Aperture and Telephoto Lenses

[Brian Hirschfeld]

Is there anyway to compare the bokeh achieved with telephoto lenses ex. a 300mm 2.8 to 85mm 1.4 lens. Since the 300mm will exhibit more bokeh @ 2.8 then an 85mm @ 2.8, I was wondering if there is any formula to determine an effective aperture as relates to bokeh for telephoto lenses, if that makes sense. thanks,

[theguywitha645d]

At the same object distance, it would be in relation to the difference in the entrance pupil size. At the same framing/image scale, the difference would be proportional to the angular size of the entrance pupil from the object. This would be with a given format. If this is comparing two different formats as well, then it becomes more complicated.

[EduPerez]

If you take into consideration that you will have to get closer to the subject with the 85mm lens, then the DOF becomes roughly the same for the same aperture; you can always go to the DOF Calculator and make some simulations yourself.

[AJSJones]

Here is a great article on the difference between bokeh and "amount of blur" but also goes to your question of the extent of blurring at different distances behind the subject with different lenses being used (and different subject distances...

[Brian Hirschfeld]

Thanks for the help, downloading the app from that guy's website