Keep Moving Forward… 08.09.10

A question of sharpness

Recently, a friend of mine commented on one of my pinhole photos. He said  it was interesting, but a bit blurry.

Blurry…

BLURY?!?

It’s not blurry, it’s soft!

It’s a pinhole image!

You should have seen some of my earlier work! Blurry…     😉

But like with all criticism, it behooves one to go back and take a look with fresh eyes, after all the image, to be fair, was hand held, for an exposure time of 0.7 seconds.

Canon EOS 7D, 0.2/40mm f/200 BCPH, 0.7 sec, ISO 12800. (35mm eqv. approx. 50mm)

On review there’s no noticeable motion blur, so… blurry?

Pinhole Softness

This begs the question. After all one person’s softness is another’s bleary eyed vision the day after the night before. So, in Pinhole Photography, what is considered an acceptable level of softness in an image?

We’ve been here before, right?

From all the guff that is out an about on the web, there are as may opinions on this as there are people taking pinhole photos. However universally, the larger the format, the sharper the image, but for each format, and at each focal length there appears to be, in general, an optimal sized hole. Or to put it another way, for each hole diameter, there’s an optimal focal length – distance between the sensor, or film, and the pinhole.

Now, the hole used for the above shot was a hand drilled, 0.2mm hole. The optimal focal length for said hole is 22.5 mm. Body cap mounted on my Canon EOS 7D the focal length (hole to sensor distance) is around 40 mm +/- a poofteenth.  So this hole is mounted 17.5 mm too far away from it’s optimal (sharpest) mounting point. Perhaps, that’s why this image may be considered a little soft.

So, I went ahead and drilled another hole. as far as I can tell, it is a 0.3 mm hole. It’s optimal focal length is 50.6 mm away from the sensor, but it is mounted 40 mm away from the sensor. That is 10.6 mm closer to the sensor that it should be. So the images should be a little sharper, yes?

Let’s see.

Canon EOS 7D, 35mm f/2.0, f/16, 0.5 sec, ISO 100. (35mm eqv. approx. 56mm)

This first image was shot using a lens to give us a benchmark for sharpness.

Canon EOS 7D, 0.2/40mm f/200 BCPH, 121 sec, ISO 100. (35mm eqv. approx. 55mm)

This next shot is with the same pinhole as the one used for the street scene above.

Canon EOS 7D, 0.3/40mm f/133 BCPH, 30 sec, ISO 100. (35mm eqv. approx. 55mm)

Can you see a difference? I’ll be buggered if I can. But looking at the piano name, perhaps… ?? I dunno.

However, not one to rest on my laurels, I still have one trick up my sleeve. These pinholes are mounted at 40 mm from the sensor inside a bodycap. This is achieved by using a plastic 35mm film canister cap. Removing this cap allows me to place the pinhole against the inside of the body cap. Giving an effective pinhole to sensor distance of around 48 mm! Which is 2.6 mm short of the optimal focal length. Well, that should be sharper than the others, right?

Let’s see…

Canon EOS 7D, 0.3/48mm f/160 BCPH, 30.0 sec, ISO 100. (35mm eqv. approx. 70mm)

I’m still not so sure… But, that Ladies and Gentlemen, is about as sharp as I can get it – short of gluing it to the front of the body cap…. hold that thought…

For today, that’s what’s in my

Line of Sight.

 

Addendum.

Did you hold that thought? An extra, approx. 2 mm increase in focal length, that’s 50 mm!  Which is 0.6 mm too short, and 0.001 mm in diameter too small – do you wanna hand drill that correction?

Canon EOS 7D, 0.3/50mm f/167 BCPH, 4 1/2 min, ISO 100. (35mm eqv. approx. 85mm)

…and on that note I’m not doing one jot more. The hole is good, the distance is almost optimal, dust can’t get in and I’m comfortable with the degree of softness that this produces, which is reminiscent of a soft focus filter.

Sunny 16 Exposure for ISO100 is 1.09 sec. When taking an exposure reading, I have to increase the exposure time by around 6 & 1/3 stops.

Alternatively, with lens on, I could up the ISO to 400, take a hand/palm exposure reading at f16, dial it in to Manual and lock in the reading, then Exposure Compensate by around +3 EV, and swap in the pinhole, before taking the shot.

For the grainy look at ISO6400 this translates into a very, very hand holdable, 1/60 sec +1/3EV exposure on a bright sunny day. Daido Moriyama anyone?

For today, that’s what’s in my

 

Line of Sight

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