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by garik

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I've decided to get back to using my Holga, and while in the past I've been happy with the the pics I have taken, I started thinking about how "accurate" the settings on the camera are. (Yes I know that you are supposed to accept what you get with this sort of camera, but dammit, I want to know!)

The camera is nominally f/8 or f/11 at 1/100s. But how would I prove this?

I can imagine using a light sensor to help measure the shutter speed by looking at the light profile over time, but how would you measure the f-stop?

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Isn't this question kind of against the spirit of a Holga? Setup a parallel shoot with a calibrated DSLR, and see what gets. Might need to shoot a moving object to see if 1/100 is not 1/50 or 1/250. But Holgas are supposed to be shoot and pray –  Pat Farrell Dec 30 '13 at 19:51
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@PatFarrell If I wanted to "Spray and Pray" with my photography I'd use a digital camera :P Learning the actual capabilities of my camera will help to improve my shots, but then again you will probably shake your head in horror when you learn a Cokin P series filter holder (of the appropriate size) slips quite nicely onto a Holga's lens. –  Peter M Dec 31 '13 at 22:18

2 Answers 2

Well, you could measure. Take a look at this article, where the author did just that. The conclusion as that the aperture is actually f/13, because there is actually a smaller hole in the light path which renders the aperture lever entirely meaningless.

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Thanks for that link .. and I just went and pulled the back off my Holga to take a look .. and went "Ooops .." as I discovered that there was a film in it. Hopefully I won't have lost too many frames (I seem to remember doing that once before and not losing much) –  Peter M Dec 16 '13 at 20:46
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Not sure about correctness of such measurements, aren't the light rays already concentrated at the described locations? Given the measurement logic in linked article, e.g. 200mm f/2.8 lens would be physically impossible for any 35mm mount since there isn't enough room in camera for fitting a 71mm light pole. Instead, the effective aperture, i.e. how big the aperture looks from front side of lens, should be measured. –  Imre Jan 29 at 13:27
    
@Imre That's really an excellent point. I'll have to dig out the holga I've got in one of the kids' toy bins and take a look. –  mattdm Jan 29 at 13:52

Even a cheap DSLR should provide a decent standard for the purpose of testing a camera like a Holga, which works on the t-shirt size (small, medium, or large) model.

Take a series of photos of a gray card or other reliable target with a camera that you trust, using a range of aperture settings. Take a series of photos with the Holga using whatever settings are available. Compare the results and pick the closest match.

You can measure shutter speed similarly. Find an object that moves at a constant rate, like a spinning wheel. Compare images taken with a DSLR at different shutter speeds to an image taken with the Holga, looking specifically at the length of the motion blur.

Another way to measure shutter speed, this time without the DLSR, is to photograph an object moving at a known velocity and measure the length of the blur. For example, you could photograph a ball bearing as it drops alongside a measuring stick. Knowing the starting height of the bearing, you can calculate the shutter speed based on the start and end distances.

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In theory I think you are on the right path, but without first isolating the shutter speed all you can compare are EV values and not f-stops. I also don't think that you could do the comparison with a digital camera, but you could do it by doing comparative densitometry between the same type of film stock in the Holga and a regular SLR - assuming you can trust the SLR :-) . (but your answer at least made me think it through) –  Peter M Dec 16 '13 at 18:27
    
@PeterM Fair enough -- added a couple thoughts on determining shutter speed with and without a DSLR. –  Caleb Dec 16 '13 at 20:34
    
BTW I have just seen an iPhone app that directly measures shutter speed. That actually may be a good start for me, –  Peter M Dec 16 '13 at 20:37

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