Question on Low Light Photography with zoom lens

Hi guys! I have a question.. Why is it that when i use a zoom lens [Nikon AF-S 55-200 (4-5.6)], when i use the maximum aperture, most of my photos appear soft and not sharp? When i get to aperture 7.1 for example, the photos are much sharper. I'm focusing on a single subject which isn't moving much, yet at maximum aperture the images are soft.

Lenses usually have a "best" aperture which is often around f/7 or f/8 but you'd have to shoot all variations to see what's yours. The same goes for the mm of a zoom. On general, the more you go towards the 200mm, the less sharp the result will be.

pianist88 said:

Hi guys! I have a question.. Why is it that when i use a zoom lens [Nikon AF-S 55-200 (4-5.6)], when i use the maximum aperture, most of my photos appear soft and not sharp? When i get to aperture 7.1 for example, the photos are much sharper. I'm focusing on a single subject which isn't moving much, yet at maximum aperture the images are soft.

Click to expand...

That is pretty much how lenses are.... It is not that they are so less sharp at f/4 (they are a little less sharp when wide open), but that the zone of sharpness is narrow. Just for an example... There are depth of field calculators, ( Online Depth of Field Calculator is one),
and say at 75mm zoom, and focused at 20 feet, then

f/4 - the depth of field (zone of sharpness, acceptable maybe) is 18.4 feet to 21.9 feet.

f/8 - the depth of field is 17.1 to 24.1 feet - a little wider range (about double) of perhaps acceptable sharpness. Called Depth of Field.

These are approximations, not biblical numbers. There is no sharp dividing line at these numbers.

The subject exactly at 20 feet is probably OK either way, but the background and foreground changes.

Thanks for the response Wayne & J-See! ... Thanks for helping me understand how the aperture relates to zoom lens

pianist88 said:

Hi guys! I have a question.. Why is it that when i use a zoom lens [Nikon AF-S 55-200 (4-5.6)], when i use the maximum aperture, most of my photos appear soft and not sharp? When i get to aperture 7.1 for example, the photos are much sharper. I'm focusing on a single subject which isn't moving much, yet at maximum aperture the images are soft.

Click to expand...

I had this thought in my head, even before you started this thread, to take a sequence of pictures with my old Vivitar 85-205, to show the effect of aperture on image quality and depth of field. I just now got around to doing so, and have posted the results in this thread. I think viewing that thread may be helpful to you in understanding the principles about which you are asking here.

Your lens will surely have different characteristics than mine, but certain principles are rather universal, and can be seen in my thread:

• Wider apertures will tend to produce a softer image overall, while smaller apertures will tend to give you a sharper image.
• Smaller apertures give you greater depth of field, allowing objects to be in focus at distances that vary more from that at which the lens is focused. Wider apertures give you less depth of field.
• Shorter focal lengths also give greater depth of field, while longer focal lengths give shallower depth of field.
• Any aberrations in the lens tend to show up more greatly at wider apertures.

Thank you soo much bob blaylock! Appreciate the help and the reply very informative thread.. I'm getting the hang of taking sharper images with my zoom lens by playing around with my aperture settings according to my distance from my subject