Another very basic Lens Rentals post - this one on ISO

Discussion in 'Beginner Questions' started by JDMvW, Aug 28, 2020.

  1. How disappointing. He didn't even mention "ASA"!:p
     
  2. Tony Parsons

    Tony Parsons Norfolk and Good

    Or Weston, DIN or even Scheiner.
     
    DavidTriplett likes this.
  3. ;)
     
  4. I appreciate the effort of these articles but would appreciate much more if someone explained how a modern (digital) camera actually takes an exposure reading.
     
    mikemorrell likes this.
  5. Don't forget our old friends Hurter and Driffield.
     
    Tony Parsons likes this.
  6. I like the way Zach Sutton has written and illustrated his 'fundamentals' series. I know people who have bought a DSLR or mirrorless system because they assume (or hope) that their photos are going to turn out better than with a cellphone. A percentage go on to take a photography course, read a few books on photography or watch a few videos. But not every camera owner does. The more widespread 'the basics' are published, the better. Just to let people know that not all photos need to - or can be- taken in 'full automatic' mode. What I like in this series (as in most books) is that photos taken with different settings are compared. So visitors can understand through visual examples what the differences are, rather than just (mentally) understanding the principles.

    Cellphones (and related apps) increasingly offer 'manual settings' when taking photos. So basic understanding of the exposure triangle is good for cellphone users too who don't always want to rely on the 'fully automatic' setting, however good it may be.

    In the first 2 'fundamentals' blogs, Zach mentioned the 'creative use' of Aperture and Shutter Speed. I missed the 'creative us'e of ISO in his 3rd blog. But, limited by the scope of a short blog post, he does it well.
     
    DavidTriplett likes this.
  7. That was not a bad, if necessarily brief, description of what an ISO rating is.

    Since he has already covered the creative use of shutter speed and aperture in previous articles, it would have been nice if he had at least made a comment about how different ISO settings affect shutter speed and aperture. If you're trying to take a portrait and you want very narrow depth of field, you want a lower ISO setting so that you can use a wider aperture.

    In answer to his question as to why one wouldn't simply always use the highest available ISO setting, all he mentioned was the increased noise at higher levels.
     
  8. I have some issues with this article.
    • First and foremost is the proposition that changing ISO changes exposure, it does not.
    • Related to that is that ISO changes the sensitivity of the camera's sensor, and technically it does not.
    • All this leads the the bad conclusion "...if you can shoot at a lower ISO, you should" offered at the end of the article, and that's wrong too.

    The exposure is the amount of light that hits the sensor, and the ISO is what is done with the exposure after it has been taken. The article offers examples of the "effect" of using higher ISO settings on a Canon 5D Mark IV camera, but what is ignored in those comparisons is that they are all taken using correspondingly different exposures. In point of fact, if you keep the exposure constant and raise the ISO as high as you can, or to put it the other way around if you don't do that and instead lower the ISO using the same exposure, then generally the higher ISO will offer a better result than the lower ISO (exactly the opposite of the advice offered in the article).

    To illustrate what is wrong with the conclusion offered in Sutton's article, take a look at this chart using the camera he used:
    Photographic Dynamic Range versus ISO Setting
    Now go to any ISO higher than 200 and hover your cursor offer it to see what the "PDR" is for that ISO setting. For example, for ISO 200 that is 10.36, then go one stop down and look at the next ISO setting, in this instance that would be ISO 400 which is 9.74; if you just underexpose by a stop then the difference in PDR should be one stop, which in this instance would be going from 10.36 to 9.36, whereas 9.74 is actually just over a third of a stop better than that. Ergo, if highlight retention allows it, you should use a higher ISO rather than a lower ISO.

    Why should a beginner care? It's a classic example of GIGO. Teaching a flawed premise at the beginning will result in flawed results later on when the beginner starts applying in practice the principle (in this instance, choosing the lowest ISO they can get away with because "...if you can shoot at a lower ISO, you should").
     
  9. You're correct, of course, increasing ISO doesn't increase exposure. It increases amplification of the signal. What he should have written is that it increases the mean brightness of the image.

    But I think your post after that is off-track

    Of course they are. That's exactly the point. If one has the option of reaching the same level of brightness of the image either by (1) increasing exposure, or (2) increasing ISO, increasing ISO will produce an inferior image. The reason is simple math: amplification amplifies everything in the data, noise as well as signal, and the second option produces a lower S/N ratio.

    Because beginners are trying to get the image to be the right brightness and need to learn that brightening an image by increasing exposure produces better results than brightening it by raising ISO. Choosing a higher ISO rather than a higher exposure results in lower dynamic range (shown clearly in the chart you referenced) and more noise.

    I go through this often with people who are starting night photography and use a high ISO. Their images are awful. I have to explain to them that they need to get a good exposure, which means a very slow shutter, instead.
     
  10. I obviously disagree, so when I wrote, "...what is ignored in those comparisons is that they are all taken using correspondingly different exposures."

    I'm not disputing that. However, where in the article is that stated? Perhaps I missed it or it's assumed based on the two previous articles I didn't bother to read.

    Regarding, "Why should a beginner care?"

    What happens when you run out of room to change the exposure at what you consider a desirable ISO and are faced with either holding the line at a lower ISO and pushing the Raw file during conversion, or biting the bullet and raising the ISO? You will be taking the wrong approach if you have the same camera as the article's author (Sutton) and you believe that "...the higher the ISO, the more sensitive your sensor is to light, but at the cost of more noise." As can be discerned from the chart I offered, raising the ISO can actually result in less noise, and while that can be counter-intuitive it is useful to teach a beginner why that can be the case.
     

Share This Page