Sharpness & the Circle of Confusion


Spoiler alert: I am, by no means, a nerd. But what you are about to read falls into the nerdy and boring side of me.

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If you followed my previous posts, you had probably read about my newfound passion for the Epson R-D1x.

The R-D1x is a vintage digital camera that I bought mainly out of curiosity and as a camera collector. I thought after a couple of days using it and writing this review in my blog I’d leave it in the drybox for good due to its outdated low-res sensor technology.

Surprisingly though, this is not the case and I madly fell in love for the R-D1x and its pureness.

And now I’m seriously into having the R-D1x as my legitimate everyday camera, the one that will follow me everywhere. Only that things are not ready yet and time is needed to fully sort out the particulars. I’m not in a hurry though. Sometimes, even time needs time.

Specifically, with the R-D1x I’m dealing with a focusing problem. I’m a bit confused because most of the times I’m able to get sharp images and the rangefinder mechanism seems to be accurate.

Yet I’ve noticed within certain distances the camera just fails to focus accurately. My target becomes blurry and, instead, the back plane is in focus. It’s frustrating.

It’s clear the rangefinder mechanism needs to be re-calibrated but, guess what. This camera is discontinued and I’m not sure if Epson is still supporting it. Maybe I could send an email to Epson in Japan and ask them? Yeah, but maybe not.

Circle of Confusion

So I started researching the internet to see if I could fix things by myself. I learned about the basics of rangefinder triangulation. And came into this article about the Circle of Confusion  – a funny sounding scientific definition.

In case you had never heard about the Circle of Confusion, below is a description from Wikipedia:

“In photography, the circle of confusion (CoC) is used to determine the depth of field, the part of an image that is acceptably sharp.

Real lenses do not focus all rays perfectly, so that even at best focus, a point is imaged as a spot rather than a point. The smallest such spot that a lens can produce is often referred to as the circle of least confusion.”

Diagram showing circles of confusion for point source too close, in focus, and too far.

“A standard value of Circle of Confusion is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement.”

Sharpness & our obsession towards it

The visual acuity part of it is what really intrigued me and prompted me to write this post.

I’ve always held the opinion that nowadays we are too obsessed with sharpness. To the point that we tend to describe a lens or camera sensor as sharp only after we assess results at the pixel level, which is ludicrous because this is not the proper way to enjoy a photograph.


Sharpness will not give you a good photo. And a good photo does not need sharpness. I know this is a cliché, but I had to say it to make things clear.

The very definition of sharpness is in fact blurry in itself. What is sharp or not depends on your own visual acuity, the size of the image and, if you ask me, your brain as well.

Sometimes what you see is not really what you see, but what your brain is telling you. This is why, back in the days, my knowledgeable Drawing Professor at the university would to tell us, when assessing our sketches made out in the streets of Oporto:

“Don’t you draw what you know. Draw what you see instead.”

Because we would add details in our sketches that, in reality, our eyes would not be able to see at far distance, like the contour of a leaf in a tree. But most of us would draw it, because we know it’s there.

Getting closer to photography now, take white balance as an example. In our everyday routine, we experience different colour temperatures when we switch to different spaces. But what we perceive as white will always look white to us – even when it’s not.

Under a tungsten light bulb, you will see a white sheet of paper and that piece of paper is white to you – because this is what your brain knows and what your brain is telling you. Even if, in reality, it is yellow because it’s being lit by a tungsten light bulb.

Back to sharpness

We all have our own Circles of Confusion. Apart from our own visual acuity and the size of the image, to some extent it’s really up to what our brain is telling us.

If the subject of the photo is captivating in itself, if it’s attractive to you, then spot-on sharpness may not be needed because your brain will work out your own Circle of Confusion and help you achieve the acceptable sharpness. You can even close your eyes and see it sharp.

This may sound a lot of rubbish to you, but frankly I’ve been going through some photos I took of my little girl with the R-D1x over the weekend and, from this perspective, I’m most happy with the levels of acceptable sharpness I’m getting.


Does all this really solve my R-D1x focusing problem? No. Because I’m still getting some blurry images at certain distances which are completely out of my own Circle of Confusion and the levels of acceptable sharpness dictated by my brain.

But in no way I am sending my R-D1x to Japan for whatever fix. Even if Epson still supports the camera – which I doubt – the risk of something going wrong on its way to Japan concerns me. This camera stays close to me. I just need time to master the situation.

Fingers crossed!

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