Base sensitivity?
Was reading elsewhere about the 'base sensitivity' of a camera. After some thought about what it could mean, it struck me that the sensor in these cameras is perhaps 'optimized' for a particular ISO or ISO range. Now, I know that higher ISOs use amplification to get the higher ISO, but it never really occured to me that they were amplifying above a 'natural' ISO that the sensor has.
It seems to me that this would mean that the sensor in our cameras has an ISO that uses the smallest amount of amplification as possible, and this would be the base ISO. If this is the case, it would make sense that all things being equal, we should set our camera to this ISO.
There are many occasions where there is plenty of light, and I have no real preference for ISO on those occasions. Having spent so many years shooting 200 speed film, I leave my camera on ISO 200 out of habit. But perhaps I should leave it at 100 or 400 or some other number?
Does anyone have any hard facts on this? Is it true or hogwash? If true, anyone know the 'base sensitivity' of the Canon XT, or recommend a preferred ISO setting?
It seems to me that this would mean that the sensor in our cameras has an ISO that uses the smallest amount of amplification as possible, and this would be the base ISO. If this is the case, it would make sense that all things being equal, we should set our camera to this ISO.
There are many occasions where there is plenty of light, and I have no real preference for ISO on those occasions. Having spent so many years shooting 200 speed film, I leave my camera on ISO 200 out of habit. But perhaps I should leave it at 100 or 400 or some other number?
Does anyone have any hard facts on this? Is it true or hogwash? If true, anyone know the 'base sensitivity' of the Canon XT, or recommend a preferred ISO setting?
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http://www.chrislaudermilkphoto.com/
I thought I read somewhere that on some cameras ISO100 can give you soft images, even if you have easily fast enough shutter speeds. Maybe it wasn't soft images, but I was thinking there was somethinga bout 100 that people have said happens soo a lot of people use ISO200 instead as a base.
Anyone know anymore about this?
Interesting. I have never adjusted ISO in that fashion.
Perhaps it is my film education, but with film, you were stuck with the ISO of the film unless you wanted to get fancy with pushes. I can't really see a situaton in daylight where adjusting ISO will deliver the only combination of shutter speed and aperture I need...afterall, what is the difference in 1/250 and 1/500 for most subjects? Likewise f/4 vs f5.6 or perhaps f/16 vs f/22 is not that big a difference for most compositions (not all). So it seems to me that at a given ISO, there is enough range for my creativity, so picking an ISO is not as critical.
Of course in low light situations, ISO is critical, but I suspect that any higher ISO is utilizing amplification to a high degree, which is why you see a difference in many camera models at high ISOs: the sensor and software are the difference.
Likewise when I was shooting an event at a club this weekend. Between bands the event organizer would get on stage, raffle off a few items or give a spech, and I was able to shoot those at iso 800 because the main stage lights were pretty bright. But when the bands were playing, the lights were a lot lower, so I had to shoot at much lower isos to get the shutter speeds I needed for sharp images.
But if the bulk of your shooting is street scenes under bright sunlight, then iso 100 should give you all the flexibility you need. Hadn't heard about the softness issue with iso 100, but I haven't experienced it either. I'd be keen to read more on it, however.
Canon 40d | Canon 17-40 f/4L | Tamron 28-75mm f/2.8 | Canon 50mm f/1.8 | Canon 70-200mm f/4 L
The following link hints what is going on:
http://www.clarkvision.com/imagedetail/evaluation-1d2/
While this particular examination deals with the imager in the Canon 1D MKII, other imagers are probably similar. Understand that the 1D MKII starts out with an expanded DR (over almost any other imager), so don't apply these figures to any other imager directly. The Canon 1D MKII and 1D MKIIN are really very special cameras, and it appears that the 1D MKIII may be even better.
Look especially at the "Table 1a: Canon 1D Mark II Read Noise and Dynamic Range".
The numbers show that while the ISO 50 improves the signal to noise, dynamic range suffers fairly significantly.
In the concluding comments, it is noted that an ISO 75 would be almost ideal for the 1D MKII, with no significant compromise to DR while improving SN. What this means is that at ISO 100, images can be slightly under-exposed and still perfectly recoverable. It also helps to explain why image detail is still discernable in the shadows of a low-ISO image to a greater degree than other imagers in other cameras.
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It's a slightly different mindset in digital. ISO is now a third parameter to go along with shutter and aperture. Often it doesn't make a difference, but can allow for some expanded choices of shutter and aperture--and of course as lighting conditions get more extreme ISO becomes a bigger issue. It's this third-parameter concept that gets many of us Canon users whining about how ISO is adjusted and displayed on various models.
I have not heard about the softness issue, and haven't really noticed it on my 20D.
http://www.chrislaudermilkphoto.com/