A Blog and discussion about that *$%%# elusive Swirly Bokeh!

**Ole Tjugen** · 6-Aug-2007, 10:10

Originally Posted by Jack Flesher

If you google "comatic flare," "spherical aberration" and "astigmatism," I'm sure you'll find several references and some should have diagrams and examples.

I wrote a long reply to your previous post but lost it all - my ISP is on the blink today.

However I have a prima example of coma here - maybe it works this time.

This image (hopefully) displays both astigmatism and coma, but coma is by far the dominating aberration. The result is just about the opposite of "swirlies".

**Paul Metcalf** · 6-Aug-2007, 13:36

Originally Posted by Jack Flesher

Vignetting is a cosine 4th falloff factor s

Jack - I'm away from my tech book right now, but isn't the falloff cosine squared since it's one way (4th would be two-way)? But again, I'm working off of memory.

**Paul Metcalf** · 6-Aug-2007, 13:45

My luck, such as it is, at swirliness is highly coupled to the amount of lens extension I'm using. Your portraits Jim look like you're using more extension than the garden photo. If so, then your experience mirrors mine. If not, then this posting is mute. I find it hard to take scenics and get the swirliness along with sufficient magnification of the main subject that I don't want to be swirly. I either end up with too much magnification and the image isn't swirly, or I end up with too small of a picture object and lots of swirly. I've had pretty good luck using just the front (or rear) element of interesting lenses like latern lenses as this usual increases the focal length which reduces the amount of magnification required to have a reasonable subject size (but the minimum focusing distance becomes an issue then). I'm striving to get to where Domenico (Foschi) is with his swirly pictures. I think they're splendid.

**Jack Flesher** · 6-Aug-2007, 14:16

Ole: That crop looks like it is exhibiting a bunch of SPHERICAL aberration, not coma.

Paul: It stands to reason the lens will exhibit more coma at infinity as the lens is at its shortest extension and correspondinly smallest IC.

**Jack Flesher** · 6-Aug-2007, 14:35

FWIW, here is a link to a few shots taken with the Leica Noctilux at f1.0. I choose it as an exemplar because the Noctilux is known to exhibit strong coma when used wide open. It is also of high relatively contrast and reputed to be reasonably well corrected for spherical aberrations and astigmatism, though both are present in the design.

Here are the shots: http://www.shinozuka.org/200110autumnlux2/

**Joe Smigiel** · 6-Aug-2007, 22:16

Originally Posted by Steve Clark

Hi Joe,
Is the Munising get together a private party, or can anybody join?
Thanks, Steve

Steve (and anyone else interested),

The trip is the August outing of the Midwest Large Format Asylum. They have a mailing list and webpage/forum at:

http://www.midwestlargeformat.com/

The MWLFA is a looseknit group of people from mainly the Chicago area but also a few in South Bend, Michigan, Wisconsin, central Indiana and Ohio. There is a revolving group of regulars who form the core of the group and usually some permutation of these 8-10 folks show for the monthly trips. AFAIK, the Munising gig is open to anyone interested.

On the mailing list they are currently discussing visiting Miner's Castle and Beach, Miner's Falls and a few others (Alger Falls, etc.,) in the area. The Seney Nat'l Wildlife Refuge nearby may also be an option for them.

I'm sure the MWLFA people would welcome your participation on the trip.

Joe

**Darryl Baird** · 7-Aug-2007, 05:47

Originally Posted by Joe Smigiel

Not too far. I'm over in Kalamazoo, Michigan but I head to the western UP every couple summers. I may yet make it there this year. There's also a get-together of midwest large-format folks the weekend of August 17 in Munising that I may rendezvous with. If I do I'll have the wetplate stuff with me.

There were also a couple folks from Minnesota at Bill Schwab's get-together in June in Cross Village near the straits. I had the collodion rig there, did a demo then,and plan to do it again next year.

Joe

Joe my friend, what a weird coincidence that you are now a collodion impresario! I was thinking I'd offer an advanced alt-process class in the near future and now I know for sure I can manage the wet-plate thingy... can you say stipend, sure you can.

Munising -- Aug. 17th? I'll try to manage at least serious consideration... (school and everything else be damned)

**Jack Flesher** · 7-Aug-2007, 14:38

Back to swirlies -- I *think* to get them to happen with any regularity, you need to have a background (or foreground) that is far enough away from the PoF to allow the coma to form a recognisable oof projection, but not so far away the shape blurs into oblivion.

Here is a shot where I attempted to induce it with a lens I own known to exhibit a small amount of coma. I was only mildly successful, but I think (hope) it's enough to illustrate my point. Also if you look at the speculars in the background, you can see the oval shapes and even tell they occur at 90 degrees to the central axis of the lens:

Cheers,

**Jim Galli** · 7-Aug-2007, 14:56

Originally Posted by Jack Flesher

Back to swirlies -- I *think* to get them to happen with any regularity, you need to have a background (or foreground) that is far enough away from the PoF to allow the coma to form a recognisable oof projection, but not so far away the shape blurs into oblivion.

Here is a shot where I attempted to induce it with a lens I own known to exhibit a small amount of coma. I was only mildly successful, but I think (hope) it's enough to illustrate my point. Also if you look at the speculars in the background, you can see the oval shapes and even tell they occur at 90 degrees to the central axis of the lens:

Cheers,

Cool, Jack to answer Darwin's question which I really wasn't ignoring, could you have used camera movements to include the flowers in the bottom right corner in the plane of de-focus while keeping the lamp focused?

**Jack Flesher** · 7-Aug-2007, 15:53

Originally Posted by Jim Galli

Cool, Jack to answer Darwin's question which I really wasn't ignoring, could you have used camera movements to include the flowers in the bottom right corner in the plane of de-focus while keeping the lamp focused?

Not with that lens on that particular camera

It's a Leica rangefinder lens -- an older 50mm f1.4 Summilux pointed down at the lamp. Focus point was the front corner of the lamp, so the PoF angled to include the lower right foreground. Another situation where camera movements rule the day!

Cheers,