How do I find the sharpest aperture on my lenses?

[technics100]

Hi,

I wanting to know which is the sharpest aperure on my lenses, I currently use a Nikon D90 and have the 18-200mm VR and 50mm F/1.8. How do I go about it?

Do I set the camera up on a tripod and shoot the same scene at every f/stop adjusting the shutter speed for correct exposure? then choose which I think is sharpest?

Thanks

Adam

 

[woof woof]

That'd do it.

But of course you'll have to come back here, post your results and talk about it at length

 

[Woodsy]

yep, that sounds reasonable to me.

 

[towershot]

Usually it's around F/8.............I say usually because it alters from lens to lens.
Just do the test you talk about,bet it's around F/8...............

 

[cambsno]

It is often around f/8 but I normally shoot my 50mm at around f/4 or f/5.6 and think its plenty sharp there. If I stick an f/8 image next to a f/4 image, it is near impossible to tell the difference.

 

[woof woof]

f8 will give you greater dof but I think that many lenses are actually as sharp as they're going to get a bit wider these days, assuming that you can get what you want in the dof at the wider aperture

 

[Robbo]

or look on here...... the table will normally tell you whats sharpest, long as they have tested your lens.

http://www.slrgear.com/reviews/index.php

 

[TinaC]

Do the experiment and let us all join in the resultant discussion

 

[HoppyUK]

The centre will be sharpest at f/5.6, and the edges will peak slightly later around f/8.

At higher f/numbers, diffraction will reduce ultimate sharpness, regardless of the lens.

 

[technics100]

Thanks for all that, must have a go. Is it better to take a landscape shot to compare or an object? How do I lock my focus so its the same on each shot..

Also, for my 18-200mm what zoom am I better trying it at or do a selection?

 

[Jim.R]

Focus, then swap the lens to MF and don't touch the focus ring?

 

[HoppyUK]

Thanks for all that, must have a go. Is it better to take a landscape shot to compare or an object? How do I lock my focus so its the same on each shot..

A distant subject, where focusing errors will be minimised and the lens will perform best. Lens performace usually reduces at very close distance and you get field curvature which might skew things. It also varies with focal length but while ultimate sharpness might change, the optimum apertures will usually be the same.

To lock the focus, switch to manual. If you are looking to see how sharp you can get, make sure the light is good and the shutter speed high to avoid any camera shake. If you can do that then there's no need for a tripod or anything.