Lens Hoods And The Crop Factor

[CoolToolGuy]

I am wondering if the angle difference that results from the crop factor would justify a different size hood. Has anybody out there done any research on this? Now that Canon has entered the consumer DSLR market there may be enough call for them to come out with different hoods for digital, or identify an alternate existing hood for each lens that is right for digital.
Have Fun

[CyberDyneSystems]

I have a lens hood from a 70-200mm telephoto (? I think thats what its from ? ) on my 17-40mm f/4 L

So yes,. it definately is worht look.

[EXA1a]

CyberDyneSystems wrote:
I have a lens hood from a 70-200mm telephoto (? I think thats what its from ? ) on my 17-40mm f/4 L

So yes,. it definately is worht look.

Are you sure you don't get vignetting at 17mm???

--Jens--

[CyberDyneSystems]

The Vignetting was tiny... so small I could not beleive how little I needed to trim off the hood to get it perfect at 17mm....

but yes,. I did have to trim it a little,. The hood I got was used,. it is an EW-83B which is much longer and narrower than the stock hood. I had also tried the 70-200mm and it was almost exactly the same size with similar vignette,. but yes it too would have been neede to be trimmed. That is why I bought the used one.

The pont is this hood is so much longer and narroer than the stock 17-40mm hood it illustrated how totally useless the stock hood really is.

Here is the post I had on the subject.

http://www.photography-on-the.net/forum/showthread.php?t=14986#78115

[Jim_T]

cooltoolguy wrote:
I am wondering if the angle difference that results from the crop factor would justify a different size hood.


FWIW, I have a Sigma 15-30 wide zoom. It comes with a removable hood.

On a 35mm film body, the vignetting is terrible at 15mm. You get a big black circle around the image. You *have* to remove the hood to shoot at 15mm.

On my 10D, I can shoot at 15mm with the hood on. There's a slight darkening in the corners of the shots, but you really have to look for it.

So yes.. Obviously you can use larger hoods when using 35mm lenses on a Digital camera with an APS sized sensor.

[PacAce]

cooltoolguy wrote:
I am wondering if the angle difference that results from the crop factor would justify a different size hood. Has anybody out there done any research on this? Now that Canon has entered the consumer DSLR market there may be enough call for them to come out with different hoods for digital, or identify an alternate existing hood for each lens that is right for digital.
Have Fun

You can use whatever hood your lens came with. And if it didn't come with a hood and you want one, you can just get the hood that was made for it. No need to complicate matters by over analysing what effect the crop factor has on the relationship of the hood and the lens because there ain't anyting to analyse. :)

[CoolToolGuy]

PacAce, Thanks for the reply. Your statement would be true in the 35mm film world, but in the case of 10D and Digital Rebel the crop factor changes the angle that the lens captures. Therefore, the hood should be longer to prevent flare while avoiding vignetting. The question is, how much?
There is an extensive reply and reference to a solution for the 17-40. That is a good one. The lens that started me down this path is the 28-135 IS. Has anyone found a solution for that one?
Have Fun

[DonCoon]

cooltoolguy wrote:
PacAce, Thanks for the reply. Your statement would be true in the 35mm film world, but in the case of 10D and Digital Rebel the crop factor changes the angle that the lens captures. Therefore, the hood should be longer to prevent flare while avoiding vignetting. The question is, how much?
There is an extensive reply and reference to a solution for the 17-40. That is a good one. The lens that started me down this path is the 28-135 IS. Has anyone found a solution for that one?
Have Fun

That doesn't make sense to me. If a hood prevents flare when used on a full-frame camera, it will prevent flare on the 10D. The 10D simply uses the center portion of the view and crops away the perimeter.

It would be better to say that a hood "COULD" be longer since vignetting is less of an issue.

Right? Or am I missing something here?

[PaulB]

Here we go again.
The problem with reasoning that the crop factor makes a difference to the hood which can be used is ignoring one important point.
The WHOLE of the lens forms the image, not just the centre portion.
Whilst there may be no vignetting PacAce and DonCoon are therefore correct in their replies.
Why mess about buying differnt lens hoods when the one which is made for the lens is either supplied or will usually be the cheapest anyway?
Those of us who may have to swop lenses between different bodies and crops - even onto full-frame digital or (God forbid!) film bodies can't even think about swopping lens hoods as well..................!

Paul

[slin100]

DonCoon wrote:
[It would be better to say that a hood "COULD" be longer since vignetting is less of an issue.

Right? Or am I missing something here?

You're not missing anything. That's right.

I have a 17-40. The included hood is a joke when used on a 10D. It barely provides any additional shielding. I purchased the EW-83DII which is the hood for the 24/1.4L and it's much better.

The easiest way to make a selection is to think about the FOV at the widest end. For the 28-135, the wide end is equivalent to 44mm on a 35mm camera. So, you want a hood that won't vignette a theoretical 44mm lens. The 28-135 has a 72mm filter diameter. If you look Canon's offering of lens hoods in a 72mm diameter, you won't find much. The only two choices seem to be the E-72 and the E-72U. The E-72U is spec'd for the 28-135, so that really only leaves the E-72, which is spec'd for the TS 24mm and 45mm lenses. I doubt that the E-72 will provide any improvement at all.

That means you'll have to buy a 3rd party hood. I think Hoya makes a screw-in, collapsible hood that won't vignette at 35mm. That might be a reasonable choice.

[CoolToolGuy]

geez, it seem like a straightforward question, but... so if you have already made up your mind on this then thanks, but for those of you that may still be interested -
The way I see it, the hood should protect against all light that enters the lens at a greater angle than the angle of view of the lens. Now the perfect hood would be rectangular, and the scalloped hoods for the wide angles approach that, but I want to try and keep it simple (may be too late)...
I have not done the research, but I'm pretty sure the Canon hoods are designed for the angle of view (AOV) of the lens when used for the 35mm film format. For the lens that got me going on this (28-135) the maximum AOV is listed as 75 degrees. Okay, fine, but when I put that lens on my Digital Rebel, the maximum AOV becomes 51 degrees. So for best results (granted it will only be best results when zoomed all the way wide), the hood should block all light coming in at greater than 51 degrees. That's a lot of difference, and I just thought it might be worthwhile to see if I can get there.
Now, am I missing something?
And one thing to keep in mind is that even though the 28-135 has a 72mm filter size, the specified hood is EW-78BII, because the bayonet portion of the lens where the hood attaches is larger than the filter diameter (probably 78mm), so the options mght be the EW78C or the EW78D. Has anyone tried either one of them on the 28-135?
I'm sorry if I started a firestorm, but inquiring minds want to know - geez, any time you mention the words 'crop factor'...
Have Fun

[DaveG]

cooltoolguy wrote:
geez, it seem like a straightforward question, but... so if you have already made up your mind on this then thanks, but for those of you that may still be interested -
The way I see it, the hood should protect against all light that enters the lens at a greater angle than the angle of view of the lens. Now the perfect hood would be rectangular, and the scalloped hoods for the wide angles approach that, but I want to try and keep it simple (may be too late)...
I have not done the research, but I'm pretty sure the Canon hoods are designed for the angle of view (AOV) of the lens when used for the 35mm film format. For the lens that got me going on this (28-135) the maximum AOV is listed as 75 degrees. Okay, fine, but when I put that lens on my Digital Rebel, the maximum AOV becomes 51 degrees. So for best results (granted it will only be best results when zoomed all the way wide), the hood should block all light coming in at greater than 51 degrees. That's a lot of difference, and I just thought it might be worthwhile to see if I can get there.
Now, am I missing something?
And one thing to keep in mind is that even though the 28-135 has a 72mm filter size, the specified hood is EW-78BII, because the bayonet portion of the lens where the hood attaches is larger than the filter diameter (probably 78mm), so the options mght be the EW78C or the EW78D. Has anyone tried either one of them on the 28-135?
I'm sorry if I started a firestorm, but inquiring minds want to know - geez, any time you mention the words 'crop factor'...
Have Fun

Canon, and everyone else, makes lens hoods that are not nearly long enough to be effective for the given focal length of the lens that will use them. The problem is that an effective hood would be too damn big, especially on telephoto lenses, or it wouldn't look cool enough. They all make hoods that are "better than nothing".

The shape of the lens hood is open to debate. My feeling is that a rectangular hood/shade just on this side of vignetting is what you want. The longer the shade (without vignetting) the more effective it's going to be in controlling flare. Once again a bellows lens shade does both. With the review you don't have to worry about vignetting and you adjust it to fit it to each lens.

[teddynet]

PaulB wrote:
Here we go again.
The problem with reasoning that the crop factor makes a difference to the hood which can be used is ignoring one important point.
The WHOLE of the lens forms the image, not just the centre portion.



Yes, but the 10D sensor doesn't see the WHOLE image made by the lens, it only records a portion from the centre. Since bright lights in that portion of the image that the viewfinder doesn't show, and won't appear in the final image, can still cause flare it makes perfect sense to mask those lights out using a lens hood that suits the actual FOV of the lens and not the FOV that the lens would have on a different camera system.

Lens hoods are relative to FOV not focal length. If you had a 6x6 camera with a 50mm lens and a 35mm camera with a 50mm lens would you expect the lens hoods to be the same shape?

[CyberDyneSystems]

Actually ,. the "flower petal" shape IS the "perfect" shape,. a lens hood that was engineered to block all light that hits the front of the lens EXCEPT the light that goes in to the rectangilar film plane/CCD will in fact look exactly like the "flower petals" we are used to. But with the smaller film plane of the 10D etc.. the petals are not long enough to do the job.

The lens elements bulge outward,. so a perfect ractanglar hood would result in a vignette shaped like a collapsing rectangle with sides like this ) ( and the same for the top and bottom,.. by using the curves of the petal,. the shadow that us cast on the bulging convex elemnts is in fact a virtually straight rectangle,. that is exactly why they are shaped that way.

[CyberDyneSystems]

O-kay super lame diagram time :D

http://images.fotopic.net/?id=1793204&outx=980&oq=0

The circle = the entire image at the focal point behind the lens.

The large rectangle = the 35mm film plane.

The small rectangle = the 10D CCD.

All the area in blue is light that a Canon "flower petal" lens hood SHOULD block for the best image. Any light that enters the lens here is not part of the rectangular image and there fore can do no good, but theoretically stands to cause harm to your image. Flare is the obvious issue,. but even without flare,. the 3xcess light can cause a hazyness in varying degrees. The idea is keep any light that is not part of your image from bouncing around in there, and casuing a degredation of the image quality.

So,. to have a hood that is equally effective as the stock hood on a 35mm,. the hood on a 1.6X crop CMOS then needs to do the same job, but now it needs to block all the light hitting the front in both the blue AND the red areas....

So,. this is not to say that you HAVE to do this.

But it does illustrate that the lens hood does not do it's job as well when a smaller film plane is used than the 35mm plane that the Canon lenses and hoods were designed for.

Any light striking the front element that is not part of the intended image,. is can be detrimental.

This why lens manufactureres have taken the time to engineer these hoods with there "perfect" "Tulip" shaped petals.

[PacAce]

Have we all lost sight of the fact that the primary purpose of the lens shade/hood is to keep stray, side light from entering the lens and thus preventing lens flares? Like I said earlier, I think we're over analysing "what effect does my hood have on my lens with the crop factor?" thing!

Discussions about which part of the image light actually hits the sensor and which parts don't and hence could possibly degrade the image and hence should be "hooded" off may be well and good for prime lens but not worth much for zoom lenses, right? After all, if we DID choose a hood for these reason on the widest side of the zoom lens, then what about the rest of the range of the zoom?

Fact: the inside of the camera is painted matt-black for a reason...to absorb any light that doesn't make it to the film or sensor. Reflection from areas outside the sensor or film is practically nill. Reflections of stray light bouncing around within the lens would be more of a concern.

[CyberDyneSystems]

I'm not saying we aren't over anylyzing!!! Heck no,. this is what we do best on this foum!!! lol :D :D

Since when is that a crime! :D

The advantages of what any of us ever claim in any subject are allways debateable,. but that won't stop us from worrying about which is the best.

But ,. even where flare is concerned,. now we have to worry about flare striking the red part of the diagram as the hood won't help....

Remeber stray light can come from anywhere,. direct sun aside,. it can be reflections from other objects,. etc..

In broad daylight,. the amount of releflected ligh bouncing around is pratically infinite,. if we could "see" the reflected waves,. it would look torrential. Remember What we see is light refelcting off of an object,. thus we are literally being bombarded with reflected light from all directions.

DOH!!! See ,. I just can't stop myself! :D

[PacAce]

CDS,

:D :D :D

CyberDyneSystems wrote:
But ,. even where flare is concerned,. now we have to worry about flare striking the red part of the diagram as the hood won't help....


If the stray light is striking the red part of your diagram then you've got bigger problems to worry about, like what the heck are you doing shooting straight into the sun!!!! 8)

[CoolToolGuy]

If the stray light is striking the red part of your diagram then you've got bigger problems to worry about, like what the heck are you doing shooting straight into the sun!!!!
_____________________________________________

Well, the sun may be the largest emitter of flare-producing light, but flare can also come from street lights, headlights, stadium lights, stage lighting, (do I need to go on?). Sometimes it provides a nice effect, but most of the time you want to eliminate it.
I love to use a polarizer as my hood, but when the light levels decrease, you can't always afford the stop-and-a-half.

CDS, your graphic really illustrates the issue.

Still hoping to find some alternatives or figure out how to lobby Canon to produce hoods for 1.6 (must not use the CF word unless it is Compact Flash!)

Have Fun

[rdenney]

PaulB wrote:
Here we go again.
The problem with reasoning that the crop factor makes a difference to the hood which can be used is ignoring one important point.
The WHOLE of the lens forms the image, not just the centre portion.
Whilst there may be no vignetting PacAce and DonCoon are therefore correct in their replies.
Why mess about buying differnt lens hoods when the one which is made for the lens is either supplied or will usually be the cheapest anyway?
Those of us who may have to swop lenses between different bodies and crops - even onto full-frame digital or (God forbid!) film bodies can't even think about swopping lens hoods as well..................!

Paul

You are responding to the wrong question here. There is no value in allowing light to enter the mirror box if it won't get on the sensor. The light that doesn't get on the sensor does not contribut to the quality of the light that does. That's why we have lens hoods. Light that doesn't get on the sensor can reflect off things, including the lens surfaces and things on them. It can also reflect off the mirror box itself, despite the effective flat black material that Canon uses.

There's a reason why studio photographers pay hundreds of dollars for fully adjustible compendium lens hoods for their Hasselblads and view cameras, and why the corners of their view-camera ground glass is notched to allow them to directly check for vignetting of those hoods. They adjust them to be tight.

The Canon 20-35 has an integral frame mask that precludes much of the light entering the front element from getting any deeper into the lens. For the small sensor, that mask could be smaller, just as the hoods could be smaller.

If Canon offered special hoods for their lenses for use on the 10D-sized sensor, I'd buy them. If the sun is just outside the frame, I want the sun's light to also be outside the frame.

Rick "a strong believer in the value of effective lens hoods" Denney

[PacAce]

rdenney wrote:
You are responding to the wrong question here. There is no value in allowing light to enter the mirror box if it won't get on the sensor. The light that doesn't get on the sensor does not contribut to the quality of the light that does. That's why we have lens hoods. Light that doesn't get on the sensor can reflect off things, including the lens surfaces and things on them. It can also reflect off the mirror box itself, despite the effective flat black material that Canon uses.

There's a reason why studio photographers pay hundreds of dollars for fully adjustible compendium lens hoods for their Hasselblads and view cameras, and why the corners of their view-camera ground glass is notched to allow them to directly check for vignetting of those hoods. They adjust them to be tight.

The Canon 20-35 has an integral frame mask that precludes much of the light entering the front element from getting any deeper into the lens. For the small sensor, that mask could be smaller, just as the hoods could be smaller.

If Canon offered special hoods for their lenses for use on the 10D-sized sensor, I'd buy them. If the sun is just outside the frame, I want the sun's light to also be outside the frame.

Rick "a strong believer in the value of effective lens hoods" Denney


Rick, I agree with your 100%...in theory. However, I must beg to differ with you in practicality. For instance, I would imagine that there is more fear of reflections bouncing off the surface of the sensor (or film) reaching the back of the lens and then bouncing right back again towards the sensor than there is of having reflections bouncing off the camera interior. However, both of these reflections are inconsequential to the regular Joe (discounting the pros with their large format cameras, black drapes and hundreds of dollar lens shades :) ) compared to the stray light reflections that go bouncing all over the interior of the lens.

I don't disagree that the closer you can get the periphery of your shade to the fringes of the lens VOF, the better it is. But, for most non-pro photographers, does it really make that much of a difference, especially if we're talking about a non-adjustable lens shade for a zoom lens?

Pac "who also thinks that your hand or cap also makes a good lens shade in a pinch" Ace.

[rdenney]

pacace wrote:

Rick, I agree with your 100%...in theory. However, I must beg to differ with you in practicality. For instance, I would imagine that there is more fear of reflections bouncing off the surface of the sensor (or film) reaching the back of the lens and then bouncing right back again towards the sensor than there is of having reflections bouncing off the camera interior. However, both of these reflections are inconsequential to the regular Joe (discounting the pros with their large format cameras, black drapes and hundreds of dollar lens shades :) ) compared to the stray light reflections that go bouncing all over the interior of the lens.

I don't disagree that the closer you can get the periphery of your shade to the fringes of the lens VOF, the better it is. But, for most non-pro photographers, does it really make that much of a difference, especially if we're talking about a non-adjustable lens shade for a zoom lens?

Pac "who also thinks that your hand or cap also makes a good lens shade in a pinch" Ace.

No disagreement from me, particularly in the use of my hand, a tree, a building, or any other device to shade the front of the lens.

I don't agree that the main issue is reflections from the surface of the sensor (actually, the AA filter) or film. Thos reflections return to the lens nearly straight on, and thus nearly none of them reflect back. It's the light reflecting off surfaces at acute angles, such as along the sides of the mirror box, that provide the greater risk.

And I'm not just speaking theoretically. I often make images with the sun in the frame or just outside the frame, using the sun for rim lighting.

Here's an example:

http://www.rickdenney.com/images/dirty_devil_river_lores.jpg

In this case, the sun is in the image, and you can see a bit of lens flare (it's a medium-format 30mm fisheye) in the form of a bluish haze over the center of the image. Any light falling on the mirror box would just exacerbate the flare, but would be visible over portions of the frame or would lower the contrast of the image over all the frame.

Here's another example:

http://www.rickdenney.com/scratch/Wichita_fountain_1.jpg

In this case (shot with the 10D and the 20-35USM), the sun is just outside the field of view. Inadequate shading would cause an overall loss of contrast if it is shining on the lens elements (which, as you say, you can shade with your hand). An efficient lens shade makes this more convenient.

You are right that with zooms, the shade can only be designed for the widest zoom setting. But at least it ought to be designed for that, it seems to me. In a perfect world, shades would retract with zoom setting, as they do on my Sigma 28-70/2.8, so that the shade stays reasonably efficient thrughout the zoom range.

The worst shades are the petal designs for super zooms where the photographer might frequently compose with the sun just outside the field of view in one corner. At least you have something to lean your hand on to provide shade.

For telephoto lenses, it isn't as critical. One reason is that the light rays are entering the mirror box much straighter, and also because the lens usually has a much tighter illuminated circle. Any shade deep enough to keep the sun from shining on the front element is probably fine. The worst are the perspective-shift wide-angles.

Again, if Canon offered a set of shades to be more efficient with the small sensor, I'd buy them.

Rick "who always invests in efficient lens shades" Denney