Diffraction Action: Six pinhole sizes at two distances from the image plane

One of the never-ending discussion points of pinhole photography has to do with the “optimization” of the size of the pinhole at a particular distance to the image plane. A basic assumption is that the bigger the pinhole, the bigger the spots it transmits and hence the smallest feature it can render.  Another basic idea is that wavy photons can turn a little when they squeeze through a too small hole and create a predictable pattern of fogging around each point. The visual effect of all this is usually described as sharpness.

Right away, I want to get out of the way the idea that sharpness and best are equivalent. Every pinhole has its unique character. Pinholes far from optimal can be used as artist’s tools, as well as other sharpness factors like pinhole shape and movement of the camera and subject. Sort of like the difference between a sharpened pencil and a stick of graphite.

But what does all this really look like? Let’s find out.

As with my experiment with pinhole materials, my subject was a little tableau under the fluorescent lights in the basement to remove lighting as a variable. In order to eliminate the variable of my clumsy craftsmanship, as well as getting out of drilling six precisely sized pinholes, I used Gilder Electron Microscope apertures. In my opinion they’re as good as pricey laser drilled holes. I wanted to try two different distances from the image plane and only wanted to invest one roll of film for my curiosity so I mounted (couldn’t get out of that) six of them, .075mm, .15mm, .2mm, .3mm, .4mm, and .5mm.  I used the 100mm and 45mm fronts for the Variable Cuboid to make it easy to switch the distances and taped the pinholes on the outside of the shutter to make them easy to change.

The film is TMax-100 developed in Rodinal 1:50. I used Pinhole Assist’s spot meter function to measure the cardboard top of the camera in the picture which looked to me like Zone 5 and went with the recommended reciprocity correction. I’m a little surprised the exposures came out so uniform, although there is a little variation and the scanner software has to put its two cents in. I tried to adjust them to match. Also, partly just to get out of it, I’m not going to touch up the dust spots, which will give some veracity to the sharpness of the scans but which creeps me out a little bit.

Don't jump over to Mr. Pinhole to see what the optimum is until you've looked at the pictures.

First the 45mm. Looks like the pinholes didn't get exactly centered in the opening.

.075mm pinhole, f600

.15mm, f300

2mm, f225

.3mm, f150

.4mm f112

.5mm, f90

Looking at the full image, it's hard to tell the difference between the .2, .3 and .4mm holes.

How about a detail at full resolution - here's some text and the label on the diagram in the left column of the encyclopedia. Each segment is 180 pixels wide. The full negative is 5000 pixels wide.

It looks to me like the .2 is just slightly more detailed than the .3. It's really obvious how diffraction reduces the image quality with the smaller pinholes.

Mr. Pinhole says the optimal diffraction is at .283mm, so maybe my habit of using smaller than recommended pinholes isn't so bad.

How about at 100mm?

.075mm, f1333.  Well, this is disappointing. This was a six and a half hour exposure. When I made the switch, I set down the 45mm front next to the scene. For some reason which escapes me now, I went down there to get it and seem to have managed to bump the tripod leg reaching over. There goes that data.

.15mm, f667

.2mm, f500

.3mm, f333

.4mm, f250

.5mm, f200

This time the .3 and .4 images don't look all that different. Let's go to the details.

This time I have to give it to the .4, but not by much. Mr. Pinhole says .422 is optimal.

One of the things that got me going in my post a couple of weeks ago was a comment that said, even with an optimal pinhole, the image is always going to be sharper with a shorter distance to the image plane, so let's bring back the 45mm set and maybe you can get both sets on the screen at the same time to compare them.

Even though I tried to capture the same field of view, there does seem to be some difference in scale, but I can't say the sharpest of the 45mm looks much sharper than the sharpest with the 100, even though the pinhole is half the size. Makes me think that diffraction is a bigger contributor to sharpness than the size of the dot projected by the pinhole. High f ratios and long exposures are better reasons to avoid longer cameras than sharpness.

Since the theme of this piece is diffraction, I thought it would be appropriate to put one of those "points" of light in the scene.  There was a lamp inside the camera shining through its pinhole.

A full resolution set at 45mm.

and at 100mm.

From this comparison, it looks like you can get away with a smaller than optimal pinhole close to the image plane, but diffraction seems to make that a bad bet for longer cameras. Maybe a little bigger pinholes on Long John Pinhole would be a good idea.

It's interesting to see how the disks vary on either side of the optimum and it's hard to tell the difference between too small and too large.

Another thing that the equations say is that the distance to the subject also affects diffraction. Where the shutter obscured part of the scene, that edge is rendered more sharply with the .075mm on the left than with the .3mm on the right.

My main take away is that there's a pretty good range around the optimum where it's going to be really hard to see the difference. If you're within a tenth of millimeter, it's probably good enough, so don't get too hung up about it and concentrate on all the other things that make a good photograph.

An evil cube template

Regular readers may have noticed that the camera I've used most often in the past two years has been the Evil Cube (6cm from 6x6cm frame). I've used it for Worldwide Pinhole Photography Days in 2017 and 2018, it went to Massachussets for my son's wedding, and it was one of the two medium format cameras I took to Europe last fall. I chose it when I went out into a blizzard recently.

It was made from cutting pieces of flat matte board and taping and gluing them together, sort of figuring it out as I went along. When I was loading it for Pinhole Day, I wondered if I could make a template that would fold and glue together like my other cameras so anyone could make one. I think I accomplished it. Here’s a link to directions to build this camera.

There's really no technical need to design a new camera.  The image format is exactly the same as a 6cm 120 Populist. But there's the issue of form factor.  When I made the Evil Cube, and the Glenmorangie Evil Cube and Compact 120 before it, my inspiration was an unreachably-expensive-in-my-youth medium format SLR. (Never mind that it's sort of the same form factor as a million mid-century Brownies, Hawkeyes, and Pioneers. I never had one of those either.)  I've recently seen a forum thread where the NOPO 120 was gushed over for it's similar shape, so I'm not the only one with this obsession.

As long as I was making a new camera, I thought I'd see if I could improve a couple issues.

The classic winders for a 120 Populist are 3/8" dowels with the ends shaped to fit into the slot of a 120 film reel, with an opaque collar glued around it to reduce the chance of light leaks through the winder holes, and with a WinderMinder over the collars to keep the winders from falling out, itself held on by a rubber band.  The problem is that the diameter of the dowels is a little small to give much torque when winding and your fingers can get really tired gripping that little thing.  I've been glueing them into the plastic cap end of a cork bottle stopper which works really great, but then you can't put a WinderMinder over it to make sure they stay put. I make my winders really tight and put tape over the tab to make them tighter in the slot, and that works, but it's a little bit of a kluge.  And the WinderMinder is a separate part that could blow away when you're reloading in the field.

The other thing that I wanted to play with was the rising front pinhole.  I got kind of interested in this with the Pinhole Lab Camera, and I recently found out the Reality So Subtle cameras have one. Recently, trying to minimize the impact of converging verticals with Stella at the Public Museum and the Paine Art Center made me wish I had this option. This may be considered trying to guilt you in to staying around and looking at the pictures below, but I really like the rising front pinhole.

The camera is made made from four main folded parts.  The image chamber and the film holder are first glued together to make the inside assembly.  You have to do something to keep your film reels parallel or your film is going to jam up.  In the Populists, it's a box just larger than the film.  In the original Evil Cube with it's triangular space for the film bay, I inserted some cut off nails through the bottom, but those are little parts that can get got lost. The simplest solution to me was a double layered piece of cardstock, the same thickness as the flange on the film reel, glued where the reel would be pressed when the winder was inserted into the top and held there firmly when the camera is closed. That should keep the bottom of the film reel from wandering.  It seems to have worked. (later edit: I subsequently made significant improvements to this.)

The film is loaded wrapped around the inside assembly.

This assembly is then inserted into the back, and the winders are inserted throught the holes and into the film reels.

The front then slides over the back in a gap between a collar and a cork stopper on the winders, which solved the problem of the winders falling out.

For the rising front, making a a pinhole that actually went up and down is way too complicated for me (another later edit: I figured that out too, but it takes more room), so I took the simple way out, two pinholes, one higher than the other.  It took me seven tries to get two identical pinholes at .3mm. I was a little disappointed to not get them a little smaller, but to entice you again, I don't think that's an issue with the pictures.

The rising pinhole is 15mm over the on-axis pinhole.  That was just a guess. It was far enough to make sure I could keep one covered while the other was opened. According to Mr. Pinhole, there's a 115mm image diameter at this distance, so I've got a little area to play with. It turned out to be a very useful rise, and I hardly noticed any vignetting.

For the shutters I just made one big really wide shutter, and cut the moving part in half. The over and under shutters open to the side, which ever handedness you prefer.

I really like the rising pinhole (or should that be The Risen Pinhole?)

All this is happening at f200, and moderately wide angle, 53 degrees. I think most people consider 80mm normal for this format.

So as is my wont, I went for a test on a bicycle ride around Oshkosh. This was my first experience with TMax 100 as well.

You knew I was going to start with the rising pinhole. The stone clad modernish Evangelical Lutheran Church on Church Street is connected to what I think is their older clapboard covered church behind it on Parkway.  This is the joint between the two.

Turning to the left, the almost-third-quarter moon was just barely visible to the right of the bell tower.  Despite getting some grey scale to the blue sky, I can't see a trace of it in the negative.  Anyway, how about those parallel verticals, and there's a seagull sitting on the left pylon if you zoom in to full resolution.

Next door, I couldn't get far back enough from the Morgan House to get the rising pinhole shot I wanted and kept getting the sun in one of the windows from that angle. So I thought, damn the converging verticals, I'll just point the camera up and use the on-axis pinhole. This is the only time I used it. Picked up a little flare anyway, and there's another seagull on the chimney.

The Public Safety Building is an equilateral triangle. Do you think they engraved those lines in the walls just to challenge me?  I was surrounded by police cars when I took this.

On the other side of City Hall, there's a hidden little courtyard with a table and bench between The Beach Building and a city garage, with this rather large tree kind of espaliered up the wall.

The back end of the Grand Opera House, with yet another seagull on the chimney.

I've tried to photograph this wall of the old Miles Kimball Building several times. Using a wide-angle camera pointing up making it look like it's falling over really distracted from what I want to portray.  Now with the rising pinhole, here's the left side of the wall.

Using the sidewalk to make sure I kept the camera parallel, the right side of the wall from twenty yards down.

And here's the diptych you're trying to imagine.

Sarah had an interview here once and described the interior as Dickensian. They used to hire artists to do drawings as piece work from a photograph of someone's house to put on Christmas cards. They're going to renovate it into an apartment building with a restaurant on the ground floor and a bar on the top. That should be a good place to take pinhole photographs. Here's the front of the building from the empty lot across the street.  It appears I didn't make sure my film was tight and I got a bit of a curve to the horizontals toward the top.  It's kind of funny that I was trying to be pinholey by waiting until a white car made streaks going by, but the camera upstaged me with the curvy film.  This combination of the view camera correctness of the verticals with pinhole funhouse cracks me up.  It looks like the building has a raised eyebrow.

This is the new "Sawdust" development area where an arena was built for a Milwaukee Bucks minor league team. The city is hoping it will spur all sort of hip development in what is a pretty blighted area. It used to be the factory district and there are still a few industrial buildings active in the area.

Restoration of the area is going slowly.

Just next door is this little brick building given a little bit of a Loony Tunes look by curved film again.

All with the new Evil Cube. two .3mm pinholes 6cm from 6x6cm frame on Kodak TMax 100 developed in Rodinal 1:50. Also with the Manfrotto Compact Advanced Aluminium Tripod extended out to it's full 66 inch height.

Nutcracker in the Castle

Over the holidays, our local art museum, a mansion surrounded by gardens, decorates with a Nutcracker theme, complete with acting and ballet.

In November, The Populist needed more tape, and I couldn't find the New Glarus Populist, when one day I was going out and thought I needed a 35mm camera with me so I grabbed the vintage PrePopulist, which has a 24x50mm semi-panoramic format. It had for some reason been stripped of it's shutter. I ripped the shutter off a 24x96mm camera I wasn't likely to use again and taped it on to the PrePopulist.  As it turned out I didn't take any pictures that day. When I got home I added some new viewfinders, and I ended up just carrying that camera around for two months.

Just before The Paine took the Nutcracker down, Sarah and I went over there so she could unleash the D750 on the decorations.  I didn't expect to take any pictures. Tripods are not normally allowed except by advance arrangement, so it's a pretty tough assignment for pinhole.  However, for the Nutcracker, they place a book stand in each room opened to a page from the story which is interpreted by the room decorations.  Under the book is a small shelf.  Just big enough to put a table-top tripod on.

The dining room is the Land of the Sugar Plum Fairy.  Too bad you can't see the outrageous pile of sweets on the table.  There is kind of a pinhole treat though.  The curved chair back overlaying the mullions of the window and a silhouette of the cake toppers look for all the world like it's being distorted by a lens.

The Breakfast Room, a glassed in porch, is the Land of Snow, echoing the view outside.

Mrs. Paine's drawing room may have been the dance of the flowers.

Another pinhole treat. All these little tree lights are a great model for diffraction.  For you fans of Lord Rayleigh, here's a full resolution crop which depicts the Airy disks that those equations predict.  n.b. .15mm Gilder electron microscope aperture, 24mm from the film.

The Chinese Dance takes place in the Great Hall.  The camera this time is on a handrail.  The trees to the left are just barely perceptibly rotating.

Upstairs they give up the ballet pretext and characterize it as the Stahlbahm family home. They don't have the books anymore, but each room has a freestanding lecturn with some text about the room that will hold a desktop tripod. Here in the sitting room I think is where she may have gotten the Nutcracker.

The parents' bedroom.

Mom's closet.

On the stairway landing is Herr Drosselmeyer's workshop.

The Gothic gallery overlooking the garden was originally built as a place for musicians to entertain guests in the Great Hall behind it below, but it never got finished. Now it's full of built-in cases to display objects, containing - what else - nutcrackers.

All with the PrePopulist. .15mm pinhole 24mm from 24x50mm frame.

Measuring pinholes with the Teslong USB microscope.

June 2019. When my university retiree account disappeared with a new change in policy, the pictures I uploaded to this blog while logged into that account disappeared. I'm working on fixing that but it's going to be at least a summer long project. 

If you follow me on Facebook, you may recall that I posted about a new favorite toy, the Teslong USB microscope. It's about the size of a pencil with a camera at the end that's held on a nicely adjustable stand.  There's a focuser on the other end so you can adjust it to various distances, and it has LED lights on the camera end to illuminate the subject. It's marketed as a microscope with up to 200 times magnification. (Just so you're not wondering about it, that's a .2mm pinhole at the right of the screen.)

In the comments to that Facebook post, Earl Johnson asked if you could measure pinholes with it. Well, since the magnification is a function of it's distance from the subject, which the device can't report to the computer, you can't tell directly what the size of anything is.

I usually measure pinholes with a scanner. Since the scanner knows exactly where the pinhole is and is scanning at a precisely known resolution, you can just read the actual size right off the screen.  The highest I can scan is 4800 dpi, which makes this .3mm pinhole about 60 pixels across. A bit of a problem is that the scanner software doesn't deal well with bright highlights and the pinhole is made from brass, so it tries to fix that and makes a way too high contrast image and it's often difficult to see just where the edge of the hole is. This example is better than most. Anyway, it works but it could be better.

I just happen to need a .2mm and a .15mm pinhole this week, so I got my brass, needles and emery paper out and tried to see what they looked like on the Teslong and see if I could measure them.

First I had to standardize some things. I wanted as much magnification as I could get, so the first thing I did was see how close I could get to something and still get it in focus. When you turn the focusing knob, you can feel stops at either end. So I put it at what I thought was its near point (lenses, ya know - by the way I just learned that term from Wikipedia) and then slowly pulled it away from the table until it was in focus.  That turns out to be about a quarter inch. It's pretty easy to get it set up to it's minimum focus repeatably.

200x magnification means movement gets magnified 200x too, so pointing is a little tricky. That swirly mark that's on the screen in the picture above was made when my drilling needle, which I was using to hold down the brass against the table, swept across the screen. Pretty exciting. By carefully moving it by nudging the base around you can get enough control moving it to find what you're looking for. The field is much less than that illuminated area, but it's possible to find the approximate center of the spot of light. You don't need the pinhole to be in the center, you just need it on the screen.

The camera uses the shareware video capture program VLC to display the image in a 1280x720 pixel window. VLC wants to capture video, so the easiest way to get a still image is to do a screen capture.

What I need now is a known object to compare my pinholes to.

I happen to have several sizes of Gilder EMS pinholes. They come in vials of 100, but Earl Johnson, I think, still resells small quantities for about $1 USD apiece.  I'll let him give you contact info in the comments if he wants to. Anyway, my stash includes some .2mm apertures - just what I'm trying to measure.

They look pretty good under magnification.

Selecting just the pinhole, it measures 100 pixels across (how convenient), so now I can measure with it and it's a little better than twice as sharp as the scanner  (recall that my scanner had 60 pixels for a .3mm hole).

I happened to have a pinhole that I recently measured with the scanner as .2mm, so I put that under the scope. I took the new image and pasted it next to the image of the Gilder aperture. I guess my measure with the scanner was pretty accurate. They're exactly the same size.  But, what you can see now is that around the edge of my homemade pinhole is a bit of fuzziness, probably dust from sanding off the burr on the exit side of the needle hole.

I bet some canned compressed air would get rid of it, but I don't have any of that. Blowing with my lips didn't do anything. So I stuck the needle tip in as gently as I could and spun it a little. That pretty much did the trick cleaning out the schmutz without enlarging the pinhole. Not bad. I think I'll use this one.

Now I've got to try to drill a .15mm.

I used my standard method for .15mm pinholes, drilling right against a hard table top, this time with the needle held in the eraser of a pencil.  Much to my surprise, it measured 75 pixels - exactly .15mm - and very clean with no fuzz. Two for two. I guess I'm starting to get the hang of this.

Both pinholes are now mounted on cameras so we'll see how they do when I get some film through them.

The Teslong seems like a pretty good deal for $41.