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Old Sep 10, 2006, 2:24 AM   #1
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Does a dSLR have a live dept of field preview?

I ask this because I am usually able to observe the dept of field on my N1 compact. In another words, I get an instant feedbacks of the dept of field.

Can I have such a thingin a dSLR when I select an aperture or do I need to press the DOF button to get it (Always)? Can I hold down the DOF button to keep on getting a life DOF preview as on a live preview LCD camera?

I like to be able to track my subject and see the dept of view changes as the camera focus on it. My N1 does that with continuous focus.

Generally does a dSLR with it's TTL viewfinder even provides you with a DOF preview when you focus on a subject...as on all live preview LCD cameras? (Withoutpressinga DOF previewbutton)



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Old Sep 10, 2006, 2:57 AM   #2
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No.
Autofocus is disabled on a 350D when you hold down the dof preview. It couldn't work anyway, if you have the aperture set to more than f5.6 as there wouldn't be enough light to focus with. Slrs use a different (and more accurate) focussing system than P&S.
You also want the aperture wide open for focusing and framing as the view finder is much brighter and easier to see. The greater detail you can see through an slr view-finder is pretty good compensation for the lack of live dof preview.
On a P&S you don't have much control over dof anyway as the difference between maximum and minimum apertures is usually only about 4 stops and even at maximum aperture the dof is already quite large.
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Old Sep 10, 2006, 3:30 AM   #3
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What happens if I bring an R1 into the situation? The R1 is just like a usual ultra compact with thelive preview except that it has an APS-C size CMOS sensorand a huge C.Z. lens. It also have a magnified manual focus center.

I read thatthe R1has a live dept of field preview so I guess that it will be everything like my N1 except that the out of focus areas will be more dramatic?

Thanks for clarifying about the dSLRs to me.


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Old Sep 10, 2006, 4:00 AM   #4
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DOF preview is IMO mainly a useless function on SLR cameras anyway, even film cameras.

Why? Because it doesn't give you an accurate picture of what will and will not be "in focus" in the final print.

Also with the entry level APS sensor cameras, the viewfinder is usually smaller and dimmer and is thus the feature is even less useful than it might be.

And if you claim that you can get a good idea of DOF from a P&S live preview on an LCD screen, then I'm afraid you are mistaken. If you don't agree then you really need to tell me how many lp/mm resolution you are able to distinguish on that screen with live preview.

The correct way to gauge what your DOF is likely to be on an SLR is to commit some basic information to memory about hyperfocal distances for different focal lengths and apertures on the sensor size you are concerned with. Mix that up with lots of practice and you will soon be getting the DOF you want.
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Old Sep 10, 2006, 4:15 AM   #5
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But don't you think that a live preview image sensor especially on an APS-C camera like the R1 will accurately preview the DOF than a mirror plane a few mm froma dSLRimage sensor? The out of focus areas on the R1 will be more obvious than on a conventional P&S; thus providing more accurate evaluation of DOF right?

I am just curious. Thanks also for enlightening me about the DOF preview on dSLRs.
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Old Sep 10, 2006, 5:36 AM   #6
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No. The preview image is very low resolution and so you can't really tell what is sharp and in focus at the sensor.
In and out of focus are not like black and white. In fact virtually nothing is in perfect focus. What matters is if it is sharp enough when printed and viewed. This depends on lots of things that happen post-camera such as the resolution of the print, how close the viewer is to it and how good their eyesight is as well as on the aperture, sharpness and resolution of the camera set-up.
In an slr the viewfinder is generally too small (especially on a crop camera) to accurately judge depth of field. If you're trying to get a lot 'in focus' then the lens is probably stopped down and using the dof preview will leave the view finder too dark to see anything at all. You work by remembering settings you have used before and how they looked after x post-processing and y printing. The low-res preview on a p&s is even less helpful - you don't even have access to the image as the sensor will record it.
What exactly is it that you wish to see through the viewer? The dof change as you adjust the aperture in Av mode? If you just want to see the subject stand out from the background then this is the default for an slr. The dof only increases when you preview. The aperture is always wide-open until the shutter button is pressed.

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Old Sep 10, 2006, 7:23 AM   #7
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Yeah, exactly what jacks said.

On most lenses you will have only a plane which is actually in focus (matters can be more complicated depending on lens curvature etc. but a plane is good enough for most purposes of discussion).

What appears in focus behind and in front of that plane depends on a very wide range of factors.

Print resolution and viewing distance are vitally important, and that is the crux - the resolution of the small optical viewfinders, and even more so with electronic viewfinders, is simply not high enough to give you any kind of accurate picture of what your prints will look like.

The R1 is no better than any other EVF in this regard.
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Old Sep 10, 2006, 11:22 AM   #8
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I was actually concerned about tracking subjects withlive DOF previewing as I focus on them. (Kind of like a video camera following the subject with the focus on it and you see the focusing processeslife!)

Anyway, I do appreciate all your helps and hope that you allwill advice me more about TTL viewfindersvs EVFs or live preview LCDs.

Just now I tested a sampleNikon D70s out at a shopping mall and found thatit's TTL viewfinder was actually much better than I had ever thought of it to be. I zoomed the 18-70 mm lens to the max and still found the TTL viewfinder a pleasure to use with no obvious light lost.

If I have to be very honest; I actually think that the TTL viewfinder of the Nikon D70s is far higher in quality than the EVF of the SONYR1. I only found that the focus pointswere a bittoo transparent so that when they glow red to indicate focus, I have to really look out for it. As an aside, I also found that the D70s's main LCDwas nothing short of amazing to me considering I never expected it to be that good. (Sometimes quality matters)

Finally, I cannot help it but to state that the Nikon D70s was one reallyhigh quality camera that I have ever held in my entire life!

Anyway, back to thetopic:

I haven't actually tried to obtain bokeh yet with the Nikon D70s since there was not much time for it during the short test, I am curious to knowif I can observe bokeh (background blur)witha TTL viewfinder? (I could with my N1's live preview LCD on macro mode).

Quote:
The low-res preview on a p&s is even less helpful - you don't even have access to the image as the sensor will record it.

How does a dSLR have access to the image as the sensor will record it?

Code:
What exactly is it that you wish to see through the viewer? The dof change as you adjust the aperture in Av mode?

Actually yes. I would like to select say F/2.8 or maybe F/1.4 and actually see the DOF change at once (Even if it is not 100% accurate).

Quote:
The aperture is always wide-open until the shutter button is pressed.
Sorry, I missed this fact...So you mean that even if I select lets say F8 or F9 I will still not see an F8 or F9 until I press the shutter button to take the shot? I will always be seeing at the lens' largest aperture setting at lets say F/2.8 or F/1.4?











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Old Sep 10, 2006, 12:53 PM   #9
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BenjaminXYZ wrote:
Quote:
I was actually concerned about tracking subjects withlive DOF previewing as I focus on them. (Kind of like a video camera following the subject with the focus on it and you see the focusing processeslife!)
Live DOF is not possible even with cameras that have DOF preview. DOF preview only stops the lens down when activated to give an idea of what DOF is. As has been said, typically the viewfinder is too dark and small to really give an accurate representation of actual DOF. Depending on what focus mode you are in, you can track a subject while maintaining focus.


Quote:
If I have to be very honest; I actually think that the TTL viewfinder of the Nikon D70s is far higher in quality than the EVF of the SONYR1. I only found that the focus pointswere a bittoo transparent so that when they glow red to indicate focus, I have to really look out for it. As an aside, I also found that the D70s's main LCDwas nothing short of amazing to me considering I never expected it to be that good. (Sometimes quality matters)
Optical viewfinders are much easier to use and higher quality than EVF in my opinion. There is no flicker in optical viewfinders which makes it easier to track moving subjects. EVF's just look way to0 artificial.





Quote:
I haven't actually tried to obtain bokeh yet with the Nikon D70s since there was not much time for it during the short test, I am curious to knowif I can observe bokeh (background blur)witha TTL viewfinder? (I could with my N1's live preview LCD on macro mode).
Bokeh is not something that you can obtain. It is a non measurable, subjective term used to describe the quality of the blurred background, specifically the highlights and how well they blend together in a pleasing way. All lenses have bokeh at all times. It's the quality that differs, and again there is no clear way to measure that as it is mostly personal preference. It is impossible to judge bokeh through the lens of a DSLR. The viewfinder is too dark and too small to make a judgement. You can only evaluate bokeh in the final image. Bokeh is mostly dependent on the lens and has little if anything to do with the camera body. This is another reason the lens choices are ultimately more important than body choice, especially at the consumer level.

You're far better off learning your camera in and out and understanding how DOF is related to change in aperature values than relying on bells and whistles like DOF preview. It's much quicker, and with practice you'll find yourself not even needing DOF preview to achieve the results you want.

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Old Sep 10, 2006, 8:59 PM   #10
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I think you are a little bit confused about what exactly dof is. What you are describing is seeing the focus follow your subject. This is servo mode in autofocus and I suspect that pretty much all modern slrs have it. Because the lens is always wide open the background will be out of focus while the subject is tracked by the autofocus mechanism. If the background is sufficiently o-o-f at this maximum aperture then this will be visible even through the viewfinder.

As to your more specific questions, the ttl viewfinder has access to the actual image as it is the same light that will go to the sensor. It has just been reflected upwards by a mirror (and passed through another element or two and a pentaprism but lets keep it simple here). In a P&S on the other hand the viewfinder shows a low resolution sampling of the picture. The difference is like the difference between looking out the window and looking at a newsprint photo.

What happens when you press the button in an slr are the following:-
1. The mirror flips out of the way of the sensor. Note that you now cannot see through the viewfinder at all. For most shooting the whole process is very rapid so its not a problem.
2. The aperture of the lens closes down to the chosen setting. Until then it is wide open. You NEVER see the image stopped down through the viewfinder as this only occurs after the mirror has popped up (that is why there is a dof preview button instead).
3. The shutter opens, exposing the sensor and then closes again.
4.... everything is reset.
So you always view the subject with the aperture wide open. This is one of the many nice things about having fast lenses - the viewer is much brighter and easy to see. Autofocus generally works better with fast lenses (and so more light) too.
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