Is the 100-400 really a 5.6?

Started Apr 22, 2012 | Discussions
zalle
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Is the 100-400 really a 5.6?
Apr 22, 2012

I notice that when I take a shot wide open (Av) at 400mm the photo is 1/3 of a stop darker than if I take it at F11 for example. If I compensate 1/3 at 5.6 then I get similar images...

If I compare it with 400 F5.6 prime wide open, I also see a darker image (1/3 stop).

Could this mean it really is a 6.3 wide open?

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Mike Engles
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Re: Is the 100-400 really a 5.6?
In reply to zalle, Apr 22, 2012

Hello

It is interesting that you say that.

I have just got a 400 F5.6 and also have a 100-400.
I have been doing some calibration using a home made checker pattern.
The fixed lens could be completely defocussed and the 5D2 AF would autofocus.
The 100-400 could only be defocussed a bit and thne autofocus worked.

If I defocussed the 100-400 as much as the fixed 400, the 5D2 AF would work and give a focus confirm, but the image in the viwfinder was still blurred. Very strange. I did wonder if the light coming into the 100-400 was less than for the fixed 400, so making autofocus with the pattern more difficult. The light today is too variable to be able to make a proper comparison of exposures

Mike Engles

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Howard
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Re: Is the 100-400 really a 5.6?
In reply to zalle, Apr 22, 2012

Can you post your pictures at f/5.6 and f/11 with technical details (shutter speed most importantly in this case)?

It is hard to say without seeing the pictures. Is your subject uniformly lit? Did the light change (e.g. if you took the pictures outdoors)?

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Howard
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R2D2
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Re: Is the 100-400 really a 5.6?
In reply to zalle, Apr 22, 2012

zalle wrote:

Could this mean it really is a 6.3 wide open?

It's definitely not as bright as my own 400 f5.6. It's a bit shorter too.

R2

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R2D2
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Re: Is the 100-400 really a 5.6?
In reply to Mike Engles, Apr 22, 2012

Mike Engles wrote:

I did wonder if the light coming into the 100-400 was less than for the fixed 400, so making autofocus with the pattern more difficult.

I too have found that the 100-400s that I've used have all seemed to require a bit more light (contrast) in order to AF as well as either my 400 f5.6L or 300 f4L IS (without TC). The difference isn't much, but it's there.

My great shooting buddy Bob (owns a great copy of the 100-400 now - his two older copies were a bit sub-par) has definitely noticed it too (we shoot birds together a LOT). He's always packing it in earlier in the evening than I am (when I have my 400), image stabilization notwithstanding. Being able to AF does trump everything else.

Now the 300 F4L IS can shoot a bit longer into the evening than either of the other two lenses (being F4 and having IS), but really the extended shooting time isn't a heck of a lot in real time (after sunset the light drops Very quickly). With a TC though, IMHO it falls a bit short of the other two options (in several areas) in any light.

So like everything else, there are tradeoffs between the various 400mm options, even though at first glance on the outside, they might appear quite similar.

R2

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zalle
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Try it
In reply to Howard, Apr 22, 2012

I know what I'm saying, it's not my first 30 minutes with a lens and a dslr.

If you have a 100-400 try it, it's pretty simple...

Take 3 shots of the same subject:

1 - Av F5.6
2 - Av F5.6 + 1/3 stop
3 - Av F11

Now compare them.

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zalle
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This is not a 400 X 100-400 X 300 post
In reply to R2D2, Apr 22, 2012

R2D2 wrote:

I'm just trying to understand why the 100-400 shoots darker pictures at the same aperture and speed.

Mike Engles wrote:

Now the 300 F4L IS can shoot a bit longer into the evening than either of the other two lenses (being an F4 and having IS), but really the extended shooting time isn't a heck of a lot in real time (after sunset the light drops Very quickly). With a TC though, IMHO it falls a bit short of the other two options (in several areas) in any light.

So like everything else, there are tradeoffs between the various 400mm options, even though at first glance on the outside, they might appear similar.

R2

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Howard
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No need to be defensive
In reply to zalle, Apr 22, 2012

I didn't mean to question your observations. I thought you had the pictures taken already, so asked you to post them. Whatever.
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R2D2
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Likely a decision made by the marketing dept.
In reply to zalle, Apr 22, 2012

zalle wrote:

I'm just trying to understand why the 100-400 shoots darker pictures at the same aperture and speed.

This is my take: The zoom has more lens elements (reducing transmitted light through the lens), and thus requires a larger entrance pupil (objective element) than it was designed with. Mebbe it really required an 86mm class objective, but cost was prohibitive. It's also possible that the exit pupil (cone of light that comes out of the back of the lens and hits the sensor) was engineered with a few too many compomises too (may be a bit too diffuse considering its coverage area).

These issues were likely addressed in the new $1200 200-400, LOL!

R2

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R2D2
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Re: This is not a 400 X 100-400 X 300 post
In reply to zalle, Apr 22, 2012

zalle wrote:

This is not a 400 X 100-400 X 300 post

BTW, sorry. Didn't mean to co-opt your thread. Was just trying to answer some of the other poster's questions, and share some long-time experiences.

R2

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R2D2
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In reply to R2D2, Apr 22, 2012

R2D2 wrote:

issues were likely addressed in the new $1200 200-400, LOL!

Ooooops, missed a BIG decimal point there... meant $12,000!!!!

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zalle
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Ok, ok here are the photos
In reply to Howard, Apr 22, 2012

I took 3 pictures under artificial light, 400mm, ISO 400, Av. Actually it looks like it's slightly less than 1/3, but the first picture is definitely darker. Maybe my F6.3 "theory" makes no sense. What can it be then?

F11 1/10

F5.6 1/30

F5.6 + 1/3 stop 1/25

Howard wrote:

I didn't mean to question your observations. I thought you had the pictures taken already, so asked you to post them. Whatever.
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lenses: 17-40 f/4 USM L, 24-105 f/4 USM L, 100-400 f/4.5-5.6 IS USM L, 24 f/3.5 TSE L, 35 f/2, 50 f/1.4 USM, 100 f/2.8 IS USM Macro L, 300 f/2.8 IS USM II, 430 EX II, Kenko Pro 300 1.4x TC, EF 2x TC III
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zalle
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Re: This is not a 400 X 100-400 X 300 post
In reply to R2D2, Apr 22, 2012

No worries, I just didn't want this topic to become one of those life or death wars

R2D2 wrote:

zalle wrote:

This is not a 400 X 100-400 X 300 post

BTW, sorry. Didn't mean to co-opt your thread. Was just trying to answer some of the other poster's questions, and share some long-time experiences.

R2

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zalle
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I meant the 2nd is darker, not the 1st.
In reply to zalle, Apr 22, 2012

I meant the SECOND PICTURE! Sorry!

zalle wrote:
but the first picture is definitely darker.

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Karl Gnter Wnsch
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f/stop against t/stop...
In reply to zalle, Apr 22, 2012

zalle wrote:

If I compare it with 400 F5.6 prime wide open, I also see a darker image (1/3 stop).

That's the difference between having only a few lens elements against a whole host of elements - called transmission stop, which in fact is worse on the 100-400L
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Karl Gnter Wnsch
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Re: Is the 100-400 really a 5.6?
In reply to R2D2, Apr 22, 2012

R2D2 wrote:

It's definitely not as bright as my own 400 f5.6. It's a bit shorter too.

The zoom only is shorter when focused on short distances - which is normal...
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Howard
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I see your point
In reply to zalle, Apr 22, 2012

But the last one is definitely brighter than the 1st one.

Since apertures and shutter speeds are discrete, not continuous, I would say that to get the exact same exposure as the 1st one, the shutter speed would have been somewhere between 1/30s and 1/25s.

But I get your point.
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cameras: 5DII, 50D, D60, Rebel 2000 (film)

lenses: 17-40 f/4 USM L, 24-105 f/4 USM L, 100-400 f/4.5-5.6 IS USM L, 24 f/3.5 TSE L, 35 f/2, 50 f/1.4 USM, 100 f/2.8 IS USM Macro L, 300 f/2.8 IS USM II, 430 EX II, Kenko Pro 300 1.4x TC, EF 2x TC III
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