Bokeh Talk - 70-200 F/4 IS vs. 70-200 F/2.8 IS

dave_s93 · May 23, 2007

NeilCUK said:
dave_s93 said:

Note, however, that the background blur will be different for the
200mm lens vs the 100mm lens, even though the DoF will be the same.
If you want more seperation of the subject from the background, use
a longer lens.

Click to expand...

how can you say that?

Easy. Because it is true ;-) Seriously, you are confusing background blur with DoF. While somewhat related, they are not the same.

NeilCUK said:
after just saying DoF is only dependent upon aperture, you then say
that separation from the background will occur more with a greater
lens?

no it won't. "separation from the background" is the effect of
having a narrow DoF

Again, you are confusing DoF with background blur.

NeilCUK said:
the only thing that will change with having a longer lens is
perspective - objects will appear closer to each other

Technically, perspective is a function of subject distance, but since you will stand farther away with a telephoto, from a practical level, I'll agree.

NeilCUK said:
if anything, if you want to exaggerate the effect of how far a
subject is from it's background then you need to get close to it
and use a wide angle

Well, you will "exaggerate" the distance between the subject and background with a WA lens, but you will have a lot more DoF with a WA lens especially if you are close to the hyperfocal distance - note that the DoF being dependant on f-stop no longer applies when the focus distance is close to the hyperfocal distance of the lens. Not only will you most likely get more DoF with a WA lens, you will not magnify the background enough to get the background blur that will isolate the subject.

dave_s93 · May 23, 2007

NeilCUK said:
no, it doesn't

DoF = isolation

focal length will change perspective

assuming the same framing, it would make no difference if you have
a similar aperture to what lens you use in terms of separation from
the background

DoF affects that

I guess you didn't bother to click on the link in my other post in this very thread where I showed how different focal lengths with the same DoF have different background blur. I guess I'll post it directly here.

dave_s93 said:
For all those that doubt that a telephoto lens will give you more
background blur, here are some examples using my phone.

Please note that all were taken at f5.6, and should have the same
DOF since the phone is the same relative size (I used the AF points
as a rough guide to keep it the same size).

50mm at f5.6

100mm at f5.6

200mm at f5.6

400mm at f5.6

Note that all these have the same DOF. Since the following are true:
1) the focusing distance was much smaller than the hyperfocal distance
2) the subject was kept the same relative size
3) and the same f-stop was used
then the DOF will be the same regardless of focal length.

If you don't belive me, use a DOF calculator. To keep the subject
size the same, you need to double the subject distance when you
double the focal length.

For a good explaination of this, see the post by DaveKl.

http://forums.dpreview.com/forums/read.asp?forum=1031&message=22790278

Hope this helps.

dave_s93 · May 23, 2007

NeilCUK said:
Bollan said:

The part where the subject isolation is increased with the distance
between subject and background i agree with but dont tell me i get
better subject isolation with 70mm than with 200mm.

Click to expand...

of course you will

This is just so wrong.

NeilCUK said:
http://www.photozone.de/3Technology/demos/focalCompress.htm

that shows pretty conclusively that the subject appears further
away from the background, thus more isolated

OK, now you are talking about perpestive changes. This is not what is generally meant by subject isolation, which is greater background blur.

NeilCUK said:
why?

because with a shorter focal length you need to get closer to the
subject

you get disproportionately closer to the subject than you do to the
background

thus, the subject appears further away from the background

This part is true.

NeilCUK said:
so if you have a narrow DoF as well as getting closer to the
subject (with the same framing), your subject will appear more
isolated from the background

Now this part is not true. Again, while a closer subject distance will give less DoF, the wider lens needed to keep the same framing on the subject will increase DoF by the same amount (or much more if the subject distance is near the hyperfocal distance). Also, you get more background blur with a longer lens at the same DoF.

Please see my example in another post in this thread that shows this is wrong, and take the time to click on the link to the explaination by DaveKl on why a longer lens will show more background blur at the same DoF.

caterpillar · May 23, 2007

Thanks for the examples. I threw away my own test pictures over 3 years ago that shows the same thing.

It never ceases to amaze me how some people don't know this. It's a simple enough experiment to do. When I had my 75-300 IS this was already obvious. Came the 100-400L, it was easy to demonstrate that you get a creamier background blur for the same aperture with a longer lens. Nothing theoretical or complicated to explain. I can shoot at f7.1 at 350mm and have that bokeh literally still dissolving at the background vs my old 28-75 at f2.8 at 50mm but still framing it to fill the frame. Even without doing an experiment, it si very noticeable especially if you compare the your lesser focal lengths vs your long ones.

The danger is some people can post things and really mislead others with their theories w/c doesn't match real world conditions.

--
--------------------

Caterpillar

'Always in the process of changing, growing, and transforming.'

caterpillar · May 23, 2007

dave_s93 said:
NeilCUK said:

dave_s93 said:

Note, however, that the background blur will be different for the
200mm lens vs the 100mm lens, even though the DoF will be the same.
If you want more seperation of the subject from the background, use
a longer lens.

Click to expand...

how can you say that?

Click to expand...

Easy. Because it is true ;-) Seriously, you are confusing
background blur with DoF. While somewhat related, they are not the
same.

dave_s93 said:

after just saying DoF is only dependent upon aperture, you then say
that separation from the background will occur more with a greater
lens?

no it won't. "separation from the background" is the effect of
having a narrow DoF

Click to expand...

Again, you are confusing DoF with background blur.

dave_s93 said:

the only thing that will change with having a longer lens is
perspective - objects will appear closer to each other

Click to expand...

Technically, perspective is a function of subject distance, but
since you will stand farther away with a telephoto, from a
practical level, I'll agree.

dave_s93 said:

if anything, if you want to exaggerate the effect of how far a
subject is from it's background then you need to get close to it
and use a wide angle

Click to expand...

Well, you will "exaggerate" the distance between the subject and
background with a WA lens, but you will have a lot more DoF with a
WA lens especially if you are close to the hyperfocal distance -
note that the DoF being dependant on f-stop no longer applies when
the focus distance is close to the hyperfocal distance of the lens.
Not only will you most likely get more DoF with a WA lens, you will
not magnify the background enough to get the background blur that
will isolate the subject.

And this is why there is an appeal and use for very wide aperture lenses at the wider focal lengths. The 35 f1.4 and the 50 f1.2 are examples where, if one wants to duplicate that background blur melting like the longer focal lengths, but you have no place to back out to, you compensate for it with a shallower DOF. With mere inches of DOF, you hope that the background melts faster with bigger apertures.

Of course, we know that it is tougher to do at 35mm vis-a-vis 50mm and vis-a-vis 85mm, but that is a given. Wedding shooters who like to get the blurred background effects can't use a 70-200 f2.8 indoors, so they either employ the 85 f1.2/1.8 or 50 f1.2/1.4 to get very close to this condition, not to mention upping the shutter speeds to make it handholdable.

As for the OP, I agree that f2.8 vs f4 would probably not be noticeable in terms of blurring the background. The only 3 options I see is getting a longer focal length, e.g. 300 f4L IS or 400 f5.6L. Or if these lenses tend to be too long there is the 100-400L IS, w/c will allow one to slide in the FL as one needs it. The 3rd option is to find a discontinued 200 f1.8L. That's as best as it goes to really throw that background off for this range. Problem is, if DOF can be too shallow, the OP must have a 1D mk2 or similar to get it to focus on target most of the time, otherwise, he will get a good bokeh, but his pics will be OOF.

--
--------------------

Caterpillar

'Always in the process of changing, growing, and transforming.'

brianz112832 · May 23, 2007

Why not get the f/2.8 zoom, compare them, and then keep just one, the better-bokeh lens of the two in your judgment? Then make your second lens the 200mm f/2.8L prime. The 200mm prime is the BOMB! Killer bokeh, super fast AF, razor sharp wide open, an absolutely amazing lens.

Bollan said:
Hiya shooters

I currently own a 70-200 F/4 IS and i must say its a fantastic
lens. In terms of sharpness, contrast and color it must be hard to
find something better in that range.

I have shot 6000+ shots with it so far, mostly sports under very
good lightning conditions, so by looking at the 70-200 F/2.8 IS its
not about speed in my case.

The reason i have started to look at the 70-200 F/2.8 IS is that i
think the 70-200 F/4 IS capacity to isolate the subject from the
background is not so good. I shoot mostly show jumping events where
good background separation is hard to achieve but ever so important
due mostly "messy" surroundings.

Money isnt really an issue for me and i guess if i got the 70-200
F/2.8 IS i would still keep my 70-200 F/4 IS for travel and for its
portability in general.

So my big question is: Is the 70-200 F/2.8 IS bokeh so much better
than the 70-200 F/4 IS that it justifies an upgrade/additional buy
in my case? Will i notice a major improvement regarding the object
isolation in my pictures?

Unfortunately where i live i have no chance to be able to test a
2.8 before i make a decision.

I would specially be interested to hear opinions from people having
experience with both lenses.

--
Wildlife galleries
http://www.pbase.com/zeiler/

NeilCUK · May 25, 2007

dave_s93 said:
I guess you didn't bother to click on the link in my other post in
this very thread where I showed how different focal lengths with
the same DoF have different background blur. I guess I'll post it
directly here.

dave_s93 said:
dave_s93 said:

50mm at f5.6
http://i26.photobucket.com/albums/c129/dave_s93/050mm.jpg

100mm at f5.6
http://i26.photobucket.com/albums/c129/dave_s93/100mm.jpg

200mm at f5.6
http://i26.photobucket.com/albums/c129/dave_s93/200mm.jpg

400mm at f5.6
http://i26.photobucket.com/albums/c129/dave_s93/400mm.jpg

Note that all these have the same DOF. Since the following are true:
1) the focusing distance was much smaller than the hyperfocal distance
2) the subject was kept the same relative size
3) and the same f-stop was used
then the DOF will be the same regardless of focal length.

If you don't belive me, use a DOF calculator. To keep the subject
size the same, you need to double the subject distance when you
double the focal length.

Click to expand...

For a good explaination of this, see the post by DaveKl.

http://forums.dpreview.com/forums/read.asp?forum=1031&message=22790278

Hope this helps.

i agree there's a clear difference... this is not something i've ever noticed in practice

i wonder if the effect is exaggerated if the background is further from the subject?

--
-----
Neil C
http://www.homelands.me.uk/gallery/

NeilCUK · May 25, 2007

NeilCUK said:
NeilCUK said:

For a good explaination of this, see the post by DaveKl.

http://forums.dpreview.com/forums/read.asp?forum=1031&message=22790278

Click to expand...

NeilCUK said:
i wonder if the effect is exaggerated if the background is further
from the subject?

i should have read that post first...

Dave concluded that the further the background is from the subject, the greater the effect

very interesting - something i'll remember in the future

--
-----
Neil C
http://www.homelands.me.uk/gallery/

timotale · May 25, 2007

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Bokeh Talk - 70-200 F/4 IS vs. 70-200 F/2.8 IS

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