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Old Aug 19, 2006, 11:50 PM   #1
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I have seen this statement a lot. Can someone explain it? I want to buy the Canon 5D and I read this staement and was wondering does this mean when I am taking shots of scenary, will this be anm issue where I would like to have a lot of DOF.

Also can I simply go to a smaller aperature and get the DOF back in a particular instance as say a crop camera would have?

Thanks for your help.

Ken




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Old Aug 20, 2006, 1:11 AM   #2
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Depth of field depends on the aperture size, the focal length and the distance to the subject. It is independent of the sensor or film. An 80mm lens at f8 will have the same depth of field on a 5D as on a 30D.
However, the size of the sensor will change the field of view of the lens as the smaller sensor effectively crops the image projected by the lens. In the above case, the 30D will give a picture similar to the 5D with a 130mm lens. To get the same view on the 30D as the [email protected] you would need to use a 50mm lens. A 50mm @f8 has a greater depth of field than an 80mm @f8 and so the 30D will have a greater depth of field in an otherwise identical (same field of view, same aperture and hence same exposure) shot.

You need a much wider-angle lens to get the same view in a crop camera, and this gets important when you take landscapes. A 16mm is very wide on a full-frame camera, but not so on a crop. A year or so ago there basically was no way to get a really wide angle on a crop camera as no-one made the necessary lenses. The canon 10-22 and sigma 10-20 fill this gap quite nicely.
The 5D is still much the better camera for landscapes but you will need better lenses, a heavier tripod and large prints to really see that difference.

Yes you can stop the lens down further to get your desired depth of field.
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Old Aug 20, 2006, 10:01 AM   #3
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Hi Jacks,

Best explanation I have read. let me ask you though, why do they say that there is a shallower DOF on a FF camera than a crop camera then. Is this a blanket staement. Is it simple to make up for this without sacrficing image quality or something else?

So the shorter the focal length, the greater DOF, or the other way around?

Does going to a smaller aperature size always do the trick in making up for the DOF difference? I would imagine that a limiting factor could be that if depending on light, if are not able to slow the shutter speed down that much with the smaller aperature, then you can increase the ISO? Is this correct? I'm coming from film so I'm trying to understand.

If I have good lenses, is the 5D the better way to go if money is not the issue?I was thinking of starting with the Canon 24-105 L series F.4. Would this relove any DOF issues or any other issues where they say that at the edges of some images, it can blur with a lens that is not real good.

I am using the camera for general purposes such as vacations (scenary), family events, when I take my son to a game, and anything else now that I don't have to pay to buy and develop film. When people refer to landscapes, does this constiture general scenary in say a National park. I know that seems like a dumb question but I don't want to make the wrong decision.

Thanks- Ken


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Old Aug 20, 2006, 10:23 AM   #4
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If you were into film photography the DOF on the 5D is the same as a 35mm film SLR with the same lens and settings. People never had problems taking landscapes with 35mm.

The problem is usually with the DOF being too large with smaller sensors so you can't properly blur the background. There are ways to increase the DOF, but once the lens is full open at a given focal length there is no way to decrease it.

There is no inherent edge blur in a FF digital. You will get the same edge sharpness with the same quality lens you got with film. The caution about blurred edges is for people with lower quality lenses who have had good edge sharpness because they are using only the sweeter part of the lens with an APS sized sensor.

If money is no object get the 5D. DOF and edge sharpness for a given quality lens will be the same as you experienced with film. You have the added advantage you already mentioned of being able to increase the ISO to improve the DOF if that is required for limited light.

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Old Aug 20, 2006, 11:30 AM   #5
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jacks wrote:
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Depth of field depends on the aperture size, the focal length and the distance to the subject. It is independent of the sensor or film. An 80mm lens at f8 will have the same depth of field on a 5D as on a 30D.
This is not true, I'm afraid.

First off, one thing left out of this is the lens itself - the actual focal length of the lens(not apparent focal length) is what is important. This is why the digicams that have a very small focal length have greater DOF.

Secondly, the circle of confusion plays a part and that is dependent upon the sensor.

Read this - it's a good article that explains DOF and Circle of Confusion:

http://www.luminous-landscape.com/tu...ries/dof.shtml

Now, given your example - the 30D with an 80mm lens will actually have a SHALLOWER DOF than the 5d. Here's an online calculater you can use to see how DOF changes with same lens and different cameras:

http://www.dofmaster.com/dofjs.html


Here are the calculations for Depth ofField:

http://www.dofmaster.com/equations.html

Here are the Circle of Confusion values for cameras:

http://www.dofmaster.com/digital_coc.html

It's a lot to read, but it could help clear up some confusion.

Also, don't forget the lens design has a lot to do with the QUALITY of the blur (bokeh) - not all blurred backgrounds will look the same.
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Old Aug 20, 2006, 8:17 PM   #6
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Thanks all.

Those links are very informative. Sometimes I have to read it, and go back again and look at it again. So after all is said and done it looks like the DOF on the 5D FF camera will be same as my 35mm film camera. Am I correct in my thinking that the smaller sensors on a crop camera is what changes the DOF with the same focal length lens with a FF sensor? It looks like you get a wider DOF then with a FF sensor. Is this correct/ Also then, to give myself less DOF with the 5D, i would open the aperature wider?

Thanks again- Ken
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Old Aug 20, 2006, 10:03 PM   #7
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At a given aperature, the 5D will have less DOF than the non full frame DSLR's. However, you overcomplicating the issue. Remember, people were able to achieve a lot of DOF with 35 mm film SLR's. Anything f11 or smaller will yield plenty of DOF, even on a full frame sensor. The basics of controlling DOF are the same whether your using a full or APS sized sensor. The difference in DOF between full frame and APS sensors is not nearly enough to be concerned about.
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Old Aug 21, 2006, 2:10 AM   #8
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Quote:
At a given aperature, the 5D will have less DOF than the non full frame DSLR's.
That's not quite right unfortunately, it leaves out too manyvariables.

The only way to understand the complex relationship is to play with the equations, but in practice it is true that on smaller formats you generally have pictures with more depth of field.

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Am I correct in my thinking that the smaller sensors on a crop camera is what changes the DOF with the same focal length lens with a FF sensor?
Correct.

Quote:
It looks like you get a wider DOF then with a FF sensor.
No you've got it backwards.

As far as film/sensor size is concerned, the relationship is very simple and intuitive. Keeping all other variables the same i.e. focal length, distance to subject and aperture, print size, viewing distance, etc. TheSMALLER the film/sensor the LESS the depth of field.

This is opposite to what most people think, but makes perfect sense. Think about a picture which runs from sharp foreground to infinity all in focus. If you cut a piece out of the middle you have less picture, and before it was all sharp, so now you have less depth of field.

The reason you generally get greater DOF with the smaller film/sensor is that we use different focal lengths (to get the same field of view), and focal length is a more important variable in the equation than the sensor/film size. In fact when you adjust for the "crop factor" the cameras with a smaller sensor/film will give pictures with a greater DOF.

So an 18mm lens on a crop camera gives less DOF than that same lens on a FF camera, but greater DOF than a 28mm lens on a FF camera, which is how it's usually compared.

I suggest you go back to the links that JohnG pointed out earlier, keep playing with them. There are a lot of variables and it's very hard to describe accurately in English because you can always say "but what about.."

In practice it means that I find it easier to take landscape shots with bigger DOF on my 20D than it was with 35mm. I can generally get pretty good results hand-holding on the 20D, on 35mm a tripod was usually required. Move up to medium format or large format and tripods become essential even in bright daylight - right?
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Old Aug 21, 2006, 7:35 AM   #9
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peripatetic wrote:
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It looks like you get a wider DOF then with a FF sensor.
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Hi. I looked at what I wrote before seeing your reply and reaiized that I typed it the wrong way. I meant it the other way around. Actually if there was no such thing as crop cameras I would have understood things as I had with film. When the 1.5 and 1.6 got thrown into the mix with digital, it clouded things for me.
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Thanks,Ken
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Old Aug 21, 2006, 8:34 AM   #10
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Yup, if you understood the issue on 35mm film v medium format then you understand the issue now.

Just think of it as big sensor v small sensor, and all the same priciples of big film v small film apply.
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