Sharpness and Exposure Question

[Mark Theriot]

Hi,
I've looked around but no luck. Also, I'm a relatively new photog and birder. Sorry in advance for the "rambling"!

As I've been trying to improve my shots over the past year, I recently moved to BIF shots and was terribly disappointed in most of my shots!! I've spent a lot of time fixing "me" and it certainly isn't the equipment!! I think I might have "fixed" one of my latest issues - would like your opinion.

I've been reticent to turn my ISO too much and have lived with images darker than I would have liked - not clipped to the left by any means - but darker. And I've been very dissatisfied with my "sharpness" in these cases. Now this Saturday I was blessed with great light and guess what - the pictures don't look too bad!!! (guess my camera is working now! :D )

I woke up Sunday to cloudy day and went to try something - less than great light, but I bumped my exposure comp and ISO up. Results, obviously not quite as good as with the great light but these were head's and shoulder's above my previous efforts!! Even with 800 ISO's it seems that I had "less" noise than ISO 200 shots that turned out under-exposed. And perceived sharpness was significantly better.

Am I safe to conclude that a good properly exposed image (maybe even a little more to the right) has the perception of much better sharpness (even with a higher ISO) than a a moderate to slightly under exposed shot (even with a lower ISO??)

Thanks in advance for the patience with my ramblings . . . learning is hard work!!
Mark

[Fabs Forns]

Proper exposure is the key element to avoid noise. As you experimented yourself, dark images loose whne brought up in p/p.
Keep reading the posts and critique and you will soon become a much better photographer.
We also have a lot of resources in the Educational Forum.

Thanks for you rmembership support and good luck!

[Charles Glatzer]

Hi,

Am I safe to conclude that a good properly exposed image (maybe even a little more to the right) has the perception of much better sharpness (even with a higher ISO) than a a moderate to slightly under exposed shot (even with a lower ISO??)

Mark


I think you are asking... if a slight increase in higher shutter speed is more important than properly exposing the image. In rare instances it may prove beneficial to under expose the image to increase shutter speed, depending on the shutter speeds in use, subject movement and your camera technique. But, I much prefer to expose correctly, increasing the ISO as necessary to render the image as desired. I am not hung up on ISO...to me a sharp well exposed image with a bit of noise is always better than a blurry one at lower ISO. Moreover, you may see greater noise, etc issues when trying to correct the under exposed image, than if you increased the ISO to intially gain shutter speed.

Best from Jasper

Chas

[Mark Theriot]

Thanks to both of you - the learning continues!

Including the fact that I should have posted this in the Education Forums!

Mark

[Daniel Cadieux]

Hey Mark, you posted his in the correct forum...Fabs simply wanted to let you know that there is lots of good stuff for you to read in Educational Resources :-)

[Kaustubh Deshpande]

Mark...I have been doing bird photography seriously for only 5-6 months now as well. I had similar dilemma as yours until recently. Now, on my 40D, with 400mm+ focal length, unless it is bright and sunny, I pretty much keep ISO at 640. In digital, as opposed to film, correct exposure means correct over-exposure :-) Make sure the histogram does not touch the right side (preferably all three channels) and you are good to go. Yes, at 100% I do see noise...but it does not look as bad when resized. And whatever is there, can usually be managed. I usually do NR only on the BG...on the bird, it does not look that bad....or rather it gets hidden in the plumage details.

KD

[William Malacarne]

There are several articles around that explain the "Expose Right", here is just one of them.

http://www.luminous-landscape.com/tutorials/expose-right.shtml

Hope it is of some help.
Bill

[Charles Glatzer]

Mark...I have been doing bird photography seriously for only 5-6 months now as well. I had similar dilemma as yours until recently. Now, on my 40D, with 400mm+ focal length, unless it is bright and sunny, I pretty much keep ISO at 640. In digital, as opposed to film, correct exposure means correct over-exposure :-) Make sure the histogram does not touch the right side (preferably all three channels) and you are good to go. Yes, at 100% I do see noise...but it does not look as bad when resized. And whatever is there, can usually be managed. I usually do NR only on the BG...on the bird, it does not look that bad....or rather it gets hidden in the plumage details.

KD

Why limit yourself to one ISO, and a 1/3rd value at that? Use the lowest ISO necessary to render the desired result.

Chas

[Kaustubh Deshpande]

Chas....I probably did not say it right. I use iso 320 and 400 a lot of times....esp. on bright sunny days. Or if I dont need to add compensation( white front lit bird etc.) But if a bird is in shade or the conditions are very overcast, with a 400+ f-length and no IS or tripod, I set iso to 640...rather have to...to get shutter speed that I can comfortably hand-hold the lens. In other words, that is, a lot of times, the lowest iso to get the desired result. If I had IS on my lenses, yes, there would be more opportunities for me to work at lower ISOs. Same if I used tripod as much as I should :-)

KD

[Emil Martinec]

There are several issues at play here. One is overall exposure -- the choice of shutter speed and aperture, which determine the amount of light the sensor receives. The other is the choice of ISO, which determines where various exposure zones of the capture fall in the range of RAW levels in the RAW file.

There are two sources of noise: One is noise from the light itself, so-called photon noise; the other comes from the camera electronics, the so-called sensor read noise. The photon noise is larger relative to the light level at lower levels of illumination; this noise is minimized by increasing the amount of light captured -- using a wider aperture, and/or lowering the shutter speed. It is the photon noise that we control better by increasing the exposure (Tv/Av) and letting in more light. Of course, this is not always possible -- we need a minimum depth of field, which sets limits on the aperture, and we need to freeze motion, which sets limits on the shutter speed. But given the choice of exposure, it's always better to let in more light. We lower the ISO to provide more headroom for increasing the exposure, and in so increasing the exposure we maximize the light signal relative to the noise.

But when shutter speed and aperture are limited, the total light capture is fixed, and so is the photon noise. The only thing left to control is the sensor read noise of the camera electronics. The electronic read noise is lowered by increasing the ISO, up to a point of diminishing returns that sets in about ISO 800-1600 for most cameras. This is why, when we need a minimum shutter speed or depth of field, we increase the ISO -- it lowers the read noise relative to the signal, at least the way cameras are currently designed. If the camera electronics were less noisy, the choice of ISO would be less important than it is. But to date, that is not the world we inhabit.

Suppose we fix the exposure (Tv and Av). What does changing the ISO do? It moves the histogram right (for higher ISO) or left (for lower ISO), but no more nor less light is captured. The only way that raising the ISO helps is if the camera does a better job capturing accurately the available light. In fact this is the case, up to a point.

The point of diminishing returns sets in about ISO 800-1600, depending on the camera. Virtually all Canons have this point at ISO 1600. There is almost no advantage to increasing the ISO above 1600 on a Canon DSLR; the read noise stops lowering relative to signal at this point, all that increasing the ISO past this point does is to chop off the amount of headroom in highlights for the histogram, by pushing it further to the right but not increasing the signal-to-noise of the capture. Underexposing at ISO 1600 yields very nearly the same result except with more room for capturing highlights.

So the bottom line is, increase the exposure as much as possible, and lower the ISO to provide the needed highlight headroom to do so without clipping the histogram. If shooting conditions limit the exposure, increase the ISO until the histogram at that exposure is pushed right as far as possible. The exception to this last prescription is that there is little to no benefit to raising the ISO beyond 800-1600 (depending on the camera), versus underexposing at this ISO and compensating in a good RAW converter. The latter choice will yield comparable noise but preserve more highlights.

[Jeff Donald]

That works fine, but doesn't take into account that ISO 1600 could result in too low a shutter speed and thus result in a blurry image due to camera movement or subject movement. All three components, Aperture, Shutter Speed and ISO play a critical role not only in exposure, but also the creative aspects of the image.

Once the aperture is wide open, the ISO will need to be raised to increase shutter speed to a level that allows subject movement and/or camera movement to be minimized to acceptable levels. The noise can be dealt with in software and via post processing techniques. People generally find a somewhat noisy image preferable to a blurry image, unless the blur is intentional and for creative purposes.

[Kaustubh Deshpande]

I will elaborate on my last note with an example. Lets say I am shooting a middle-toned subject like a Mallard female in overcast/ shade conditions. camera 40D. lens is 400 f/5.6 non-IS and I am not using a tripod. I set aperture to f/5.6. I dont want the shutter speed to be less than 400. I have two options

(a) iso 400. SS 1/400. 0 exposure compensation
(b) iso 640. SS 1/400 with +2/3 exposure compensation

I choose option (b) because of the subject and the conditions. I find it is better than '(a) + pushing in raw conversion'. In simple words, I prefer proper exposure to lower ISO.

What do others do when faced with this kind of dilemma?

KD

[Jeff Donald]

I think we're saying basically the same thing, just stating it differently. We agree that it is important to achieve the correct exposure (based on the histogram/expose to the right) in the camera. This means raising the ISO to obtain the correct histogram.

In my statement I go a little further by suggesting that if a shutter speed is not sufficiently fast enough to stop action the photographer needs to raise the ISO. In your example if I felt 1/400 was too slow to stop action, then I would raise the ISO to 1250 (from ISO 640) and thus the shutter speed would increase to 1/800. The exposure would stay the same, but I would have a faster shutter speed to stop action. The noise would also increase because of the higher ISO, but could be dealt with better in post processing than a blurry photo.

[Mark Theriot]

Great discussions, thanks everyone!

Mark