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I have a Fuji GW690 III medium format film camera. There is a ring on the lens where you select the shutter speed and the aperture. The lens is built-in to the camera, and is the 90MM f/3.5 version.

I noticed that most of the aperture settings allow a selection in between the standard aperture values-- e.g. the dial can come to rest between f/8 and f/11. I'll list all the in-between settings/values below.

I downloaded a PDF of the manual from butkus.org, but as far as I can tell, it doesn't explain what the in-between values are, or even mention this feature at all.

I'm assuming that these not-standard aperture settings are to get even closer to a recommended exposure using a light meter. If that's the case, I'd like to know what they actually are. For example, my light meter app has the values 9.0, 9.5, and 10.0 between the values 8.0 and 11.0. If I can select one of those non-standard apertures on my camera, I would like to know precisely which one it is.

Here's the list of in-between aperture settings:

  • 4 and 5.6
  • 5.6 and 8
  • 8 and 11
  • 11 and 16
  • 16 and 22
  • 22 and 32

What are the values of these in-between aperture settings?

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3 Answers 3

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Good question.

Short answer... it probably doesn't matter ;) Most film, and modern film workflows, have enough exposure latitude that if your exposure is out by a fraction of a stop, this becomes basically insignificant.

But, since you asked, there are accepted (rounded) ½-stop and ⅓-stop increments for the ISO scale, for the f-stop scale and for the shutter speed scale.

For f-stops, the standard ½-stop scale is...

full stop   -½-stop
1.0         1.2
1.4         1.7
2.0         2.4
2.8         3.5
4.0         4.5
5.6         6.7
8.0         9.5
11          13
16          19
22          27
32

The standard ⅓-stop scale is...

full stop   -⅓-stop     -⅔-stop
1.0         1.1         1.3
1.4         1.6         1.8
2.0         2.2         2.5
2.8         3.2         3.5
4.0         4.5         5.0
5.6         6.3         7.1
8.0         9.0         10
11          13          14
16          18          20
22          25          29
32

It might be interesting to note how this is physically implemented... When you turn the aperture ring, you are setting the aperture to any arbitrary size along the scale. They've just decided to incorporate detents at the full-stop and half-stop locations – but you don't actually have to use the detents if you don't want to. Again, I think it's not too important to worry about absolute preciseness here – who's to say that the detents are precisely where they are supposed to be?

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  • \$\begingroup\$ So I checked, and indeed, the in-between stops do change the aperture! \$\endgroup\$
    – user151841
    Commented May 6 at 1:03
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    \$\begingroup\$ Shooting on reversal (slide) film, half stops can be pretty useful, at least if the shutter speed can only be set in full steps. The wide exposure latitude you are talking about only apply to negative film. \$\endgroup\$
    – jarnbjo
    Commented May 8 at 9:15
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Early on, it was deemed appropriate to make exposure adjustments by tweaking the lens opening (aperture) via an incremental change that doubled or halved the exposing light energy.

The first practical method of adjustment was the Waterhouse stop, invented in 1858 by John Waterhouse. The lens barrel had a slot that accepted a flat plate with pre-drilled hole. This method was superseded by the modern adjustable iris diaphragm.

An opening change that grants a 2X change uses as its factor, the square root of 2 = 1.4. In other words, multiplying the diameter of the iris opening by 1.4 calculates the next incremental diameter that grants a 2X change in area, thus a 2X change in exposure. The inverse is to reduce the exposure by 2X by dividing by 1.4. The number set is: 1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 – 45 – 64.

The 2X incremental change was OK for negative / positive film photography. Color films demand higher precision, thus the ½ stop adjustment.

This is achieved using the fourth root of 2 = 1.189. This number set is: 1 – 1.2 – 1.4 – 1.7 – 2 – 2.4 – 2.8 – 3.5 – 4 – 4.5 – 5.6 – 6.7 – 8 – 9.4 – 11 – 13.5 – 16 – 19 – 22.

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    \$\begingroup\$ Worth noting that "positive film" (aka slide film, aka reversal film) does indeed usually benefit from increased preciseness around exposure. \$\endgroup\$
    – osullic
    Commented May 6 at 18:39
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The aperture adjustment on the GW690 III only has the full stops numbered. Similarly, the shutter speed is only numbered (selectable) at full stop intervals. However, the aperture can be set to 1/2 stop values (the in-between detents); or even in-between the detents.

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  • \$\begingroup\$ Hi Steven. Your answer doesn't seem to address the question whatsoever. The OP knows that 1/2 stop values can be set. The question posed is: "What are the values of these in-between aperture settings?" \$\endgroup\$
    – osullic
    Commented May 8 at 22:24
  • \$\begingroup\$ @osullic, your answer already gave what the 1/2 stop values are; I didn't see the point in repeating it. \$\endgroup\$ Commented May 9 at 0:15
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    \$\begingroup\$ Fair enough. Just thought your answer could be improved, considering you are getting downvotes. (Just to state - I didn't vote.) \$\endgroup\$
    – osullic
    Commented May 9 at 8:51

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