Dof preview button

[praphul]

i am using a canon eos system (canon 550d) and i would like to know about the role of dof preview button. i did read upon it in manual but i dint completely understand.

[Mike Buckley]

I'm assuming your Canon 550d is a digital camera. Even if it is not, I think my explanation shown below will make sense.

This is actually an unhelpful holdover from the depth of field preview that was in film cameras. When you are normally viewing the scene through the viewfinder, the aperture is fully open. That allows maximum light, which enables you to see the scene as brightly as possible. However, you might plan on capturing the image with an aperture that is smaller than the maximum aperture. In that situation, you might want to review the depth of field before capturing the image. The depth of field preview button makes that possible by stopping down the aperture to your setting. After reviewing the scene in the view finder, you might want to change the aperture and check the depth of field again before releasing the shutter.

As I mentioned, that was especially helpful in the days of using expensive film and having to pay for related developing and printing costs. You might not have wanted to capture the scene using a lot of different aperture settings because doing so on a regular basis could significantly add to the cost of your photography hobby over time. In periods of war when film was being rationed even to the pros (because the silver used in black-and-white film was needed to fight the war), it wasn't just a matter of cost; the very real issue was that film was in relatively short supply.

The significant drawback of using the depth of field preview is that it necessarily uses the smaller aperture setting, which allows less light into the lens and the viewfinder. If that aperture is just one stop smaller than the largest aperture available to you, half the light is available for use in the viewfinder. If your aperture setting allows one-fourth of the amount of light, the image in the viewfinder can be seriously dark. That makes it very difficult to see the image, much less critique the depth of field.

In today's world of using digital cameras, the issues about the cost or availability of film of course are not a factor. So, you are far better off ignoring the depth of field preview capability. Instead, use the Live View capability if your camera has it at its largest magnification to review the depth of field. Even if your camera doesn't have Live View, bracket your shots using multiple aperture settings. When you review the depth of field of the various image files at your computer, simply delete the images that have an improper depth of field.

Make sense?

[William W]

i am using a canon eos system (canon 550d) and i would like to know about the role of dof preview button. i did read upon it in manual but i dint completely understand.

Depth of Field (DoF)

Depth of Field Preview stops the lens down to the shooting aperture such that the scene can be viewed and the areas of the scene will appear in “acceptable focus” or “not acceptable focus”

The Depth of Field does NOT mean the area which is all “in focus”, but it is an area which is sort of agreed to be in ‘acceptable focus’.

***

In this image:



whilst there is only one PLANE of SHARP FOCUS, we might agree that ALL of that ONE SEAGULL is in “Acceptable Focus” and hence we would say the length of that seagull, is the Depth of Field for that shot (about 25cm).

***

The components of DoF

Depth of Field is dependent upon these factors:

• The Focal Length of the Lens (FL)
• The Subject Distance (SD)
• The Aperture used (Av)
• The Format of the Camera which defines the Circle of Confusion (CoC)

***

The Axiom of DoF

For all practical purposes, for most of the Shooting Distances we generally use, the DoF will be identical for any one FRAMING of any particular shot at any given APERTURE for any given Camera Format: this is the Axiom of DoF.

What this means is, if you make a Head and Shoulders Shot with a 35mm Lens at F/5.6 and then make the SAME FRAMING (i.e. looks the same in the viewfinder) with an 85mm lens at F/5.6, the DoF will be the same for both shots.

This does not apply to Macro Photography.

***

The Split of DoF, front and back:

There is a general saying one third in front, two thirds behind - this is a good rule of thumb ONLY for longer SD. If one is shooting close (or a tight shot), the DoF split is closer to half and half.

As a practical example - for a Group shoot of a sports team, with managers and the like, in three or four rows shooting at about 8~10 metres, we will expect that the DoF split will be about one third in front of the Focus Point and Two Thirds behind it:



BUT for a tight head shot, the split in front of and behind the focus point, will be about half and half:


***

Using the DoF Preview Button

The Depth of Field preview can be very useful with a digital camera, arguably more useful than on a film SLR.

DoF Preview will work in Live View Mode on your 550D, which means you can very accurately interrogate the range of acceptable focus, in any scene using any particular aperture. This fact should be specifically mentioned in the notes in your User’s Manual.

Moreover, if you wish to link your DSLR to a laptop Computer or Studio Monitor, you can analyse the DoF of any shot to a very detailed degree – many Studios work this way.

However, it appears than many photographers do not use the DoF Preview with their modern DSLRs – perhaps because they think that to only option is to view through the viewfinder: and as with Film SLR cameras that is often quite difficult, because the viewfinder will be quite dark as the lens is stopped down.

***

Other uses:

Also, peculiar to Canon DSLRs: the DoF preview can be used to “lock” an EF or EF-S lens to a particular aperture, such that it can be removed from the camera (and will stay stopped down) and then replaced on extension tubes or bellows or other device which has no electronic connections to the camera.


WW

[dubaiphil]

I can honestly say that I've never used it! I tend to check the LCD for DoF after the fact and adjust to suit, using the DoF preview button for another assigned action that I use more often (artificial horizon in my case)

[pnodrog]

I use DOF preview - not a lot but I would not buy a camera that did not have it. In the (good?) old days with medium format camera's I used it a lot, mind you my eyes were much better then so picking out the focus range in a dark viewfinder was a bit easier than it seems to be now..

[Mike Buckley]

DoF Preview will work in Live View Mode on your 550D

That's an interesting idea that I have never thought of. I have Live View on only one of my cameras and that camera has no depth of field preview button.

[HenkB]

I still use the DoF preview button on my Nikons (none of which allow its use in Live View, BTW). I find it far more useful when shooting handheld than Live View, which last I regard as an ergonomic horror. On tripod with a static subject, though, the reverse is true - Momma, don't take my Live View away! Like the DoF preview, Live View doesn't have to be universally useful to be indispensable when it is appropriate.

Back to the preview button. Things can get murky with the generally dimmer viewfinders we have in today's cameras geared primarily to autofocus (especially crop sensor bodies), but I find that repeatedly flicking the button allows me to assess the stopped-down result for change. By examining different parts of the image and comparing the change I can usually arrange the focus to balance the front and rear elements.

[HenkB]

I have Live View on only one of my cameras and that camera has no depth of field preview button.

Really? The D7000 is specced with both. Have you reassigned the DoF button to something else?

[Mike Buckley]

Really? The D7000 is specced with both. Have you reassigned the DoF button to something else?

Thanks for catching my mistakes, Hendrik. It has been so long since I have used the D7000 Live View that I forgot that it has it. I prefer the D5100 for use with Live View because, unlike the D7000, it has the articulating LCD, which I use regularly when photographing glass in my makeshift studio. I also had forgotten that I have configured the Depth of Preview button on the D7000 to function as the Virtual Horizon. Yikes!

[HenkB]

I prefer the D5100 for use with Live View because, unlike the D7000, it has the articulating LCD, which I use regularly when photographing glass in my makeshift studio.

I agree entirely. I used to have the services of a Coolpix 5700 whose major advantage was an articulating screen which, though teeny by today's standards, could even be arranged to display forward. And of course, with no mirror, it was always in Live View. Process heaven!

[GiacomoD]

I have a Canon 550D too. I tried many times to use the DoF button, but honestly all I can see through the viewfinder is just a darker image. I like to think that it's only because of my astigmatism

Actually I never tried to use it with Live View, I hope to get better results

[praphul]

while pressing the button , i have found that the diaphragm blades coming in corresponding to the aperture setting..and the overall scene in the viewfinder it gets darkened..and the metering reading gets changed i mean the exposure comensation value (EV) . is it just that it ?

[Downrigger]

I think it's a bit of a bogus concept, but maybe I don't understand how to use it, and someone can help me out.

I've had this feature on my Nikon 8008s and now my D600, but have not found that it affords me any confidence as to what is actually going to be appear satisfactorily sharp in the final result. On the ground glass screen of my 4x5 zone six, it was a bit more helpful (to see the image at the f-stop to be used) but still not certain.

Who, for instance would expect to see diffraction blur in DoF preview at high f-stops? And if the intent is to have infinity sharp, are there folks who actually are comfortable using DoF preview to focus nearer than infinity and use DoF preview to assure infinity will be sufficiently sharp?

It is somewhat more helpful in telling my what is NOT going to be sharp when I am interested in whether I have isolated my subject from fore- or background, but that's about it. Or am I needing some help with use of this feature?

Thanks, all

[kdoc856]

My only consideration of the DoF preview button was to find out what I could change to. I check out DoF with a test shot and look at it on LiveView- not perfect but I can see it better than the stopped down darkness I got with DoF preview.

[Hero]

I find it a usefull tool for close-up focussing. Specially when shooting tiny stuff (flowers, bugs) out in bright light. It can also help when you just want your subject in focus. Just push the button and see if you can open up your aperture a stop more. (I'm not much of a live-view user because most of what I do is outdoors in bright sunlight when the lcd is of limited use)

[rambler4466]

Nice explanation, William W. The photo examples are helpful.

One nice feature with the D7000 is that the viewfinder shows the entire frame as seen on the LCD. With other cameras the view finder often crops the actual frame or the entire composition. For example, you might be looking at a view with no sky in the viewfinder, but then have it show up in the final image. With the D7000 this is not an issue. What you see in the viewfinder is what you get.

For me the DoF button is rarely used, just too dark as mentioned. I like the idea of having it replaced with the virtual horizon. No need for the bubble level on top that is so easy to lose!

[William W]

while pressing the button , i have found that the diaphragm blades coming in corresponding to the aperture setting..and the overall scene in the viewfinder it gets darkened..and the metering reading gets changed i mean the exposure comensation value (EV) . is it just that it ?

Yes - pressing the DoF Preview Button will close the diaphragm blades and the scene will get darker in the viewfinder if the aperture chosen is smaller than the maximum aperture of the lens.

The REASON for using the DoF Preview, is to interrogate the scene so you can estimate what will be in acceptable focus at any particular aperture used.

No - there is no effect on the metering.

No – the Exposure Compensation does not change.

As I mentioned previously, the DoF preview button can be used in Live View Mode on your EOS 550D, also this fact is mentioned as a special note in your user manual: the effect of the DoF preview button in reckoning what will be in ‘acceptable focus’ is often easier for many people to see using Live View Mode.

If using the Viewfinder, the idea of flicking the DoF Preview Button in and out so that the view of the scene changes rapidly, is a good technique, as this often makes the expected DoF easier to envisage.

If using the Viewfinder, the usefulness of the DoF Preview Button is also dependent upon having the Dioptric Adjustment correctly positioned and using correct Dioptric Lens, if necessary. On an EOS 550D the Dioptric Adjustment is made by the knurled knob situated on the Top Right corner of the Viewfinder frame, as you look at the back of the camera.

NOTE - There is NOT the capability to assign the DoF Preview Button for another purpose, on your EOS 550D.

WW

[Graystar]

In addition to the good info already given, some cameras provide a modeling light function on the DOF preview. This is useful in studio photography where you can evaluate shadows. The light is only on for less than 2 seconds, but I find that's enough to help with precise positioning of small objects in a scene (for example, the shadow of a chess piece on a chessboard.)

Also note that DOF preview is more helpful on a full-frame camera, where the DOF is more shallow for any given framing when compared to APS-C cameras.

[William W]

I think it's a bit of a bogus concept, but maybe I don't understand how to use it, and someone can help me out.

I've had this feature on my Nikon 8008s and now my D600, but have not found that it affords me any confidence as to what is actually going to be appear satisfactorily sharp in the final result. On the ground glass screen of my 4x5 zone six, it was a bit more helpful (to see the image at the f-stop to be used) but still not certain.

Who, for instance would expect to see diffraction blur in DoF preview at high f-stops? And if the intent is to have infinity sharp, are there folks who actually are comfortable using DoF preview to focus nearer than infinity and use DoF preview to assure infinity will be sufficiently sharp?

It is somewhat more helpful in telling my what is NOT going to be sharp when I am interested in whether I have isolated my subject from fore- or background, but that's about it. Or am I needing some help with use of this feature?

Thanks, all

The concept is not false or misleading. The concept is predicated on mathematics and historically used in larger format cameras on ground glass screens, as you mentioned.

The outcome of how good or accurate the evaluation of the DoF using the DoF Preview, will be dependent upon many factors, one of which is dedicated practice and another is trying some different techniques. Experimenting with various techniques such as using live view or the ‘quick flicking’ techniques already mentioned would be a good idea. The fact that you mention DoF Preview has been useful to tell you what will NOT be in focus, already shows that there has been some benefit to you.

In any case, DoF Preview is only another tool on the camera which can be used as an helping device. It is not definitive of itself: and was never intended to be so.

DoF is NOT a definitive, either.

There is not, nor was there ever, the intent of using the DoF Preview neither to show Diffraction Blur nor to show accurate Infinity Focus. If you are using the DoF Preview Button for these purposes, then your use is incorrect and ill-informed.

WW

[William W]

Regarding the comments about using DoF Preview on APS-C cameras - OR - ‘Full Frame’ cameras:

Many ‘FF’ digital Cameras have brighter/ clearer viewfinders anyway, when compared to their APS-C counterparts; also some cameras have the capacity to interchange focussing screen (for better/accurate manual focussing).

These facts also make the DoF Preview often easier to note on the larger format digital camera.

WW