A technical query

[John Liddle]

My recent efforts with my new Sigma 150-300 highlighted the fact that when light conditions are not the best, you can find yourself making compromises to get a shot.

If one sets the aperture to give an acceptable depth of field and the exposure time to freeze the action (or minimise wobble), then the only variable left to get the exposure right is the ISO speed.

Here's the question - is it better to let the camera bump the ISO up to give correct exposure (and thus get more noise in the image) or is it better to keep the ISO down, get an under-exposed (but less noisy) image, and then correct (increase) the exposure in LightRoom?

Which route gives the least noise in the final result? Or is the end result the same?

[Swanny48]

Re: A technical query

My suggestion would be for you to experiment with both ways. Go out in dull light and use both methods on the same shot, to see what works for you. Different cameras and lenses may give different results.

John

[Richard W]

Re: A technical query

I don't know the true answer, but from my reading around on ISO etc., my understanding is that you shouldn't be too concerned about using high iso provided that you are within the "official" range and not going into the expanded range, which is really for emergency use only, or perhaps keeping one stop lower than the maximum official range e.g. with the 5D III you might go up to 12,800.
I'd avoid under exposure if there are significant dark/shadow areas in the image, as there will be very little light coming from them and hence any photon noise will be a relatively large percentage of the total which will be more enhanced when you lighten the image. Also there will be very little dynamic range in under exposed shadows, which might lead to posterisation if you try to lift them.

I might be writing nonsense though ...............

I think it probably is a case of try it and see.

[the black fox]

Re: A technical query

hmmm a hard one to quantify from my own recent experiences with the 80d modern sensors will happily shoot at very high iso ,and often noise is controllable in that scenario ,but a lot depends on the camera model,card type CF or SD does seem to make a difference . and sensor size itself also seems to impact on it .
again from recent experience i have now gone back to a far older camera and lost 14mp but seemed to have gained in general clarity of finished item .ask steve dawes why he shoots with a full frame 1DX rather than his 7d2 which would give hime twice the reach .
all sorts of factors come into play that only use and experience will know the answer to so the answer is ????

[ColytonJohn]

Re: A technical query

ISO performance is dependent on camera i.e. my 5D3 is pretty good while my 7D is rubbish. That said some night shots I tried recently with the 5D3 lifted the ISO into 12,800 and it was as noisy as a noisy thing yielding nothing usable. My understanding is that is you if overexpose there's nothing you can do to recover any lost detail so best to err on the side of underexposure where you may (that's an unqualified italicised may) be able to recover detail in post. I'd suggest, if circumstances permit, you bracket shots with a view to either select the best, HDR or layer.

Cheers,
John

[@imagesBV]

Re: A technical query

I think if you underexpose and then recover in post processing you'll get more noise....even at ISO100.
Overexposure makes for a better signal to noise ration.....so unless you blow highlights uncontrollably then thats the best bet.
The jpeg on the monitor will show blown highlights with a margin of safety such that you can recover some highlights that look blown on the LCD....must use RAW of course.

[H2OJunkie]

Re: A technical query

You are correct Brian. An under-exposed image recovered will exhibit more noise than a properly exposed image at a higher ISO in the dark portions of the image. Either direction you go (under or over) will create unusable data. Recovering underexposed images will result in high noise in the darkest spots and you will still not achieve an image that will compare with a properly exposed image.

Upper ISO performance depends on sensor size, not really the camera. An APS-C sensor will produce lower high ISO performance than a full frame sensor. A full frame sensor will produce lower high ISO performance than a medium format sensor. But each comes at a price. A medium format produces a huge image but due to that size, it is slow to write. It is more difficult to get fast frame rates from a medium format camera.

If speed is not an issue, then most SLR type cameras will produce quality low light images. But when speed is a factor, the only real way to go to have a reasonable expectation of both is full frame DSLR. Even Leica medium format cameras have heavy limitations that won't work for speed applications. But in slow speed photography (landscapes and portraits) medium format just rocks!

[El Sid]

Re: A technical query

I'm with H20Junkie on this... My experience of pulling up the exposure in post processing is that the noise is worse than an equivalent exposure made in camera at a higher ISO.

[John Liddle]

Re: A technical query

Thanks to all who have responded with their thoughts - despite the fairly firmly expressed view that bringing up shadows in LR creates more noise I must confess I find myself unconvinced about that.

I can readily see how increasing ISO in the camera introduces noise since you are merely turning up the gain of the amplifier associated with each pixel and as in any amplifier, more gain means more distortion (noise).

When raising the shadows in LR, you are increasing the brightness of the darker pixels, but it seems to me that you merely altering a number and it is hard to see how that introduces additional noise - it will make any existing noise more visible, but I don't see how it can add noise.

I shall have to experiment!

[Richard W]

Re: A technical query

The amount of noise is there in the image as soon as it's saved onto the card. Processing can exaggerate it, different from increasing it. But the main issue with underexposure is the lack of information in the shadow areas, if you try to lighten them too much they look ugly. The aim of exposing to the right as a technique is to avoid this by producing more information in the darker areas. Underexposure is, in effect, "exposure to the left" which will have the opposite effect. Of course, if the shadows are clipped through underexposure, there's nothing that can be done. Photography is always a compromise between ISO, aperture and shutter speed, I think it depends as much on the subject as anything else as to which compromise we make, a landscape photographer will nearly always want maximum dynamic range, not so important for wildlife or action where shutter speed will often be the priority.

[H2OJunkie]

Re: A technical query

Thanks to all who have responded with their thoughts - despite the fairly firmly expressed view that bringing up shadows in LR creates more noise I must confess I find myself unconvinced about that.

I can readily see how increasing ISO in the camera introduces noise since you are merely turning up the gain of the amplifier associated with each pixel and as in any amplifier, more gain means more distortion (noise).

When raising the shadows in LR, you are increasing the brightness of the darker pixels, but it seems to me that you merely altering a number and it is hard to see how that introduces additional noise - it will make any existing noise more visible, but I don't see how it can add noise.

I shall have to experiment!

You misunderstood me. Underexposure is what creates the noise. The more underexposed, the more pronounced the noise in the dark areas will be. Bringing those dark areas up in Photoshop or Lightroom will simply make them visible and the more the darks are brought up, the more visible they will be. You will get the least noise from a properly exposed image...