How far from film should pinhole be?

<p>I know thats an open question but I would like to make a pinhole to use in an old and big camera. I am able to move the front and rear of the camera in or out and so can alter the distance between film and pinhole from about 18 inches to about 3 feet. I know depth of field will be huge at approx f512 but what about depth of focus? Camera back can take film up to 16x20 when fully extended. Could you give me a starting point as to what distance I should put the pinhole from the film. Thanks for any help.</p>

<p>The distance from pinhole to film is the focal length. I would try it first at 18".</p>

<p>Why not try it at several distances and see what works best for you? That was always my experience with much smaller pinhole camera.</p>

<p>I think that actually you can set the film where you want it, but of course, the further away, the dimmer the image and the longer the exposure.<br>

Wkipedia has a nice article on this topic (<a href="http://en.wikipedia.org/wiki/Pinhole_camera">link</a> ) and they say</p>

<blockquote>

<p>Optimally, the size of the aperture should be 1/100 or less of the distance between it and the screen.</p>

</blockquote>

<p>A pinhole has neither depth of field or depth of focus. Both are, essentially, unlimited. All distances from the subject to pinhole result in equal sharpness (or lack thereof).</p>

<p>For any given distance from pinhole to film, there is an optimal pinhole diameter. Diameters smaller than this result in a loss of sharpness due to diffraction. Diameters larger than the optimum result in a loss of sharpness due to insufficient "culling" of rays. According to the "Mr. Pinhole" pinhole camera calculator <a href="http://www.mrpinhole.com/calcpinh.php">(link)</a> ...</p>

<ul>

<li>18 inches: 0.035 inch, f514 </li>

<li>24 inches: 0.041 inch, f585 </li>

<li>36 inches: 0.050 inch, f600</li>

</ul>

 

<p>Joseph is correct. You could also check out <a href="http://www.f295.org">f295</a> website... great pinhole information.</p>

<p>Just been messing about with this sort of thing. As a 'cheapskate' I tried making my own pinhole, instead of buying a commercially available one. Check out the webbased sites suggested, they will give you info on 'optimum' pinhole size for focal distance. Make your pinhole, measure it using a flatbed film scanner, then set your focal distance to match the pinhole size - presuming you want maximum sharpness. I suspect getting hold of large negatives will be a problem. Or were you going to use pop? (not used that myself).</p>

<p>I made a spreadsheet to calculate optimum pinhole diameters using various formulas I found here on PN as a guide. In a little while it occurred to me that if one goes to all the trouble to base his pinhole diameter on a optimum size formula then it makes a lot of sense to get it dead on right! But how reasonable is this requirement for the hobbyist? Pinhole drilling techniques seem to depend on a repetitive process of bore an measure to reach any known size at all.</p>

<p>My next step was to make another spreadsheet using the same optimum pinhole size formulas solved to yield the optimum focal length for any pinhole diameter a person actually made. This approach seems ideal for Jim because it proposes that a pinhole camera builder start by selecting a reasonable size for the hole, and then tune the focal length of the apparatus to suit the actual hole mounted on the camera. His old camera would a good candidate for this approach because it is adjustable by design.</p>

<p>I should clarify my previous remarks to remove the idea that all one has to do is pick any old diameter for his aperture and then drill away.</p>

<p>Jim should note that the film he loads in his camera is always the size his film carrier will allow. That is, if he is using a 16"x20" carrier, then his film will always be 16"x20" no matter whether the bellows is extended or not. A bellows camera like Jim's allows one to observe the motion of the lens with respect to the film plane as he focuses on objects in various locations in his field of view. Jim's description of the mechanics of his camera being accurate, 18" is the position of the lens at infinity, and 36" would be the distance for focusing on the maximum equivalent of close up macro work the camera will allow. It makes sense for ease of use for pinhole work to use a focal length closer to 18" than 36". The thing to remember with an adjustable camera is that pinholes work best at a single fixed distance from the film. That is, once the best focal length is known to you, you must treat the camera as a rigid fixed instrument. 'X' marks the spot. Adjusting the pinhole away from this position will produce inferior pictures.</p>

<p>Also note that the optimum aperture for a camera this size is larger than the most common pins and needles in an ordinary sewing kit. However you can find ones that will work. Lord Rayleigh's formula for an 18" (457.2 mm) focal length, for example, yields an optimum aperture of .9528 mm (.0375"). A #4 sewing needle from Lance is .94 mm. Conveniently, an ANSI #63 drill bit is .037" in diameter, and an ISO Metric .95 mm drill bit is .0374" in diameter. Using one of these tools bore your aperture hole through a very thin metallic membrane.</p>

<p>This is where the focal length adjustment comes into play. IMO no matter how careful you are, and no matter how perfectly round your hole is, it will not be the .9528 mm in diameter Rayleigh says is best. Of course there is lots of room for hit and miss, but it would be better to be as accurate as you can in setting up the engineering so that when you take your actual pictures the only experimental variable will be the exposure time. At this point measure the diameter of the hole you made as accurately as possible.</p>

<p>Download the Kyoto Photo Press pinhole exposure field guide to use with your camera. Note that is has a circular scale with f/500 and f/720 marked on it. f/500 works pretty well. Say you made a hole exactly 1 mm in diameter. Now we will reverse the typical formula used in photography (focal length / f/stop = aperture) to get (focal length = f/stop x aperture). That is, multiply f/500 by 1 mm to find your new focal length, 500 mm in this example. 500 mm is 19.685" or approximately 19 11/16".</p>

<p>After completing this step make it a point to always read the exposure time next to the f/500 mark on your guide for your pictures.</p>

<p>19 11/16" works well with your camera and is, from Lord Rayleigh's point of view, an optimum pinhole setup. What's more, you have a convenient exposure guide to use with an ordinary light meter to time your exposure, noting that it is up to you to make the necessary reciprocity adjustment according to your film manufacturer's instructions.</p>

<p>Albert, thank you that is all very helpfull. I find there is quite a bit of conflicting information on size of pinholes; some saying the smaller the better while other places say too small causes curveature of light. I have made a 0.4mm pinhole but I think I will make a 0.9mm to try first. Before I try the pinhole I am going to try the lens that came with the camera. You may be interested to see my post regarding the camera of about 10 days ago in the large format forum "can I use a process camera" which has pictures of it.</p>

<p>Check out pinhole.cz. Download the app and install it. It is very useful and allows you to do many calculations in one place, basically everything you need, no spreadsheets required. ;)</p>

<p>As a matter of fact, a spreadsheet that I have, prepared by Robert Mikrut adn Kenneth A. Connors, states the focal distance for .4mm is 110-120mm while .9 gives 590-600mm.<br>

I don't think a small hole curves light but rather diffracts it.</p>

<p>I think the value of making your own spreadsheet for pinhole mathematics lies in the pleasure one gets from building a calculation engine that can handle all kinds of possibilities and at the same time clarify the principles that form the foundation of pinhole design. It's certainly not a prerequisite for building a camera, and if one has no interest in this sort of thing there are other good resources available. </p>

<p>I put ten different optimum formulas in my own spreadsheet, partly at least because I was curious about them, and, if I frankly admit it, because I have no idea which one of them is any better than the others. I also included an average of them all by reasoning that if each one of them is slightly wrong then all together they must be pretty near right! Applying this reasoning to Stephen's remarks in the last post, I find that for an aperture .9 mm, Connors optimum focal length is 598.44 mm, and the average of all the formulas I used is 545.67 mm. A basic principle that is implied in Stephen's remarks, but not explicitly spelled out, is that the focal length best suited for the pinhole you use must be within the travel range for the carriage in your camera, and if you build a rigid box like instrument, it must be as nearly dead on the actual hole to film distance a possible. In short, .4 mm is too small for your camera.</p>

<p>Clearly this illustrates the value of trial and error testing to see for oneself what works best. Who would have thought that getting advice on optimum pinhole size would turn out to be like advice one seeks on anything else in life! There are many authorities to sift through who say similar but slightly different things, often reflecting a sophisticated and very technical understanding of the problem at hand. The point is to simply pick one for any or no reason (The guy sounds like he knows what he's doing - I liked the article I read that incorporated Mr. X's formula, & etc.), and then carry it though to your camera. You can always repeat the exercise using another authority if you don't like the result you get after a few tries. </p>

<p>This is not to understate or diminish the actual effort and value found in the work of Lord Rayleigh, Kenneth Connors, and others. All of them have earned the respect of a great many pinhole camera builders because their formulas explain the unexpected idiosyncrasies found in an ordinary hole, and they work. </p>

<p>To pick up on albert's comments, to start with pick some numbers from some reference or other then do the trial and error thing - to see what works best for you. If you're not careful, you may end up chasing sharpness, spending and inordinate amount of time trying to 'get it right' - if all you want is a sharp image - stick a lens in! </p>