Grainy Photos in Long Exposure

Can someone tell me why my photos look grainy when I'm shooting long exposures?, I'm shooting at 100 ISO
Thanks
Steve

Can you post examples?

1:1 examples help a lot.

When you expose for a long period of time, you are heating up the sensor significantly and that heat creates a lot of random noise, even at base ISO. Older sensors will be noiser in general too. And sensors that have seen a lot of long exposure or lots of video use will also tend to show quite a bit of noise over time (eventually hot pixels develop, etc too).

Your camera has long exposure noise reduction (LENR) as an option for this very purpose. You may want to start using it.

Very best,

Just so you know, the long exposure noise reduction takes a second "image" that is equal in length to the original, so be prepared to wait in between shots.

Thank you so much for explain this to me, i didn't know exactly what was going on, i did switch ON the LENR, I'm hoping this would help me out, i do have an older canon 7D and i can't afford a new camera at the moment...thanks again!
Steve

No way, are you serious? so for every time i take a shot, the camera is going to take another picture too?
Steve

Steve Sanchez Photography wrote in post #18482825
Thank you so much for explain this to me, i didn't know exactly what was going on, i did switch ON the LENR, I'm hoping this would help me out, i do have an older canon 7D and i can't afford a new camera at the moment...thanks again!
Steve

LENR will work very well for your purpose.

When using it, after you expose, LENR will expose a 2nd image for the same amount of time (so a 30 second exposure will take 60 seconds total, etc). You don't have to do anything special. But it takes care of pattern noise very nicely. You will still get some random noise, but it won't be profound unless you severely underexpose and push exposure/shadows in post.

Some sensors are noisier than others. My 7D was noisy at ISO 100 even in normal, well exposed images. One of my 5Dc's is super noisy for long exposure.

Very best,

Just for clarity here.

LENR, does not really take another picture, it leaves the shutter closed while taking a "black" exposure that is used to subtract out the sensor noise present in the original exposure/photo.

Oh ok thank you for explaining that.
Steve

I’m shooting a 7D but I don’t see noise in a normal exposure at 100 iso.

Steve Sanchez Photography wrote in post #18485919
I’m shooting a 7D but I don’t see noise in a normal exposure at 100 iso.

Because the "noise" you're seeing is not ISO noise, most likely it's hot pixels.

The longer the exposure the more the sensor heats up causing hot pixels. So it's not actual noise that you're seeing it's just hot pixels.

The long exposure noise reduction takes a second exposure, a black exposure, and compaires the hot pixels from that shot to the hot pixels of the actual photo to get rid of them. The down side is your exposure times are basically doubled with long exposure noise reduction.

The longer the exposure the more likely you are to get "long exposure noise". Long exposure noise can even get wore then ISO noise so it might be better to up your ISO to lower exposure times if you can. Obviously that will depend greatly on what you're shooting and the effect you're going for.

That's too small of an image to see much noise, but it's a 20 second exposure. The longer you expose, the more noise you will get from the sensor just being on that long. It's not ISO noise - it's caused by the sensor heating up. This is where the long exposure noise reduction helps because it takes another shot to map out those same hot pixels and reduce the amount of noise.