I'm struggling to reconcile the recommended exposure times of a Holga 120 Wide Pinhole Camera as suggested by Holga, vs the values I am getting via an app like Pinhole Assist (or even when computing times from the EV captured by my Sekonic L-408 - which are in the same ball park as the app)

The specs of the Holga state that its aperture is f/133 (for a 0.3mm pinhole). And the film plane is 40mm/1.6" from the pinhole.

The Holga recommended exposures for ISO 100 is:

   Fine Weather 7-9 seconds
   Overcast     10-12 seconds 
   Morning/Dusk 13+ seconds

But when metering a +15 EV outdoor scene, both the Pinhole Assist app and my calculations give a shutter speed of around 1/2 seconds (which is impossible to accurately time anyway). This is so significantly different from the Holga value that it confuses me.

Can anyone explain why I am seeing this difference, or even if it is critical? (Or is EV 15 considered way more than a "Fine Weather"?)

I have only run 1 roll of film through the camera and haven't yet gotten it processed. But I want to feel comfortable that I am sort of in the right ball park before committing a lot more film to it, but also don't want to waste film/$$ characterizing the exposure of my camera.

And finally, yes I know it's a Holga (I also have a non-pinhole Holga 120 that I have used and enjoyed) and that part of the "fun" is that it isn't a perfect camera, but there is a difference between capturing something interesting and a negative that is either fully clear or totally black.

  • Starting with the 'Sunny F16' rule roughly extrapolated to F133 I get ~1 second exposure for ISO100 film in full sun. Reciprocity (depending on film) might double that. – BobT Sep 6 at 19:56
  • @BobT You should get around 1/2 second. f/128 is exactly six stops darker than f/16, upon which the Sunny 16 rule of thumb is based. EV15 is actually about one-third stop brighter than "sunny 16", so we usually base EV15 on 1/125 at f/16 with ISO100. – Michael C Sep 6 at 19:59
  • f/133 is only about 0.04 stops darker than f/128. – Michael C Sep 6 at 20:08
  • How far is the pinhole from the film plane in your Holga 120 camera? – Michael C Sep 6 at 20:17
  • I would expect the difference between fine weather and overcast to be about 3 stops (or maybe 2 or 4, depending on how "fine" is understood). With that in mind, and especially taking reciprocity failure into consideration, the difference between 7–9 seconds and 10–12 seconds just doesn't compute. I'm thinking Holga's values are way off here. – Kahovius Sep 7 at 17:55

Why would you commit any more film until you have had the first roll from any film camera developed? Get the first roll developed and see what it looks like.

If it's massively over or under exposed, then dedicate the next roll to test shots where you systematically start at a longer exposure and then decrease the exposure time about one-half stop each frame or two. Don't forget to write down the exposure times for each frame so you'll know what you did for the frames that come out properly exposed.

Doing it systematically for one roll will almost certainly get you where you want to be with less "wasted" film that trying to hit the nail on the head haphazardly for several rolls before you get lucky and hit it.

EV15 at ISO 100 and f/133 is around 1/2 second. This should be proper exposure for a brightly sunlit scene. The problem with calculating an f-number from the absolute size of a physical aperture to determine exposure with a pinhole camera is that "focal length" isn't exactly defined in the same way as it is with refractive lenses.

Having said that, most 120 cameras have more than 39.9mm between the lens board and the film plane. Does your Holga only have about 40mm (1.6 inches) between the pinhole and the film plane? That's the focal length that figures to f/133 with a 0.3mm entrance pupil (aperture).

Another consideration is that with an aperture that narrow, an appreciable amount of the light going through it will be scattered due to the effects of diffraction. Much of that scattered light will fall outside the area of your negative.

Don't forget that with film, any exposure longer than about one second or so will be subject to the Schwarzschild effect.

Most film manufacturers publish data sheets for each of their films that outline development times for shooting the film at different speeds as well as for developing the film when it is shot at the advertised sensitivity. They also include data regarding exposures longer than about one second (for most films) that are affected by the Schwarzschild effect, also known as reciprocity failure. Each film has different characteristics, and how much compensation must be made for long exposures can vary significantly from one film to the next.

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  • I understand reciprocity failure, but I don't think that it should come into play at a 1/2 s exposure. My question is more about Holga saying 6-7 s vs 1/2s - it's too much of a difference to hand wave away. The only thing in your answer that may explain this is the physics of a pinhole not matching that of a "real" lens. And yes I just measured 1.6 inches – Peter M Sep 6 at 20:16
  • Reciprocity failure is based on each film emulsion. But, yeah, for most normal 120 films it shouldn't be that much of an issue at 1/2 second. However, if the uncompensated exposure time calculates to, say, two to four seconds, then extending that to 6-7 seconds is fairly conservative for most films. – Michael C Sep 6 at 20:19
  • @PeterM I added a paragraph about the effects of diffraction with an aperture that small about the same time you posted your above comment. You may not have seen that. – Michael C Sep 6 at 20:22
  • I did see that. Also in a lot of images I have see online for this camera I have noticed a huge amount of vignetting. IMHO if diffraction was scattering the light inside the camera I wouldn't expect a lot of vignetting. (Although I might take that back in hindsight) – Peter M Sep 6 at 20:25
  • How thick is the material around the pinhole? The theoretical f-number = FL / ep diameter is based on assumption of the entrance pupil having zero thickness. – Michael C Sep 6 at 20:27

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