pinhole image quality

One of the nicest sites featuring pinhole images I've come across

lately is that of the Finnish photographer, <a

href="http://pinhole.galactinus.org/vilva/pinzin.html"><b>Veijo

Vilva</b></a>. He has a crisp, clean style, along with some excellent

graphic and web design skills. Vilva has also done some good work

with old, conventional cameras.<br>     In addition to

showing some nice images, the photographer also has provided some

thorough documentation of his work with the pinhole. I thought the

following passage about the results he got from a Zeiss folder

converted for pinhole use was particularly interesting as it indicates

that the pinhole to film distance can influence image

quality:<br><br><b>"The pinhole to film distance F is about 72m and

the pinhole diameter D = 0.3mm, which is optimal as calculated from F

= sqrt(D/750). The f-stop is 240. The angle of view is 42.5 degrees

both horizontally and vertically, and 57.6 degrees diagonally.</b>

<i>The photos taken with this camera aren't quite as sharp as those

taken with the Zero 2000 because of the relatively narrow field of

view</i>,<b> for F = 72mm the negative ought to be about 95mm wide to

get the same number of lines/negative width as Zero 2000 gets with its

F = 25mm. However, about 5" x 5" prints ought to be, for many

purposes, large and sharp enough, sometimes even larger prints will be

OK."</b><br><br>If I understand this correctly, Vilva is not talking

here about optimizing pinhole size to the distance from pinhole to

film plane. Rather, what he is saying, I think, is that moving the

same size negative away from the pinhole means that the given negative

format will intercept a smaller portion of the cone of light from the

pinhole, and thus result in a poorer quality image.<br>    

So, getting to some actual questions here: <b>(1)</b> Am I correct in

my interpretation of what Vilva is saying? and <b>(2)</b> Is Vilva

correct in his assertion about the relationship between film to

pinhole distance and image quality? A further assumption by me is

that such a relationship does not hold when one considers images

obtained through lenses of different focal lengths. I'm not very

smart about this sort of thing, so will appreciate some informed

opinions on these issues.

No expert here, and as soon as we start talking about wavelengths of light I leave the calculations to others, but I don't feel too happy about the logic in this quote. He's discussing the sharpness and presumably in the center rather than in WA areas of light fall-off. He seems to be implying that with the same pinhole at the same focal length, a smaller sheet negative will be sharper than a larger one. I didn't see any reference to light fall-off or refraction the text I looked at, which surprised me. But I may have misunderstood what he's driving at ...

<p>

Quoting from John Evans' book, <i>Adventures with Pinhole and Home-Made Cameras</i> ... "There is an optimum pinhole diameter for each focal length. (...) If hole size is increased above optimum, the image becomes brighter, but less sharp. When hole size is reduced below optimum, the image is fainter and also less sharp, due to the bending effects of diffraction."

<p>

However, Evans also writes that plus or minus 15% is perfectly acceptable and has no effect on sharpness - largely because the so-called 'optimum' is calculated using an average of the differing light wavelengths.

<p>

With my box, the focal length is 90mm with a 4x5" DDS, but 110mm when using a medium format Polaroid back. It was built that way because that's what I had at the time. The 0.4mm pinhole seems OK so far, though I can't run it through any test tougher than eyeballs.

<p>

I took this shot this afternoon - it's fast becoming a series of rear-window-through-the-seasons shots, started when I got back here last summer.

<p> <img src="http://d6d2h4gfvy8t8.cloudfront.net/3479719-lg.jpg"><p>

 

A 4x5 sheet of HP5, dev'd in Rodinal 1+25, at 24 degrees (run out of ice) ... I suspect using a different film or dev and temp would have had as much an effect on sharpness as a different diameter of pinhole.<div></div>

Disclaimer: I'm not a mathematician.

 

First off, his calculation is stated incorrectly: It should read D=sqrt(F/750), the inversive being F=D*D*750. This is based on emperical measurements by Chris Patton to determine an "optimum" pinhole size and focal length pair. See his page here: http://www.stanford.edu/~cpatton/pinholemath.htm

 

Take a good read of that page. It appears that Mr Vilva is mis-stating the information presented there.

 

He states in his page about the Zeiss folder that "In theory, the resolution is only about 0.58 times the resolution of a Zero 2000.", but where does he get this value from? The Zero 2000, with F=25mm and a film format of 6x6, is also not at the 'optimum' focal length for the format (42mm). The relative apertures of the two cameras produce this ratio (138/240=0.58, or 58%), but that seems hokey. This ratio should probably not be used to indicate the expected relative quality of the camera, but if his ideal aperture is 138 on 6x6 (based on his statements regarding the Z2000), it may be useful to himself. Your mileage may vary.

 

Finally, his statement about "lines/negative width" is a little bit cryptic, and perhaps misleading. By increasing the negative size to 95mm, you would decrease the *effective* focal length, but you don't decrease the *physical* focal length, so you don't change the aperture (aperture=F/D). You get a wider angle of view, and therefore more information on the negative, from the same pinhole, but it's still an aperture of 240, with all of the diffraction that goes with it.

 

Despite all of this, his pictures are good, and it's very interesting to see in the detailed scans that there are details on the negatives that are actually smaller than the aperture, which AFAIK shouldn't actually happen.

 

Thanks for the link, and a chance to exercise my brain a little bit! If anyone finds that I'm incorrect in any way, please let me know. I welcome the opportunity to learn.

dpi, natch. And one pass of the USM. <p>It was a high contrast scene. We're up to high-eighties fahrenheit ... rare enough in the UK.

Thanks for the excellent thoughts and examples. What the Vilva pages got me to thinking was that a box camera might not be the best pinhole platform if one is after sharpness as the typical focal length is around 100mm. However, in his examples, it seems like the excellence of his laser-drilled pinhole is more significant than the differences due to focal lengths. I'd certainly be very happy to get something like that picture of the chessboard done with his converted folder.

I gotta tell you - I have no idea what you guys/gals are talking about-

 

I take a tube, cut a hole in it ,cover the hole with a piece cut from a soda can with a pinhole in it ,and shoot(paper negs). My pinholes are fairly sharp but what I'm really looking for is distorsion.

 

I don't have a scanner,but I'm trying to get one hooked up. the problem is I shoot mostly 11X14 in a 6" tube.I have an old scanjet 4C,that's 8 1/2 X 14 , I don't think it's compatable with Windows-XP, but I know large format guys use the 4c for 8X10 contacts.

I might have to break down and buy a *new*(gasp) flatbed/film scanner.

 

btw- here's a good thread on pre-flashing paper negs- if you've ever priced 11X14 film-well you know-

 

 

http://spitbite.org/pinhole-discussion/2004/0411/0800.html

Don, I'd be very interested in seeing some of your images. Sounds like you've come up with a system that works for you. One of my problems is that I don't have the patience for one-shot cameras. I want something that will take a roll of film, and which also has a shutter and a tripod mount. My box camera conversion is fine on all those counts, but I'm thinking the focal lenth may be too far from the ideal for 120 film which appears to be around 45mm.

Mike -I know what you mean about one shot camera-pain in the azz.I have an Argoflex that I turned into a pinhole,but the problem is enlargement-after 2X the quality fades. I have 4 pinhole tubes,8X10 and 11X14,but I've found that post 911, It's better to keep them in the stix,than the city. I Usually bring an slr, a rangefinder,and a pano with me when I go out,if I get 1 or 2 pinholes,that's OK.Even using paper,one 11X14 print(2 sheets) costs as much as a whole roll of 35mm.You gotta use a large format mentality.

btw-Mike-

 

I think? one of the main ingredients to pinhole sharpness,is the curvature of the film/paper.If you hold the pinhole up to bare lightbulb and see how the strands? of light come through it you'll see how a flat film plane will be effected negatively.(no science,just an intuitive guess)

Mike,

 

Forget "ideal" and build it. Give it a try, and if necessary try different pinhole sizes. If you can't get it right, buy a beat up folder and try again. You could even remove the bellows and door, and build a plate that mounts flush with the body for something super wide like the Zero 2000 (probably around 20-25mm). On 6x9, that'd be fun!

 

BJ

<i>...You could even remove the bellows and door, and build a plate that mounts flush with the body...</i><br><br>I'm leaning in that direction. I believe claudia % has illustrated that possibility recently.

Claudia % did a few months back ... with an Agfa Billy Clack.

Here's the link to Claudia's camera: http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00AuSO

This should have been different, but I misread the light. Whatever - I cut a new pinhole this afternoon and wanted to try it close-up. This is about half the 4x5 FP4 negative and it's sharp. The pinhole came in exactly at 0.36mm. Sharpish.<div></div>

That's an excellent image. I bought some new materials yesterday, so will see if I can get close to that kind of sharpness.