Question of the day

A reader recently asked this:

I noticed in a forum that you much like the Pentax k-7. I am wondering whether you have used the Pentax K10D before and under what low setting should this or a any digital Camera take a photograph without the results being blurred. ie: 50mm 1.4 lens and at ISO 100. Are there any differences between film or digital sensitivity, should the results be the same and do you forgive digital cameras for its own idiosyncrasy. if it was film would digital cameras be better designed today. And finally, how is it possible for a camera to register a photograph out of focus when what you see is in focus?

My reply:

Yes, I have used both those cameras. They’re great, as are most all digital cameras today. The results should never be blurred if you do not want them to be. But with an f/1.4 lens set to f/1.4, you need to focus very carefully. Depth of field is minimal and even a very slight movement after focusing makes the picture blurry.

Also, use one focus area that you choose and move that over the part of the image that should be sharpest.

Sensitivity is the same: 100 ISO is equal to 100 ASA. Noise is not much different either. And you will find most experts agree that a modern sensor of, say, 10 Mpixels or more is at least as good as a negative. Beyond that, better. True, the dynamic range of film is greater, and it drops off gradually at the end, but sensors can be more sensitive. If you shoot in RAW, you minimise that difference.

When what you see is in focus, the image should be sharp. But what you see is small, and perhaps you are moving the camera? Could it be motion blur? Or “slow flash” bluer due to slow shutter speed? Or are you perhaps moving the camera slightly after focusing?

You may want to (re-)read this post here on why studio shots are sharper. And perhaps post an image you think is unsharp.

Here’s one I took yesterday, of my niece’s cat:

Click to see it in its full sharpness.

0 thoughts on “Question of the day

  1. That’s a very good summary. Thank you. Given that the DoF of a fast lens is small, how often do you use your fast lenses wide open? It would be interesting to do some statistics from your Lightroom database plotting aperture against number of pictures taken for each lens.

    I wonder if you’d find that, for example, 90% of the time you use your 50mm F/1.4 at F/1.8 or greater to get the DoF you need for the picture.

    The other point you make, I think, is that auto-focus can give us a false sense of security especially with fast lenses. It gives that satisfying beep when you half-press the shutter button and it focuses. Even if the focus is what you wanted (using the many focus points of a modern DSLR) it doesn’t make another noise to say “sorry, I just lost focus” if I or the subject moves a centimetre.

    Do you use the optional focusing screens on your EOS-1D? I talked about my embarrassing manual focus problem at and wish I had the old-style split-prism aids.

  2. I tend to use the fast lenses wide open, but in fact when I get back home (I am in Mono, Ontario, in the snow belt, this weekend) I shall check the statistics as you suggest.

    Agreed re autofocus; plus, on Canon it can be inconsistent wide open. It is not a panacea, and no I do not use the focus screens but like you, I really do miss the split-prism aids.

    That said – AF is faster and speed is very important nowadays.

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