How can I avoid fuzzy photos at 300mm zoom?

Question

I'm so disappointed in my new 70-300mm lens (AF-S Nikkor ED lens.) I use auto-focus because I'm such an amateur. Is it my camera, (D40x) or the lens? It's probably me, but is there a trick to getting a clear, crisp photo while zoomed all the way out? Thanks everyone.

Answer 1

There are many contributing factors:

• Longer focal-lengths require faster shutter-speeds to reproduce details sharply when hand-held. The general rule-of-thumb is 1 over the effective focal-length of the lens. So a 300mm on a DX camera has an angle of view equivalent to 450mm and so you should expect 1/500s at least to get sharp images. The solution against this problem is simple: Use a tripod or a faster shutter-speed, exposure permitting.
• Should you have the Nikkor AF-S 70-300mm F/4.5-5.6D ED, the optics are really poor towards the long end. Lenses do not have exactly the same performance at all focal-length. In particular that lens is extremely soft at 300mm at F/5.6-8. Things get better at F/11 but never quite match the performance at 70mm F/8 where the lens performs optimally. Should you want to visualize what is happening, check this out.
• This is a variable aperture zoom, so at 300mm you can only open the lens to F/5.6 which is not even desirable due to optical performance but already reduces the amount of light reaching the sensor which causes shutter-speed to lower. This can be partially compensated by increasing ISO but that introduces noise which destroys fine details after a point.

Answer 2

The DX 40 is a “compact digital”; the imaging chip measures 16mm height by 24mm length. We can calculate the diagonal measure of this rectangle and that works out to 30mm. This tells us that setting the zoom to 30mm delivers a “normal” angle of view. That would be an angle of 45⁰ with the camera held horizontal (landscape).

70% of normal or shorter is considered wide-angle and 200% of “normal” or longer is the realm of telephoto. That’s 20mm or shorter for wide-angle and 60mm or longer for telephoto.

The key value is the “normal” which is 30mm. If you zoom to 300mm, your camera delivers a highly magnified view. How much magnification is 300mm? We divide 300 by 30 = 10 (written as 10X). This tells us that if you zoom to 300mm the view will be about the same as delivered by 10 power binoculars.

Now 10X magnification is challenging for any optical system. However Nikon lenses are up to snuff in this regard. The likely culprit is too slow a shutter speed.

When we zoom out to extreme magnification we are confronted by the fact that camera motion is also magnified; thus it has great influence in the sharpness of the captured image. As a rule of thumb we should set the shutter to 1/zoom = 1/300 of a second or faster to negate camera movement. This rule of thumb is valid for a full frame camera, so I think it best if we multiply by the magnification factor of 1.5 = 1/450 of a second or better. This is true if you are hand-holding the camera. If you mount the camera on a tripod or brace it against a post etc. you can use a slower shutter. The object is super sharp images by avoiding camera movement during the exposure.