Can I just ask why so many people seem to use IOS 640 ? As far as i am aware, ISO sensitivity is better on all DSLR's at "standard" ISO's, 100, 200, 400, 800 etc, and intermediate ISO's are "pushed" in film terms from the lower full setting, therefore ISO 500 and 640 are derived from ISO 400, creating more noise than if the camera was set to ISO 800. Or am I incorrect saying this ?
I like 640 on my 1D3, 800 is a bit noisy in certain situations but if I need a shutter speed boost from 400 then 640 is ideal and certainly not as noisy as 800. I guess the results vary from camera to camera.
I am not sure your basis is correct - sensors are optomised for a single signal /noise ratio and everything else is a modification of that. Sensors have a base "iso" which used to be 100 but is now increasingly 200
Older DSLRS used to have curtailed iso ranges which could be expanded but effectively the manufacturers were saying we cannot guarantee image quality if you use the expanded range.
Hi actually all ISO's except the base ISO are amplified ( what you call a pushed ) the accuracy of the amplification varies between manufacturers canon being particularly inaccurate with there ISO settings of the intermediate values and also anything below base ISO you also have to remember when measuring the ISO that the cameras are set to 12 percent grey and not 18 percent as the is usual with film.
Also any settings in the high 1 and up range of ISO settings are designated that way because none of the camera manufacturers can guarantee a true ISO sensitivity and the high settings past designated ISO can be different from one camera manufacturer to another and even between the same manufacturers cameras.
Phil.
agree with steves original statement, i have always found the round numbers 100, 200, 400, etc to be lease noisey and was taught this by a certain talented guy on here, i was told to stick to the old scale as if you were buying film!
Being an old fogey, I date from film days, and am quite used to pushing film in the darkroom, and dealing with the consequent effects. I also appreciate what ISO actually is, and agree various manufacturers vary considerably, but as far as I am aware, they all lie within the designated standard, which is of course what ISO actually is, a standard level of noise to be attained within certain tolerances. I do disagree however that all ISO's are derived from ISO 100, as I have read in several paces that intermediate ISO's are derived from the next lowest full rating using a different algorithm and are therefore noisier than the next full step up, I posed the question as I have seen independant test results from various camera manufacturers which seem to back up my original statement. By the way, I have never used intermediate ISO's as i find the "old film" settings more than adequate for my needs.
Posted by David Taylor on March 31, 2010 at 8:14 AM
ISO 50 for me, despite the problems it can cause.
Sigma's advice
"This firmware upgrade provides users with the ability to capture images at low-noise levels. However, unlike the SD14's ISO 100 and above settings, ISO 50 has less headroom. This means photographers need to work a bit more carefully.
To use the ISO 50 setting for the best results, Sigma advises its photographers to pay attention to the following points.
* The ISO 50 is only available when the camera is set for Extended Mode.
* Please meter accurately when using ISO 50. The camera's built-in metering system will produce excellent results under most conditions. In high dynamic range settings, however, we advise using the center meter and taking a reading of the brightest part of the image. You can then adjust the EV by one or two stops to account for the brightness of that object.
* Sigma recommends using manual mode for shooting. In critical landscape settings where ISO 50 provides exceptional detail with little noise, we advise using manual (M) mode to shoot. Meter carefully and then adjust the settings after taking a test shot and reviewing the histogram.
* For subjects with a normal range, Sigma recommends using P, A, or S. Under normal circumstances, the camera will produce exceptional results using matrix metering and the camera's normal automatic functions. If conditions require it, you may wish to adjust the EV setting to -0.3 for a little more protection of the highlights.
ISO50 can provide the exceptional result with the fine details and the lower noise. We hope all the photographers enjoy shooting the high quality images at ISO50."
full incemental iso values are an electronic variation from that base point and optomised as best can be by the manufacturer
intermediate iso steps are taken from the lower full step and further modified, ie are not a separate full revision
The question posed is whether the incremental step modification is better or worse than the effect of a full Iso step
Sensors are not set to run at different Isos, if they were then there would in theory be no difference in noise between iso 100 and iso 1600 etc
experience would suggest the difference in generated noise between iso 400 and iso 640 is less than iso 400 and iso 800, otherwise as you say there is no benefit you may as well run the higher iso
David - iso 50 dynamic range is always worse than the base iso setting, you are always better off using iso 100 or iso 200 and using ND filters if the slower shutter speed of iso 50 is required - its a bit like RAW vs JPEG, base iso setting offers the best dynamic & range/signal noise ratio possible, (it always used to be an expanded range user option on early DSLRS as it fell o/s of the optomised iso range)
Hi there is no such thing as a standard level of noise, the only thing that can be measured is the full well capacity of each pixel and the resulting signal ready for amplification.
signal interference is a property of conversion and amplification as for the design standard there are several in use it depends which design standard the manufacture is using to set his ISO to
The amplification of the original signal can be set to give a precise equivalent film ISO settings it's just that some manufacturers don't think this is necessary and prefer to cheat its customers simply because they're too lazy or cheap to actually implement the correct amplification of the original signal and use a heavy-handed implementation with software within the camera.
Phil
Posted by John Robinson on March 31, 2010 at 9:05 AM
Interesting thread this. I always had my ISO on 800 for a couple of years. I never really had a problem as I usually had the contrast on low anyway to reduce the noise a bit, and never had the sharpening on.
I've just been out and done some quick tests with the contrast normal , I degree sharpening. on 400,640 and 800. I am having a hellof a job to tell the difference - especially between the 800 and 640.The diference in speed was 640-400th, 800-500th which could be useful.
jr
Posted by Andy Elliott on March 31, 2010 at 2:22 PM
This is going to be gear specific... I do recall that some cameras, if you choose ISO 640, say, will actually be using a sensor gain equivalent to ISO 400, then the output is scaled up AFTER analogue to digital conversion. This looks like ISO 640, but it is actually ISO 400 with reduced tonal range.
Other cameras can vary the sensor gain at these intermediate values - so ISO 640 really is ISO 640. I have also read that the auto-ISO on some cameras (some Nikons) can have steps smaller than this to optimise the exposure for a given set of fixed aperture and exposure steps, but they aren't visible to the user or in the EXIF.
Reply posted by Phillip Tomkinson on 03/31/10 at 2:04 pm BST
Registered on 07/14/05, 585 Topics, 1302 Replies
Hi there is no such thing as a standard level of noise, the only thing that can be measured is the full well capacity of each pixel and the resulting signal ready for amplification.
Surely there has to be some standard within certain tolerances, otherwise the term ISO has no meaning whatsoever. If there is no "standard" noise tolerance, why is it governed by ISO, meaning International Organisation for Standardisation ?
ISO 12232:2006 specifies the method for assigning and reporting ISO speed ratings, ISO speed latitude ratings, standard output sensitivity values, and recommended exposure index values, for digital still cameras.
Hi Steve the ISO is only the sensitivity value of the ccd/cmos after amplification of the original signal to a set standardisation /sensitivity as noise is completely random and can vary from a sampling rate of 1 to 2 bits in 12 bit and 2 to 4 in 14 bit this is why they can be no constant sets standard for noise, and only for the amplification of signal to a standardised ISO sensitivity, just because there is less noise at the lower ISO's only means that the signal was better before analogue to digital conversion, therefore containing less signal noise you also have to remember that noise can also be increased by the length of the ADC columns on the back of the censor and also signal degradation due to the circuitry within the camera.
Phil.
Ps of course I am more than happy to be corrected if my understanding is wrong
Discussion
12 repliesI am not sure your basis is correct - sensors are optomised for a single signal /noise ratio and everything else is a modification of that. Sensors have a base "iso" which used to be 100 but is now increasingly 200
Older DSLRS used to have curtailed iso ranges which could be expanded but effectively the manufacturers were saying we cannot guarantee image quality if you use the expanded range.
Also any settings in the high 1 and up range of ISO settings are designated that way because none of the camera manufacturers can guarantee a true ISO sensitivity and the high settings past designated ISO can be different from one camera manufacturer to another and even between the same manufacturers cameras.
Phil.
Sigma's advice
"This firmware upgrade provides users with the ability to capture images at low-noise levels. However, unlike the SD14's ISO 100 and above settings, ISO 50 has less headroom. This means photographers need to work a bit more carefully.
To use the ISO 50 setting for the best results, Sigma advises its photographers to pay attention to the following points.
* The ISO 50 is only available when the camera is set for Extended Mode.
* Please meter accurately when using ISO 50. The camera's built-in metering system will produce excellent results under most conditions. In high dynamic range settings, however, we advise using the center meter and taking a reading of the brightest part of the image. You can then adjust the EV by one or two stops to account for the brightness of that object.
* Sigma recommends using manual mode for shooting. In critical landscape settings where ISO 50 provides exceptional detail with little noise, we advise using manual (M) mode to shoot. Meter carefully and then adjust the settings after taking a test shot and reviewing the histogram.
* For subjects with a normal range, Sigma recommends using P, A, or S. Under normal circumstances, the camera will produce exceptional results using matrix metering and the camera's normal automatic functions. If conditions require it, you may wish to adjust the EV setting to -0.3 for a little more protection of the highlights.
ISO50 can provide the exceptional result with the fine details and the lower noise. We hope all the photographers enjoy shooting the high quality images at ISO50."
I think we are all coming to the same conclusion;
Sensors are optomised for a base iso100 or iso200
full incemental iso values are an electronic variation from that base point and optomised as best can be by the manufacturer
intermediate iso steps are taken from the lower full step and further modified, ie are not a separate full revision
The question posed is whether the incremental step modification is better or worse than the effect of a full Iso step
Sensors are not set to run at different Isos, if they were then there would in theory be no difference in noise between iso 100 and iso 1600 etc
experience would suggest the difference in generated noise between iso 400 and iso 640 is less than iso 400 and iso 800, otherwise as you say there is no benefit you may as well run the higher iso
David - iso 50 dynamic range is always worse than the base iso setting, you are always better off using iso 100 or iso 200 and using ND filters if the slower shutter speed of iso 50 is required - its a bit like RAW vs JPEG, base iso setting offers the best dynamic & range/signal noise ratio possible, (it always used to be an expanded range user option on early DSLRS as it fell o/s of the optomised iso range)
signal interference is a property of conversion and amplification as for the design standard there are several in use it depends which design standard the manufacture is using to set his ISO to
The amplification of the original signal can be set to give a precise equivalent film ISO settings it's just that some manufacturers don't think this is necessary and prefer to cheat its customers simply because they're too lazy or cheap to actually implement the correct amplification of the original signal and use a heavy-handed implementation with software within the camera.
Phil
I've just been out and done some quick tests with the contrast normal , I degree sharpening. on 400,640 and 800. I am having a hellof a job to tell the difference - especially between the 800 and 640.The diference in speed was 640-400th, 800-500th which could be useful.
jr
Other cameras can vary the sensor gain at these intermediate values - so ISO 640 really is ISO 640. I have also read that the auto-ISO on some cameras (some Nikons) can have steps smaller than this to optimise the exposure for a given set of fixed aperture and exposure steps, but they aren't visible to the user or in the EXIF.
Andy
Surely there has to be some standard within certain tolerances, otherwise the term ISO has no meaning whatsoever. If there is no "standard" noise tolerance, why is it governed by ISO, meaning International Organisation for Standardisation ?
ISO 12232:2006 specifies the method for assigning and reporting ISO speed ratings, ISO speed latitude ratings, standard output sensitivity values, and recommended exposure index values, for digital still cameras.
Phil.
Ps of course I am more than happy to be corrected if my understanding is wrong