Why do lenses with the same filter size and min focal length have different hoods?

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Vertigo1

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This is just something random that's been puzzling me. Take the Canon 24mm prime and the 24-105mm zoom. Both have the same minimum focal length and front element size so why do they utilise different hoods?
 
The hood you need depends on the angle of view, you couldn't put a telephoto hood on a wide angle lens as you'd just be looking down a tunnel in you shots. That's why the zoom has a different hood.
 
LOL I know that :p

My point is that the hood (with the exception of odd-balls like the 24-70) will always be designed to "just" accomodate the widest focal length of a lens without vignetting. Since the 24-105 is, at its widest, the same focal length as the 24mm prime, why do they need different hoods?
 
The 24-105 hood is probably designed so it can still have some effect at 105mm, whereas the 24 prime only needs to be effective at 24mm?
 
But surely if the hood is outside the field of view at 24mm, it'll be outside the field of view at all longer focal lengths too - basically it's only the widest length that matters?
 
The widest focal length will determine how far the hood can encroach without being in the FoV, but it's not the only focal length that matters.

I expect the 24-105 hood is designed to also be as effective as possible at longer focal lengths as well (I doubt it'll be much use at 105, but perhaps in the 24-50 range it still has some merit).
 
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Different lenses have different curvature on the front element and have different tolerances for flare, hence different shaped hoods for different lenses.

* This is relating to the op's question relating to lenses starting at the same focal length. Lenses of differing focal lengths have different hoods for the reasons above.
 
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As Jim says - different lenses (even with the same focal length) are affected differently by flare.

Dedicated Lens hoods are tailored to deal with reducing flare on a specific lens - not just to fit the field of view.

Generic lens hoods work fine - some perfectly - just not the optimum.
 
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Ozei said:
Two of the petals are shaped differently - on the 24mm hood they're rounded but on the 24-105 hood they're cut off:


http://www.amazon.com/Canon-EW-83DII-Lens-Hood-24mm/dp/B00009R6V6
http://www.amazon.com/Canon-EW-83H-Lens-Hood-24-105mm/dp/B000B6A4S6
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^^^ Simply this. The hood for the zoom has the front squared off so you can stand the lens upright on it. Otherwise no difference.

Other lenses might vary if the front element is more or less recessed, but focal length/angle of view is the determining factor.
 
I can see where the OP is coming from, but on an L lens it's nothing to worry about as they come with free hoods, as for other lenses, Canon want to squeeze every single penny they can out of us all, so making you need different hoods increases their profits.
 
If the 24mm prime was f/4 then it could probably use the 24-105's hood... but it's not, it's f/1.4 and would vignette horribly wide open.

Bob
 
Canon Bob said:
If the 24mm prime was f/4 then it could probably use the 24-105's hood... but it's not, it's f/1.4 and would vignette horribly wide open.

Bob
Click to expand...

But as Richard pointed out, the hoods are nearly identical.
 
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squishy said:
But as Richard pointed out, the hoods are nearly identical.
Click to expand...

Maybe Canon have changed them at some time in the past then. The one I got with my 24-105L has the side scallops 20% longer than the ones on the 24L

Bob

Edit....they are the same reference numbers as linked by Richard
 
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HoppyUK said:
^^^ Simply this. The hood for the zoom has the front squared off so you can stand the lens upright on it. Otherwise no difference.
Click to expand...

smilielol.gif


The reason that the petals are different is that the sensor is rectangular, If it were square then all four petals should be the same. Simple fact - any hood on a zoom is a compromise. If it is small enough to provide full protection against flair at the longest setting, then it will vignette at the widest setting.
 
I'm sure they're interchangeable optically. Maybe a mm or two difference to account for front element recess. Other slight changes may be to account for reversing them back over the lens for storage.

The squaring off on the front is mainly so you can stand the the lens up. Could also be to allow access to the zoom ring when the hood is reversed, but that's kinda marginal. You could argue that squaring the front reduces optimum efficiency, but since zoom hoods tend to of marginal efficiency anyway most of the time, that's a handy trade-off that also makes the overall lens shorter.
 
Oggy said:
smilielol.gif


The reason that the petals are different is that the sensor is rectangular, If it were square then all four petals should be the same. Simple fact - any hood on a zoom is a compromise. If it is small enough to provide full protection against flair at the longest setting, then it will vignette at the widest setting.
Click to expand...

Unless it's a 24-70 ;)
 
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