Depth of Field Preview

[kkamin]

I just bought my first DSLR and then discovered its 'Depth of Field' preview feature. Initially I thought it was a weird work around for a digital camera to show you your depth of field, since I am without an f-stop ring on my lens, on my Canon DSLR it's all computer set.

But then I went to investigate my analog SLR and realized, for the years I have been shooting, the aperture is always full open, and doesn't close down until you hit the shutter. If the aperture did close when I increased my f-stop, the image would dim. Panic took me over. I think for all these years, my depth of field hasn't been completely accurate. I always thought looking TTL was giving me an accurate picture.

1. With my analog SLR, I was never getting an accurate depth of field by looking TTL, right? Kind of still in shock.

2. How do analog SLR users get an accurate idea of their depth of field?

3. When you look TTL, is the shutter positioned by default at the largest aperture or is it open even larger?

4. My xsi lens doesn't have a focusing distance scale. If I'm in a tricky situation, like photographing a large group photo, how am I suppose to make sure everyone is in focus if I can't take a measurement with a tape measure, or even know what my depth of field measurement is--and if I use depth of field preview, it gets too dark since I am shooting at a high stop?

[joedlh]

I think for all these years, my depth of field hasn't been completely accurate. I always thought looking TTL was giving me an accurate picture.


I'm not sure you understand what depth of field is. In both film and digital SLRs when you look through the view finder, you are seeing the scene with the lens wide open. This is, as you note, to give you the brightest viewfinder image for purposes of composition. If your camera has a depth of field preview button, it works the same way in any kind of SLR -- film or digital: it closes the diaphragm down to the aperture that either you or the camera's meter have set. This will result in a darker image in the viewfinder. However, unless you are really stopped down, it should be enough for you to discern the range of objects that will be in focus when you release the shutter -- in other words, the depth of field.

1. With my analog SLR, I was never getting an accurate depth of field by looking TTL, right? Kind of still in shock.


This is correct. You would have to press the depth of field preview button if your camera had one.

2. How do analog SLR users get an accurate idea of their depth of field?


The depth of field preview button.

3. When you look TTL, is the shutter positioned by default at the largest aperture or is it open even larger?


As explained above, yes.

4. My xsi lens doesn't have a focusing distance scale. If I'm in a tricky situation, like photographing a large group photo, how am I suppose to make sure everyone is in focus if I can't take a measurement with a tape measure, or even know what my depth of field measurement is--and if I use depth of field preview, it gets too dark since I am shooting at a high stop?

If you use autofocus, you don't need a distance scale. You can eyeball it. I think your subjects might get a bit impatient if you pulled out a tape and started measuring the distance between the people in the front and rear row. Most experienced photographers can estimate what aperture they need to get everybody in focus. It is advised that you focus on the subject that is 1/3 of the distance in the area that you want to be in focus.

If you're shooting at such a high stop that you can't see anything in the viewfinder, then you don't have to worry about depth of field unless your subjects are quite distant from each other or you want the foreground or background also to be in focus.

[RDKirk]

A couple of points to add:

Depth of field is ultimately dependent on the final display enlargement. The greater the enlargement, the less the depth of field will appear. If you make a 4x6 and then a 24x36 from the same image, the depth of field will appear much more shallow in the larger print.

The preview you see in the camera with the depth of field preview is a view of a small image. It will show you more depth of field than you will actually get with a substantial enlargement, so you have to take a conservative view of what you see with the depth of field preview.

If you have a Live View camera, the camera automatically boosts the screen brightness when you use the depth of field preview, so you can clearly see what you're getting at shooting aperture. This is a tremendous boon--I've used everything from view cameras to digital, and this is the first time it's been possible to get full use out of depth of field preview at smaller stops.

[yogestee]

1. With my analog SLR, I was never getting an accurate depth of field by looking TTL, right? Kind of still in shock.

2. How do analog SLR users get an accurate idea of their depth of field?

3. When you look TTL, is the shutter positioned by default at the largest aperture or is it open even larger?

4. My xsi lens doesn't have a focusing distance scale. If I'm in a tricky situation, like photographing a large group photo, how am I suppose to make sure everyone is in focus if I can't take a measurement with a tape measure, or even know what my depth of field measurement is--and if I use depth of field preview, it gets too dark since I am shooting at a high stop?

Firstly what's an analog SLR??? Or do you mean film SLR??

Depth of Field preview button is a wonderful tool.. When I was shooting analog ;) I used it all the time especially when shooting close quarter portraits at wide apertures.. Very useful when shooting medium format because mediun format has a much shallower depth of field..

Film camera viewfinders are much larger than DSLR viewfinders so the effect is easier to see when you stop the lens down.. You get to see exactly what's in the zone of acceptable sharpness or not..

I find I rarely use the Depth of Field preview with my DSLRs..

[kkamin]

Firstly what's an analog SLR??? Or do you mean film SLR??

Depth of Field preview button is a wonderful tool.. When I was shooting analog ;) I used it all the time especially when shooting close quarter portraits at wide apertures.. Very useful when shooting medium format because mediun format has a much shallower depth of field..

Film camera viewfinders are much larger than DSLR viewfinders so the effect is easier to see when you stop the lens down.. You get to see exactly what's in the zone of acceptable sharpness or not..

I find I rarely use the Depth of Field preview with my DSLRs..

Thanks for your reply. 'Analog' is a technically accurate way to describe a film camera.

[SkipD]

'Analog' is a technically accurate way to describe a film camera.While technically true, "Film" is a much better term to use when referring to a film-based camera. :rolleyes:

[kkamin]

While technically true, "Film" is a much better term to use when referring to a film-based camera. :rolleyes:

ok, sorry

[RDKirk]

While technically true, "Film" is a much better term to use when referring to a film-based camera. :rolleyes:

We had an imaging sensor in the SR-71 that wrote digital imagery data on film using a laser. It was developed in standard chemistry, then read by a computer using another laser to an output that was printed by the computer...to a film positive print. Digital film! I think....

[Scottes]

Digital film! I think....
That sounds exactly like LightJet printing.

From Wikipedia:
"Silver-halide photographic paper is fixed on an internal drum, where three digitally controlled lasers simultaneously expose the photo-sensitive paper (or back-lit transparency medium) with red, green, and blue light. This light-path includes a spinning surface coated mirror mounted on an air-bearing that travels along the axis of the internal drum, thus reflecting the laser light at 90 degrees to ensure a perfectly round imaging dot across the entire area of the photographic paper. This round imaging dot is critical for edge to edge sharpness of the print. The print is then processed using traditional photochemical means. After which, the photographic print is handled just as any other photo-print."
http://en.wikipedia.org/wiki/LightJet