The camera keeps the aperture of it's lens wide open while you are composing the shot and only stops it down to the taking aperture when you press the shutter. By pressing the DOF button it stops the lens down to where you set it physically enabling you to judge by eye the extent of the field of view which remains in acceptable focus. Yes, it will be dim and so it is best used in bright daylight. You can get DOF tables but most of us know we need to stop the lens down to f8 or so in order to get a reasonbly wide DOF..

John.Please visit me at:http://www.pbase.com/johnfr/backtothebridgehttp://www.pbase.com/johnfr..

John farrar wrote:.

The camera keeps the aperture of it's lens wide open while you arecomposing the shot and only stops it down to the taking aperturewhen you press the shutter. By pressing the DOF button it stops thelens down to where you set it physically enabling you to judge byeye the extent of the field of view which remains in acceptablefocus. Yes, it will be dim and so it is best used in brightdaylight. You can get DOF tables but most of us know we need tostop the lens down to f8 or so in order to get a reasonbly wide DOF..

So the dimming of the viewfinder isn't a part of the information, just an effect of the function?.

I think I got it. Finally someone who speaks my language  Thanks...

You're welcome; it's darkening of the image in the finder has nothing to do with the actual exposure as in using the +/- on a digicam with live preview. In the old days of the first film SLRs the aperture was always set to where you set it physically so you can imagine how difficult it was to see anything at f16, I can remember using an old Russian Zenit now. The coming of Auto diphragms that only stopped down at the instant of taking the shot was a huge benefit for composition. They had larger more tactile DOF buttons than today's cameras which were often on the lenses as it was a big deal not seeing the DOF when you'd always glimpsed it dimly in the past.John.Please visit me at:http://www.pbase.com/johnfr/backtothebridgehttp://www.pbase.com/johnfr..

John farrar wrote:.

You're welcome; it's darkening of the image in the finder hasnothing to do with the actual exposure as in using the +/- on adigicam with live preview. In the old days of the first film SLRsthe aperture was always set to where you set it physically so youcan imagine how difficult it was to see anything at f16, I canremember using an old Russian Zenit now. The coming of Autodiphragms that only stopped down at the instant of taking the shotwas a huge benefit for composition. They had larger more tactileDOF buttons than today's cameras which were often on the lenses asit was a big deal not seeing the DOF when you'd always glimpsed itdimly in the past.John.Please visit me at:http://www.pbase.com/johnfr/backtothebridgehttp://www.pbase.com/johnfr.

I never had to put up with the condition you describe above. Bought my first SLR in 1970, and lenses already stayed wide open till the shot..

But you've certainly cleared up one mystery... .

Dave..

I had a couple of lenses for my old Exacta that incorporated a "preset diaphram." One could set sort of a detent at the aperture you wanted to use to take the photo, return the lens to the wide-open position to compose and focus, then rapidly close the lens down to the pre-set aperture to take the picture..

We've come a long way.Art Caputi..

TimBrandt wrote:.

I have never gotten the DOF-Preview button. I currently have aNikon D80, and when I press it, I can sometimes see part of theviewfinder getting darker... but... how do I use that"information"? I couldn't get the search-function on this site towork (again). I have googled it, but haven't been able to findanything that I could make sense of..

The DOF button closes the lens down to the aperture that will be used to take the picture. This generally makes the view darker since the lens lets less light in this way. What's supposed to happen is that, with the lens stopped down, you can see what will be in focus and what won't..

The bad news is that with the clear screens that cameras come with now, you can't tell what's in focus and what isn't. Consider it a just another useless button. It wasn't even that good a feature when you could focus on a focusing screen..

Leonard Migliore..

I do not agree that the DOF button is useless. When I shoot macros of flowers I often press my camera's DOF button. Yes, the viewfinder dims and my eyes squint. Yet the DOF check enables me to make a reasonable focus check. When I shoot landscapes I sometimes use the DOF button to check foreground focus. I am grateful my cameras have DOF buttons.thezero..

Leonard Migliore wrote:.

TimBrandt wrote:.

I have never gotten the DOF-Preview button. I currently have aNikon D80, and when I press it, I can sometimes see part of theviewfinder getting darker... but... how do I use that"information"? I couldn't get the search-function on this site towork (again). I have googled it, but haven't been able to findanything that I could make sense of..

The DOF button closes the lens down to the aperture that will beused to take the picture. This generally makes the view darkersince the lens lets less light in this way. What's supposed tohappen is that, with the lens stopped down, you can see what willbe in focus and what won't..

The bad news is that with the clear screens that cameras come withnow, you can't tell what's in focus and what isn't..

It has nothing to do with whether a screen is clear or has a split circle with microprisms ... I would actually claim that a clear screen is even of a slight advantage over the other version, as you don't have anything obstructing the view..

Unfortunately the DOF is more often than not mistaken as a pointless feature. Most often due to the lack of knowledge how to use it properly and the misunderstanding the dimming image in the viewfinder causes at first glance. Most people only notice the viewfinder getting darker and falsly assume that that is the intended effect of the DOF button. If you actually sit down and play with different settings for a while, you will quickly realize that there is more to it and than the first impression. It can be a very useful tool when composing a picture. Especially nowadays where lens don't even have hyperfocal distance scales (to determine the range of the DOF) anymore..

Cheersbecksi.

Consider it ajust another useless button. It wasn't even that good a featurewhen you could focus on a focusing screen..

Leonard Migliore..