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?

 

[PhotoXopher]

Aperture is always wide open until the shot is taken, or the DOF preview button (if equipped) is pressed.

My Nikon N75 has one, so does my D90 - so they were available in the film days.

I guess you either have to bring a calculator or download one of the many free applications for hand held devices, I have one on my phone for example (never use it, but it's there).

 

[Big Mike]

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

Same deal with any modern SLR. The viewfinder looks TTL with the aperture wide open. So you are only seeing an accurate DOF if you are set to shoot at the max aperture.

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

By using the DOF preview button, by using the distance scale, by using a DOF chart (or calculations)...but I'd guess the most common way is just with experience.

Yes, the problem with DOF preview is that because it stops down the aperture (if you are set at a smaller aperture) it dims the viewfinder. The smaller the aperture, the dimmer it gets. You can usually get your eye to adjust but sometimes it's just too dark. Also, back in the film days, viewfinders were often bigger, making it easier to see the image and ascertain the DOF. Higher end SLR bodies still have larger viewfinders but entry level DSLR bodies (like the Rebel series) have rather tiny viewfinders, which makes it quite hard to really see the image well enough to be sure of your DOF.

Of course, you can take a test shot and zoom into the image on the LCD. Or just take several shots at different apertures, to be sure that you get one with the DOF you want.
Heck, you can even take several shots with different focus points and combine the shots with what's known as 'focus stacking'.

 

[Garbz]

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

You were, assuming you were shooting wide open . TTL is through the lens. Didn't you ever look into the lens from the front and notice the lack of aperture blades?

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

DoF preview isn't new. My Nikon FE from the early 70s has it. A friends Nikkormat has it too and that's even older. In the case of my FE the DOF preview lever actually physically actuates the lens's aperture blade release lever. My D200 does the same except via a computer inside the camera that drives a little electric motor and my haven't we complicated things in the last 50 years

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

The shutter is totally closed at all times. That's what the mirror is for. You're looking past the shutter. The lens is open at it's max aperture. The aperture where the blades completely give way to all lens elements. There is no larger aperture since the glass isn't larger.

Look into the front of your lens and hit the DOF preview button to get an idea for this.

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?

You can focus on the middle of the group and then use a Online Depth of Field Calculator. You can google Depth of Field charts too and print them out and carry them with you (quite handy, I keep a few in my camera bag).

Or god forbid take a photo. It's digital. Look at the screen

 

[kkamin]

You were, assuming you were shooting wide open . TTL is through the lens. Didn't you ever look into the lens from the front and notice the lack of aperture blades?

I'm glad you find some type of satisfaction in trying to make me feel unintelligent.

I appreciate everyone else's replies.

 

[Goontz]

I'm glad you find some type of satisfaction in trying to make me feel unintelligent.

I appreciate everyone else's replies.

Well I suppose that's one way it could be taken...

 

[JerryPH]

You were, assuming you were shooting wide open . TTL is through the lens. Didn't you ever look into the lens from the front and notice the lack of aperture blades?

I'm glad you find some type of satisfaction in trying to make me feel unintelligent.

I know garbz, and that was not what he was trying to do, he was asking you an obvious question if you never noticed the lack of aperture blades. Emotions are hard to convey in writing, but you need to grow a thicker skin if your intentions are to stick around here for more than 1 post.

 

[robertwsimpson]

I'm not certain that when you look through your camera you're seeing with the aperture wide open. With my 50mm 1.8, the DOF looks WAY deeper through the viewfinder than it turns out being after I take the picture at f1.8

just sayin.

 

[bhop]

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

My film SLRs have DOF preview.

 

[robertwsimpson]

I can open and shut my aperture on my AE-1. there's a button right next to the lens.

 

[Sn00bies]

I'm not certain that when you look through your camera you're seeing with the aperture wide open. With my 50mm 1.8, the DOF looks WAY deeper through the viewfinder than it turns out being after I take the picture at f1.8

just sayin.

Great point, now that you mention this, it makes sense... so what happens on the 50mm 1.8 then? *curious*:scratch:

 

[coreduo]

Make your shutter speed 4 minutes and your aperture f/45, you'll get a good DOF. I read it in a magazine that teaches basic photography. It arranges all arrays of f-stops and shutter speeds corresponding to each other under the title "Depth of Field". It is still available in bookstores although I forgot the title of the magazine.

 

[Soocom1]

Years ago, many of the older non auto film cameras had the aperture closed to the set stop BEFORE the film was wound. I.e. you took a shot, and before you advanced the film, the aperture was stopped down to what you set it to.

After the Automatic cameras came into being, DoF buttons went away on many consumer grade cameras as a matter of the "idiot light" syndrome. This being that like in the automotive world, the lights replaced the gages because industry thought no one used them any more.
In the film world, they scaled back a large amount of the features like DoF, mirror lock up etc. on many cameras because of that mentality.

So when the DSLRs came out, same concept occurred until people started complaining about the lack of things like DoF preview, etc.

As for the other parts of the question, the best thing to remember is this:
follow ALL of the old rules regardless of camera used if in doubt.
Dont let the camera think for you....lol

 

[kkamin]

Thanks for all the replies!

The Pentax 35mm film camera I started with back in art school didn't have a DOF preview, and when I used higher end film cameras, for whatever reason I was oblivious to that feature.

It is ironic, since I took many advanced photography classes in school but never thought about getting an accurate DOF reading TTL; for some reason I thought what I saw was what I got. I think my style of shooting is to blame. I tend to either want the background completely out of focus or else everything in focus--so my camera is either almost wide open or I'm shooting at mid-high stop and everything is fairly far from the camera or I'm using a fairly wide lens. So I never had results that puzzled me. And for still lifes or portraiture I would often use a tape measure to ensure sharp focus on the eye or whatever and use the guide on the lens to figure out my range of focus.

Thanks again for all the replies!

 

[Garbz]

I'm glad you find some type of satisfaction in trying to make me feel unintelligent.

I appreciate everyone else's replies.

If by making you feel unintelligent you actually mean posing a question that may tickle your interest further into investigating the operation of your camera, then yes I get satisfaction.

2 things to point out:
1) The most intelligent mechanical engineer I know has never looked in the front of his camera while taking a photo. Why would he? That's not how you use a camera! It's about interest not intelligence.

2) I teach electrical engineering students and I could crap on all day about waveforms and measurements and all I get is people falling asleep in the class. But tell someone to look at the oscilloscope or actually just try and see what happens, and they stay interested and may even get excited about exploring further.

Make your shutter speed 4 minutes and your aperture f/45, you'll get a good DOF. I read it in a magazine that teaches basic photography. It arranges all arrays of f-stops and shutter speeds corresponding to each other under the title "Depth of Field". It is still available in bookstores although I forgot the title of the magazine.

Assuming it would be possible (most SLR lenses have a minimum aperture of f/22 or f/32) you'd end up with a very out of focus and blurry picture. The smaller the aperture the more light diffracts through it. On DSLRs the diffraction limit is around f/11 to f/16 on full frame cameras f/16 to f/22.

The larger the sensor the lower the circle of confusion as the lens is designed to project a larger image (ok it's far more complicated than that). The book you were referring to was likely written for medium format or large format photographers.