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Old Jul 12, 2005, 9:29 PM   #1
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I recently bought an EOS 20d with the 17-85mm lens. I've never used a lens hood before, but it sounds like a necessary item. The Canon hood for this lens is petal-shaped. Is there a reason for that? Does anyone know if the hood works for both the wide angle and telephoto focal lengths? Any other reccomendations would be welcome.

thanks.


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Old Jul 13, 2005, 2:18 AM   #2
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Well, my guess for it being petal is exactly because the lens covers wide to tele.

Normally a lens with a fixed length is really simple: just make a cylindrical hood and make sure you don't have it too long to interfere with the picture. However if you try to do something like that for the 17-85mm, your only possibility is a lens hood that can only be useful at 17mm. Although it still useful at the tele end, it's not nearly as effective as it could be.

From the pictures I keep seeing of petal hoods, it looks like the horizontal sides of the hood are shorter. This is probably made for the wide angle of the lens. The vertical sides of the hood is probably there for the tele.

Just a guess... but it seems to make sense to me... :?

I like guessing.
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Old Jul 13, 2005, 3:18 AM   #3
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Just a piece of advice - make sure you remove the hood when using the on-camera pop-up flash.

If you don't you get very large shadows in the picture at the wide end of the zoom. This is actually a bit of a problem - you wouldn't want to use the hood at night obviously.

But consider a backlit daytime subject - you want the hood because there might be light direct from the sun entering the lens, but if you use the hood you get big ugly shadows at the bottom of the picture.
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Old Jul 13, 2005, 12:34 PM   #4
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IMHO it's a combination of what Boyfrmspc said and a cost/weight thing. The petal shape uses less material and thus costs less to manufacture - it also has less weight which makes it more desirable for a photographer. The fact that most unwanted light will 'generally' come from above the lense and the fact that most times a wide angle lense will be used in portrait orientation allows the hood to have less material at the side but still be effective.

That's my three cents worth (hey gas prices keep going up so I'm charging more for my opinion now )
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Old Jul 13, 2005, 1:13 PM   #5
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Is this a joke , no seriously.

It can only be fitted in one position and is thus shaped for one reason. So that it doesn't interfere with the shot at the corners. Isn't this obvious. :roll:

if it were not shaped thus and was say completely round.... then at the wide end you would see the hood at the corners due to the oblong shape of the sensor, mirror, photographic standard etc.

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Old Jul 13, 2005, 1:28 PM   #6
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LBoy wrote:
Quote:
Is this a joke , no seriously.

It can only be fitted in one position and is thus shaped for one reason. So that it doesn't interfere with the shot at the corners. Isn't this obvious. :roll:
Hmm...

So the reason is just for the 'corners'. Tell me why are the petals on top/bottom longer than pettals on sides? If the whole reason was for the corners all 4 petals would be the same length wouldn't they?
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Old Jul 13, 2005, 2:13 PM   #7
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DigitalDad wrote:
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... Any other reccomendations would be welcome.
-> you can duct tape the side of the tulip shade (@ various points) and see what effect it does to your shots... :idea:
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Old Jul 14, 2005, 1:45 AM   #8
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Lenses are round. Film and camera sensors are rectangular. If you block light that would land outside of the rectangle of the sensor it won't affect the picture. Because of the rectangular shape there is more unused space in the (round) image formed by the lens above and below the actual picture than there is at the sides, and the corners of the photo come closest to the edge of the lens. Thus you can block more light at top and bottom (big petals) less at the sides (small petals) and the least at the corner (no petal) without getting in the way of your picture.
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Old Jul 14, 2005, 3:08 AM   #9
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The question that was asked if I look back was :

Quote:
The Canon hood for this lens is petal-shaped. Is there a reason for that?
Thank you Jacks for explaining what I thought I had done very quickly to the strange but obvious confusion of Big John. hahaha. Your not quite getting the hang of this stuff are you John..... ?

Quote:
The petal shape uses less material and thus costs less to manufacture - it also has less weight which makes it more desirable for a photographer.
Did you really write this.... Thanks for the laugh John, absolute class..... :lol::lol::lol::G:?:lol::lol::-):-)
(and you call me out for photographic knowledge.....?)
Quote:
Hmm...

So the reason is just for the 'corners'. Tell me why are the petals on top/bottom longer than pettals on sides? If the whole reason was for the corners all 4 petals would be the same length wouldn't they?
Yip as I previously explained and again by Jacks, what you say above would be true if only the darn sensor was square..... I did mention just for the corners. However I did mention that the sensor was rectangular. If you cant work it out from there then fine. Considering the original post never mentioned the length of the petals I think your just looking for another little argument John. ?




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Old Jul 14, 2005, 3:09 AM   #10
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LBoy wrote:
Quote:
Is this a joke , no seriously.

It can only be fitted in one position and is thus shaped for one reason. So that it doesn't interfere with the shot at the corners. Isn't this obvious. :roll:

if it were not shaped thus and was say completely round.... then at the wide end you would see the hood at the corners due to the oblong shape of the sensor, mirror, photographic standard etc.

yea.. everyone does know this right?
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