is to get the cleanest image.  

Bias takes out the underlying noise in the camera (coupled with darks) and flats take out vignetting and aberrations caused by any potential dust etc.

Depending on the camera, it can become more advanced still with flat darks playing a part for some also.

My camera is very basic, a 1200d with crop cmos

[Jbro1985]

Not familiar with that particular camera but Cmos generally the bias noise is fairly random.  Particularly if it's cooled (presuming 1200d isn't).

Flats will be needed.

[spillage]

Hi

No calibration frames are need if you are happy with the image after just stacking the light, but if you want a cleaner image then they are very important. With the canon I would do darks, bias and flats.

I would say try it and see what you think. With your camera you will need to take the darks at the same temp as your lights.

Have a look here.

[Jojo204]

11 hours ago, Jbro1985 said:

Not familiar with that particular camera but Cmos generally the bias noise is fairly random.  Particularly if it's cooled (presuming 1200d isn't).

Flats will be needed.

Ok thanks

[Jojo204]

11 hours ago, spillage said:

Hi

No calibration frames are need if you are happy with the image after just stacking the light, but if you want a cleaner image then they are very important. With the canon I would do darks, bias and flats.

I would say try it and see what you think. With your camera you will need to take the darks at the same temp as your lights.

Have a look here.

Ah ok, yeh without them I experienced hot pixels making the software detect fake stars messing up the overall image

[tooth_dr]

With my Canon I use flats bias and no darks, and dither between each light exposure.  Darks are hard to temp match and I don’t notice any detrimental effect without them, so i don’t use them.

BUT I see you are taking two second exposures. So you aren’t guiding so dithering isn’t really going to work. 

Can you take longer exposures?

 

[Alien 13]

If I am using my DSLR with a camera lens on a static tripod for exposures of a few seconds then I just switch the "long exp noise reduction" on, this gives you a matched dark frame for every sub (it does double the effective sub length though) and use the generic lens correction data to deal with vignetting rather than taking flats.

Alan

[Jojo204]

9 hours ago, tooth_dr said:

With my Canon I use flats bias and no darks, and dither between each light exposure.  Darks are hard to temp match and I don’t notice any detrimental effect without them, so i don’t use them.

BUT I see you are taking two second exposures. So you aren’t guiding so dithering isn’t really going to work. 

Can you take longer exposures?

 

I can take longer exposures but don't risk it as I'm not sure from what point the earth's rotation would become apparent. I'm not using a tracking mount so if you could suggest how long I would have, that'd be amazing.

[Jojo204]

8 hours ago, Alien 13 said:

If I am using my DSLR with a camera lens on a static tripod for exposures of a few seconds then I just switch the "long exp noise reduction" on, this gives you a matched dark frame for every sub (it does double the effective sub length though) and use the generic lens correction data to deal with vignetting rather than taking flats.

Alan

I will look to turn it on now, thanks!

[Jojo204]

This was my first attempt to capture M42 last night without a scope or anything. Quite proud of it! 27 Lights, 20 Darks, 10 Flats and 10 Bias. How many Bias and Flats do you think I need for e.g. 32 lights?

[tooth_dr]

2 hours ago, Jojo204 said:

This was my first attempt to capture M42 last night without a scope or anything. Quite proud of it! 27 Lights, 20 Darks, 10 Flats and 10 Bias. How many Bias and Flats do you think I need for e.g. 32 lights?

That’s actually really good! For a static tripod very excellent!

I take 30-50 images for each calibration set 

[Jojo204]

1 hour ago, tooth_dr said:

That’s actually really good! For a static tripod very excellent!

I take 30-50 images for each calibration set 

Thanks man! And ok I’ll use about that much in future then too!