Private ISO (part II)

As promised, part II of my investigation on ISO settings and their effects. I was a little bored looking at the bottle labels so I set up my chess board and decided to shoot the pieces under incandescent light, increasing ISO with a fixed shutter speed of 1/60s. Not only was there a significant effect on the apertures, there was a giant difference in depth of field AND in jpeg file size. Who knew?

I took a few shots and then cropped a segment out of each of the shots. So each shot has a full-size jpg and a cropped jpg. I went in to Windows Explorer and added columns for ISO, Exposure time, and shutter speed. I then moved the file time column to the end when I discovered ISO has a marked impact on jpeg file size. Here is a breakdown of the file details.


Notice the ISO 12800 file has nearly three times the size of the ISO 100 size. Also odd is the file size increases until ISO 1600, where it dips slightly and then keeps increasing.

For the results… ISO 100 and 200 appeared too dark, so instead of just doing 100 and multiplying by 2 each time, I increased the ISO until the aperture moved from f/1.4, which was at ISO 320. Therefore I also took all ISO values from 320, so 320-640-1250-2500-5000-10000.















According to my favorite online depth of field calculator the depth of field at f/1.4 for this shot, using the A77 and 85mm f/1.4 lens is about a centimeter. At f/3.2 or 3.5 I’m up to about 2 centimeters. At f/10 I get 5 centimeters, or about 2 inches of depth. So I start out with a very shallow depth of field and the higher the ISO at 1/60m, the greater the depth of field. So more detail at the expense of more noise.

Don’t we lose detail at the expense of noise post-processing? Absolutely we do. So an exercise like this helps find the “sweet spot” for a given situation. Take hockey, for instance. I’ve found on my A77 a good starting point is 1/400s at f/4 and ISO 400. I can raise ISO for more detail or open the aperture to drop ISO. If I want to increase my speed, I have to do it at the expense of ISO noise or opening the aperture.

F0r the shot above, I prefer the shots in the ISO 1250-1600 range. The depth of field blurs some of the game pieces out, while retaining enough detail without being too noisy.

I received my 70-300mm f/4.5-5.6 G SSM lens in the mail today. I shot 1-2 shots with the lens to make sure it worked OK. The SSM is super-quiet as expected, though it is way darker than I am used to. Here is the first shot (f/5.6, 1/2s, 230mm):


Next time I hope to show more of the initial results of the new lens. Until then, have a great night!

2 comments on “Private ISO (part II)

  1. Hi Joe, the change in filesize is interesting but probably a combination of two things I suspect; one directly associated with the ISO and one indirectly. JPEG compression works (or at least my limited knowledge leads me to believe it works) by saving in vectors – shapes – of colour. Therefore, the larger the shapes of colour, the smaller the file size. E.g. a photo of a black tile and a white tile saves a colour of white and a vector of wx and a colour of black and a vector of yz. As you boost the ISO though, you do get in increase in noise. The jpeg compression probably picks this up as a different vector to be saved, so as noise increases, so does the complexity of the image.

    The indirect impact is for the same reason as the above (the number of coloured shapes) but due to the increasing depth of field. At f1.4 you’ve got larger areas of creamy bokeh that are captured as single vectors. As you tighten down the aperture to say f8, there’s more detail and so again a great complexity to the image.

    I’m sure someone can blow all of that ‘knowledge’ to pieces, but I think it’s in the right direction!

    Re the 70-300, it is a surprisingly bright lens and it’s best feature is how sharp it is wide open. Whereas a tamron or sigma f2.8 70-200 might need bringing down to f4.5 before being sharp, this delivers straight away. A very nice lens, but that hood is huge isn’t it!

  2. Wow. That totally makes a ton of sense. I imagine the more detail combined with more noise means bigger files, in a rudimentary sense. I am thrilled about the brightness and the sharpness wide-open of the 70-300G so far. The lens hood is out of control, yes. It makes it look cool, though.

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