DoF preview

[NiceCupOfTea]

Can somebody tell me a little more about this? I have it on my D70S and as I understand it it stops down the lens to the actual aperture when you take the photo giving a chance to see how much light is coming into the lens. As far as I can see it won't take into account the shutter speed so I can't see how it would help from a light point of view...

Assuming it's to preview the DoF (;)) I really can't see any difference looking through the viewfinder, so how useful is it?

[SamHH]

It's not for seeing how much light is reaching the sensor. It's, as you latterly suggest, for previewing the depth of field that you will get with the selected aperture. As to how useful it is, I guess the answer for you is that it's not useful at all if you can't see the difference.

[flat-planedCrank]

NiceCupOfTea said:

Can somebody tell me a little more about this? I have it on my D70S and as I understand it it stops down the lens to the actual aperture when you take the photo giving a chance to see how much light is coming into the lens. As far as I can see it won't take into account the shutter speed so I can't see how it would help from a light point of view...

Assuming it's to preview the DoF (;)) I really can't see any difference looking through the viewfinder, so how useful is it?

Indeed it is to preview the dof

When normally looking through the viewfinder the lens aperture is set wide open - when you press dof-preview it closes the aperture to the 'final shot' aperture.
Try setting the aperture to f11-f16 and focus on something close to you - look at the amount of dof avaliable - what is no longer in-focus in the background. Now press the dof-preview button, chances are the viewfinder will become darker, but if you look carefully you will see that amount of dof has changed. Your looking at the scene as the sensor will see it when the photo is taken

Hope this helps.

Cheers.

[GetCarter]

How useful. There's the rub. Personally, I've never found it that useful as the darkened view makes it a difficult spot. Plus, If I'm trying to get everything in focus (foreground and background) I'm going to go way past what I can see in the DOF preview, and if I want to make a subject sharp against a burred background, I'm going to go as far as I can in the other direction.

But that's probably just me. There will, I'm sure be many professional situations when 'just the right amount of DOF' will be important

Edited by GetCarter on Wednesday 2nd July 18:53

[VxDuncan]

DOF preview promise so much, deliver so little (light). Too dim to be of much use, on digital you press the shutter to get a DOF preview on the rear screen!

The old "scale on the lens" was far more fun!

[Simpo Two]

NiceCupOfTea said:

Can somebody tell me a little more about this? I have it on my D70S and as I understand it it stops down the lens to the actual aperture when you take the photo giving a chance to see how much light is coming into the lens. As far as I can see it won't take into account the shutter speed so I can't see how it would help from a light point of view...

Assuming it's to preview the DoF (;)) I really can't see any difference looking through the viewfinder, so how useful is it?

If it doesn't make any difference then you have the camera set to max (or near max) aperture. It is indeed to help you judge the depth of field, but in a viewfinder that's rather small and dark to start with, it's hard to see since as well as showing the DOF, it will also darken the scene as aperture decreases.

It had a useful role with film, but of course now you can simply guess, take a photo and look at it to see the DOF! I now always estimate DOF from experience, bearing in mind the front and back of what I want to get sharp and the lens. After a while you get used to looking at the scene and dialling in an aperture that will do the job.

[NiceCupOfTea]

Thanks guys!

As GetCarter suggests I am either wanting all in focus, or subject in focus everything else not, so it's not too much of an issue, I go one way all the other, not down the middle

[Simpo Two]

NiceCupOfTea said:

As GetCarter suggests I am either wanting all in focus, or subject in focus everything else not, so it's not too much of an issue, I go one way all the other, not down the middle

That's a sound approach but simply cranking it up to f22 will screw your shutter speed, so it's a juggling act between aperture, shutter speed and ISO. At the other end, using f1.8 can make the DOF so shallow that the AF misses (or the subject moves a bit). For example, although my 70-200 is f2.8, I usually use it at 3.2 or 3.5 to give some extra leeway.

[NiceCupOfTea]

Simpo Two said:

NiceCupOfTea said:

As GetCarter suggests I am either wanting all in focus, or subject in focus everything else not, so it's not too much of an issue, I go one way all the other, not down the middle

That's a sound approach but simply cranking it up to f22 will screw your shutter speed, so it's a juggling act between aperture, shutter speed and ISO. At the other end, using f1.8 can make the DOF so shallow that the AF misses (or the subject moves a bit). For example, although my 70-200 is f2.8, I usually use it at 3.2 or 3.5 to give some extra leeway.

That makes sense

[RobDickinson]

Its usefull.

For shots where you want say the central item of 3 included in the DoF and the other 2 not, how else do you do it , prehaps calculate it (I have DOFmaster on my phone) but a bit of patience and DOF preview is easier.

[VxDuncan]

RobDickinson said:

Its usefull.

For shots where you want say the central item of 3 included in the DoF and the other 2 not, how else do you do it , prehaps calculate it (I have DOFmaster on my phone) but a bit of patience and DOF preview is easier.

Take a picture. Look at on the screen. Make adjustments. At least that way it's bright enough to actual see what's in focus!

[trackdemon]

Simpo Two said:

NiceCupOfTea said:

As GetCarter suggests I am either wanting all in focus, or subject in focus everything else not, so it's not too much of an issue, I go one way all the other, not down the middle

That's a sound approach but simply cranking it up to f22 will screw your shutter speed, so it's a juggling act between aperture, shutter speed and ISO. At the other end, using f1.8 can make the DOF so shallow that the AF misses (or the subject moves a bit). For example, although my 70-200 is f2.8, I usually use it at 3.2 or 3.5 to give some extra leeway.

Perhaps worth adding that most lenses lose performance at either end of their respective aperture ranges, generally giving best sharpness around the f8-f11 range. Not a one-size-fits-all fact (eg 50mm f1.4 is super sharp @ f4) but probably a decent rule of thumb for most zooms.

So I'd avoid using the extremes unless its absolutely necessary to get full front to back sharpness or minimum DoF, and use a support (whenever possible) to prevent having to compromise on aperture or pushing ISO.

The DoF preview button is bobbins though

[pete]

Also note that most cropped digital cameras suffer from noticeable diffraction effects at apertures smaller than f16 (a generalisiation assuming full-screen viewing or an 8x10 print), so another good reason not to stop down too much. In simple terms, diffraction will introduce blur at the edges of objects, regardless of how perfect your lens is.

The effect is related to the difference between the sensor size and physical aperture diameter, so on a full-frame or 35mm camera you could stop down by approximately 1 stop without diffraction becoming a problem.

Pete