Depth of field

[ROBFH]

I use a Nikon 70-200 f2.8 lens and get a shallow depth of field at f2.8 Can someone explain what happens to the depth of field when I attach a 1.7 converter? It shows as f4 but does this mean that I can therefore expect to get a slightly deeper focus? I am a novice and find it difficult to get accurate depth of focus when photographing birds.
I use shutter priority because Blue Tits and the like do not hang about so I am working with speeds of 500 up.
Thankyou and all have a Happy christmas.
Robfh

[Bobobird]

For bird photography -

DOF - you need as much as you can get because most birds will not be on a parallel plane to get the whole in focus with a wide aperture. A good starting point would be f5.6-f11.

Speed - unless the bird is quite large and moves slowly you will want as much speed as you can get. A good starting point will be 1/1000, preferably 1/1600 or higher.

If you are unable to maintain those settings then up the ISO. On most DSLRs of the past 2 maybe 3 years, the higher ISO performance is pretty good. I regularly go to 1600 on my 550D. Do not worry too much about the noise. If the exposure is correct the noise will clean up well in post and the loss of detail is quite insignificant.

[Dave Humphries]

Hi Rob,

I agree with Bobo's advice on bird photography.

I'd suggest a 70-300mm, used at f/8, is going to be easier to hand hold than your combination if you're shooting BiF (birds in flight).

However, this doesn't answer your question about whether the 'enlarged by teleconverter' image, which changes the EXIF and camera display to the "f/4" gives the same DoF as a non teleconverted lens of same focal length (340mm) and aperture (f/4).

I can't work it out tonight, too late and I have no experience, but I'm sure someone here will have.

Cheers,

[Bobobird]

Oops! Forgot that bit about the TC.

The use of a TC on a zoom lens does bring a loss of image quality, particularly with the details.

So in an unscientific way one can say that there is an effect on DOF due to the general softening brought about by using a TC. A blurred background at 300mm will be more blurred at 420mm (in my case with a 1.4 TC) but so will the main subject.

[Hero]

Not realy Bobobird. The TC and it's loss of IQ affects the whole picture not just the fore- or background or the proportions between them. Anyways, according to some experimenting with Julian's DoF-calculator a 200mm f2.8 lens with a 1.7 TC will have the same DoF as a 340mm f4. But as Bobobird said, with anything you stick on a lens or between lens and camera you will lose a bit of IQ. How much depends very much on the quality of the lens itself and the TC used.

[ROBFH]

Thanks you guys. I have always been scared of letting ISO go too high. I have a Nikon D300.
I am not computer literate enough to upload pictures (thickness they say is a sickness in which case I am very sick) I will wait for a friend to come and show me, then I can get some educated criticism. Thanks again, much appreciated.
Rob