Re: confusion re: pinholga

I am interested in numbers, to some extent. YOur explanation below was
useful.

I got the prints back today from my experiment with 35mm film, and they
were fuzzier than my usual pictures with my other pinhole camera. The
focal length for the Holga seems to be about 30mm. According to this
Pinhole Designer software that I've been playing with, the optimal
pinhole for that focal length is 0.244 mm, which is f/123. I might try
enlarging the pinhole a bit to see what happens.

On the positive side, the velcro cap appears to work fine! Also,
shooting 35mm film in the HOlga was easier than I thought.

--shannon

On May 23, 2007, at 10:54 AM, Pinhole wrote:

> ----- Original Message ----- From: "Shannon Stoney"
> <shannonstoney@frontiernet.net>
>
> You seem to be interested in numbers, most people in this list aren't,
> nor they need to make good images. Nevertheless, I could send the
> "long answer" with numbers/formulas if you ask for it (meaning if you
> want it or need it), otherwise, bellow is the somewhat short answer to
> your questions:
>
>> The pinholga exposure guide on the website
>> (http://www.holgamods.com/pinholga/exposure/exposure.html) says to
>> multiply the f/64 reading by 12 to get the exposure time (and add
>> time as needed for reciprocity failure). But the Pinhole Designer
>> software (recommended on the Pinholga site and downloaded by me) says
>> that this pinhole diameter is f/199 and that you should multiply
>> f/64 by a factor of 10. It also says that this pinhole diameter is
>> optimal for a focal length of 20mm, not 40mm, as stated on the
>> holgamods site.
>>
>> So I am wondering: are my images going to be sort of fuzzy because
>> the pinhole is not the optimal size? And, should I multiply by 10 or
>> by 12?
>
> If diffraction didn't exist a pinhole would cast an image point about
> the same size as the pinhole diameter, this is equated to the
> geometric resolution of the pinhole. With that in mind and knowing
> diffraction do exists: an optimum Pinhole size is a compromise
> between a small pinhole that causes lots of diffraction but that has
> better geometric resolution and a larger pinhole that has less
> diffraction but also less geometric resolution. The pinhole size that
> Holga uses seems to be smaller than optimum, this will cause more
> resolution loss due to diffraction and at the same time better
> geometric resolution due to the smaller pinhole. If good resolution is
> what interest you, I think is better to err using a smaller pinhole
> than optimal than a bigger one, as IMO the geometric resolution has
> faster impact on the resolution of the image than some extra
> diffraction due to smaller pinhole. Should you multiply by 10 or 12?
> There are lots of factors affecting exposure "accuracy": focal length
> may not be 40mm as stated, pinhole size may not be exactly what
> Holgamods says it is, reciprocity corrections aren't perfect, your
> film ISO is exact and correct only for the manufacturer labs
> processing, your meter (if using one) maybe inaccurate, shutter is
> manually actioned, light conditions may change during a long exposure,
> etc. So again, Should you multiply by 12 or 10? It really doesn't
> matter, the difference between multiplying by 12 or 10 is just about
> 1/4 of a stop, which is negligible on itself and even more so when
> there are other factors, mentioned above, that also affect the
> "exposure accuracy" you seem to look for.
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Received on Wed May 23 10:43:28 2007