Meticulously Obscure

2

Q: When’s An f/1.8 Not An f/1.8?

A: When You Give A Shit About Sharpness

I’d heard from people before that lenses were not always sharpest at their widest aperture settings, but never really sat down and checked it out. Reading an “e-book” about street photography just now and seeing the topic brought up again however, made me decide to check it out.

Well Gee That Sounds Exciting

Shut up!

Sorry. You Were Saying?

My 50mm f/1.8 prime seemed a perfect candidate to experiment with, so I stuck my Xbox360 pad in my light tent, both my 100W bulbs on it, and snapped four shots from my tripod, at f/1.8, f/2.8, f/4 and just for the shit of it f/8. At f/8 it was down to 1/40 shutter timing, even under dual 100W brightness, so it’s unlikely that’d ever get used, but I wanted a reasonably high end point.

Yawn

Well it turns out that, yes, the thing is rather pants when at its widest. See here, a nice four way 50% crop of the thing I was focussed on (the text of the “space” bar, set manually, at 10x zoom on the LCD, to make sure it was proper tight) essentially SOOC:

That’s Pretty Shit At f/1.8 Then

Yes, yes it is. I was quite surprised by exactly how shit it was. I think the shitness is exaggerated by the extreme bright light, mind, which is why it’s never been so clear before, but it’s always looked mildly pants when wide open, and I’ve always shot with it wide open because I bought it thinking it was an f/1.8. Now I know better, I’ll stick to f/2.8, or maybe even f/4, or above. Husss.

Oh and here’s the full shot of the pad at f/4 because why not.

Steve • 11th October 2011


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Comments

  1. hrblaine 15th July 2012 - 15:19

    Anybody who expects a lens to be sharper wide open than stopped down ain’t never been nowhere and ain’t never done nuthin’.

  2. Steve 15th July 2012 - 15:53

    Exactly. I was new at this, so this was my going somewhere and doin’ suttin’

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