Bokeh at 50

[Tom W]

Since I'm between night shifts, I decided to set up a little bokeh demonstration for the purpose of trying to learn a little more about it. I took 3 lenses that I have that are all capable of shooting at 50 mm - the 50/1.4, the 24-70L, and the 28-105 f/3.5-4.5. I shot all my test shots with the same framing, resulting in some minor differences in reported focal length from the 2 zooms. Not perfect, but I got them as close as I could without resorting to serious measurements and such.

I stuck to one focal length to eliminate as many variables as I could.

The test setup looks like this:

http://www.pbase.com/photosbytom/image/42655309.jpg

All comparison shots were done at f/4, since that is the widest aperture available on the 28-105 at this focal length. ISO is at 400, and lighting was a combination of overhead general lighting, 2 diffused incandescant lights on the main subject, one direct clamp-on round reflector light on the glassware to enhance the "sparkle" (and perhaps bring out the worst in the bokeh) and light-overcast window light regulated by verticle blinds to add another color to the glassware.

I did a couple of shots with the 50 at various apertures - here's one wide open just to show how nice a big aperture can be:

http://www.pbase.com/photosbytom/image/42655310.jpg

Now, for the actual bokeh comparison, we start with the 28-105 consumer zoom. It has a 7 blade aperture, but that really isn't relevant here since it was shot wide open (round aperture). Here's the shot.

http://www.pbase.com/photosbytom/image/42655308.jpg

Note that the OOF circles are nice and round, but have a very solid bright ring to them. This makes for choppy bokeh.

Next, we have the 24-70L. Again, it's shot at f/4, but this time, we can make out the 8-sided aperture blade in some of the bokeh. However, it is much smoother, exhibiting just a little edge to the OOF circles. The circles blend much more readily here.

http://www.pbase.com/photosbytom/image/42655307.jpg

Finally, the 50 mm f/1.4 lens, also at f/4. It is fairly similar to that of the 24-70, with a little sharpness to the edges of the OOF circles, but again, the blend is quite good.

http://www.pbase.com/photosbytom/image/42655306.jpg

These shots seem to reinforce what Rick Denney has stated in other threads concerning aperture blades and bokeh - there are obviously other design factors in play that help determine smoothness, as all these lenses have adequate roundness to their OOF spots.

Please note that this test wasn't designed to show the best bokeh, but merely to demonstrate to myself and others what factors might affect bokeh besides aperture blade count. Obviously, the wider the aperture, the smoother the bokeh as illustrated by the f/1.4 shot above.

I wish that I had the Zeiss 50/1.4 to test here, along with a Canon 50/1.8 because I'd love to see how these perform on equivalent subject material.

All comments are welcome.

[rdenney]

I wish that I had the Zeiss 50/1.4 to test here, along with a Canon 50/1.8 because I'd love to see how these perform on equivalent subject material.

All comments are welcome.

Tom, this is an excellent test, and demonstrates bokeh very clearly.

Bright-edge bokeh comes from highly corrected and even over-corrected spherical aberration. We see it with lenses that are highly optimized for MTF performance, requiring trade-offs with other features. We see this in zooms and other inexpensive lenses that are well-corrected, but not designed to allow less correction of spherical aberration. The Canon consumer zoom demonstrates this.

Soft-edge bokeh is a characteristic of certain designs, notably the Sonnar design, which leaves a residue of uniformly undercorrected spherical aberration, especially at wider apertures.

Perfect rendering of out-of-focus highlights comes from a lens that is perfectly corrected. The disk has neither a bright edge nor a soft edge. The best Canon lenses approach this ideal, but most that I have seen (including the 24-70 and the 50 above) approach it from the bright-edge side. I would say that the 50 does well in comparison to moust double-gauss 50's (and most 50's are double-gauss designs).

The problem with the Sonnar is that it requires placement of the rear element too close to the sensor for use in shorter focal lengths on SLR's that have a mirror. The only 50mm Sonnar I know of is the 50/1.5 Sonnar for the Leica, which was made by Zeiss in the 40's and early 50's. (The shortest medium-format Sonnar I know of is a 150, and the shortest recently available for 35mm is the 135/3.5 Sonnar that started me down this path.)

Some double-gauss lenses are improved for bokeh, and I think the 50/1.4 is not too bad, especially at wider apertures.

When my 135 Sonnar arrives, I'll do some similar comparisons in that focal range. My test will include a 120mm Zeiss Biometar (symmetrical double-gauss), 120mm Vega (Ukrainian optimized double-gauss with known bad bokeh), 135mm Canon soft-focus, 135mm Zeiss Jena Sonnar, and 135mm setting on the 70-200/4L. I'd love to at the 135/2L to that test, but that ain't gonna be happening.

Rick "noting that good bokeh is a trade-off with good MTF, with the possible exception of the Sonnar" Denney

[Tom W]

Tom, this is an excellent test, and demonstrates bokeh very clearly.

Thanks - It was educational to me as well as others, I'm sure. I really thought that the aperture blades were a primary factor in bokeh smoothness, but it seems that they are secondary to many other factors.

Bright-edge bokeh comes from highly corrected and even over-corrected spherical aberration. We see it with lenses that are highly optimized for MTF performance, requiring trade-offs with other features. We see this in zooms and other inexpensive lenses that are well-corrected, but not designed to allow less correction of spherical aberration. The Canon consumer zoom demonstrates this.

With a zoom ratio of 3.75, spanning fairly wide to moderately long, I'm sure that there's a lot of correction going on in that lens. I may test it again at 85 against my 1.8 and the 70-200. Really wish I had access to that Canon 85/1.2, which is noted for its bokeh.

Soft-edge bokeh is a characteristic of certain designs, notably the Sonnar design, which leaves a residue of uniformly undercorrected spherical aberration, especially at wider apertures.

Perfect rendering of out-of-focus highlights comes from a lens that is perfectly corrected. The disk has neither a bright edge nor a soft edge. The best Canon lenses approach this ideal, but most that I have seen (including the 24-70 and the 50 above) approach it from the bright-edge side. I would say that the 50 does well in comparison to moust double-gauss 50's (and most 50's are double-gauss designs).

The problem with the Sonnar is that it requires placement of the rear element too close to the sensor for use in shorter focal lengths on SLR's that have a mirror. The only 50mm Sonnar I know of is the 50/1.5 Sonnar for the Leica, which was made by Zeiss in the 40's and early 50's. (The shortest medium-format Sonnar I know of is a 150, and the shortest recently available for 35mm is the 135/3.5 Sonnar that started me down this path.)

Interesting stuff. I really need to read up on this a bit. I'm tempted to take the CZ or Leica R lens plunge just to get a feel for these other designs.

Some double-gauss lenses are improved for bokeh, and I think the 50/1.4 is not too bad, especially at wider apertures.

Perhaps that extra lens element in the 50/1.4 serves to improve the Bokeh, as you alluded to in another thread. The bokeh does seem to smooth out nicely at wide apertures. The slight softness at f/1.4-2 probably aids a bit in this. Perhaps I'll do a little investigating on ultra-wide apertures on the 50. I have too big a distance ratio between the primary subject and background to get a good view of OOF circles at f/1.4 the way my test is set up now, but it won't take anything to move stuff around a bit.

When my 135 Sonnar arrives, I'll do some similar comparisons in that focal range. My test will include a 120mm Zeiss Biometar (symmetrical double-gauss), 120mm Vega (Ukrainian optimized double-gauss with known bad bokeh), 135mm Canon soft-focus, 135mm Zeiss Jena Sonnar, and 135mm setting on the 70-200/4L. I'd love to at the 135/2L to that test, but that ain't gonna be happening.

Well, if you're anywhere near Eastern Tennessee, I could help you with that 135/2.

Thanks for the response - Its your commentary on another thread that peaked my curiousity.

Rick "noting that good bokeh is a trade-off with good MTF, with the possible exception of the Sonnar" Denney

[cmM]

nice, thanks for the comparisson Tom ;). The shot with the 50 f/1.4 wide open looks awesome btw


Rick, I'm gonna be waiting for your comparisson ! :)

[Andy_T]

I feel that thanks to RDenney (Applause :D ) some of us have really risen to the next stage of geekdom ... er ... technical photographic knowledge.

Before this discussion, my idea was somewhere near 'larger aperture = more blurred = better bokeh in general' with the limitation that you just shouldn't take shots against backlit tree leaves, as it makes for bad bokeh. Now I know better.

Thank you, RDenney :wink:

Now let's all hope this increased knowledge will result in better photos...

Best regards,
Andy

[Andy_T]

When my 135 Sonnar arrives, I'll do some similar comparisons in that focal range. My test will include a 120mm Zeiss Biometar (symmetrical double-gauss), 120mm Vega (Ukrainian optimized double-gauss with known bad bokeh), 135mm Canon soft-focus, 135mm Zeiss Jena Sonnar, and 135mm setting on the 70-200/4L. I'd love to at the 135/2L to that test, but that ain't gonna be happening.


Well, if you're anywhere near Eastern Tennessee, I could help you with that 135/2.


We might also devise a 'POTN standard bokeh test' using a bottle of Chivas Regal, 6 glasses at defined distances to each other and standardized lighting. Ideally the glasses and lighting fixtures would come from the IKEA lineup, as this is globally available :lol:

Best regards,
Andy

[tim]

Ideally the glasses and lighting fixtures would come from the IKEA lineup, as this is globally available :lol:


They've not taken over New Zealand yet ;)

[rdenney]

nice, thanks for the comparisson Tom ;). The shot with the 50 f/1.4 wide open looks awesome btw


Rick, I'm gonna be waiting for your comparisson ! :)

Could be soon. My 135 Sonnar just walked in the door, heh, heh.

Rick "thinking it to be a mid-80's model that needs new grease on the helicals--not a problem" Denney

[Andy_T]

We are eager for the comparison!

If I am not mistaken, you also have a Jupiter 9, right?
I would really like to see the comparison of the 85/1.8 and the Jupiter 9 85/2.0 :D

Best regards,
Andy

[Tom W]

Two more shots since I had already taken them. These are both at f/2.8, and same setup as earlier.

First, the 24-70L:

http://www.pbase.com/photosbytom/image/42687286.jpg

Note that wide-open, the OOF circles are getting that sharp bright ring, or at least some of them are. Its not as bad as the consumer zoom, but it isn't as good as the 50/1.4 that follows:

http://www.pbase.com/photosbytom/image/42687287.jpg

Now THAT is pretty smooth.

I really wish I had that 85/1.2 - think of the test shots I could make with that....

[rdenney]

We are eager for the comparison!

If I am not mistaken, you also have a Jupiter 9, right?
I would really like to see the comparison of the 85/1.8 and the Jupiter 9 85/2.0 :D


Send me an 85/1.8, and I'll do the comparison, heh, heh. It may take me a while. I think I could get it done in two, maybe three years.

Rick "whose only beef with the J-9 is ergonomics" Denney

[Andy_T]

I really wish I had that 85/1.2 - think of the test shots I could make with that....

No problem ... just supply Pekka, Roanjohn, Mvonditter and HKFever with the details of your test ...
one of them will most likely take up the challenge and provide the images :D

And CDS, Bearsummer or AdamHicks might provide the 200/1.8 perspective...

Send me an 85/1.8, and I'll do the comparison, heh, heh. It may take me a while. I think I could get it done in two, maybe three years.

Don't have one, unfortunately. Otherwise I could do the comparison myself :cool:

Best regards,
Andy

[Tom W]

No problem ... just supply Pekka, Roanjohn, Mvonditter and HKFever with the details of your test ...
one of them will most likely take up the challenge and provide the images :D

And CDS, Bearsummer or AdamHicks might provide the 200/1.8 perspective...

Best regards,
Andy

I'm afraid that the test setup is copyrighted, so if people want the Official TM bokeh test, they'll have to send the lenses to me. My setup is authentic.

[O/confusion]

We might also devise a 'POTN standard bokeh test' using a bottle of Chivas Regal, 6 glasses at defined distances to each other and standardized lighting.

I suspect that extensive testing will reveal thats perceived bokeh smoothness has a direct correlation to number of glasses of Chivas consumed. :D

Terry

[Andy_T]

I hereby announce a test that is totally different from the now copyrighted Tom W approach.

Main components are a bottle of Glenfiddich (15 y.o.) and five corresponding shot glasses :wink:
Of course, the number or glasses to be consumed before each stage of the test is also strictly defined. Details will follow :lol:

Best regards,
Andy

[Tom W]

I hereby announce a test that is totally different from the now copyrighted Tom W approach.

Main components are a bottle of Glenfiddich (15 y.o.) and five corresponding shot glasses :wink:
Of course, the number or glasses to be consumed before each stage of the test is also strictly defined. Details will follow :lol:

Best regards,
Andy

Any test involving a coveted single-malt Scotch requires a photographer's assistant. I hereby volunteer to assist. I'll bring my own glass and some ice (to soften the bokeh).

[Andy_T]

Hehe ... OK if with 'I bring my own glass' you are referring to the 135/2.0 L :lol:

Best regards,
Andy

[Mike H]

If I may make a serious comment, I like this test because it convinces me to stop being concerned with bokeh, at least when it comes to lens purchasing decisions. If you stare at Tom's images long enough you can see some differences, but they're so minor that the test indicates that bokeh varies little among lenses of the same focal length when the aperture, focused distance, and background are the same.

To me, the bottom line is that if you want good bokeh carefully choose the focal length, aperture, and critically, the background in your shot. Thanks for posting the test images.

Mike H

[rdenney]

If I may make a serious comment, I like this test because it convinces me to stop being concerned with bokeh, at least when it comes to lens purchasing decisions. If you stare at Tom's images long enough you can see some differences, but they're so minor that the test indicates that bokeh varies little among lenses of the same focal length when the aperture, focused distance, and background are the same.

To me, the bottom line is that if you want good bokeh carefully choose the focal length, aperture, and critically, the background in your shot. Thanks for posting the test images.

Mike H

I agree with this.

But I also look at images from lenses and see if they are pleasing. The whole point of selective focus is to bring the viewer's attention to the subject. If the background rendering competes with the subject, that objective is lost.

Yes, you can avoid bokeh problems by avoiding troublesome backgrounds, but a lens with good bokeh can opens some doors with those backgrounds.

But I agree it's nothing to obsess over.

Rick "who thinks all art is a sum of subtleties" Denney