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Author Topic: Does a lens hood reduce the light?  (Read 9312 times)

TexPhoto

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Re: Does a lens hood reduce the light?
« Reply #15 on: November 10, 2011, 04:06:04 PM »
Even if the hood were designed to perfectly fit the edges of the image, and zoom as the lens does (a few do this, Canon 24-70 2.8), it would not protect 100% fom flair. 

Hoods provide some protection from flair, not 100%, but it is a whole lot better than none.  A gobo can still be useful.

The hood of a 70-200 is shading the front element exactly the same amount at 70 vs 200.  So it makes no sence to say  hoods protect mostly/only at the wide end of zooms.

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Re: Does a lens hood reduce the light?
« Reply #15 on: November 10, 2011, 04:06:04 PM »

EYEONE

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Re: Does a lens hood reduce the light?
« Reply #16 on: November 10, 2011, 04:18:50 PM »

The hood of a 70-200 is shading the front element exactly the same amount at 70 vs 200.  So it makes no sence to say  hoods protect mostly/only at the wide end of zooms.

You have a point (kinda) but what they are saying is that the hood is designed for 70mm in that case. The hood for a 200mm prime could be much much deeper and keep even more stray light out of the lens. But if you put that hood on the 70-200 it would vignette at 70mm

For the 70-200 (with the proper hood) there is a lot more light entering the lens that is not part of the picture at 200mm than at 70mm.
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Re: Does a lens hood reduce the light?
« Reply #17 on: November 10, 2011, 04:46:02 PM »
dr croubie shame your image examples wernt of exactly the same scene, would have beena little more obvious then, with the shutter speeds and stops.

neuroanatomist

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Re: Does a lens hood reduce the light?
« Reply #18 on: November 10, 2011, 05:22:20 PM »
So it makes no sence to say hoods protect mostly/only at the wide end of zooms.


Angle of view matters. 

Look at the ET-74 hood for the 70-200mm f/4L IS (which is 3.15" long).  Imagine the level of flare protection provided by that hood at 70mm and f/4. 



Now, look at the EW-83H hood for the 24-105mm f/4L IS (which is 1.7" long). 



Do you think the dedicated hood for the 24-105mm lens is going to provide the same level of flare protection at 70mm and f/4 on that lens?  What would a shot at 24mm look like if you put a round, 3.15" long hood on the 24-105mm?  Holding a toilet paper roll up to your eye might give you some idea...
« Last Edit: November 10, 2011, 05:24:20 PM by neuroanatomist »
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Meh

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Re: Does a lens hood reduce the light?
« Reply #19 on: November 10, 2011, 06:03:11 PM »
To be fair, I think @texphoto is pointing out that in a zoom lens such as a 70-200mm the lens hood limits the angle of incident light to the front element the same regardless of the internal positions of the zoom mechanism.  This much is true.   However, he's not correct in his statement (I'm paraphrasing) that the zoom position doesn't matter at all.  Clearly, at 200mm the front element is being exposed to a far greater angle of incident light than will be in the field of view of the lens which is how flare is created


neuroanatomist

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Re: Does a lens hood reduce the light?
« Reply #20 on: November 10, 2011, 06:08:07 PM »
To be fair, I think @texphoto is pointing out that in a zoom lens such as a 70-200mm the lens hood limits the angle of incident light to the front element the same regardless of the internal positions of the zoom mechanism.  This much is true.   However, he's not correct in his statement (I'm paraphrasing) that the zoom position doesn't matter at all.  Clearly, at 200mm the front element is being exposed to a far greater angle of incident light than will be in the field of view of the lens which is how flare is created

Makes sense.
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dr croubie

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Re: Does a lens hood reduce the light?
« Reply #21 on: November 10, 2011, 06:50:53 PM »
dr croubie shame your image examples wernt of exactly the same scene, would have beena little more obvious then, with the shutter speeds and stops.

Well, the point was more to show that:
In the first shot, the sun is right in the top left of the frame. Washes out everything because of flare.
In the second shot, the camera is rotated maybe 90 degrees to the right. The sun is nowhere near the frame. But because it's a Medium Format Fisheye lens, there is still glass facing the sun. You can still see how the colours are washed out, it looks like an old film photo, there's no contrast, the green looks hopeless, it looks like there's a reddish-orange cast in the centre of the frame. Even with the camera set to AutoWB (which the 7D does very well, according to most accounts), it couldn't make this shot look realistic. A hood and/or gobo would have made this shot a whole lot better.

I don't have any others taken at the same time, maybe I'll get out and some direct comparisons when i've got time (coincidentally, I bought fleabay ripoff hoods from china for everything I don't have last week. Less than $4 each, you can't go wrong). The only lens I've currently got a hood for is the 70-300L, which I use all the time, except when I'm using a CPL.
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Re: Does a lens hood reduce the light?
« Reply #21 on: November 10, 2011, 06:50:53 PM »

TexPhoto

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Re: Does a lens hood reduce the light?
« Reply #22 on: November 10, 2011, 09:02:44 PM »
To be fair, I think @texphoto is pointing out that in a zoom lens such as a 70-200mm the lens hood limits the angle of incident light to the front element the same regardless of the internal positions of the zoom mechanism.  This much is true.   However, he's not correct in his statement (I'm paraphrasing) that the zoom position doesn't matter at all.  Clearly, at 200mm the front element is being exposed to a far greater angle of incident light than will be in the field of view of the lens which is how flare is created

You guys are missing the point entirely. If you are shooting a 70-200 zoom, and you have the stock hood: you have 2 choices:  Use the hood or don't.   Which of these 2 choices will better control flair at 70mm? Using the Hood.  Which will control flair better at 200mm?  Using the hood.  In fact, if the hood is preventing all flair at 70mm, I will guarantee there is no flair when zoomed to 200mm assuming no other changes.

Now if you want to argue that you should not use the hood you have because a theoretical 200mm only hood (that you do not have) would be better than the stock hood, then you are right from a theoretical standpoint, but wrong from a reducing flair/practical/not just being difficult standpoint. Now if anyone here owns a 200mm only hood for their 70-200, I will... eat a bug/admit defeat/ etc  Whatever.

Meh

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Re: Does a lens hood reduce the light?
« Reply #23 on: November 10, 2011, 09:44:50 PM »
You guys are missing the point entirely. If you are shooting a 70-200 zoom, and you have the stock hood: you have 2 choices:  Use the hood or don't.   Which of these 2 choices will better control flair at 70mm? Using the Hood.  Which will control flair better at 200mm?  Using the hood.  In fact, if the hood is preventing all flair at 70mm, I will guarantee there is no flair when zoomed to 200mm assuming no other changes.

Now if you want to argue that you should not use the hood you have because a theoretical 200mm only hood (that you do not have) would be better than the stock hood, then you are right from a theoretical standpoint, but wrong from a reducing flair/practical/not just being difficult standpoint. Now if anyone here owns a 200mm only hood for their 70-200, I will... eat a bug/admit defeat/ etc  Whatever.

Sorry but who was saying don't use the hood.   Of course not using the hood is worse than using the hood despite it not providing maximum protection at focal lengths greater than the widest focal length.

The hood on 70-200mm zoom is designed to limit the incident light to to the FOV of a 70mm focal length.   Zoom to anything greater than 70mm and the hood is still allowing the same light to fall upon the front of the lens.   Therefore, at any focal length greater than 70mm light from outside the FOV is entering the lens and can cause flare.

The only point of contention is your assertion that the lens hood prevents all flare regardless of zoom position.

« Last Edit: November 10, 2011, 09:49:56 PM by Meh »

neuroanatomist

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Re: Does a lens hood reduce the light?
« Reply #24 on: November 10, 2011, 10:01:22 PM »
You guys are missing the point entirely. If you are shooting a 70-200 zoom, and you have the stock hood: you have 2 choices:  Use the hood or don't.

Not quite. There's a third choice, the one you raised - use a gobo.  If you understand that the flare protection the hood provides to a zoom lens is maximal at the short end, and minimal at the long end...that tells you when you'd want to use a gobo.  If you (incorrectly) believe the hood is equally effective at all focal lengths (assuming you're not using the 24-70mm, that is), you're either risking more flare and less contrast at the longer end, or wasting your time mucking about with a gobo when the hood could do the job at the short end.
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Rocky

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Re: Does a lens hood reduce the light?
« Reply #25 on: November 10, 2011, 11:22:05 PM »
A hat with big rim will do wonder. with shorter lens, you just wear your head low and use the rim to shade the sun.  If you can hold and shoot with one hand,, then the other hand can really manipuate  the hat for shade.

TexPhoto

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Re: Does a lens hood reduce the light?
« Reply #26 on: November 11, 2011, 10:15:58 AM »

The only point of contention is your assertion that the lens hood prevents all flare regardless of zoom position.


I am not sure how to argue this because that is pretty much the opposite of what I have been saying.

Here's the thing, unless your shooting with a pinhole camera and the pinhole is size .00001" you cannot make a perfect hood.  The lens people keep bring up here is the 70-200 f4, which has a round hood.  And I have yet to see a petal hood for any lens that is not squared off on the top and the bottom.  So none of these hoods are close to perfect at even the wide end of the zoom.  They are a compromise in size/shape etc.

In every post I've made here my advice has been use the hood because it will help, and if you need to, even add a gobo. (hand/hat gobos are cool too Rocky)

And the reason I've been stating this is because the original poster here seems on the fence of whether to use his hood or not.  My advice: use the hood (and maybe a gobo).  Lots of other peoples advice here: "So, hoods protect mostly/only at the wide end of zooms." Or some longer version of that.   Which does not seem too encouraging to the OP.
« Last Edit: November 11, 2011, 10:22:48 AM by TexPhoto »

neuroanatomist

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Re: Does a lens hood reduce the light?
« Reply #27 on: November 11, 2011, 12:58:43 PM »
Let's recap. 

OP asked if a hood results in a loss of light that would impact the exposure setting, making reference to the large hood on the 70-200/2.8 II. 

The consensus was no, but it does reduce unwanted light (i.e. flare). 

Everyone agreed that hoods were good things, and recommended using them. 

NotABunny indicated trying a hood on a 70-200/4 IS, and at 200mm it made no difference in the shot, i.e. no reduction in flare.

Now...why was that the case?  For the reasons previously stated, i.e. zoom lens hoods are designed to not vignette at the long end of the zoom, and as a consequence, they do not protect from flare at the long end of the zoom.

Then TexPhoto made an assertion that it makes no sense to say that hoods protect from flare only/mostly at the wide  end of a zoom lens.  The most straightforward interpretation of that statement is that you're saying the corollary is true - i.e., if it's wrong to say hoods protect only at the wide end, then they must protect throughout the zoom range.  That was the point of contention. 

Now, in retrospect, you may have meant that it makes no sense to say that, becuase it might be construed as a reason not to use a hood at all.  Clearly, neither you nor anyone else in this rambling thread is saying that (I hope!).

To correct a few other minor points, it's flare, not flair.  Flair is a distinctive elegance or style, something you almost always want in your photography, vs. flare, which you usually want to eliminate (unless it's used for artistic effect, in which case maybe the flare is contributing to your flair). 

Also, the EW-83K hood (for the 24/1.4L II) is a petal-type hood with the ends of the petals rounded off.



But yes, most are squared off a bit, I expect as a design compromise for the convenience of being able to set the lens front-down on it's hood to facilitate changing lenses, etc.

My advice: use the hood (and maybe a gobo).  Lots of other peoples advice here: "So, hoods protect mostly/only at the wide end of zooms." Or some longer version of that.   Which does not seem too encouraging to the OP.


Again, 'use a hood' is everyone's advice, as far as I can tell.  If someone stated that the Canon front lens caps are easier to knock loose because of the side-pinch design, would you construe that as advice against using a lens cap?  'Hoods protect mostly/only at the wide end of zooms' is a statement of fact...not advice against using a hood. 
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Re: Does a lens hood reduce the light?
« Reply #27 on: November 11, 2011, 12:58:43 PM »

Rocky

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Re: Does a lens hood reduce the light?
« Reply #28 on: November 11, 2011, 01:14:36 PM »
May I stress that the hood also help protect the lens from foreign objects like dust, water splash your own finger etc.

Meh

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Re: Does a lens hood reduce the light?
« Reply #29 on: November 11, 2011, 01:45:01 PM »

The only point of contention is your assertion that the lens hood prevents all flare regardless of zoom position.


... that is pretty much the opposite of what I have been saying.


Sorry but I don't see how that is the opposite of what you're saying, a generous paraphrasing perhaps but certainly not opposite.   Your exact words were "if the hood is preventing all flair at 70mm, I will guarantee there is no flair when zoomed to 200mm".   Sounds very like zoom position doesn't matter.




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Re: Does a lens hood reduce the light?
« Reply #29 on: November 11, 2011, 01:45:01 PM »