Depth of field scale for the D90, confused.

Would someone be so kind as to explain the scale. I have tried several sites, and all I end up with is . Or head me in the right direction to a site that is not so technical. I know it has to do with the lens, and maybe the sensor on my D90 and the type of lens that I may be using at the time. Oh ya and the Aperture, and distance. I have printed out a copy of several focal lengths based on my D90 which I found on a site.

Distance- Near----- Far---- Focal Length 18mm---- F1.4

1 foot--- 0'11.7"--- 1'0.3"
2 feet--- 1'10.8"--- 2'1.3"
3 feet--- 2'9.4"---- 3'3.1"


Now is the information based with just the lens and no filter? If so what happens when you use a neutral density filter or a polarized filter. Do you step down the info to a 2.8?

I realize this may be asking alot of someone, but I would really appreciate it.

Thanks
Michael.

I'm not able to explain the calculations to you, but thought that these might be of some value:
Depth of Field: Optical: Glossary: Learn: Digital Photography Review
Online Depth of Field Calculator

Here's the brief explanation of depth-of-field (DOF):

Depth-of-field is the portion of a scene, from near to far, that appears acceptably sharp in the image. Although a lens can precisely focus at only one distance, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.

The shorter the focal length of the lens, the greater DOF (i.e. an 18mm lens will have greater DOF than a 200mm lens, at the same focused distance & same aperture)
The smaller the aperture, the greater the DOF (i.e. f/16 gives greater DOF than f/2.8)
The greater the focused distance, the greater the DOF (i.e. Focusing at 20 feet gives greater DOF than focusing at 3 feet)

So, as an example, an 18mm lens @ f/16 focused at 20 feet would yield tremendously greater DOF than a 200mm at f/4 focused at 6 feet.

And no, filters do not have any effect on DOF.

Filters have an effect only to the extent that they may reduce the f/stop.

Joseph, are my calculations then based on the new f/stop?

Michael

[FONT=&quot]Filters may reduce the amount of light entering the lens, but this does not necessarily mean that it results in a larger aperture, thereby reducing DOF. The light loss can be compensated for by using a slower shutter speed. So a filter, in and of itself, does not effect DOF. In the example that the original poster asked, no, using a neutral density, or polarizing filter would not change the effective aperture from 1.4 to 2.8 for purposes of the DOF chart. In fact, the opposite would be true in the sense that if by using an ND or polarizing filter, the aperture was opened to compensate for the light loss, the DOF would be reduced. However, just as easily the shutter speed could be adjusted to compensate for the light loss caused by the ND or polarizing filter so therefore the light loss, and consequentially, the filter itself does not have any effect on DOF.

[/FONT]

Michael - I should have put mind in gear before posting the above statement. I should have explained how filters have an effect on f/stops. The correct answer is yes and no. If you set the camera on, "Aperture Priority", f16 and you add a two stop neutral density filter the DOF is based on f/stop, f16. In this shooting mode the f/stop is locked in and does not change even with a two stop ND filter. Your calculations are based on the Aperture Priority setting of f/16. The exposure will be two stops down because of the ND filter will slow down the shutter speed and not effect the f/stop. If you set the camera on "Shutter Priority", and add a two stop ND the metering system will read the exposure through the filter and reduce the f/stop by two stops. In this mode the shutter speed is locked in and the f/stop is allowed to change by two stops. In this case your calculations would be based on f/8 which is two stops down from f/16. Most advanced amateurs and professionals shoot in the "Aperture Priority Mode" and set the f/stop they want. That is the recommended shooting mode. Use shutter priority only in cases where maintaining a certain shutter speed is more important than the f/stop. Hope this is more help than my first post.

I think I have it now, except for 2 things. On a telephoto lens are the calculations based on the maximum focal length of the lens, or everything inbetween? And what is Hyperfocal distance.
Many thanks Lenswork, and Joseph.

Michael

M.Hinch said:

...what is Hyperfocal distance.
Michael

Click to expand...

Hyperfocal distance - Wikipedia, the free encyclopedia
Definition 1: The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp; that is, the focus distance with the maximum depth of field. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.
Definition 2: The hyperfocal distance is the distance beyond which all objects are acceptably sharp, for a lens focused at infinity.
The distinction between the two meanings is rarely made, since they have almost identical values. The value computed according to the first definition exceeds that from the second by just one focal length.

Hyperfocal Distance
The concept of hyperfocal distance is easy to understand: focus a lens at the hyperfocal distance and everything in the photograph from some near distance to infinity will be sharp. Landscape photographs are often taken with the lens focused at the hyperfocal distance; near and distant objects are sharp in the photos.

Then there is the term "Circle of Confusion" which also relates to DOF, but I won't get into that here, just to say that "Circle of Confusion" is what you get when you have a group of Photo 1 students gathered around the instructor while he/she tries explain depth-of-field (haha).

The DOF is a function of f/stop and focal length. The DOF range gets shallower as the focal length gets longer. If you are using a DOF calculator then it should have a place to enter the focal length. The focal length to use is the one the lens is zoomed to. If a 70-300mm lens is zoomed to 200mm then use that in the calculations. If it's zoomed to 125mm then use that number. As far as the hyperfocal distance and circle of confusion is concerned I would recommend getting a good handle on using and understanding DOF first. Hope this helps.