Sensor size and out of focus rendering

[Lindolfi]

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Sometimes there is some confusion about the effect of sensor size on the out of focus rendering of the image. What difference does it make if I use a sensor the size of an M8 sensor or I use a sensor the size of an M9 or M 240 sensor?

 

Perhaps this document is of some use to answer the question: what is the influence of sensor size on the out of focus rendering in an image?

 

http://www.photoplaza.nl/lindolfi/sensorsizeoof3.pdf

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[lct]

Hi Brent, interesting thanks. 40 and 50 are very close for sure but at the same subject distance and aperture, there is always some DoF difference anyway (half a stop?). In practice i use 35mm lenses on my M8.2 the same way as 50mm ones on full frame and i need to shoot one stop wider on the former to get more or less the same results.

[Lindolfi]

The ratio of sensor size is 75% of M8 to M9.

40 mm is 80% of 50 mm

35 mm is 70 % of 50 mm

 

So you can pick what you like best for this experiment. The principle that I wanted to show does not depend on it.

[lct]

Perhaps i did not understand what you mean by "local dependency" then:

"There is however no influence of sensor size on the local dependency of out of focus rendering in the image."

For me there is necessarily some influence of sensor size on DoF hence on OoF rendering in the image. This influence being more or less visible depending on the size difference of the two sensors.

[Lindolfi]

Yes, there is an effect of sensor size on DOF. I was talking about the change in the out of focus rendering when moving from the center to the edges of the image. How is a light pointsource that is not in focus rendered when moving from the center (circular) to the edges and corners (elliptic) of the image.

 

So there is the size of the aperture discs in the image and their elongation. The swirly character of the image from some lenses (like the Noctilux 50/1) comes from this elongation. The short axis pointing at the center of the image and a kind of vortex or swirl is visible in the image, slightly disturbing, slightly pleasant

[pico]

[...]The swirly character of the image from some lenses [...]

 

Swirl?

 

A photograph by the large format photographer, Mr. David Higgs using an ancient lens.

[SJP]

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mmmm, how is that done? Any info on the technique he used Pico?

[pico]

mmmm, how is that done? Any info on the technique he used Pico?

 

It is all about the old lens design and not using an aperture device such as a Waterhouse stop. IOW shooting wide open.

 

Consider that many 19th century lenses were very fast and long focal lengths. A 500mm F/4 lens was not unheard of. Add poorly corrected spherical distortion and enjoy, or not, the outcome.

 

I think, but will try to verify, that the lens was a Petzval.