sacrafice ISO or speed?

[forestgnome]

How do you decide which one to sacrafice? Assuming you don't want to alter your aperature and you have a still scene, what do you prefer to sacrafice when you need more light than your initial setting choice allows?

What are your thoughts specifically about ISO with a digital SLR?

I'm sure there are different ideas in different situations. Moderate thread drift welcome.

happy trails

 

[David Metsky]

With most current DSLRs, a small change in ISO isn't going to be noticeable unless you are making very large prints. Not true with P&S cameras, where anything above ISO 200 starts getting ugly.

 

[bikehikeskifish]

Here's an example of automatic exposure in a P&S (Canon A570IS) gone bad:

# Exposure Time (1 / Shutter Speed) = 1/640 second = 0.00156 second
# Lens F-Number/F-Stop = 71/10 = F7.1
# ISO Speed Ratings = 400



Trust me -- the full-size original is REALLY grainy (Click through and find the "full size" link to see what I mean.) I'm not sure what went wrong

Tim

 

[MichaelJ]

I'd recognize Canon ISO 400 grain anywhere.

As you say the question is why it did it. Did you perhaps have it on High Auto instead of Auto? Or one of the special shooting modes?

The Canon cameras will prioritize shutter vs aperture differently for fully-automatic exposure based on which of the various "modes" the camera is in, such as portrait, sports, landscape, etc.

Got the EXIF data?

 

[DougPaul]

IMO, every case is different.
* What camera are you using--different camera sensors produce differnt amounts of noise. (Newer DSLRs are generally much better than P&Ses and can be used at higher ISOs before the grain becomes an issue. Bigger sensors are also better--full frame is better than crop.)
* What is your scene like? Noise is more visible on smooth colors (eg sky) than on busy areas (eg leaves). Noise is also more visible on darker areas.
* What lens are you using--rule of thumb: you can handhold at speeds down to 1/eFL.
* Is your lens/camera body image stabilized (vibration reduced)? If so, use it.
* Do you have a tripod? Or can you brace yourself or the camera against something?

Also, take multiple shots of the same scene and pick the best one if you are shooting at a slow speed--the amount of camera shake can vary significantly between the individual images.

Doug

 

[bikehikeskifish]

Yes, I have the EXIF. I posted a fragment of it above. Here's the complete block, using exiftool. Actually, it looks like it was in aperture priority mode, which may explain it. I still don't get why it would push 400 and the shutter speed up to 1/640, rather than lower the ISO and the shutter speed.

My #1 complaint with the old A70 was the selector wheel was easily moved, especially pulling it out of a pocket. The A570 is not so easily fooled, plus I have an external pouch for it.

This may have been a fill-flash situation. I offer it for discussion and learning anyway....

ExifTool Version Number         : 6.66
File Name                       : IMG_0383.JPG
File Size                       : 2 MB
File Modification Date/Time     : 2007:11:11 11:41:28
File Type                       : JPEG
MIME Type                       : image/jpeg
Make                            : Canon
Camera Model Name               : Canon PowerShot A570 IS
Orientation                     : Horizontal (normal)
X Resolution                    : 180
Y Resolution                    : 180
Resolution Unit                 : inches
Modify Date                     : 2007:11:11 10:41:29
Y Cb Cr Positioning             : Centered
Exposure Time                   : 1/640
F Number                        : 7.1
ISO                             : 400
Exif Version                    : 0220
Date/Time Original              : 2007:11:11 10:41:29
Create Date                     : 2007:11:11 10:41:29
Components Configuration        : YCbCr
Compressed Bits Per Pixel       : 5
Shutter Speed Value             : 1/636
Aperture Value                  : 7.1
Max Aperture Value              : 2.8
Flash                           : Off
Focal Length                    : 6.6mm
Warning                         : Overlapping MakerNotes values
Macro Mode                      : Normal
Self-timer                      : 1648.4
Quality                         : Superfine
Canon Flash Mode                : Off
Continuous Drive                : Single
Focus Mode                      : Single
Record Mode                     : JPEG
Canon Image Size                : Medium 1
Easy Mode                       : Manual
Digital Zoom                    : None
Contrast                        : Normal
Saturation                      : Normal
Sharpness                       : Normal
Camera ISO                      : 400
Metering Mode                   : Evaluative
Focus Range                     : Auto
AF Point                        : Manual AF point selection
Canon Exposure Mode             : Aperture-priority AE
Lens Type                       : Unknown (-1)
Long Focal                      : 23.2mm
Short Focal                     : 5.8mm
Focal Units                     : 1000
Max Aperture                    : 2.8
Min Aperture                    : 8
Flash Bits                      : (none)
Focus Continuous                : Single
AE Setting                      : Normal AE
Image Stabilization             : On
Zoom Source Width               : 3072
Zoom Target Width               : 3072
Focal Type                      : Zoom
Focal Plane X Size              : 5.84mm
Focal Plane Y Size              : 4.39mm
Auto ISO                        : 100
Base ISO                        : 400
Measured EV                     : 8.59
Target Aperture                 : 7.1
Target Exposure Time            : 1/636
Exposure Compensation           : 0
White Balance                   : Auto
Slow Shutter                    : Off
Shot Number In Continuous Burst : 0
Optical Zoom Code               : 1
Flash Guide Number              : 0
Flash Exposure Compensation     : 0
Auto Exposure Bracketing        : Off
AEB Bracket Value               : 0
Focus Distance Upper            : 2.44
Focus Distance Lower            : 0
Bulb Duration                   : 0
Camera Type                     : Compact
Auto Rotate                     : None
ND Filter                       : Off
Self-timer 2                    : 0
Canon Image Type                : IMG:PowerShot A570 IS JPEG
Canon Firmware Version          : Firmware Version 1.01
File Number                     : 100-0383
Owner's Name                    : 
Canon Model ID                  : Unknown (0x2130000)
User Comment                    : 
Flashpix Version                : 0100
Color Space                     : sRGB
Exif Image Width                : 2592
Exif Image Length               : 1944
Interoperability Index          : R98 - DCF basic file (sRGB)
Interoperability Version        : 0100
Related Image Width             : 2592
Related Image Length            : 1944
Focal Plane X Resolution        : 11520
Focal Plane Y Resolution        : 11502.96
Focal Plane Resolution Unit     : inches
Sensing Method                  : One-chip color area
File Source                     : Digital Camera
Custom Rendered                 : Normal
Exposure Mode                   : Auto
Digital Zoom Ratio              : 1
Scene Capture Type              : Standard
Compression                     : JPEG (old-style)
Thumbnail Offset                : 5120
Thumbnail Length                : 4536
Image Width                     : 2592
Image Height                    : 1944
Aperture                        : 7.1
Drive Mode                      : Self-timer Operation
Flash                           : Off
Image Size                      : 2592x1944
Lens                            : 5.8 - 23.2mm
Scale Factor To 35mm Equivalent : 5.9
Shooting Mode                   : Aperture-priority AE
Shutter Speed                   : 1/640
Thumbnail Image                 : (Binary data 4536 bytes, use -b option to extract)
Circle Of Confusion             : 0.005 mm
Focal Length                    : 6.6mm (35mm equivalent: 39.1mm)
Hyperfocal Distance             : 1.21 m
Lens                            : 5.8 - 23.2mm (35mm equivalent: 34.3 - 137.3mm)
Light Value                     : 13.0

Tim

 

[David Metsky]

Since most P&S allow you to set ISO, and most P&S cameras in Auto will choose awful ISO settings, I never leave my camera in Auto ISO. I always set it at 80 or 100, and will bump to 200 if needed. If I'm in low light (indoors, night) I will choose 400 if needed and just accept that the shot will have noise.

 

[kmorgan]

Definitely try to use as much manual control as you can. I like to shoot in aperture priority mode for snapshots unless something's moving and I want to stop it. Otherwise I keep an eye on the shutter speed the camera is wanting to set and try to stay above 1/30 sec. Keep the ISO as low as you can all the time and use fill flash. If I'm just hiking in a group and want to take really quick shots I set my ISO on 100 or 200 depending on conditions and use my "P" program mode which is NOT fully automatic.

You can recover the photo with some noise reduction.

Kevin

 

[DougPaul]

I also generally use P mode on my digital cameras. This allows me to set the ISO manually. My DSLRs display the time and F stop so I can decide if I want to take manual control of one or both of them.

One P&S displays the time and F stop and the other does not. In either case, there is only a very limited range over which one can change them due to the limited range of F-stops for the lens.

Doug

 

[DougPaul]

You can recover the photo with some noise reduction.

Noise reduction, unfortunately, often (generally? always?) sacrifices some resolution.

Doug

 

[bikehikeskifish]

I usually follow most of these tips -- Use Av (aperture priority) and set the ISO low, and decide on the flash. Somehow, this one just didn't listen :roll: and was meant as an example of grain at higher ISO values, more than a "What did I do wrong". I know what's wrong with it. I'm not sure how I ended up that way, but it's only happened that one time.

Full manual is nice but when you're cold, wearing mittens, and have tiny camera controls, well, you take what you can get.

Tim

 

[MichaelJ]

Sorry, but according to the EXIF data you were not using auto ISO.

First of all, it won't go beyond 200 if it's set to auto ISO, unless you have "High ISO" set which you can only do in "P" mode, not in aperture-priority.

Second of all, if you'd had the camera in auto iso, then the "Camera ISO" field in the EXIF data would say "Auto" while the "ISO" field showed the actual used.

I just tested this on my own camera to confirm it.

 

[bikehikeskifish]

Good to know, thanks.

Tim

 

[NewHampshire]

Good question. For me there are too many vaiables. I generally give priority to aperture over ISO. But that can depend on the situation.

Brian

 

[Grumpy]

My general practice is to shoot using aperture priority and select the lowest ISO setting that will give me a shutter speed that works for the particular photo being shot.

That is a vague answer, but it's the best one I have without writing a treatise. And even then, what I wrote would have to be interpreted to fit your own particular style of working, expectations and tastes.

Back in the dark ages (or good old days, depending on your point of view) I loaded up my cameras with good old Kodak Tri-X black & white film, used an EI (exposure index -- same idea as ISO) of 1,000, processed the film in Acufine. This combo covered 80% of my daily newspaper shooting needs.

Digital is a different world, though. I find myself adjusting ISO frequently, now.

G.

 

[darren]

I'm in line with Grumpy. I shoot in AE (aperture priority) 90% of the time. I start at ISO 100 and set the aperture according to how much depth of field (DOF) I want in the shot. For a lanscape I will start at f16 and meter the scene (push the shutter button half way) and see what the resulting shutter speed is. If the shutter speed is fast enough to hand hold* then I shoot the shot. If the shutter speed is too slow then I reduce the aperture until I get a fast enough shutter speed. If I need to reduce the aperture significantly (resulting in not enough DOF) then I bump up ISO to 200 and try again. If it is still too slow then I bump up the ISO to 400 and try again. If it is still too slow then I reduce my aperature so I get a faster shutter speed and deal with the reduced DOF. I generally do not go above ISO 400 unless I have to (stop subject motion blur).

Note: I do not actually bump the ISO up and meter again. I just do it in my head. Doubling ISO speed cuts shutter speed in half at the same aperture. So if you need 1/60 sec for a shot and you meter the scene at ISO 100, f16, 1/15 sec then you know that you can go to ISO 400 and the shutter speed will now be 1/60 sec (1/15 *2 *2).


* Required shutter speed for hand holding is generally 1/focal length. So to hand hold a 100mm lens you need to shoot faster than 1/100 of a sec. Remember that most DSLR camera are crop cameras so a 100mm on a 1.6x crop body is a 160mm lens and you need to hand hold at faster than 1/160 sec.

Exceptions: even with a wide angle lens you need practice to hand hold below 1/60 of a sec. It doesn't too much practice though to shoot a 24mm lens at 1/20 sec. Also IS (image stabilization - VR for nikon) allows you to shoot 2 to 3 stops below the 1/mm guidance. (Yes, IS works)

- darren

 

[forestgnome]

Thanks for all thoughts. I notice noone mentioned a little trick that I do, which is to underexpose by 1/3 or 2/3, then brighten it a bit later. That allows a slightly faster shutter, all else remaining equal. Thoughts?

Much of my work happens in darkish conditions. I'm just looking for assurance that I'm not overlooking any tricks.

 

[darren]

Yah, I do that. It was called pushing in the days of film (ha, still is). You underexpose a stop (shoot 50 speed film at 100) and then tell the lab to push the development a stop higher to gain it back. You get some grain but you live with it if you need the speed.

I do that a lot on digital. I look at the histogram and use exposure comp to dial it down to the left end of the histogram. As long as you dont go off the left side you are not really losing data and you can gain it back in the computer later. Pixel peepers will say that it is better to stay in teh middle of the histogram or even towards the right side, but when you need to get the shot and you need the speed then stick to the left end of the histogram. Those pixel peepers spend too much time peeping and not enough out there actually making nice photos.

- darren

 

[Grumpy]

Thanks for all thoughts. I notice noone mentioned a little trick that I do, which is to underexpose by 1/3 or 2/3, then brighten it a bit later. That allows a slightly faster shutter, all else remaining equal. Thoughts?

Much of my work happens in darkish conditions. I'm just looking for assurance that I'm not overlooking any tricks.

While trick you describe here will work, in its way, it also puts the shadow areas of your image further into the underexposed zone. That is almost guaranteed to increase the image noise -- especially in those areas.

G.

 

[DougPaul]

Thanks for all thoughts. I notice noone mentioned a little trick that I do, which is to underexpose by 1/3 or 2/3, then brighten it a bit later. That allows a slightly faster shutter, all else remaining equal. Thoughts?

The ISO setting is just an amplifier (between the analog sensor and the A/D converter) gain setting. Using as high a gain as possible before the A/D is best because the quatization step (wrt the original image) is as small as possible.

Your trick simply increases the gain after the A/D conversion and because you are only using a limited part of the A/D range, you effectively have a larger quantization interval. This will lead to increased posterization (quantization in the image intensity) and decreased detail in the shadows.

Doug