Bokeh at different focus distances 85L vs 35L

I'm curious, if I frame a full body portrait using my 85L standing say 25 feet back or frame it identical standing say around 10 feet back with a 35L, which lens will have greater bokeh? I'm completely just thinking about DOF based on the focusing distance of each lens. I understand the background will be compressed differently.

Heya,

I think longer focal length with wider aperture generates more bokeh. But I could be wrong.

Very best,

would be hard to get the same framing, and perspective way different

Are you asking which scenario would give the greater background blur? This is something different from "bokeh", of which there can be neither more nor less, as it is the subjective quality of that blur, not its degree.

There is a calculator somewhere for this, maybe a search would reveal it. You will need to supply focal length, f ratio, subject distance, background distance and possibly crop factor or equivalent, and you'll get out the size of the blur disk, that is, the diameter of the image formed of every point in the background.

If you can't find the calculator, and nobody chimes in with a link or definitive answer, do a corresponding experiment with your existing lenses at different distances and focal lengths. The results can be extrapolated to 35 mm. Indeed, you could just set your 17-40 to 35 and do a direct comparison with one of your 85s.

you can do a mockup test if you wanted, just set the 17-40 to 35mm F4, and your 85mm to F4 and try it out. You can shoot the 17-40 at MFD to create the greatest background blur.

As a general rule, the longer the focal length used for a given framing, the greater the background blur will be. If the framing and aperture are equal, the DOF will be the same but the blur will certainly not be the same.

That's why I can totally smear a background into blur with my 100-400L even though the maximum aperture is f/5.6.

Try shooting at 25mm and 5 feet, 50mm and 10 feet, 100mm and 20 feet etc and note the changes in perspective and blur. The DOF will be the same in each shot (if you use the same aperture) but you will see less and less of the background with the longer lenses and what you do see will appear progressively blurrier.

And to second xarqi, it's best to use the work 'bokeh' for the aesthetics of the blur. We already have a word in English for the amount....it's 'blur'. You can say 'more blur' or 'blurrier' without needing to import a foreign word, while the aesthetic effects (rings, doubling etc) implied by 'bokeh' are hard to suggest in English.

If you have the lenses (and you do not have to do this with super fast lenses) you can experiment a bit to see how this works.

The lens with the largest aperture will always produce the greatest background blur. Remember the diameter of the aperture is equal to the focal length divided by f/number. So for the 85L, 85mm/1.2 = 70.83, 135mm/2 = 67.5. Thus, the 85L will blur the background more than the 135L at all focus distances, all other things being equal. Remember that focus distance has nothing to do with subject to background distance. The 85L produces more background blur than the 135L period, but the 135L comes close when the subject to background distance is large. The next lens to blur the background more than the 85L is are 200mm f/2.8 lenses, but the difference is negligible. To really get more background blur than the 85L you have to go to a 200mm f/2 or a 300mm f/2.8. That's what makes the 85L so special - so much background blur at such a relatively wide angle.

MalVeauX wrote in post #16416475
Heya,

I think longer focal length with wider aperture generates more bokeh. But I could be wrong.

Very best,

Respectfully,,, you are wrong

Wider aperture will not give 'more' bokeh, but greater background blur.

Bokeh is a very subjective term. Bokeh can not be measured.

thepilgrimsdream wrote in post #16416410
I'm curious, if I frame a full body portrait using my 85L standing say 25 feet back or frame it identical standing say around 10 feet back with a 35L, which lens will have greater bokeh? I'm completely just thinking about DOF based on the focusing distance of each lens. I understand the background will be compressed differently.

bokeh is factor of DOF AND background compression so you really have to factor both.

Given an equivalent framing, the 85L will blur the background more, as the longer subject distance will create more compression.

There's a time and place for both though! If you have interesting elements in the background, 35 f1.4 creates a great sense of dimensionality by keeping the background elements in the frame, but giving you a shallow DOF to isolate your subject.

85L does a better job of compressing distracting background elements

Sigma 35 @ f1.4

IMAGE LINK: http://www.flickr.com …s/carloalcala/9​429445664/

IMAGE LINK: http://www.flickr.com …s/carloalcala/9​403389905/

35L

Sigma 35mm @ f/1.4:

IMAGE LINK: http://www.flickr.com …asselmudarris/9​474070543/

IMAGE LINK: http://www.flickr.com …asselmudarris/9​532176900/

Thank you all! I definitely still want the 35L just in terms environmental portraits. But I'm more than happy with the 85L ii and its ability to isolate a subject from its background. Thanks so much for the examples!

Graph of amount of background blur (not amount of 'bokeh'), at various distances behind subject, for 35mm at f/2.8 and for 85mm at f/2.8, assuming subject distance is increased for 85mm FL, so that a full length shot of a person is framed similarly in both shots (of course, background content will be different, due to change in camera position, but the primary subject is the same in both shots)

So can there be bokeh WITH ZERO BLUR? If not, then bokeh cannot exist without some blur. Can blur exist without being Bokeh? Even a small amount of blur can have it's subjective qualities liked by someone, which means that any blur can be called bokeh. So it sounds like the proper definition of bokeh is any area of a photo that is blurred because of the depth of field being placed on a subject and yet not being deep enough to bring all elements of the frame in to focus. So I agree that amount of blur is not bokeh other than that there must be some blur more than zero. Any amount of blur can be called nokeh, because anyone might like the qualities of that blur.

yogestee wrote in post #16417428
Respectfully,,, you are wrong

Wider aperture will not give 'more' bokeh, but greater background blur.

Bokeh is a very subjective term. Bokeh can not be measured.

This would indicate that there can be bokeh with zero blur. Since blur can be measured, and any blur can be called bokeh if someone subjectively likes it, and zero blur can never be called bokeh, sounds to me like bokeh requires a certain amount of blur, it has to be an amount MORE than zero. So it sounds like it can be measured and must have a definite amount other than zero.