Long exposure questions on 5D MK3

[bjd]

Hi,
I've been trying a few long exposure shots lately, mainly nighttime photos and a few questions came up
where I'm not sure about the correct answers. Please bear with me if they seem bleeding obvious to you :-[

1. Talking to a guy with a 6D, he assured me that on the 6D that auto lighting optimizer, Long Exposure NR and High ISO speed NR are used, even when shooting RAW. Is that really so? I thought they are never applied when shooting RAW.

2. If I need a 40sec exposure at ISO100 for correct exposure, how do I determine which combination will have the least noise? 20sec at ISO200, 10sec at ISO400? Obviously disregarding any other issues that would speak against a really long exposure, for example wind, etc.

I ask because some really low light exposures at ISO 100 seem very noisy to me.

3. When using a tripod the recommendation is always to switch IS off. When using a tele on long exposures, does it really never help to have IS on? For example at 200mm?

4. What ISO value would you try to never go above on a 5D3 for long exposures?


Cheers Brian

 

[YuengLinger]

Brian, I'm glad you asked about the High ISO NR, as I hadn't thought much about it since buying my 5DIII almost two years ago. Rather than summarizing an excellent article on the subject, I'd refer you to this post on Canon USA's website:

http://www.learn.usa.canon.com/resources/articles/2011/high_iso_noise_reduction_article.shtml

The key word in this article might be "experiment."

As for question number two, I'd be very interested to hear what some of the more engineering-minded regulars of CR have to say, but from my own experience, in the lower ISO values (400 and below), factors like wind or the steps of a passerby or the passing of something in front of the field of view are much more important than a little difference in noise. That said, even a normal exposure (eg 1/200th) is going to reveal a little more noise at ISO 400 than at ISO 100, so starting out lower seems pretty sensible when possible. But you do raise a good question about length of sensor operation effecting noise more than ISO value.

But if you are seeing "very noisy" at ISO 100, I wonder if you are trying to boost the shadows too much in post processing?

Question 3...The longest lens I have with IS is the 70-200mm 2.8 II. In my experience, turning IS off on the tripod is a must, no matter how long my exposure. Page 10 of the user manual suggests turning IS off for long exposures, otherwise "the stabilizer function may introduce errors." From my undertstanding, I don't think IS gives any real benefit once the shutter speed is below 1/15th of a second or so for a still shot.

Question 4 is probably another candidate for experimenting, especially with Milky Way type shots, but page 145 of the 5DIII manual, referring to Long Exposure NR, does state: "Images taken at ISO 1600 or higher may look grainier with the [Enable] setting than with the [Disable] and [Auto] settings."

This seems to be suggesting a ballpark answer.

I'm going to go back and experiment more with High ISO NR. I've had very good luck with cityscapes at night with Long Exposure NR, but I turned off High ISO NR two years ago and left it off, depending on Lightroom and sometimes Photoshop to deal with noise.

Here's a link, also to Canon USA, that puts a lot of nighttime exposure advice in one place, with a good reminder about mirror lockup: http://www.learn.usa.canon.com/resources/articles/2012/long_exposure_landscapes.shtml

Also explains Long Exposure NR a bit.

 

[Loswr]

High ISO NR is not applied to RAW files, nor is ALO. Long exposure NR is applied to RAW, with that setting the camera takes a dark frame after the exposure (a 40 s exposure means a 40 s dark frame), then subtracts the dark frame before writing the RAW file. That effectively removes hot pixels, but it can actually add random noise.

I'd turn IS off to save battery power during long exposure shooting.

 

[bjd]

High ISO NR is not applied to RAW files, nor is ALO. Long exposure NR is applied to RAW, with that setting the camera takes a dark frame after the exposure (a 40 s exposure means a 40 s dark frame), then subtracts the dark frame before writing the RAW file. That effectively removes hot pixels, but it can actually add random noise.

I'd turn IS off to save battery power during long exposure shooting.

Thanks Neuro,
I remember having Long Exposure NR switched on at one time in the past, and wondering why the Camera took progressively longer to save Images, in step with the exposure time...... A bit of reading told me it was exactly what you said that was being done.

Cheers Brian

 

[bjd]

But if you are seeing "very noisy" at ISO 100, I wonder if you are trying to boost the shadows too much in post processing?

Nope, I very rarely push the dark areas because of the noise, on some shots I zoom in to check how well focussed they are, and usually am surprised at the amount of noise I see.

Thanks for the links.

Cheers Brian

 

[heptagon]

To 3.:

The lens measures the movement of the lens and applies a counter-movement with a corrective optical element. This works well for medium-fast shake in the speed range of 1/10th-1/200th of a second. (Not sure if these are the actual frequencies where the IS works properly, it may be a bit more or less.) Ultra-slow and ultra-fast shake cannot be corrected by this method.

A problem is, that the measurement is error-prone especially in the slow-shake regime and it will move around the picture considerably in the order of seconds. (Just use 10x Zoom and push the Shutter button half-way to activate IS and see how the picture shifts around slowly.) Newer lenses switch off if they detect being mounted on a tripod - this may or may not work with your lens and tripod, so switch it off for long exposures.

You need a very sturdy tripod and a remote release and should use mirror lock-up to minimize camera shake.

 

[pedro]

High ISO NR is not applied to RAW files, nor is ALO. Long exposure NR is applied to RAW, with that setting the camera takes a dark frame after the exposure (a 40 s exposure means a 40 s dark frame), then subtracts the dark frame before writing the RAW file. That effectively removes hot pixels, but it can actually add random noise.

I'd turn IS off to save battery power during long exposure shooting.

Well, that is an intresting statement, Neuro. In my 5DIII Long exposure NR is set on automatic mode. As I do lots of night shots, would you recommend to switch it off? Thanks for your creative input on this.

 

[Loswr]

High ISO NR is not applied to RAW files, nor is ALO. Long exposure NR is applied to RAW, with that setting the camera takes a dark frame after the exposure (a 40 s exposure means a 40 s dark frame), then subtracts the dark frame before writing the RAW file. That effectively removes hot pixels, but it can actually add random noise.

I'd turn IS off to save battery power during long exposure shooting.

Well, that is an intresting statement, Neuro. In my 5DIII Long exposure NR is set on automatic mode. As I do lots of night shots, would you recommend to switch it off? Thanks for your creative input on this.

Auto means the camera decides whether or not it thinks there's enough noise to apply LENR. Personally I leave it off. Many RAW converters detect and remove hot pixels anyway. You can take your own dark frame to subtract other non-random noise. A good way to remove random noise (with static subjects) is to take several exposures and combine them (e.g. median layer blend in PS). Some recent Canon cameras implement that onboard as 'multishot noise reduction' (but I don't think you can get RAW output that way).

 

[pedro]

Thank you Neuro, for your expertise and sound advice.