Do I need dark frames?

[Calzune]

I'm new to Astrophotography but I have learned alot these couple of months about ap and processing. 

I recently checked the forum about dark frames and dithering, and I have a question. 

I use a Canon eos 1100d (modded) and I have recently started using guiding = dithering. 

Do I need Darks if I'm dithering?

I know that temperature is an important factor when taking frames and because I'm using a dslr I cannot control the temp. I know that Darks is best to shoot right after the light frames but still, it's not the same temperatures..

I have read that some people say it can make the picture worse if I'm shooting darks (if dithering) because of the temp change. 

And some people says it make a small improvement. 

Darks can take a long time to shoot, I go for minimum 20 and max 40. But this is time that I can have put in on lightframes. 

What are your thoughts on this? 

I usually go for 20 Darks, Bias and Flats. 

 

[bottletopburly]

No you don’t if you’re dithering, and to be honest I take a batch of bias  frames and keep them for a while before redoing, I just take flats on the night using a light panel , the during processing load the bias frames into the darks tab in DSS or what ever stacker you use , that seems to be the way to do it from reading on here .

Edited November 4, 2019 by bottletopburly

[Ronclarke]

That's the way I do it but I use a library of Flats and take 20 Bias frames just after finishing my lights..

Ron

[vlaiv]

If you want to do proper calibration - yes you do.

There are certain cases where you can get away with not using darks, and in case when one does not have set point temperature - it can be difficult do properly apply them, so you need to be careful.

Not doing darks can lead to problems with flat calibration.

You need to try different scenarios and see which one works for you. If you want to try without darks - use bias subs instead whenever darks are required (for dark calibration of lights and for creating master flat). If you decide to use darks then you should do dark optimization (there is option in some software that does this) - it is algorithm that tries to compensate for mismatched temperature in your darks. It is also not bullet proof technique and it will depend on characteristics of your camera. Some cameras have issues with bias subs and can't use dark optimization / dark scaling.

[Adam J]

9 hours ago, Calzune said:

I'm new to Astrophotography but I have learned alot these couple of months about ap and processing. 

I recently checked the forum about dark frames and dithering, and I have a question. 

I use a Canon eos 1100d (modded) and I have recently started using guiding = dithering. 

Do I need Darks if I'm dithering?

I know that temperature is an important factor when taking frames and because I'm using a dslr I cannot control the temp. I know that Darks is best to shoot right after the light frames but still, it's not the same temperatures..

I have read that some people say it can make the picture worse if I'm shooting darks (if dithering) because of the temp change. 

And some people says it make a small improvement. 

Darks can take a long time to shoot, I go for minimum 20 and max 40. But this is time that I can have put in on lightframes. 

What are your thoughts on this? 

I usually go for 20 Darks, Bias and Flats. 

 

I would not use dark frames with a DSLR as you just cant control the temperature sufficiently. 

Dithering is the way forward. 

[newbie alert]

You don't need any calibration frames, lots of people don't use them at all..

If you use a decent sized dither you don't need darks.. 

If you don't have issues with dust bunnies or coma then you don't need flats...

As with most of use that used a DSLR we used calibration frames out of habit, I failed to see any benefit from them so just stopped doing them.. you just need to know what you're trying to calibrate out..

[carastro]

Quote

You don't need any calibration frames

Flats are essential for vignetting and removing dust.  I can't process an image properly without flats as the centre is always brighter than the edges.  Any-one who says you can get away without doing flats is kidding themselves and will probably be able to get a much better result if they used flats. 

Carole 

Edited November 17, 2019 by carastro

[Skipper Billy]

13 minutes ago, carastro said:

Flats are essential for vignetting and removing dust.  I can't process an image properly without flats as the centre is always brighter than the middle.  Any-one who says you can get away without doing flats is kidding themselves and will probably be able to get a much better result if they used flats. 

Carole 

+1

[tooth_dr]

1 hour ago, newbie alert said:

You don't need any calibration frames, lots of people don't use them at all..

If you use a decent sized dither you don't need darks.. 

If you don't have issues with dust bunnies or coma then you don't need flats...

As with most of use that used a DSLR we used calibration frames out of habit, I failed to see any benefit from them so just stopped doing them.. you just need to know what you're trying to calibrate out..

I would say like @carastro as a minimum flats are essential.  I don’t even bother to process my data without good calibration frames.  I use flats bias and darks and a BPM. With a DSLR I don’t use darks but dithered. I still dither now with a ccd. 

[newbie alert]

1 hour ago, carastro said:

Flats are essential for vignetting and removing dust.  I can't process an image properly without flats as the centre is always brighter than the middle.  Any-one who says you can get away without doing flats is kidding themselves and will probably be able to get a much better result if they used flats. 

Carole 

Carole, you use the same camera as me..is this with your frac or newt?

[ollypenrice]

Flats you need. No question. Darks, if you are dithering, maybe not. When you find the community disagrees it is best to experiment for yourself. However, using imaging time for taking darks will never make a profit.

Olly

[carastro]

Quote

Carole, you use the same camera as me..is this with your frac or newt?

I have used both but I no longer have the Newtonian, but same applies to both.

Excuse my typo earlier which I have now corrected.  The middle is always brighter than the edges. 

Carole 

Edited November 17, 2019 by carastro

[newbie alert]

You've all seen this from Lee from a few weeks back..

He says he's the laziest imager going..

Never uses flats,  or darks as he dithers.. he may use a master bias..not sure where the bright bit is in the middle , I can't see it.

[tooth_dr]

11 minutes ago, newbie alert said:

You've all seen this from Lee from a few weeks back..

He says he's the laziest imager going..

Never uses flats,  or darks as he dithers.. he may use a master bias..not sure where the bright bit is in the middle , I can't see it.

There is no doubt it’s possible to make images without flats.  Without a comparison here you won’t know the difference/gradient won’t be easier to see/obscured by nebulosity. It’s just so much easier to process gradients and vignetting with flats.

[ApophisAstros]

10 hours ago, newbie alert said:

You've all seen this from Lee from a few weeks back..

He says he's the laziest imager going..

Never uses flats,  or darks as he dithers.. he may use a master bias..not sure where the bright bit is in the middle , I can't see it.

Obvious dust bunnies there though,...................^ look up from the arrow a couple there.

Roger

[kirkster501]

Don't need darks with my Atik 460.  However, I very much need them with the KAF8300 camera; the lights are a blizzard of noisy pixels.

But if you image at a set temperature with a cooled camera, what's the issue with darks?  Take a dark library at the temperature you image at.  I have found the noise stays the same for years and that, in actual fact, you do not need to constantly refresh the library at all, as some people say.  I have found this by experimentation with cosmetic correction; older darks are just as good as ones just off the camera.   So I now have a master dark and BIAS for bin 1x1, 2x2 for 5, 10 and 15 minutes, so six master darks and BIAS.  Per camera.  That's it now.  For 2/3 years.  All in my calibration directory and I just select the appropriate ones.

Indeed, I have also found that during image calibration and integration, the darks do not need to be at the same temperature even and that Pixinsight takes care of the linear change in noise with temperature and will scale accordingly.  So a 10 minute dark is fine for 15 minute lights.  OK, not the best practise, but I see no discernable difference.

So why not have darks and BIAS?

 

EDITED as olly was posting below

Edited November 18, 2019 by kirkster501

[ollypenrice]

1 minute ago, kirkster501 said:

Don't need darks with my Atik 460.  However, I very much need them with the KAF8300 camera; the lights are a blizzard of noisy pixels.

I find it depends on temperature with mine. A master bias-as-dark works fine when I can get down to -15 or so but when I can't, in summer, it does need darks.

Olly

[Skyline]

When dithering,  I found darks to inherit more noise into your picture when using DSLR.

I used to take with my modded 1100d, lights, flats and bias. 

20-30 flats with 20 bias 

Edited November 18, 2019 by Skyline

[ollypenrice]

It might be worth citing Tony Hallas, here, too. He advocates dither, bias as dark and that the dither be of at least 12 pixels to combat DSLR 'colour mottle.'

Olly

Edited November 18, 2019 by ollypenrice
Typo

[Star101]

I had a line in a column for some time. Then a slight knock by accident cleared it lol.

Darks do change over time....But not often.

300 seconds Darks 16 March, 14 April and 17 Nov 2019.

 

Edited November 18, 2019 by Star101

[newbie alert]

4 hours ago, apophisOAS said:

Obvious dust bunnies there though,...................^ look up from the arrow a couple there.

Roger

Take it that's a joke Roger??

[newbie alert]

4 hours ago, kirkster501 said:

Don't need darks with my Atik 460.  However, I very much need them with the KAF8300 camera; the lights are a blizzard of noisy pixels

Lee also has a 383 and the noise looks bad if the camera isnt run at 13v, below that and the noise increases but calibrates out very easily... not sure if it's with darks thou, which is purely my point, you got to look at what you're trying to calibrate out and not just use calibration frames out of habit..

Personally I need to use flats as my filters are as clean as I hoped..don't use darks as it added noise to my 16hr images, just going to try bias with the 460 and see if that works for me..

Edited November 18, 2019 by newbie alert
Damn phone

[ollypenrice]

2 hours ago, Star101 said:

I had a line in a column for some time. Then a slight knock by accident cleared it lol.

 

Aha, I was baffled when one camera lost its long-time column defect. Maybe I nutted it while fumbling around in the dark!

Olly

[Calzune]

4 hours ago, Skyline said:

When dithering,  I found darks to inherit more noise into your picture when using DSLR.

I used to take with my modded 1100d, lights, flats and bias. 

20-30 flats with 20 bias 

I have a modded 1100d, so you skipped Darks completely? I tried skipping Darks but the noise was even worse... Maybe I should try again.. 

[Skyline]

I never used to take darks, spent more time processing data. Always used ISO800 less noise to deal with.