Thursday, June 25, 2009

Bokeh Test -- Nikon 50mm 1.8 AF

So I have this really cool photography workshop with Chrombie McNeill coming up this Sunday. It promises to teach me how to work with (lots of) models in a studio and location setting under natural and studio lighting. All in all, sounds like a blast.

I tried to rent two of Nikon's best lenses for my DX cameras, the 17-55 f2.8 AFS for the D70s and the 70-200 f2.8 AFS VR for the D300. This is the combination I used for my niece's wedding in 2007, but alas that marriage, and therefore that gallery is no more. I was quite proud of many of those shots, and more importantly I was stunned by the quality of images produced by those lenses. They embarrass my consumer glass in a fair fight.

But ... all that said, HeadShots had no lenses, all the interesting stuff was already rented out. There is a price to be paid for spontaneity. But then she realized that there had been a cancellation on a 70-200VR and she would be able to send it to me! This is a $2100 lens in Canada and I could rent it from 3pm Friday until Monday noon for $40. A great deal.

Now to choose a lens for the D70s as a closer in shooter. Well, I have the manual focus 28mm f3.5 AI, which is also wicked sharp, but we were warned that the models change looks very quickly and we need our trigger fingers dancing. So I chose instead the 50mm f1.8 AF, a lens that is very close to professional quality. The only issue I had was how would the bokeh look? I know it's pretty good generally, but I wanted to check spectral response in case we had water dropelts shining in the sun.

What I found is just a tad disappointing. It degrades slightly at anything above about f2.2. But it's still wicked sharp and if we don't have too many spectrals, it should look terrific. Very smooth, almost buttery.

If what I am writing sounds like Greek to you, or more accurately Geek, take a look at these definitions for Bokeh. Here, and here.

So, on to the test. I shot an image at 1600 ISO in my kitchen with only the range hood lamp on in the far background. The swan-shaped lamp is the focal point, specifically the beak. Everything fades out from there ...

In the shot with the lens wide open at f1.8, the background is almost unrecognizable, and the spectrals are circles. Not perfect circles, it's not that good a lens. But decent. No rings around the edge or bloom in the middle, so it looks pretty nice.

Stopping down just a tad already puts a distinct heptagonal shape, caused by the seven-bladed diaphragm with square blades. But otherwise still a nice bokeh.

Quality professional lenses, and even the more expensive consumer lenses use either 7 or 9 blades, and the best lenses use rounded blades. The bokeh is smooth and does not change shape as much as you stop down. This lense cost $150cad, so who can really complain. Well, I can ... but it won't get me anywhere.

Stopping a full 1.33 stops to f2.8 leads us to a more pronounced heptagon, and it's smaller. The shrinking of spectrals also tends to make them more obvious. Unfortunate, but the light just does not spread as much, so tough. But note that the surface of the heptagon remains uniform and smooth, so not all that bad really ...

Also, the bokeh remains smooth, which is a very good thing.

Finally, at f5.6, things get kind of ugly. Very small points of heptagonal light and a rather busy background make it obvious that you want to avoid stopping down to far if you want smooth bokeh.

Still, give credit where credit is due ... the lense is still giving a smooth background. Just more of it comes into focus ... which is inevitable as you stop down.

It's a fantastic lense, though, for a lousy $150cad. It's going to be my first gambit on the D70s. If I find I need to get up closer and I want a wider view, I'll move to the 28mm. And if that is not enough, I'll mount the 18-200VR, but that's not quite in the same league with these others.


John said...

Hey I just wanted to say that I liked the post. Also, I wanted to make a comment on the I'm going to have to say the Nikon 50mm 1.8 lens. Most people look down upon the lens, but I actually think it is a great buy for the price. Just thought I'd throw that in there. Have a great day!

Kim Letkeman said...

Thanks John, I agree that this is an awfully good lens for the low price. Should be in everyone's toolkit ...