Can someone please explain the depth of field preview thing


Link Posted 14/08/2003 - 11:42
I have a *ist but have not understood the depth of field preview feature. I understand what depth of field is but it is not obvious what the preview feature is showing me and how to interpret it.

I have tried extremes of appeture and note that a lot of the preview image is dark with a large opening. I guess this means in depth of field terms that the areas shown as dark will be out of focus.

Some guidance on how best to understand what I am seeing on the preview, especially with more subtle appeture variances, would be greatly appreciated.



Link Posted 14/08/2003 - 23:04
Hi Stuart,

When you select a depth of field preview the lens aperture shuts down to that which will be used for the exposure, this will make the image in the viewfinder darker (the smaller the aperture the darker the image). With the lens 'stopped down' in this way you can see exactly what is in focus (providing the image isn't too dark!). This is particularly useful when trying to guage the correct focus point to gain the maximum area in focus.

Hope this helps


Link Posted 14/08/2003 - 23:16
I've always thought this was a very over-rated facility and hardly ever feel the need to use it. The size of the viewfinder image is so small that you cannot really judge depth of field from it.

I do use the depth of field guides on the lens barrel, where available, but always set the aperture to one stop smaller than the one indicated. So, if I use the scale to measure depth of field at f8, for example, I will actually use f11. This is to make sure that the areas will still be in focus even with big enlargements.
Best regards, John


Link Posted 15/08/2003 - 09:35
I too find it overrated, and rarely use DOFP. I have occasionally found it useful to see what happens in macro images - you can see how background light blurs.

If I need to work out distance and focus, I use a neat little application on my Psion Revo called PhotoPal ( ) that can do calculations like hyperfocal distance, near and far distance, as well as a whole load of other things. I have got the 'raw' equations somewhere if anyone needs 'em.

(For gallery, tips and links)


Link Posted 15/08/2003 - 14:10
It seems I am not missing out on anything. Use of brain or some calculation software seems to be the way forward. Thanks to all.

Peter Bargh

Link Posted 17/08/2003 - 23:05
I'd have to disagree on this one. I find the depth of field preview one of the most useful features of a camera. Once you get used to the darkening of the screen you'll be able to check focus accuracy much better. As an experiment focus on a nearby subject with something such as a car number plate in the distance. Set the widest aperture and look at the plate - it will be blurred. Then stop down to the smallest aperture and depress the depth of field preview - the number plate will become sharper. Depth of field preview is also ideal when using filters to check for position of graduation or effect of a soft spot.


Link Posted 18/08/2003 - 23:11
Quite a few professionals writing in magazines over the years would agree with you, Peter!

Probably it doesn't help when using a 20mm f4 lens and peering through a red filter.....(Sometimes it's hard to see anything under those circumstances!)
Best regards, John

Peter Bargh

Link Posted 18/08/2003 - 23:17
Ah yes, with a lens as wide as 20mm everything is already sharp! Well okay, it works well with standard and telephoto lenses


Link Posted 21/08/2003 - 09:09
I have to agree with Peter on this, I do a lot of macro work and use the DOFP button frequently.

When your taking a butterfly at 1:1 you can use the DOFP to check that the wings or antenna are sharp, also when composing the shot the backgound may appear to be an out of focus green blur but when the lens is stopped down to F8 or F11 it's amazing how a blade of grass can suddenly appear as a bight spot.



Link Posted 08/09/2003 - 07:44
I do find the DOFP button very handy, specially for macro work and close-up portraits!! And oh, the MZ-S has greatly improved it's ease of use by placing it in the shutter button collar!!!

Yes, the image will darken, but the idea is to look at the areas that are in focus. I have to agree with Rod on this, especially in macro work where you need lots of DOF.
"It's only a Pentax!"
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