Question for Zero 75B

<p>Hello everyone.<br />(sorry for my English)<br />I am new in pinhole photography. I got from my uncle the Zero Image 75B with 2 backs. The camera has 3 pinhole (in gold color) whith the numbers 25/50/75 and more 3 bigger pinhole (in black colors) without numbers. I don't know how to to find the diameter of pinholes to calculate the exposure and which pinhole to use. I post 2 photos from the camera.<br />Can someone help me?<br />Thank you.<br /> <img src="http://s3.postimg.org/9of4ynj6b/4b1318c4_dbf8_4fbf_b0eb_1bf9731595e7.jpg" alt="" /> <img src="http://s29.postimg.org/cftt5hvvb/DSC_0007.jpg" alt="" /></p>

<p>According to the Zero Image webpage, the 75B pinhole camera has the following pinholes: <br>

0.18mm (25mm) - f/138 <br>

0.28mm (50mm) - f/176<br>

0.35mm (75mm) - f/216.5<br>

<br>

And has these zone plates: <br>

25mm w/11 zones - f/43.25<br>

50mm w/21 zones - f/45.54<br>

75mm w/33 zones - f/44.7<br>

<br>

More details on the Zero Image webpage: http://www.zeroimage.com/Pinhole_Camera_45_2015_BTN.html</p>

<p>A mighty fine looking pinhole camera. I wish I had one, too! Have fun!</p>

 

<p>Hey thanx RT, <br />The zone plates for 75mm are 44.7, how can i caclulate it if they are 33 zones?</p>