Taking my cue from the subject of this post: What the *$%%# is bokeh?
--Gary
Taking my cue from the subject of this post: What the *$%%# is bokeh?
--Gary
Got Google?
Gary, "bokeh" is a Japanese term for an idea. Trying to quantify and define the areas of our images that are not in focus. We did that historically in the USA also but did not have a term for it. The Japanese took things a magnitude further by naming the discussion and going much further in the study of 'good bokeh' 'bad bokeh'. In the last 10 years the idea has taken hold in LF and much is made of the different effects that our antique soft focus lenses have on out of focus areas of images.
Sorry for posting this 'messy' question in this brilliant thread...
I have been playing around with an old brass projection lens (magic lantern?), which has two different focal lengths depending on which way one puts it. In one direction it is a 300 mm with a very large image circle and in the other it becomes approx 90mm lens with an image circle that barely covers 4x5.
The lens does not have any aperture so I have not yet been able to take any photographs with it. The entrance pupil is very large seen from on side and smaller seen from the other.
The highlight areas are different in front and behind the focus, i.e. for highlights closer to the camera the highlights have a stronger lit ring and further away from the focus they are more even with barely noticable stronger lit centers.
Vignetting (?) makes the ringlit highlights look like swirls, i.e. the further away from the center the highlight is, the more flat it will become. This is not really visible in the highlights behind the focus...Unfortunately this means that the foreground swirls rather than the background.
Look at rippo's photo of the hanging doll where the ringlit highlights swirl on one side of the plane of focus (left) but not the more ordinary looking highlights on the other side (right).
Is there any way to get the ringlit highlights to show up on the other side of what is being focused or is this a rule of optics?
And what is the cause of these rings around the higlights?
The rings are caused by overcorrected spherical aberration, which is usually complemented by undercorrected spherical aberration on the other side of the focus plane. All of this is to be read as "most of the time", of course.
There's a very good article by Harold Merklinger on the subject, which should be compulsory reading. It's on the net, so just google "merklinger bokeh".
Thank you Ole!
Seems bokeh is very much about spherical abberation, and said to be better when there are no rings in the background highlights. It's just that I think the swirls are not easy to see if the highlights are too blurry and hence I think that the ring effect adds to the swirl effect in the background.
I also found this great page with lots of Bokeh links:
http://members.aol.com/dcolucci/bokeh.htm
This one has some info about the rotation...'cat's eye'... caused by optical vignetting.
http://www.vanwalree.com/optics/bokeh.html
Looking at the wonderful photograph on Domenico Foschi's website of the boy on the fence/bridge I see that the swirling highlights in the background show the ring effect.
What type of highlights do the 'Petzval swirling lenses' generally produce in front and behind the plane of focus, when the swirling effect appears?
Bookmarks