Aperture help!

nightflower

Dear all,

I need some help on this.

The other day I went to the mountain. I was on top of it overlooking a terrace rice field in the valley below. I shot a photo and set the aperture to very small, it was probably around f/29. And the photo came out like this:

Terrace rice field

(Sigma 70-300, photo shot at 300 mm)

My question it: If this was your case, what would you set the aperture to be? In my case the photo doesn't look sharp and that upsets me.

Great thanks to any answer of yours! Cheers, mate!

thapamd

Hi nightflower,

First of all, welcome to DGrin!

It's a beautiful image of the rice fields, BTW. It sorta reminds me of the rice fields in Nepal.

Now to your question about sharpness.

First of all, 300 mm is a large focal length. What was your shutter speed and was the camera/lens on a sturdy tripod? If so, did you use mirror lock-up? Did you use a cable release or timer or did you press the shutter button with your finger?

f/29 is an awfully small aperture. As a general rule, any aperture beyond about f/16 will begin to show noticeable defraction-related softness. That may be part of what happened to your image.

Remember that depth of field is related to both the aperture value and the focal length. In fact, depth of field is influenced as the inverse square of the focal length and the inverse of the aperture. In other words, the longer the lens or the larger the aperture, the shallower the depth of field will be. Not only that, the focal length actually has a bigger influence than the aperture on depth of field. That's why it's nearly impossible to obtain a great depth of field with a long telephoto lens vs. a wide angle lens.

Is your original photo tack sharp anywhere in the field of view? If it is sharp at one area and not other areas, it may have to do with the limited depth of field you can achieve. If it is sharp in the center and soft at the periphery, it may be related to corner softness associated to certain lenses. If it is unsharp everywhere it may be due to defraction issues or unintended motion.

If there were no technical issues, I would see what the MTF curve of the lens looked like and use the aperture that gave the best sharpness. If I didn't know the MTF curve of the lens, I'd just shoot at f/8 to f/11 and forget about it.