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I wrote a long reply to your previous post but lost it all - my ISP is on the blink today.Quote:
Originally Posted by Jack Flesher
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".
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.Quote:
Originally Posted by Jack Flesher
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.
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.
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/
Steve (and anyone else interested),Quote:
Originally Posted by Steve Clark
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
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.:DQuote:
Originally Posted by Joe Smigiel
Munising -- Aug. 17th? I'll try to manage at least serious consideration... (school and everything else be damned)
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:
http://jack.cameraphile.org/albums/a...B_Wlamp_md.jpg
Cheers,
Quote:
Originally Posted by Jack Flesher
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 :D 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!Quote:
Originally Posted by Jim Galli
Cheers,