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Stopping down a lens on a digital sensor gives stop-sign bokeh... but would film handle the stop-sign bokeh better?


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I was watching Shane Hurlbut compare lenses in the Cooke, Leica, Canon, and Rokinon lines using a pretty standard comparison setup. He mentions something at 08:45 in the linked video below about how the vintage Cooke lenses were able to retain circular globes of bokeh even when stopped down when shot on film. However in the digital age, sensors will show the more angular bokeh on lenses like these with a lower number of iris blades.

I understand the relationship between the shape of bokeh and the iris blades and aperture, but I couldn't wrap my mind around the physics of why a stopped down lens would retain globe shapes on film versus a digital sensor. 

Does anyone have a nifty wiki article or an explanation about this phenomenon?

Shane Hurlbut explains stop-sign bokeh on older lenses on digital vs film

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I could be wrong, but I think the phenomenon is called "Shane Hurlbut talking out of his arse".

I guess you could say that increased resolution might make small out of focus highlight shapes more visible, but other than that I can't think of any reason why the recording medium would affect the shape of a lens attribute.

At 9.40 he talks about a T1.5 Canon lens compared to a T1.9 Xeen as being "four tenths difference", which tells me all I need to know about Shane Hurlbut's grasp of optical science.

(For those new to aperture stop calculations, stops are not a decimal scale. T1.5 to T1.9 is not "four tenths" but 2/3 of a stop difference. T1.4 to T2 is not "six tenths" different, but a whole stop. Further down the scale, T4 to T5.6 is not "sixteen tenths" difference but also a whole stop. It kind of shocks me that Hurlbut doesn't actually know this, and is teaching people. Or perhaps he knows perfectly well, but he's just a shill trying to minimise the difference for marketing purposes.)

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I have a film stills photography background, not a cinematographer or even close.....but how the hell does a lens change characteristics based on whether image is recorded on film or digital.

I've used/own quite a few quality lenses for my Hasselblad, Nikon, Leica cameras and ONLY the 'texture' as I call it changes to my eye - i.e. film and digital have different flavours that's it...

same with all this SDR and HDR and 'lighting for it' ....eh.......what the hell is going on....is this the 'masterclass' and 'buy my course with this 20% off token' trying to pull wool over our eyes with pseudo revelations in order for us to become their clients or what hahahah wtf

Edited by Stephen Perera
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Looking back at the video, you can hear the audio track have a noticeable cut/edit right around the timestamp I give for when he talks about it. Maybe two sentences that were out of context with each other got spliced together with the magic of editing. I think it could have been a weird decision by the editor to just frame the sentence that way. While it did make English sense, it doesn't make much lens sense. Deadlines and etc who knows what happened.

I like Shane he's got mountains of experience and wisdom. I'm betting that the video got pressed to tape fast, and Shane didn't edit the video himself. 

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Unrelated-is but since we're talking about lens blades.....here's my Hasselblad (Zeiss) 110mm f2 Planar that gives different bokeh from f2 to f5.6 and then at f5.6 and a half down to f16. Beautiful lens.

zeiss_f2_blades.jpg

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and why not....a comparison of the difference between the blades themselves! Note the straight sides on the blades of the pentagon on the 80mm as opposed to the rounded sides of the pentagon on the 110mm

The 80mm Planar, in my opinion, is a beautiful lens offering beautiful drop off in focus and bokeh

 

hazzy_zeiss_blades2.jpg

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12 hours ago, Dom Jaeger said:

I could be wrong, but I think the phenomenon is called "Shane Hurlbut talking out of his arse".

I guess you could say that increased resolution might make small out of focus highlight shapes more visible, but other than that I can't think of any reason why the recording medium would affect the shape of a lens attribute.

At 9.40 he talks about a T1.5 Canon lens compared to a T1.9 Xeen as being "four tenths difference", which tells me all I need to know about Shane Hurlbut's grasp of optical science.

(For those new to aperture stop calculations, stops are not a decimal scale. T1.5 to T1.9 is not "four tenths" but 2/3 of a stop difference. T1.4 to T2 is not "six tenths" different, but a whole stop. Further down the scale, T4 to T5.6 is not "sixteen tenths" difference but also a whole stop. It kind of shocks me that Hurlbut doesn't actually know this, and is teaching people. Or perhaps he knows perfectly well, but he's just a shill trying to minimise the difference for marketing purposes.)

I think I'd accept "four tenths" as a way of expressing the difference between the numbers 1.5 and 1.9, but it's rather imprecise, and I'd rather have said two thirds of a stop, certainly.

I really don't know where he's coming from with the iris blade count stuff, but I haven't watched the entire video. is there a point where he actually compares the same lens on film and video? I can't see how it could significantly differ. It sounds to me more like he's comparing different lenses and rather imprecisely describing how he preferred to shoot certain lenses on film, and certain other lenses on digital, and how those different lenses behave differently. 

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