help with some math please!

[aleks_biteman]

so i made a pinhole camera out of a kit today. and

the diagram says the times for iso 100 are 2-3 sec

daytime, 3-4 sec cloudy, 10 mins night, the

aperture is f/130 btw. I use 400 iso film. what

would the proper exposure times be? is there a

chart that goes to this extreme? thanks!

[Mattman944]

<p>400 ISO is 2 stops faster than 100 ISO, so you need to divide your times by 4 (2X for each stop). </p>

<p>However, this does not account for reciprocity failure. Their daylight exposure recommendation has included about 1.5 to 2 stops of reciprocity failure. So, it is more complicated than you thought.</p>

<p>Assuming no reciprocity failure, the correct exposure for daylight (converting sunny f16 rule) at f/130 and ISO 400 is 1/6 sec. You should have minimal reciprocity failure at this speed, so this should be good. Now you have a new problem, estimating 1/6 sec will be difficult.</p>

<p>Someone with more practical experience can probably help you more. </p>

[kris-bochenek]

<p>Just do 1 second. From 1/6th to full second is not that big of a gap and BW film has quite a bit of latitude. Simply put, open and close that will be about 1 second. Pinhole is fun. For more math and pinhole mental masturbation please visit. http://mrpinhole.com/</p>

 

[aleks_biteman]

<p>Awesome! thanks guys, this helps a lot! And I'll be sure to masturbate my pinhole knowledge lol.</p>

[john_robison3]

<p>There is a printable pinhole exposure online. It is on the Ilford site but I could not find where. Just type 'ilford pinhole calculator' into google and it will come up as the second or third item. It is a pdf file. You print it out, glue the sheet to some card stock, like cereal box card board. Then carefully cut out and assemble. </p>

[rdm]

<p>Also, you can always tape a piece of ND filter film over the pin hole if that would help you keep the exposure time up for easier guesstimating in daylight.</p>

[drew bedo]

<p>A front mounted shutter would be on solution. check E-Bay for lleaf shutters used in large format photography. . The oscilloscope lenses have a good enough shutter and can be inexpensive. Ubscrew the lens elements from the shutter and mount it in front of your pinhole.</p>

<p>Alternativly: Remove the glass as described above, and mount a pinhole into the shutter as Ansel Adams did.</p>

<p> </p>