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In this review, there's this paragraph explaining f-stop and ISO equivalents:

The two aperture settings are marked with the sunny and cloudy symbols which equate to f16 and f8.0 respectively (set via Waterford stops). Some additional exposure ‘control’ is available by loading different speed film. Lomo says the Spinner 360° settings are based on using ISO 400 film so you could get f11 and f5.6 with ISO 200 film or f22 and f11 with ISO 800 film.

However, from what I understand about equivalents, this has gotten things backwards... It should be ISO 200 gives you f22 and f11 and ISO 800 gives you f11 and f5.6, because the slower film is equivalent to less light, therefore a smaller aperture gap (i.e., higher f-stop). Am I right here, or mistaken? If mistaken, could anyone offer a brief explanation?

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I believe it's saying that if you load say the higher ISO (800) film, you would be able to use the smaller aperture, hence less light (f22&f11) to maintain the correct exposure. Your way, you would be raising the light sensitivity by using the ISO 800 film, and also raising the amount of light (f11& f5.6), which would overexpose the image. –  forsvarir Jul 3 '12 at 13:37
    
@forsvarir — that would make sense if the camera had more aperture settings. –  mattdm Jul 3 '12 at 13:38
    
The camera only has the two aperture setting (f16 and f8.0) so when it says "get" I assume it means it would change the theoretical value of the aperture. Calculating what this be is what I'm trying to achieve. But thanks for your reply. –  negatron Jul 3 '12 at 13:40

3 Answers 3

up vote 2 down vote accepted

You can't change the aperture by changing the ISO. There's an equivalence for exposure, but the wording of the review is confusing.

Your understanding of how the equivalence works is exactly right.

The review may be trying to say what forsvairr notes in a comment — that (assuming constant shutter speed) to maintain the same exposure given by f/16 @ ISO 400 with ISO 800 film, you'd need to go down a stop to f/22. But since you can't with this camera, that really makes no sense.

Or they could be trying to say that using faster film gives an exposure change like opening the aperture but getting the numbers wrong. (Not to mention mashing the idea of stop equivalence into "aperture is exposure".)

I'd just ignore any parts of this review that include math. :)

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Thanks for your reply! You explain it well and it's good to know I was thinking along the right lines. –  negatron Jul 3 '12 at 13:42

The terminology in the review is pretty horrible but my understanding is:

the camera in question has 2 aperture settings (sunny and cloudy) which provide an exposure value that is roughly equivalent to f/16 or f/8 with ISO 400 film (with "somewhere between 1/125 and 1/250 second")

What they then try to say is that you can adjust the exposure from there by using a different speed film. Essentially, this is what you have to work with:

Shutter Speeds

variable (estimated between 1/125 and 1/250)

Aperture

Two settings (estimated to be f/16 and f/8)

Film Speed (ISO)

uses standard 35mm film (100 - 800), but only limited by what is available to purchase.

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The way I read it, it's saying to perform exposure compensation you have to change film speed, so by using ISO 200 film you get the same effect as if you were able to make the aperture smaller. However the review has the numbers the wrong way round, as you correctly observe.

I can't see any other way to make sense of the text.

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This is how I read it, and thank you for confirming my calculations! –  negatron Jul 3 '12 at 14:41

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