Petal Shaped Lens Hoods

Just out of interest, what is the purpose of petal shaped lens hoods?

Is it so that you can still access filters and lens cap with the hood
installed, or is it because they are designed to let more light to the
corners of the photo? Or maybe something else?

"Ed" wrote in message
...
Just out of interest, what is the purpose of petal shaped lens hoods?

Is it so that you can still access filters and lens cap with the hood
installed, or is it because they are designed to let more light to the
corners of the photo? Or maybe something else?

Petal shaped hoods control flare better than round types because they take
into account the aspect ratio of the camera's sensor, so the angle of view
is greater in one direction than the other.

On Sat, 17 Mar 2007 20:54:17 -0000, Ed wrote:

Just out of interest, what is the purpose of petal shaped lens hoods?

Is it so that you can still access filters and lens cap with the hood
installed, or is it because they are designed to let more light to the
corners of the photo? Or maybe something else?

When mounted correctly, notice that the largest petals are above
and below the lens, corresponding to the shortest dimension of the
sensor. The petals on the left and right are shorter, and
correspond to the greater horizontal width of the sensor. The lens
hood's cutaways in the corners are shorter than any of the petals
and correspond to the greatest dimensions of the sensor, the
diagonals. If sensors were circular, lens hoods could also be
circular without compromising protection in any direction vs. any
other direction. My old Nikon lenses all used circular lens hoods,
for whatever that's worth.

That's not what I am sure about.

The Canon 24mm prime and 35mm prime have a petal hood, however the 50mm and
85mm have a round hood. Then the 70-200 2.8 has a petal style hood.


"ASAAR" wrote in message
news

When mounted correctly, notice that the largest petals are above
and below the lens, corresponding to the shortest dimension of the
sensor. The petals on the left and right are shorter, and
correspond to the greater horizontal width of the sensor. The lens
hood's cutaways in the corners are shorter than any of the petals
and correspond to the greatest dimensions of the sensor, the
diagonals. If sensors were circular, lens hoods could also be
circular without compromising protection in any direction vs. any
other direction. My old Nikon lenses all used circular lens hoods,
for whatever that's worth.

Is it not to stop vignetting in the corners of wider angle lenses?

Geoff.

"Ed" wrote in message
...
That's not what I am sure about.

The Canon 24mm prime and 35mm prime have a petal hood, however the 50mm
and 85mm have a round hood. Then the 70-200 2.8 has a petal style hood.


"ASAAR" wrote in message
news

When mounted correctly, notice that the largest petals are above
and below the lens, corresponding to the shortest dimension of the
sensor. The petals on the left and right are shorter, and
correspond to the greater horizontal width of the sensor. The lens
hood's cutaways in the corners are shorter than any of the petals
and correspond to the greatest dimensions of the sensor, the
diagonals. If sensors were circular, lens hoods could also be
circular without compromising protection in any direction vs. any
other direction. My old Nikon lenses all used circular lens hoods,
for whatever that's worth.

Sorry, I should have said "vignetting in the corners of photographs taken
with wider angle lenses".

Geoff.

"Geoff. Hayward" wrote in message
...

Is it not to stop vignetting in the corners of wider angle lenses?

Geoff.

"Ed" wrote in message
...
That's not what I am sure about.

The Canon 24mm prime and 35mm prime have a petal hood, however the 50mm
and 85mm have a round hood. Then the 70-200 2.8 has a petal style hood.


"ASAAR" wrote in message
news

When mounted correctly, notice that the largest petals are above
and below the lens, corresponding to the shortest dimension of the
sensor. The petals on the left and right are shorter, and
correspond to the greater horizontal width of the sensor. The lens
hood's cutaways in the corners are shorter than any of the petals
and correspond to the greatest dimensions of the sensor, the
diagonals. If sensors were circular, lens hoods could also be
circular without compromising protection in any direction vs. any
other direction. My old Nikon lenses all used circular lens hoods,
for whatever that's worth.

In article , Ed
wrote:

That's not what I am sure about.

The Canon 24mm prime and 35mm prime have a petal hood, however the 50mm and
85mm have a round hood. Then the 70-200 2.8 has a petal style hood.



That's because the wider thhe angle of the lens, the more critical it
is to keep the hood out of the way to prevent vignetting. Longer focal
lengths don't *need* to go with a petal style, usually, although some
come with them.

"ASAAR" wrote in message
news

When mounted correctly, notice that the largest petals are above
and below the lens, corresponding to the shortest dimension of the
sensor. The petals on the left and right are shorter, and
correspond to the greater horizontal width of the sensor. The lens
hood's cutaways in the corners are shorter than any of the petals
and correspond to the greatest dimensions of the sensor, the
diagonals. If sensors were circular, lens hoods could also be
circular without compromising protection in any direction vs. any
other direction. My old Nikon lenses all used circular lens hoods,
for whatever that's worth.




--
You need only reflect that one of the best ways to get yourself a
reputation as a dangerous citizen these days is to go about repeating
the very phrases which our founding fathers used in the struggle for
independence.
-- Charles A. Beard

On Sat, 17 Mar 2007 22:31:00 -0000, Geoff. Hayward wrote:

Is it not to stop vignetting in the corners of wider angle lenses?

No. It's possible for a lens hood to increase vignetting, but
they're not used to prevent it. Their purpose is to prevent the
wrong light rays from hitting the lens, the ones that produce
unwanted reflections and flare. Think of how people sometimes put
their hands up to their eyes to help eliminate glare it they're
looking in a sunwards direction. It's not to reduce vignetting. g

On Sat, 17 Mar 2007 22:27:07 -0000, Ed wrote:

That's not what I am sure about.

The Canon 24mm prime and 35mm prime have a petal hood,
however the 50mm and 85mm have a round hood. Then the
70-200 2.8 has a petal style hood.

The ultimate lens hood will let only light hit the lens that's
going to end up impacting the sensor. The light rays that are
blocked should be those that would go wide of the sensor. A round
lens hood could only meet these qualifications if the sensor was
round. Since the sensor is rectangular, the more effective lens
hoods are the ones that use petals. If they're circular, they'll
either pass some light rays that they shouldn't, or block others
that shouldn't be blocked (causing a bit of vignetting). If a well
designed round lens hood is used, you could always add some petals
to it to make it a bit more effective. This might not provide
enough additional benefit to compensate for the larger size that
might make it harder to pack and store conveniently.

"Ed" wrote in message
...
Just out of interest, what is the purpose of petal shaped lens hoods?

Is it so that you can still access filters and lens cap with the hood
installed,

No.


or is it because they are designed to let more light to the corners of the
photo? Or maybe something else?

That's closer. "Petal-shaped" or "cookie cutter" lens hoods, also sometimes
called "perfect" lens hoods, are designed to keep non-image-forming light
rays out of the lens as much as is practicable, by blocking more of the
light from the top, bottom and sides that would fall outside the rectangle
of the film or sensor.

Neil