Adding filter (polarizing, ND) or 1.4x/2x extenders can have an impact on aperture from the metering point of view. Does it have an equal impact on bokeh?
In other words is the bokeh of a f/2.8 lens equipped with a polarizing filter comparable with the bokeh of a lens of same focal length at say f/4 (assuming the filter has a 1 stop impact). How does it go for extenders?
Sorry if the answer is obvious or been posted a million times
Not sure about extenders, but with a filter, the lens is still at that aperture, it's just getting less light (if you're talking about NDs and CPs). It's about the same thing as if you just knocked down your ISO one stop or however many. You'll retain the depth of field regardless of filter, provided that you keep that aperture.
A polarizer affects the amount of light entering into the lens. It does not affect the DOF of the shot and thus doesn't change the bokeh.
A TC, on the other hand, alters the focal length, changes the optical properties of the overall lens, and distorts the image itself. Thus it sill affect the bokeh and degrade the quality of the resultant image.
I'm guessing the bokeh of a bare 70-200 @ 200mm will look better than a 70-200 @ 100mm and a 2x, even at the same f/stop. Same lens, but more image degradation due to the TC.
Ariel Bravy wrote:
I'm guessing the bokeh of a bare 70-200 @ 200mm will look better than a 70-200 @ 100mm and a 2x, even at the same f/stop. Same lens, but more image degradation due to the TC.
Ok, that's clear for filters. Thanks.
Also, I agree that bokeh quality is likely to degrade because of additional lenses from the TC.
Now, for TC, to come back to your example, are we saying that DOF stays the same, even if f/stop reads slower w/TC?
Ariel Bravy wrote:
The following setups will have the same DOF:
70-200 2.8 @ 200mm, f5.6
70-200 2.8 @ 100mm, wide open, 2x TC, for a net f/stop of f5.6
If I understand correctly: @ 100mm, the zoom is set at f/2.8, but because of the TC, overall f/stop of the system is 2 stops higher (your net f/5.6)?
Well, if that's what you mean, it seems real odd to me. I thought that DOF was solely defined by focal length and aperture, irrelevant of other considerations.
AlexTokyo wrote:
If I understand correctly: @ 100mm, the zoom is set at f/2.8, but because of the TC, overall f/stop of the system is 2 stops higher (your net f/5.6)?
Well, if that's what you mean, it seems real odd to me. I thought that DOF was solely defined by focal length and aperture, irrelevant of other considerations.
But I had a doubt, that's why I asked
thats correct but what you have after the TC is a 200 5.6 (in the example above)
A Better example would be to have the 200 + 2X tc against the 400 5.6 prime. both wide open (5.6) these should produce the same DOF ,bokeh ma not be the same visually as for the zoom youve just gone thru alot more glass and may not look as good.
The character of bokeh can be dramatically affected by certain optical aberrations, including spherical aberration, coma, longitudinal chromatic aberration, mechanical vignetting, etc.
It is quite possible that a filter attachment such as a c.pol could contribute to these aberrations and therefore affect the character of the bokeh.
I think that bokeh will generally *tend* to improve with a TC... hard edges will be a little softer etc... some lenses look a lot better when used with tubes tubes... same thing... image sharpness goes down a little and bokeh improves.
>>Also, I agree that bokeh quality is likely to degrade because of additional lenses from the TC.
In my experience (using Canon 1.4x and 2x TCs), the TCs can do very strange things with the bokeh. Instead of simply enlarging a soft, blurry spot into larger soft, blurry spots (as mh2000 suggests), out-of-focus specular reflections go from round, soft disks to much harsher shapes. Blurred areas end up with hard, double-line edges. Try stacking a 2x on a 1.4x TC for even more bad bokeh fun: specular reflections end up as colorful, lumpy, irregular splatters.
ok, who's the first person that wants to do a little experimenting?
(testing bokeh with different FL's is always a challenge to be meaingful... but still way more fun that sharpness testing!) I'm probably too busy tonight... but maybe.
mh2000 wrote:
I think that bokeh will generally *tend* to improve with a TC... hard edges will be a little softer etc... some lenses look a lot better when used with tubes tubes... same thing... image sharpness goes down a little and bokeh improves.
>>Also, I agree that bokeh quality is likely to degrade because of additional lenses from the TC.
In my experience, my 1.4x TC degrades the bokeh on my 70-200 f/4L IS. It's not terrible, but it introduces a slightly nervous character to the bokeh. Sharpness is still quite good, though. Still, if I need 280mm, the TC goes on. It's not enough of a difference to have the wrong focal length for the shot.
