Doesn't look like bokeh . . . is it a reflection?

<p>Kinda' makes me want to go and make light blob pictures with a hand full of lenses.</p>

<p> </p>

<p>No worries, William! I didn't even get my high dudgeon down off the top shelf! :-)</p>

<p>Andrew: The lens involved is a Canon EF 100 mm f/2.</p>

<p>:)</p>

 

<p>Looking at Matt's test images, it appears that the point sources indeed produce hard-edged blobs (mostly the orange ones). The red ornament with the specular highlight toward the base of the tree produces a hard-edged white blob overlaid with a fuzzy red blob. The ornament at the corner of the candle (the ornament looks like a fruit with a missing slice) produces a big fuzzy blob. This all appears to support the hypothesis that the sharp blobs in my image came from some sort of point sources in the background, while the fuzzy blobs came from larger sources.</p>

<p>This has been very informative. So here's the addendum to the question: would things look different if the lens had been stopped down to a more typical aperture? I understand that the shape of the blobs would theoretically become polygonal depending on the number and shape of the diaphragm blades in the lens; apart from that, would I still have the same mix of hard- and fuzzy- edged blobs?</p>

<p>Barry: well, what the heck. It's only pixels and bandwidth, right? I've taken that same test scene, more or less (the lights a little different today), and walked through several stops' worth of aperture changes, allowing the twinkly stuff in the background to exhibit the expected behavior from the artifact-ish lens that I used for the first test. So, this series runs from f/1.8 up through f/11. The shots were all hand-held, so there's a bit of compositional variation - but you'll get the idea.</p><div></div>

<p>Not a full stop, this time, but closed up a hair from that wide-open shot above.</p><div></div>

<p>Another stop, and things are starting to get a bit more geometric looking!</p><div></div>

<p>Holy Hexagons, Batman! But now, another stop down, the larger objects are starting to look like themselves.</p><div></div>

<p>Another stop, and things are starting to look more real, size-wise, relative to each other.</p><div></div>

<p>Another stop, and surprisingly little difference, here.</p><div></div>

<p>And our last stop, at f/11, and we're starting to see a new artifact: a bit of starbursting on the point sources.</p><div></div>

<p>That's so good! Thanks<br>

***<br>

Also, there is a guy whose work I have seen a while ago who takes OoF images, to make light patterns - including a lot of night street scenes, I can't find anything of his though I have been looking on and off for a few days - I read his notes and he spoke of what Matt wrote about "special lenses" - this guy collects these special lenses to make specific OoF light patterns.<br>

I'll keep looking as I am sure I made a note of him somewhere.<br>

WW </p>

<p>Matt: Many thanks! I think this thread has just about turned into a tutorial on bokeh! After all these years photographing, I thought I pretty much understood my camera, but this has been enlightening. Thinking back, I expect the reason I hadn't noticed such artifacts before is that I normally don't photograph things wide open, at least not where there are point source highlights in the background. I wouldn't think twice about an image that displayed the spots you got at f/5.6 and up, and I would have immediately recognized the shape of the diaphragm in the somewhat larger apertures (I had read about that effect before). But those big, sharp-edged blobs . . . something new!</p>

<p>Just to put a little more frosting on this Bokeh Cake, I thought I'd use that same backdrop to show some of the subtle differences that can appear between two lenses when it comes to this sort of thing. I used the same Nikkor 50/1.8 to shoot (wide open) a Sigma 50/1.4 HSM sitting in front of those point-source background lights. I then used the Sigma, wide open, to shoot the Nikkor in the same spot. At first glance, you see the same basic visual artifacts (not to mention the razor thin depth of field when those are used at their max apertures).<br /><br />But if you look more closely, you can see that the OoF blobs rendered by the Nikkor lens are less symmetrical and have harder edges, and that features like the seam on that leather ottoman create some odd hard-line artifacts. </p><div></div>

<p>The Sigma, used here to shoot the Nikkor, is a little more even-handed, and produces a more buttery OoF area. Of course, it should, at four times the price - and that's if your style of shooting even begins to have any of this make a single bit of difference!</p><div></div>

<p>Matt -</p>

<p>Beautiful demo. Thanks. It's almost enough to make me go out and pick up one of those Sigma 50/1.4's.</p>

<p>It's not quite bokeh, but if you happen to have an old 35/f2 AIS around, any chance you could be persuaded to turn off all the lights in your room (except for the tree) and take an in-focus shot of the lights on your tree (exposed so the core of each light is not blown out). It should demonstrate yet another type of optical aberration, ie, the pattern I reported on in this thread: http://www.photo.net/nikon-camera-forum/00XX8p. ;-)</p>

<p>Tom M</p>

Tom: I don't have that lens, alas, so I can't test for that spun-corners behavior (interesting!). Since I'm still using DX, I

reach for Sigma's 30/1.4 when I want a fast prime in that range. It looks just like its 50mm big brother, though the 50

is good for FX.

<p>Matt: It takes a big man to admit when he's wrong - and I'm extremely fat. You've convinced me. Along with having had some sleep and then gone back to look at what I wrote (ahem). Barry: sorry for misleading you. I guess I'm used to having easier-to-identify artifacts in the background, or at least only analysing images that I took myself! I have to say that Barry's 100 f/2 seems to have <i>really</i> uneven bokeh (it's supposed to be sort of okay for bokeh, and a nice lens - I've been vaguely considering one for my Canon set-up), but it may be exacerbated, as you said, by digital processing. Cool effect, reflecting the bokeh in the table, by the way! Thank you for your efforts putting the educational sequence together.<br />

<br />

For what it's worth (since Tom mentioned considering the lens), I've had a play with a Sigma 50 f/1.4 (on loan), and it's pretty nice, although not very sharp in the corners of a full frame near wide; arguably it's a better short portrait lens for crop sensors. That said, with the proviso that I've never shot a modern Leica, I've never met a normal lens that actually <i>is</i> sharp wide open and has decent bokeh without LoCA, which is why I've never upgraded my 50 f/1.8 AF-D - notably the f/1.4 AF-S is reasonably sharp wide open, but the bokeh and LoCA aren't, from the reviews I've seen, all that good. Perhaps if Nikon makes the rumoured AF-S 50mm f/1.2 (and it doesn't have the LoCA of the 85mm f/1.4). Of course, most normal primes are pretty spectacular once you stop down a bit.<br />

<br />

Tom - cool sagittal flare demo!<br />

<br />

Thanks for the education, everyone - and happy (optionally-recycled) winter solstice festival. :-)</p>

<blockquote>

<p>"and I'm extremely fat." . . . "and happy (optionally-recycled) winter solstice festival"</p>

</blockquote>

<p>ROFPML</p>

<p> </p>

<p>Hey, Andrew, I'm just glad it all worked out! But I can tell you that if Nikon <em>does</em> come up with a 50/1.2 AF-S ... that I don't think I'll be buying one. If their other new AF-S fast prime prices are anything to go on, that one's going to have to wait!</p>

<p>Matt and Andrew: consider me enlightened. This has been a very rewarding discussion.</p>