DOF Preview

Dman

Dman

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Is there any real need to use this? I ask as my D90 doesn't show any difference in the viewfinder with or without the DOF button pressed, or if it does then it's a very negligible difference that I can't see.

Does anyone else have this issue?
 
Depends if you set your aperture to anything that isn't the maximum/widest setting. Set it to say f11-f22 and you'll see a big difference in DoF and dimness of the viewfinder.
 
If you set your lens to f16 or f22 then try it out, you should definitely see a change in DOF. However, that is combined with a reduction in light level so you may not be able to see it anyway!


Steve.
 
Right, I'll give it another go tonight, I assume it will work in Live View.
 
You do see dimming of the viewfinder, but I find it impossible to see what's in focus and what's not. Waste of time I think.
 
I found that my eye looking through the veiwfinder produces a much larger DoF than the camera capture. (for whatever reason)

So unless i'm seeing what the camera sees, i have to guess, so its rarely used.....its faster to take the shot, look at the LCD screen and decide if another is required.
 
Blue Eagle said:
I found that my eye looking through the veiwfinder produces a much larger DoF than the camera capture. (for whatever reason)
Click to expand...

How is that possible. If it's out of focus on the ground glass screen, there is nothing that your eye can do to bring it back into focus again.


Steve.
 
Steve Smith said:
How is that possible. If it's out of focus on the ground glass screen, there is nothing that your eye can do to bring it back into focus again.


Steve.
Click to expand...

Well when I look out of the window here ii can see the bushes below my window just as sharp as the trees in the distance. Everything I look at is in focus. SO when looking thru the viewfinder that is the same, as its only a piece of glass like a window.

When we see these bird shots on the forum with wonderful soft mushy out of focus background, that is only some feet behind the bird but you dont see it like that when you look at the bird with your eyes do you.

Its the lens and aperture that makes the dof surely. :shrug:
 
Janice said:
SO when looking thru the viewfinder that is the same, as its only a piece of glass like a window.
Click to expand...

It's not a piece of glass like a window. It has a frosted surface onto which the image is focused (or not).

If part of the image projected onto the ground glass is not in focus, the best eyes in the world or any amount of optics will not be able to get it back into focus again.

It would be the same as looking at a print of an out of focus image and being able to see it in focus - it can't be done.


Steve.
 
Janice said:
When we see these bird shots on the forum with wonderful soft mushy out of focus background, that is only some feet behind the bird but you dont see it like that when you look at the bird with your eyes do you.
Click to expand...

But when you look with your eyes, you don't look at everything at once, you look at it a bit at a time.

Try looking at a tree or some clouds in the distance and hold a pencil at arm's length in front of you. You should then be able to change your focus from one to the other.

As one comes into focus, the other will go out of focus.

This is also a good excercise for the eye muscles.


Steve.
 
When you look out your window as you move your eyes to different places you will not only be changing your focus but also every think about what you see such as white light balance there is nothing that can match what your eyes can do
The focus screen will only show you what the lens has focused on and if you stop down then it will also show you the DOF
I find it’s better to take a shot and view its on the LCD to check it
 
Janice said:
Well when I look out of the window here ii can see the bushes below my window just as sharp as the trees in the distance. Everything I look at is in focus. SO when looking thru the viewfinder that is the same, as its only a piece of glass like a window.
Click to expand...
Your eyes have automatic aperture and focus adjustment.

If you look at something nearby your pupil will adjust accordingly and you will focus on what you are looking at. if you then look at something in the distance your pupil may change and the focus will change.

To replicate the bird shot you were on about, put your finger about 12" infront of your face and focus on it. Without detracting from your finger you'll notice the background is all out of focus. That is your eyes creating a wide aperture and narrow depth of field.

Also, don't forget that your eyes see in 3D whereas a camera can only see in 2D so there is no real comparison between what they can see.
 
Steve Smith said:
It's not a piece of glass like a window. It has a frosted surface onto which the image is focused (or not).
Click to expand...

I think you have a different type of focus screen to the rest of us?
If I shine a beam of light through the viewfinder of my camera, it will come out like a beam of light. If there were a frosted glass focus screen in between, then I should see a point object shining through the lens instead.
 
Dman said:
Is there any real need to use this? I ask as my D90 doesn't show any difference in the viewfinder with or without the DOF button pressed, or if it does then it's a very negligible difference that I can't see.

Does anyone else have this issue?
Click to expand...

Can I just be the awkward one who says that they use the DoF preview all the time, and find it really useful for checking depth of field, etc? Always have.
 
jerry12953 said:
Can I just be the awkward one who says that they use the DoF preview all the time, and find it really useful for checking depth of field, etc? Always have.
Click to expand...

I use it too. It's either that or wait until I have printed the picture!


Steve.
 
Janice said:
Well when I look out of the window here ii can see the bushes below my window just as sharp as the trees in the distance. Everything I look at is in focus. SO when looking thru the viewfinder that is the same, as its only a piece of glass like a window.

When we see these bird shots on the forum with wonderful soft mushy out of focus background, that is only some feet behind the bird but you dont see it like that when you look at the bird with your eyes do you.

Its the lens and aperture that makes the dof surely. :shrug:
Click to expand...

Everything you look AT is in focus because that's what happens when you look AT something. If you're looking at a bird, you're hardly aware of whatever's behind it and as soon as you try to see what's there, you're looking at it rather than the bird so you AF kicks in and focusses on the background. Try holding a finger about 2" (50mm) away from your computer monitor and look at your finger. Now, without shifting your eyes away from your finger, can you read what's on your screen?

While the human eye is actually quite a poor optical instrument, the processing power we use to interpret the images is way beyond that used in cameras, hence the dynamic range, the fast AF, colour balance etc.
 
I find it very useful when shooting groups - helps to work out if the rear-rows are acceptably sharp compared to the front - since we no longer have DoF scales on the lenses, I'd say for me it's invaluble...

If it's not working for you, I have to say you're probably not using it right...
 
i used it on my 35mm slrs..usually it was bright enough to see the results
for an open lens and a long one you can check also lack of dof...which you may want if shooting at smaller apertures than open
on a wide angle not really a great help...

i dont have one now so its look at the magnified image on playback
 
Arkady said:
I find it very useful when shooting groups - helps to work out if the rear-rows are acceptably sharp compared to the front - since we no longer have DoF scales on the lenses, I'd say for me it's invaluble...

If it's not working for you, I have to say you're probably not using it right...
Click to expand...


How should it be used? what is it we're looking for?

Its something to do with spotting the brightly lit right!?
 
IVe found it difficult to notice in the viewfinder because its so dark.
But I find if i'm in liveview its brightens the image up a bit after you press the DoF preview button and you can zoom in digitally too to check the focus and depth of field.
 
Forbiddenbiker said:
How should it be used? what is it we're looking for?

Its something to do with spotting the brightly lit right!?
Click to expand...

I'm going to have to chastise you, young man...:D
You know very well how it works and how to use it...


DOF Preview stops the lens down to the taking-aperture and shows how much of the subject is in acceptable focus - granted it can be tricky to use in low light, but with practice it shows what is and what isn't in acceptable focus.

Obviously if your lens is set to wide open or near that, you'll not notice an appreciable difference...
 
Lol, It was a perfectly serious question I promises. No intention otherwise bud.

I find I struggle to see the resulting dof, yes its dark but I understand its the brightness remaining that shows the dof range? perhaps its down to the limits of my lesser cameras viewfinder as you can see the edges of focus so clearly when you use yours.

I really thought there might be a technique to understanding how to see it. ...my camera shows very little, or its me older eyes, that doesn't help I guess
 
Forbiddenbiker said:
Lol, It was a perfectly serious question I promises. No intention otherwise bud.

I find I struggle to see the resulting dof, yes its dark but I understand its the brightness remaining that shows the dof range? perhaps its down to the limits of my lesser cameras viewfinder as you can see the edges of focus so clearly when you use yours.

I really thought there might be a technique to understanding how to see it. ...my camera shows very little, or its me older eyes, that doesn't help I guess
Click to expand...

always carry a torch..just for those dof preview moments
 
Blue Eagle said:
I found that my eye looking through the veiwfinder produces a much larger DoF than the camera capture. (for whatever reason)
Click to expand...

This is true. The following proves it:

Manually focus your lens on some text, and then move it out of focus until you get to the point where you can just about read the text. Then take a photo at about f/2.8. When I do this, the text in the photo is far too blurred to make out, but I could read it in the viewfinder. With a 28mm lens at a close distance I have to stop down to about f/5.6 for the photo to represent the depth of field I'm seeing.
 
Janice said:
Well when I look out of the window here ii can see the bushes below my window just as sharp as the trees in the distance. Everything I look at is in focus. SO when looking thru the viewfinder that is the same, as its only a piece of glass like a window.

When we see these bird shots on the forum with wonderful soft mushy out of focus background, that is only some feet behind the bird but you dont see it like that when you look at the bird with your eyes do you.

Its the lens and aperture that makes the dof surely. :shrug:
Click to expand...

Thats not the same as looking through a camera, your looking through lens and a ground glass screen, not plain window galss, if it all looks the same in the camera maybe theres something wrong somewhere, either with the camera or maybe your eyes? is the eyepiece focusing set properly (diopter correction)
 
Steve Smith said:
The image projected onto the ground glass is exactly the same image which the lens projects onto the film or sensor.
Steve.
Click to expand...
I think you're forgetting that our DSLRs do not have ground glass focusing screens. I came from an OM1 and OM4 and regularly used DOF preview, which showed the effect very clearly. When finally moving to digital I made sure I bought a camera (D70s) with preview, but was disappointed to find that it was barely usable, partly because the viewfinder was so much smaller, and partly because the bright screen of the DSLR doesn't render the effect nearly so strongly - I don't know why.

My new D300 has a larger viewfinder and I can see the focus a bit better, but I still can't see the DOF as well as I could on the 35mm OMs, let alone what you will see on your medium format film cameras.
 
Sorry, I didn't make myself clear. I meant that the screens aren't ground glass. I have thought of putting in a Katz Eye or similar but haven't decided so far.
 
Tracer said:
Sorry, I didn't make myself clear. I meant that the screens aren't ground glass.
Click to expand...

Perhaps they're not glass but they definitely have a similar matt surface otherwise it would be impossible to form an image on them.

And what I said is still true. The image projected onto that screen (of whatever substance) is exactly the same image which is projected on your image recording medium of choice (film or sensor).


Steve.
 
My take on this:

The illusion of DoF is based on the final MEDIUM which it is viewed. In this case it's the viewfinder; on smaller sensored cameras and less expensive cameras, the viewfinder is smaller (and sometimes likened to looking through a tunnel). As the viewfinder is so small, DoF becomes much less apparent. Shrink any image with a sharp subject and blurred background to the size of a postage stamp, and the amount of background 'blur' will be nil. The blur is more apparent on your computer screen/print as it's a bigger size than the diminuitive viewfinder.
 
Arkady said:
WTF..? Of course they do - what they do not have is a fresnel focussing-screen...
Click to expand...

Oops - sorry! My mistake. The screen on my OM 4 looks grittier to my eye than the D300's, hence my confusion. Probably just because it is bigger.

But the bottom line for me is that on a DSLR, presumably owing to the smaller viewfinder, the DOF preview is harder for me to use.
 
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