I'd suggest the following:

- Change the settings so that you're no longer using hard contrast and hard sharpness. Use medium settings instead.
- Forget about depth of field for now
- Set the camera to use the centre auto-focus point
- Pick a subject in the middle of the frame, and take several shots of it. Ensure that for each one...

... it is far enough away (the camera can't focus at all, closer than a certain minimum distance).

... you have focus confirmation (steady green hexagon in viewfinder). If the hexagon is flashing, the camera has not been able to focus.

... the Shake Reduction is on, and has stabilised ('hand' icon in viewfinder).

Then, look at it on the computer, and learn to judge what is sharp, and what is not. Post a couple of examples of what you think is sharp... and tell us what you were trying to achieve for each one.

Once you can reliably get the main subject in focus, it'll be worth moving on to controlling the out-of-focus areas of the picture.

Ok, well firstly you're one up on a lot of newbies - you've successfully uploaded some pictures

It appears that you were intending to get the foreground in focus, and the background out of focus.

If this is so, then you've pretty much achieved it (although the fencing isn't really sharp), apparently focusing on the closer parts of the subject, and using a relatively wide aperture to ensure that the distance range over which objects appear in focus, is short. Hence you've got an out-of-focus background.

But that's just my inference from how the photos appear, and from the EXIF data embedded in the images themselves.

So, over to you. What, in detail, were you trying to achieve, how did you go about it, and to what extent do you feel your objectives were met?

Well the Harvard and Catalina are right.

Never even heard of the other two

Interesting. I trust you did this experiment with the lens wide open, to eliminate depth of field as a contribution to the sharpness?

I definitely agree that pre-focusing and then leaving the focus alone will be better than winding the ring round to its infinity stop.

But if this theory were right, and the lens was focused at infinity most of the time, I'd expect almost all my airshow shots to be sharp, whereas in fact, I have an enormous number that are just slightly out of focus.

I'd also expect the AF to be doing nothing at all while following moving aircraft, and in actual fact you can hear it adjusting on every half-press (or indeed almost continuously with AF-C).

So I'm not convinced. I might do some experiments of my own when I get a chance. Thanks for coming back on this one.

Edit... BTW... I notice that your shots above are taken at F16, F11, F11 and F9.5 respectively. So DOF may contribute a lot there. Jury's still out round here!!

PS... What are the 2nd and last aircraft?

I'm usually in the 'no caption' camp.

Obviously, if the picture is intended to document a very specific story, then as much or as little supplementary information as appropriate is perfectly fine.

The trouble with captions is that it forces you to look at a picture in a particular way. For factual documentary, this is a good thing.

But as soon as you move away from this, the caption overlays one's impression with the photographer's. My preference is usually to not have this - and as Ted says, it does often strike me that it's compensating somehow. Not always of course - 'September morning west of Keswick' would be fine, whereas I'd balk at 'Misty dreaming', for a landscape shot in the Lake District shortly after dawn.

Particularly for the comps - if what links the photo to the theme is so tenuous as to need one, one might almost argue that a caption constitutes an unfair advantage.

I'm sure it's also about the amount of money they paid for them!!

Joking apart, I wouldn't be at all surprised if some very good lenses, that can achieve a very sharp foreground, coupled with a very smooth, non-distracting, OOF background, illustrate the effect better than others.

But no-one's claiming a '3D' effect at F16, where everything's sharp, surely?

This is simply not true.

Here's a test I just did. I live close to the Heathrow inbound flight path, and the aircraft were coming past at a range of a little more than half a mile - *much* further away than airshow aircraft.

K10D, DA 55-300 (@300mm), F8. Tripod.

Here's the full frame, focused using AF-S:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Technical/FocusOnInfinityTest/IMGP1722.jpg[/IMG]

Here's a 100% crop:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Technical/FocusOnInfinityTest/IMGP1722-crop.jpg[/IMG]

Next up, lens at infinity, MF:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Technical/FocusOnInfinityTest/IMGP1723.jpg[/IMG]

100% crop:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Technical/FocusOnInfinityTest/IMGP1723-crop.jpg[/IMG]

There are two reasons why the infinity/MF approach is doomed:

1. Focusing rings can be rotated beyond infinity anyway, by unpredictable amounts.

2. The aircraft are nowhere near far enough away for the difference between their actual distance and infinity to be insignificant. My experiment was at a range of a bit over half a mile; at airshows they're *much* closer than that.


What is perfectly valid, is getting it focused at the distance they're coming past, and then, if they're reliably at that distance, switching to MF and leaving the focus where it is. It's easy to move it accidentally, and personally, I don't find airshow flight paths reliable enough for this, as I've said before, but your experience may be different from this.

Nothing to do with medium format. Any reasonably sharp foreground subject against a very out-of-focus background will have this effect.

You don't often see this in the EXIF:
[quote="Cayman's pictures"]
Focal Length: 55.0mm (35mm equivalent: 43mm)
[/quote]Made me smile, anyway..

This appeared almost overnight on my sensor.

The Arctic Butterfly didn't touch it, and I had to resort to a wet clean.

I can only assume I was particularly unlucky when changing lenses outside at some point.