Help understanding Distance settings

[Gazman]

Hi, I`m currently reading through "Understanding Exposure" and after reading the chapter on "storytelling Apertures" i`m struggling a little to take it in.

In it the author goes on about modern zoom lenses not having depth of field scales, but instead use distance settings to help get Sharp images from near to far, for wide angle shots.

How does this work? He says he presets the depth of field before taking the shot. So, after setting apperture as small as possible (to get sharpest image possible) he then aligns distance above his distance setting mark on the lens, with the focal length determing the distance. This is what i dont understand, mainly im guessing because this is the first time i`ve heard about this.

in the book it says how through the viewfinder the image will look completely out of focus, but once the shutter has been released , all will become clear, as it were.

Sorry for long post, its late, im tired and i can`t get this to sink in
I`m going to play around tommorow to see if i can grasp it anymore. But any feedback would be a bonus.

 

[prodigy2k7]

That makes... no sense to me...

 

[tirediron]

I think I understand what's being asked. Essentially what is being discussed in the book is a modern method of obtaining the hyperfocal distance of a lens. Older camera lenses usually had a DoF scale on them. If you look at the image below:

You can see the scale which appears between the distance markings and the actual apeture and marked "Depth-of-Field" scale on the image. This allows you to determine what area of an image will be in focus by looking at the distances between whatever apeture you have set. IE: Assume the lens is set to f16; look at where the '16's are relative to the distance scale. This tells us that everthing from about 2.8m to infinity is going to be in focus, but when you look through the viewfinder, most of this will appear out of focus unless you use your DoF preview function.

Since modern lenses don't have this, you need the addition of a DoF calculator ( http://www.dofmaster.com/dofjs.html ). Decide what area you want to be in focus, then stop your apeture down (usually to maximum, but this is also useful if you only want a specific range) and then set your lens so that the the subject distance is at the distance mark on your lens; you will now have the greatest possible part of the image (or that portion want) in sharp focus.

With a little bit of measurement, you can also mark your lens with the necessary scale so that you can eliminate the DoF calculator.

More reading here: http://www.dofmaster.com/hyperfocal.html

I hope that explains things...

 

[Gazman]

It does help a little bit yea, so the subject you want to shoot needs to be the same distance as what is set on the lens i guess?

I`ll also take a look at the link you posted later. Thanks

 

[Computer_Generated]

Remember that when he says the smallest possible he means the higher numbers like 22 or higher. I think this is what he was getting at by giving best DOF on the lens. If i remember the book right there's a section where he took a picture of some beach boulders and the background is as clear as the boulders. Again, if I remember correctly he set to a small apature then focused 1/3rd into the frame to give best DOF for his "storytelling" scene.

 

[Gazman]

Yea, getting my head round high numbers = small aperture is fine, i`m understanding that fine.
It was just how he goes on about taking a photo that is blurry through the viewfinder, but comes out crystal sharp once shot that was the issue.
Furthermore, how he actually set up the shot , i.e using the distance setting technique discussed in the OP

 

[Chris of Arabia]

It was just how he goes on about taking a photo that is blurry through the viewfinder, but comes out crystal sharp once shot that was the issue.

That's because when you view the scene through the viewfinder normally, the lens is at it's maximum aperture (e.g. f/2.8), but when you take the shot, the aperture gets stopped down to something smaller (e.g. f/22). At f/2.8 you get a very shallow DoF (lots of blurry stuff), whilst at f/22 the DoF is increased hugely and much of the scene will appear to be sharp and in focus.

 

[Computer_Generated]

That's because when you view the scene through the viewfinder normally, the lens is at it's maximum aperture (e.g. f/2.8), but when you take the shot, the aperture gets stopped down to something smaller (e.g. f/22). At f/2.8 you get a very shallow DoF (lots of blurry stuff), whilst at f/22 the DoF is increased hugely and much of the scene will appear to be sharp and in focus.

Exactly, so when he sets his small apature to give the furthest DOF and views the scene through the viewfinder, it's going to look like he took it with like an f5.8 until he clicks the shutter button and then the camera sets the chosen apature. Some cameras come with a DOF Preview button too. This will let you preview what your small apature will look like. Just remember that when you do this the viewfinder will get darker because you're letting less light in.

 

[Gazman]

Ok, cool, i think i understand a little better now thanks.

So, if that is the case, does this mean whenever you view an image through the viewfinder, it will always essentially be representing the widest aperture on your camera/lens , no matter what aperture you have set?

So say im shooting at 8.0 , until i release the shutter , the viewfinder will actually look more like 3.5 or whatever largest aperture is?

 

[ejcarrol]

i'm also reading the same book. in my understanding, yes, what you see through viewfinder is when aperture is at it's largest opening (ie, smalle number). but in the book, he also talked about the depth of view preview button. there's that section on page 50 in the book that talks about the specific function.

 

[prodigy2k7]

So say im shooting at 8.0 , until i release the shutter , the viewfinder will actually look more like 3.5 or whatever largest aperture is?

Yes.


My camera (Canon XTi) has a DoF Preview button next to the lens on the body, you press it and change the apreture at the same time and you can see the DoF changing, also getting darker/lighter.

Yes I would assume when you take a picture it sets the aperture first then opens and closes the shutter then releases the aperture.

 

[reg]

This is one of the areas where "Understanding Exposure" fell flat.

It has a lot of good info but the whole "storytelling aperture" etc. is really stupid IMO. If he had left all that crap out and just said "More dof = high f number, less dof = low f number" then the whole section would have been a lot better.

The other thing is that, since you had to even ask what he meant (it made no sense to me either, w/o further explanation) then to me that means he didn't explain it well enough.

 

[Gazman]

i agree, although im in no position to comment properly yet, as im only on pg47 and so far, excluding the chapter mentioned in this topic, it`s the only place i`ve become stuck.

Rest of the book to date has been a good read, and some of his pics are real quality.