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kameraobskura
14-Mar-2014, 16:26
Im one of those who actually want the swirl, however my 9" Darlot wont give it to me. All the glass is there / right position, however I barely only get bokeh.

What am I doing wrong?

112161

Will Frostmill
14-Mar-2014, 17:24
Supposedly swirl is caused by a kind of mechanical vignetting, essentially the same thing as cat's eye bokeh. Try using as much rise and shift as you can, at the largest aperture, at maximum extension, and see if anything shows up in the opposite corner. Make sure you've got some point sources of light in the background - the more the merrier. Backlit leaves at a distance work best, Christmas lights can be pretty good too.

Will

Emil Schildt
14-Mar-2014, 17:36
hmm - If I want to ex make a portrait with swirley background, this is what I do:

I "Think reverse"...

First I find the background I want (you need something to actually swirl) - then I slowly pull the focus away from that background while whatching the matt screen.. Suddenly it is there.. Stop; place then the model where the image is sharp, and you have it....

(others might work differently, but this works for me)

Monty McCutchen
14-Mar-2014, 18:24
Petzvals were designed for their speed and in their heyday swirl would have been considered poor craftsmanship so their intended use was for a format size that hit the sweet spot so to speak. If you want swirl shoot the lens on a format that pushes the coverage limitations of the lens

Amedeus
14-Mar-2014, 19:41
+1, that is what I do if I want swirl ... use a 4x5 Petzval on 8x10 ...


Petzvals were designed for their speed and in their heyday swirl would have been considered poor craftsmanship so their intended use was for a format size that hit the sweet spot so to speak. If you want swirl shoot the lens on a format that pushes the coverage limitations of the lens

StoneNYC
14-Mar-2014, 21:52
I don't own a petzval lens. When I want swirl I shoot my Mamiya 7 150mm lens wide open...

I've always wondered why a non petzval can produce this but I understand very little about optics ...

I like the "working in reverse" example, that makes sense to me.

alex from holland
14-Mar-2014, 23:15
Use a petzval for a larger size as it was made for. Make sure you have a background wich can swirl. So trees, leaves or when inside a wall paper with a classic design in it. Than you will get swirl.

kameraobskura
14-Mar-2014, 23:24
I got a 1:2 scale T-Rex skeleton wall paper in our living room, (my wife is awesome btw.) I'll see if it will swirl! Thanks for all the good help all of you, appreciate it!

Steven Tribe
15-Mar-2014, 03:48
Nice simple early camera by the way - 1870?

kameraobskura
15-Mar-2014, 04:36
Nice simple early camera by the way - 1870?

Actually is a Folmer Multiple from the 1930's

Andrew
15-Mar-2014, 05:48
sorry for the silly question, but is the image in the original post made with the lens you're unhappy with or is it OF the camera and lens you're unhappy with?

if it's made with the lens, your background is too close to the subject and the background is too uniform to effectively show the swirl effect anyway. I'd reinforce the comments about stretching the lens because I thought a 9 inch lens had no swirl when I tried it on 4x5... that was because the format didn't include the periphery of the image circle but it's there it in larger formats.

goamules
15-Mar-2014, 11:30
Also, if your Darlot happens to be a slow one, it won't swirl. The Petzvals faster than F5 do it, but the slower ones usually don't. Swirl is one of the common aberrations, called coma. Several designs do it, but always at the extreme edge (unless someone has misconfigured the glass, then you'll sometimes see a ring if swirl between the middle and edge).

John Berry
16-Mar-2014, 01:19
Take back airspace elements out.
flip the rear element, then flip the two elements as an assembly. Reinstall and you should have a huge curvature of field that will give you swirls.

goamules
16-Mar-2014, 06:18
But you'll also have the swirls in the wrong places, extreme coma, and less sharpness anywhere in the frame. I don't recommend misconfiguring lenses just to show aberrations.

Dan Fromm
16-Mar-2014, 09:47
Supposedly swirl is caused by a kind of mechanical vignetting

Will
Not vignetting, uncorrectable (with the Petzval design) off-axis aberrations.

Mark Sawyer
16-Mar-2014, 10:04
Not vignetting, uncorrectable (with the Petzval design) off-axis aberrations.

Any idea what the aberration is, Dan? All I can think of is coma, but it doesn't look like coma...

We've never come to a conclusive answer about this, but I've suspected mechanical vignetting. But that doesn't explain how the mid-range swirls in a misconfigured lens occur.

CCHarrison
16-Mar-2014, 10:21
My research led me to:

off-axis uncorrected coma combined with spherical aberration...

Other Dan

goamules
16-Mar-2014, 10:57
I've always said the elongated orbs in the edges are coma, but I'm starting to think it may be Astigmatic difference or Saggital Astigmatism. Probably combined with normal Coma (which I believe usually has a pointed "trailing edge" as in an astronomical comet. Either way, I think it would be hard for anyone but an optical scientist to predict or prevent it.

http://www.nikon.com/products/instruments/resources/tech/info/microscope_tech/aberration/index.htm
http://www.handprint.com/ASTRO/ae4.html

http://www.handprint.com/ASTRO/IMG/seidel3.gif