Teleconverter questions

reaper7534 · Mar 17, 2013

I currently have a 70-200 f/2.8 L and ordered a Kenko 1.4x tc for it today. I know I lose a stop of a light, so I will essentially have a f/4 lens. Question is, does it also effect DoF ? Will my background not be as out of focus ?

Thanks

KmH · Mar 17, 2013

Yes effectively the lens becomes f/4 max aperture.
Only from the effective, TC induced, f/4 to smaller apertures.
That depends on all the factors that determine depth-of-field. Lens aperture is just one of them. The others are - point of focus distance, image sensor size, and lens focal length. The further away the background is, the more likely it will be beyond the far limit of the DoF.
Understanding Depth of Field in Photography

djacobox372 · Mar 21, 2013

Unless you have a really low resolution camera body, you'd be better off just cropping. Teleconverters are really only useful for video now days IMO.

hirejn · Mar 21, 2013

The lens focal length is not a factor in DOF. If you zoom in and hold the DOF preview button, it will look the same as if you zoom out and hold the DOF button and zoom back in. The focal length doesn't change DOF. All lenses have the same DOF at a given aperture, regardless of focal length or manufacturer. The crop of the image created by focal length affects the perspective, creating the illusion of different DOF. But technically lenses of different focal lengths, even when set to different focal lengths, have the same DOF at a given aperture. If you add a TC and the aperture changes, then you know the aperture is affected. But DOF at f/4 is DOF at f/4. What can affect it is distance between subject and bg. But again if you frame a subject with a 105 mm at f/8 and get close enough to frame the same subject identically with a 35 mm at f/8, the DOF is identical.