Are dark frames really needed when using system camera?

[RealWorldPhoto]

Do we really need dark frames with today's system cameras (DSLR and mirrorless), due to the very low noise with CMOS sensors?

For those who are not used with the term "dark frames", this is exposures without light, taken with the same duration and at the same temperature as the image files, used to reduce noise. The filtering process is done with astro software.

Years ago I used cooled CCD-cameras, and every astro session included dark frames and flat frames. I also added bias frames when processing the files. For CCD sensors, using dark frames made sense.

Now I have scaled down my astrophotography to system cameras with CMOS sensors (I like to call them cosmos sensors) and small telescopes, up to about 350 mm focal length. I also use small unguided trackers to keep everything as simple as possible.

I keep the camera sensors clean, so flat field frames are not needed to remove dust spots. I skip these too, and correct for vignetting at post processing. No specialized astro software is used, just Photoshop, except for Registar for stacking files.

This works fine for my small scale astrophotography, since the end result is just for pleasure and not intended for any kind of scientific studies.

So: Do dark frames make a visible difference when using system cameras?


This photo showing the Faming star nebula and surroundings in Auriga, should tell something about what level of astrophotography I am doing with a standard system camera, a small refractor and a not guided star tracker.

 

[Gergob]

Here is what a heavily stretched 600 sec master dark looks like on my QHY600 while cooled to -15C:



While Cosmetic Correction in WBPP would take care of most of these hot pixels, I still find darks to be quite effective. For non cooled cameras, dithering and flats will go a long ways. Calibration frames are all incremental changes that add up to producing a cleaner finer image.

 

[RealWorldPhoto]

Here is what a heavily stretched 600 sec master dark looks like on my QHY600 while cooled to -15C:

While Cosmetic Correction in WBPP would take care of most of these hot pixels, I still find darks to be quite effective. For non cooled cameras, dithering and flats will go a long ways. Calibration frames are all incremental changes that add up to producing a cleaner finer image.

If you read the first line in my post, you will find that I am not takling about astro cameras with cooled sensor.

After posting, a friend made me aware of an article at ClarcVision.com showing that using dark frames for standard system cameras will probably result in added noise and more visible walking noise. With other words: Counter-productive.

 

[Larry Rexley]

My answer is 'yes' if you are doing astro that if you're trying to squeeze every last ounce of detail out of the image, which is typically the case with faint deep-sky objects. It can also help correct for sensor faults where a particular color is 'stuck' etc at high sensitivities.

For Moon and planetary work on relatively bright objects, I don't use dark, bias, or flat frames in general, I only use them for deep sky work and wide-field Milky Way etc.

 

[RealWorldPhoto]

My answer is 'yes' if you are doing astro that if you're trying to squeeze every last ounce of detail out of the image, which is typically the case with faint deep-sky objects. It can also help correct for sensor faults where a particular color is 'stuck' etc at high sensitivities.

The Clarvision article I point to says that likely you get more noise when using dark frames on long exposure light frames from system cameras with cmos sensor.

 

[reinhard becker]

My answer is 'yes' if you are doing astro that if you're trying to squeeze every last ounce of detail out of the image, which is typically the case with faint deep-sky objects. It can also help correct for sensor faults where a particular color is 'stuck' etc at high sensitivities.

The Clarvision article I point to says that likely you get more noise when using dark frames on long exposure light frames from system cameras with cmos sensor.

Where is the difference between between system cameras and astrocameras using the exact same sensor? The astrocameras should be even better because of cooling…

so why should system cameras get more noise using darks in comparison to astro cameras? I have no idea how to answer this question!



But: I use no darks, because I don‘t want to loose time during the night and I do not really need them (anymore). I have now an astro modified S5 and this camera is so much better then my old modified EOS5DII, that even heavily stretched darks are not showing disturbing amount of noise. If you then stack dozens of pictures, the noise is not harming the picture anymore…

 

[RealWorldPhoto]

so why should system cameras get more noise using darks in comparison to astro cameras? I have no idea how to answer this question!

Cameras come with different sensor filter stack even if they are based on the same sensor, many astro cameras are monochrome, cooling might affect the noise level of the light and dark frames, etc.

But: I use no darks, because I don‘t want to loose time during the night and I do not really need them (anymore). I have now an astro modified S5 and this camera is so much better then my old modified EOS5DII, that even heavily stretched darks are not showing disturbing amount of noise. If you then stack dozens of pictures, the noise is not harming the picture anymore…

The EOS 5DII had a maximum photographic DR of 9.1 and the S5 measures at 11.4. Also, the S5 sensor has dual gain and this is helpful when doing astrophotography.

 

[reinhard becker]

so why should system cameras get more noise using darks in comparison to astro cameras? I have no idea how to answer this question!

Cameras come with different sensor filter stack even if they are based on the same sensor, many astro cameras are monochrome, cooling might affect the noise level of the light and dark frames, etc..

all right, but all these topics will raise quality and not lower it. So by default real astro cameras should deliver better results for astro then normal photographic camera bodies. That‘s why I‘m asking why darks should decrease the quality…

 

[RealWorldPhoto]

so why should system cameras get more noise using darks in comparison to astro cameras? I have no idea how to answer this question!

Cameras come with different sensor filter stack even if they are based on the same sensor, many astro cameras are monochrome, cooling might affect the noise level of the light and dark frames, etc..

all right, but all these topics will raise quality and not lower it. So by default real astro cameras should deliver better results for astro then normal photographic camera bodies. That‘s why I‘m asking why darks should decrease the quality…

With low noise CMOS sensors, it seems from serious tests that dark frames in many cases will increase noise, also the ugly walking noise. Light frames has noise, and so has dark frames. Hot pixels can be removed without using dark frames.

 

[reinhard becker]

so why should system cameras get more noise using darks in comparison to astro cameras? I have no idea how to answer this question!

Cameras come with different sensor filter stack even if they are based on the same sensor, many astro cameras are monochrome, cooling might affect the noise level of the light and dark frames, etc..

all right, but all these topics will raise quality and not lower it. So by default real astro cameras should deliver better results for astro then normal photographic camera bodies. That‘s why I‘m asking why darks should decrease the quality…

With low noise CMOS sensors, it seems from serious tests that dark frames in many cases will increase noise, also the ugly walking noise. Light frames has noise, and so has dark frames. Hot pixels can be removed without using dark frames.

But if true this statement is not restricted to photographic cameras. If any astro camera uses the same sensor like a photographic camera it should be the same idea…

so I still do not understand the inital question…

 

[RealWorldPhoto]

so why should system cameras get more noise using darks in comparison to astro cameras? I have no idea how to answer this question!

Cameras come with different sensor filter stack even if they are based on the same sensor, many astro cameras are monochrome, cooling might affect the noise level of the light and dark frames, etc..

all right, but all these topics will raise quality and not lower it. So by default real astro cameras should deliver better results for astro then normal photographic camera bodies. That‘s why I‘m asking why darks should decrease the quality…

With low noise CMOS sensors, it seems from serious tests that dark frames in many cases will increase noise, also the ugly walking noise. Light frames has noise, and so has dark frames. Hot pixels can be removed without using dark frames.

But if true this statement is not restricted to photographic cameras. If any astro camera uses the same sensor like a photographic camera it should be the same idea…

so I still do not understand the inital question…

The question is: How to deal with dark frames when using CMOS versus CCD sensors?

 

[reinhard becker]

so why should system cameras get more noise using darks in comparison to astro cameras? I have no idea how to answer this question!

Cameras come with different sensor filter stack even if they are based on the same sensor, many astro cameras are monochrome, cooling might affect the noise level of the light and dark frames, etc..

all right, but all these topics will raise quality and not lower it. So by default real astro cameras should deliver better results for astro then normal photographic camera bodies. That‘s why I‘m asking why darks should decrease the quality…

With low noise CMOS sensors, it seems from serious tests that dark frames in many cases will increase noise, also the ugly walking noise. Light frames has noise, and so has dark frames. Hot pixels can be removed without using dark frames.

But if true this statement is not restricted to photographic cameras. If any astro camera uses the same sensor like a photographic camera it should be the same idea…

so I still do not understand the inital question…

The question is: How to deal with dark frames when using CMOS versus CCD sensors?

That is a another question. You asked about usage of darks with modern system cameras (DSLR or Mirrorless). Actually more than 95% of the sold astrocameras are using the same sensors like system cameras, only very few models are still available with CCD. So both are based on the same sensors…

Most astrophotographers are still using the full process with bias, flats and darks with the modern astrocameras based on CMOS. The results from today are awesome.

My summary of todays processes is, you can skip the darks if you are satisfied with a 80 90% result, because some of the sensors are so good today. but if you want to get the best of the best you still work with darks.

For anything else there is still no good argument. You told that someone said, but I could not find this statement. Do you have a link where we can check this statement?

 

[RealWorldPhoto]

The question is: How to deal with dark frames when using CMOS versus CCD sensors?

That is a another question. You asked about usage of darks with modern system cameras (DSLR or Mirrorless).

If you read my initial post, this is what my question is about: CMOS in modern system cameras versus previous handling of astro files and dark frames when we used CCD cameras.

 

[reinhard becker]

The question is: How to deal with dark frames when using CMOS versus CCD sensors?

That is a another question. You asked about usage of darks with modern system cameras (DSLR or Mirrorless).

If you read my initial post, this is what my question is about: CMOS in modern system cameras versus previous handling of astro files and dark frames when we used CCD cameras.

And I gave you the answer, that darks are not that relevant like years ago and you will get good results without darks. But the high end astrophotographers are still using darks, even with modern CMOS sensors to get most out of the files.

you are laking the link, where the information that darks can reduce the quality is coming from….

 

[RealWorldPhoto]

you are laking the link, where the information that darks can reduce the quality is coming from….

Here:

Stacking with Master Dark vs no Dark Frames, Clarkvision.com