Lower Light And Depth Of Field

[rugerfly]

Ok, lets see if this comes out right. I took this in Lowish light inside, using 2,500 ISO with a 50mm lens. I was focusing on nothing particular, but on Fly's head on the nose bridge I think. How do I achieve a better DOF without loosing any quality/sharpness? Is it to do with the lens, ie if I moved further away and used a longer lens? or entirely to do with F stop?

This is using 2,500 ISO but focus doesnt go much beyond her head, even rugies nose is blurred slightly..

[Damabelle]

Better depth of field - I am not sure what you mean. Do you mean more depth of field (more in focus)? What is better really depends what you want to achieve.

The aperture (f-stop) of the lens is what is primarily used to control the depth of field. If you want a shallow depth of field (a limited plane that is sharply focussed, and the rest blurred) you use the lens wide open (lower f-stop numbers) eg f2.8 or f4, for more sharpness throughout you close the aperture of the lens down - ie higher f-stop is used (eg f16 or higher). The focal length of the lens can also make achieving the effect you want eaier or more difficult.

A 50mm lens is known as a "normal" lens, and gives roughly the same perspective as the human eye.

Wide angle lenses have a focal length shorter than normal (eg 24mm), and are easier to use if you want a picture that is sharp throughout.

Telephoto, or lenses longer than 50mm (eg 85mm) are easier to use if you want a narrow depth of field, and background blur (blurring the background reduces distraction and helps focus the viewer on your subject).

Hope this helps...

Anne

Edited September 3, 2008 by Damabelle

[Luke W]

You can increase DOF by:

Moving the lens further away from the subject (makes the subject smaller)

Decreasing the focal length (eg...by using a 35mm lens rather than a 50mm lens) - again makes the subject smaller.

Descreasing the aperture (a higher FSTOP) - this will reduce the shutter speed...you MAY end up with camera shake problems without a tripod - depending on how slow the shutter speed is...

Understanding the impact of aperture (fstop), shutter speed, and ISO on correct exposure is crucial. Then factor in focal length and subject distance to get a feel for DOF.

[rugerfly]

Cool, thanks for your replies. I understand how F Stop affects DOF, but never really got to focal length. Im ok with it all using good lighting, but want to be really good in low light. Your reply's make sense, thankyou..

[Damabelle]

That's good. One of the keys to focal length and a broad depth of field is the hyperfocal distance. Focusing your camera at the hyperfocal distance ensures maximum sharpness from half this distance all the way to infinity, the hyperfocal distance varies with the aperture (f-stop) used and the focal length of the lens, and really demonstrates the difference between using wide angle and telephoto lenses. The web-site below includes a hyperfocal distance calculator I would recommend you try out.

http://www.cambridgeincolour.com/tutorials...al-distance.htm

Your picture was taken with a 50mm (f1.4 min) lens at F5.6 and 1\320 at ISO 2500 with a Nikon D3 (Full frame DSLR - very nice kit by the way...)

For a "standard:DSLR with a 1.6X crop factor (or using DX lens on a full frame nikon) the hyperfocal distance for a variety of lens at f5.6 and f16 is

Focal Length f5.6 f16

16mm 2.2m 0.8m

24mm 5.0m 0.9m

35mm 10.6m 1.9m

50mm 21.7m 3.8m

85mm 62.6m 11m

135mm 158m 27.6

200mm 346.7m 60.7

Your camera is full frame, so as long as you are not using a DX lens you need to change the camera type in the calulator to 35mm. So for your camera using

Focal Length f5.6 f16

16mm 1.4m 0.5m

24mm 3.1m 1.1m

35mm 6.6m 2.3m

50mm 13.5m 4.7m

85mm 39.1m 13.7m

135mm 98.6m 34.5

200mm 216.5m 75.8

So using the settings you used, (50mm at f5.6) your hyperfocal distance would be about 13.5m.... So for everything to be completely in focus the end of the lens would need to be half that distance away from the closest object you want in focus 6.2m (and you couldn't get that closeup look you have at that distance). Stopped down to f16, you would have considerably increased your depth of field, but would have needed to reduce your shutter speed to about 1/90 second (and could have gotten movement blur if the animals didn't co-operate) if you were less than 2.4 meters away the background would not have been completely sharp (but I personally wouldn't want it that way anyway).

I would have been happy with the sharpness of shot you have (at least in the resolution I see on the post). For the iso (2500) there is very little noise (makes me jealous and really want to switch from my canon 1Dmk3 to one of the new nikon cameras). The fact that you have a full frame camera and great noise reduction (nikon d3) means you really do have the best equipment for these kind of shots. A slightly wider lens would make your job easier. For most portrait work, the part that is really important to be in focus is the eyes - so really check for this when you are framing the shot. Dogs can be more of a challenge to photograph than humans as more depth of field is required to get the nose and eyes in focus (particularly head on).

If you have stationery objects in low light adjusting the depth of field by increasing the shutter speed is relatively simple using a tripod to stop camera shake. With moving objects in low light, and no flash lighting there are optical limits to what you can achieve.

Anne

[rugerfly]

OH MY GOD I UNDERSTAND EVERYTHING YOU SAID

Thanksyou for your explanations! Yes its an excellent camera, I really love it. I took another shot, more of a front on shot of Ruggies face, and same type of thing as you said, I have his eyes in focus, and his nose is slightly blurry

If I can find it i'll post it.

[rubiton]

And this is why with something like horse photography getting lens that go down to F1.8 or whatever are of no interest to me. I need to go no lower than about F5 or the animal will look wrong. At F8 its a nice DOF.

In lowlight the ability to push the ISO right up helps immensely before having to sacrifice speed (once down to F5.0).

[Scotty]

As I undersand it DOF relates to Aperture.

Wider aperture equals shallower DOF - ie less stuff in focus.

So you narrow the aperture and consequently have to slow down your shutter speed. Or if you have faster film you can have a faster shutterspeed.

[Scotty]

That's good. One of the keys to focal length and a broad depth of field is the hyperfocal distance. Focusing your camera at the hyperfocal distance ensures maximum sharpness from half this distance all the way to infinity, the hyperfocal distance varies with the aperture (f-stop) used and the focal length of the lens, and really demonstrates the difference between using wide angle and telephoto lenses. The web-site below includes a hyperfocal distance calculator I would recommend you try out.

http://www.cambridgeincolour.com/tutorials...al-distance.htm

Your picture was taken with a 50mm (f1.4 min) lens at F5.6 and 1\320 at ISO 2500 with a Nikon D3 (Full frame DSLR - very nice kit by the way...)

For a "standard:DSLR with a 1.6X crop factor (or using DX lens on a full frame nikon) the hyperfocal distance for a variety of lens at f5.6 and f16 is

Focal Length f5.6 f16

16mm 2.2m 0.8m

24mm 5.0m 0.9m

35mm 10.6m 1.9m

50mm 21.7m 3.8m

85mm 62.6m 11m

135mm 158m 27.6

200mm 346.7m 60.7

Your camera is full frame, so as long as you are not using a DX lens you need to change the camera type in the calulator to 35mm. So for your camera using

Focal Length f5.6 f16

16mm 1.4m 0.5m

24mm 3.1m 1.1m

35mm 6.6m 2.3m

50mm 13.5m 4.7m

85mm 39.1m 13.7m

135mm 98.6m 34.5

200mm 216.5m 75.8

So using the settings you used, (50mm at f5.6) your hyperfocal distance would be about 13.5m.... So for everything to be completely in focus the end of the lens would need to be half that distance away from the closest object you want in focus 6.2m (and you couldn't get that closeup look you have at that distance). Stopped down to f16, you would have considerably increased your depth of field, but would have needed to reduce your shutter speed to about 1/90 second (and could have gotten movement blur if the animals didn't co-operate) if you were less than 2.4 meters away the background would not have been completely sharp (but I personally wouldn't want it that way anyway).

I would have been happy with the sharpness of shot you have (at least in the resolution I see on the post). For the iso (2500) there is very little noise (makes me jealous and really want to switch from my canon 1Dmk3 to one of the new nikon cameras). The fact that you have a full frame camera and great noise reduction (nikon d3) means you really do have the best equipment for these kind of shots. A slightly wider lens would make your job easier. For most portrait work, the part that is really important to be in focus is the eyes - so really check for this when you are framing the shot. Dogs can be more of a challenge to photograph than humans as more depth of field is required to get the nose and eyes in focus (particularly head on).

If you have stationery objects in low light adjusting the depth of field by increasing the shutter speed is relatively simple using a tripod to stop camera shake. With moving objects in low light, and no flash lighting there are optical limits to what you can achieve.

Anne

Um, or of course wot she sed.

[rugerfly]

Yes Yes