Grainy picture

[Chefgage]

Hello. I was out last night with the canon 200d and tripod hoping to get some decent shots of the cresent moon.  One particular picture i took appears to be very grainy. I am not sure i have had one as bad as that before. What causes the graininess and what steps can you use to avoid it if possible. The image is shown.  Thanks.

[knobby]

Not a Canon man but did you have auto ISO turned on ? the higher the ISO, the more grain/ noise

[Z3roCool]

I am guessing it is the ISO setting used? What setting did you have?

[Chefgage]

5 minutes ago, knobby said:

Not a Canon man but did you have auto ISO turned on ? the higher the ISO, the more grain/ noise

No it was all in manual.

[Chefgage]

5 minutes ago, Z3roCool said:

I am guessing it is the ISO setting used? What setting did you have?

Right just checked the picture details and the iso was 25600 😀.  The other settings were aperture - F36.0, exposure time - 0.5s

[Z3roCool]

6 minutes ago, Chefgage said:

Right just checked the picture details and the iso was 25600 😀.  The other settings were aperture - F36.0, exposure time - 0.5s

 Bump that ISO down and open up the Aperture then play with the setting to get your exposure right. Should see a massive difference in noise (Grain).

[Chefgage]

4 minutes ago, Z3roCool said:

 Bump that ISO down and open up the Aperture then play with the setting to get your exposure right. Should see a massive difference in noise (Grain).

So i need to lower the iso, lower the f number and then increase the exposure time?

[knobby]

The moon is actually quite bright, try ISO 400 f6.3 ish and 1/200 sec as a test, then tweak as needed

[Z3roCool]

22 minutes ago, Chefgage said:

So i need to lower the iso, lower the f number and then increase the exposure time?

Yeah, as Knobby states above. Try around those settings and then increase/decrease exposure time to get the correct exposure you like. I managed this shot with my 400mm Canon lens jammed against a Velux window in my roof.  Think the setting were ISO 100 f 5.6 and 1/200s exposure. Obviously will be a little different when you take into account the rest of the sky at a shorter focal length. Best way is to just play with the settings and see what you get, keep the ISO down low though

[Chefgage]

9 minutes ago, Z3roCool said:

Yeah, as Knobby states above. Try around those settings and then increase/decrease exposure time to get the correct exposure you like. I managed this shot with my 400mm Canon lens jammed against a Velux window in my roof.  Think the setting were ISO 100 f 5.6 and 1/200s exposure. Obviously will be a little different when you take into account the rest of the sky at a shorter focal length. Best way is to just play with the settings and see what you get, keep the ISO down low though

Sorry i might have misled you a bit here 😀. I can get a good picture of just the moon with plenty of detail, no problems there. I was after a shot with the sky not fully dark and showing the buildings in the forground.  So i focused on the forground buildings (so the moon was obviously out of focus).  I get that the moon in this case would be over exposed. 

In this situation should i be concentrating on increasing the exposure time?  I am not after any real detail showing on the moon.

Edited June 7, 2019 by Chefgage

[Z3roCool]

5 hours ago, Chefgage said:

Sorry i might have misled you a bit here 😀. I can get a good picture of just the moon with plenty of detail, no problems there. I was after a shot with the sky not fully dark and showing the buildings in the forground.  So i focused on the forground buildings (so the moon was obviously out of focus).  I get that the moon in this case would be over exposed. 

In this situation should i be concentrating on increasing the exposure time?  I am not after any real detail showing on the moon.

Ahh, no worries. You may need to increase the exposure time, depends on how dark it will be. Just make sure ISO low and aperture low (Not always wide open - maybe stop down a few) and then play with the exposure time to see what exposure you get. Good luck

[Kev M]

I would have though an iso nearer 800 or 1600 would be better.

What lens is this....couldnt see it in the thread ?

[bobro]

11 hours ago, Chefgage said:

Sorry i might have misled you a bit here 😀. I can get a good picture of just the moon with plenty of detail, no problems there. I was after a shot with the sky not fully dark and showing the buildings in the forground.  So i focused on the forground buildings (so the moon was obviously out of focus).  I get that the moon in this case would be over exposed. 

In this situation should i be concentrating on increasing the exposure time?  I am not after any real detail showing on the moon.

To give a slightly detailed answer to your questions. Your exposure for the sky looks spot on (exposure for the buildings and Moon are ignored). The reason for the graininess in the image is due to the way photons (light) arrive from the sky - photons don't arrive in a smooth fashion but more like buses, which may come all at once or with long gaps between. The result is that adjacent pixels on the camera sensor collect different number of photons for a given exposure time, resulting in differences in brightness that we perceive as grain.

With buses, if we averaged the arrival rate of them over a day it would work out ok. Same thing for light - the longer the exposure the smoother the grain appearance as the arrival rate of photons on adjacent pixels starts to even out and the image becomes smoother. ISO makes no great difference as it only amplifies the pixel capture readout (including random photon arrival variation noise) received on pixels but makes no difference to what the pixel captures. 

The key way to reduce apparent image grain (ignoring post processing of images and thermal sensor noise) is to increase the number of photons captured as this will even out noise. The simplest way is to use the lowest f# with the setup that produces an acceptable image as a wider aperture lets through more photons in a given time. The most used method is to increase the overall exposure time - with a single image this may mean reducing the ISO to prevent sensor readout saturation whilst increasing the exposure time. When imaging exposure time results in the target starting to become saturated or stars become linear (star trails) in the captured image, multiple stacked exposure are the way to achieve the aim of lowering noise whilst keeping an acceptable image as this increases the overall exposure time.

A different perspective compared to one shot photography, but that's the way long exposure imaging works to reduce noise.

Getting a little more technical, modern DSLR cameras tend to have small pixels. Whilst that is great for images taken in bright light, in astrophotography the small pixels accentuate the noise due to random photon arrival rate over the small pixel surface. To counteract this, images are binned, which means combining the images capture from adjacent pixels, resulting in lowered noise due to the effective larger surface. This can be done in camera by using a lower resolution or in post processing.

Hope this is useful in some way.

Edited June 7, 2019 by bobro

[Chefgage]

On 07/06/2019 at 17:14, Kev M said:

I would have though an iso nearer 800 or 1600 would be better.

What lens is this....couldnt see it in the thread ?

Its a Canon EF 75-300mm f/4-5.6 III 

[Chefgage]

On 07/06/2019 at 22:21, bobro said:

To give a slightly detailed answer to your questions. Your exposure for the sky looks spot on (exposure for the buildings and Moon are ignored). The reason for the graininess in the image is due to the way photons (light) arrive from the sky - photons don't arrive in a smooth fashion but more like buses, which may come all at once or with long gaps between. The result is that adjacent pixels on the camera sensor collect different number of photons for a given exposure time, resulting in differences in brightness that we perceive as grain.

With buses, if we averaged the arrival rate of them over a day it would work out ok. Same thing for light - the longer the exposure the smoother the grain appearance as the arrival rate of photons on adjacent pixels starts to even out and the image becomes smoother. ISO makes no great difference as it only amplifies the pixel capture readout (including random photon arrival variation noise) received on pixels but makes no difference to what the pixel captures. 

The key way to reduce apparent image grain (ignoring post processing of images and thermal sensor noise) is to increase the number of photons captured as this will even out noise. The simplest way is to use the lowest f# with the setup that produces an acceptable image as a wider aperture lets through more photons in a given time. The most used method is to increase the overall exposure time - with a single image this may mean reducing the ISO to prevent sensor readout saturation whilst increasing the exposure time. When imaging exposure time results in the target starting to become saturated or stars become linear (star trails) in the captured image, multiple stacked exposure are the way to achieve the aim of lowering noise whilst keeping an acceptable image as this increases the overall exposure time.

A different perspective compared to one shot photography, but that's the way long exposure imaging works to reduce noise.

Getting a little more technical, modern DSLR cameras tend to have small pixels. Whilst that is great for images taken in bright light, in astrophotography the small pixels accentuate the noise due to random photon arrival rate over the small pixel surface. To counteract this, images are binned, which means combining the images capture from adjacent pixels, resulting in lowered noise due to the effective larger surface. This can be done in camera by using a lower resolution or in post processing.

Hope this is useful in some way.

Thanks for that, it was indeed helpful.