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Hi everyone,

I recently bought ist dl with 18-55mm lens for my vacation and I loved
it. Toady I bought the 50-200mm lens. I did some tests and have some
questions here hope someone can help me out. Thanks in advance.

When I set camera to AF with auto flash and try to focus on a dark
point with pressing the shutter halfway, the flash just keeps flashing
with a noise 'ZZZ...' until I release the shutter. It happened to the
18-55mm lens once in a really dark place. But with 50-200mm lens that I
just bought, it happened more, in some places it was ok with the
18-55mm lens.

Does the 50-200mm lens have any problem that causes it happened more,
or it's just normal because it's a big lens?

Thanks and regards,
John

<> wrote:

> Hi everyone,
>
> I recently bought ist dl with 18-55mm lens for my vacation and I loved
> it. Toady I bought the 50-200mm lens. I did some tests and have some
> questions here hope someone can help me out. Thanks in advance.
>
> When I set camera to AF with auto flash and try to focus on a dark
> point with pressing the shutter halfway, the flash just keeps flashing
> with a noise 'ZZZ...' until I release the shutter. It happened to the
> 18-55mm lens once in a really dark place. But with 50-200mm lens that I
> just bought, it happened more, in some places it was ok with the
> 18-55mm lens.
>
> Does the 50-200mm lens have any problem that causes it happened more,
> or it's just normal because it's a big lens?

You should try both lenses on the same subject matter in a darkened room
for comparison.

The flash comes on to help the camera autofocus by providing more light.

The 18-55 is f/3.5, and the 50-200 is f/4. So all other things being
equal, the 50-200 won't let as much light in. Thus, a longer hunting
time for the autofocus, and more need for the focus-assist flash firing.

<> wrote in message
news: ups.com...
> Hi everyone,
>
> I recently bought ist dl with 18-55mm lens for my vacation and I loved
> it. Toady I bought the 50-200mm lens. I did some tests and have some
> questions here hope someone can help me out. Thanks in advance.
>
> When I set camera to AF with auto flash and try to focus on a dark
> point with pressing the shutter halfway, the flash just keeps flashing
> with a noise 'ZZZ...' until I release the shutter. It happened to the
> 18-55mm lens once in a really dark place. But with 50-200mm lens that I
> just bought, it happened more, in some places it was ok with the
> 18-55mm lens.
>
> Does the 50-200mm lens have any problem that causes it happened more,
> or it's just normal because it's a big lens?
>
> Thanks and regards,
> John


Hi.

Don't know your camera or lens.

If the 55-200 is large, with perhaps an even larger lens hood on the front,
could it be casting a shadow onto the area on which the lens is trying to
focus.

Roy G

Paul Mitchum wrote:
> <> wrote:
>
> > Hi everyone,
> >
> > I recently bought ist dl with 18-55mm lens for my vacation and I loved
> > it. Toady I bought the 50-200mm lens. I did some tests and have some
> > questions here hope someone can help me out. Thanks in advance.
> >
> > When I set camera to AF with auto flash and try to focus on a dark
> > point with pressing the shutter halfway, the flash just keeps flashing
> > with a noise 'ZZZ...' until I release the shutter. It happened to the
> > 18-55mm lens once in a really dark place. But with 50-200mm lens that I
> > just bought, it happened more, in some places it was ok with the
> > 18-55mm lens.
> >
> > Does the 50-200mm lens have any problem that causes it happened more,
> > or it's just normal because it's a big lens?
>
> You should try both lenses on the same subject matter in a darkened room
> for comparison.
>
> The flash comes on to help the camera autofocus by providing more light.
>
> The 18-55 is f/3.5, and the 50-200 is f/4. So all other things being
> equal, the 50-200 won't let as much light in. Thus, a longer hunting
> time for the autofocus, and more need for the focus-assist flash firing.

Thanks, Paul,

I did the tests on the exact same subjects with same condition. If it's
not the lens problem, then I think the only difference is the size of
the lens. The problem is I don't know for sure which one is the cause.
>From what you saying, it seems that it is possible that the 50-200 can
cause more flash firing than 18-55 does, right?

Regards,
John

<> wrote:

> Paul Mitchum wrote:
> > <> wrote:
> >
> > > Hi everyone,
> > >
> > > I recently bought ist dl with 18-55mm lens for my vacation and I loved
> > > it. Toady I bought the 50-200mm lens. I did some tests and have some
> > > questions here hope someone can help me out. Thanks in advance.
> > >
> > > When I set camera to AF with auto flash and try to focus on a dark
> > > point with pressing the shutter halfway, the flash just keeps flashing
> > > with a noise 'ZZZ...' until I release the shutter. It happened to the
> > > 18-55mm lens once in a really dark place. But with 50-200mm lens that I
> > > just bought, it happened more, in some places it was ok with the
> > > 18-55mm lens.
> > >
> > > Does the 50-200mm lens have any problem that causes it happened more,
> > > or it's just normal because it's a big lens?
> >
> > You should try both lenses on the same subject matter in a darkened room
> > for comparison.
> >
> > The flash comes on to help the camera autofocus by providing more light.
> >
> > The 18-55 is f/3.5, and the 50-200 is f/4. So all other things being
> > equal, the 50-200 won't let as much light in. Thus, a longer hunting
> > time for the autofocus, and more need for the focus-assist flash firing.
>
> Thanks, Paul,
>
> I did the tests on the exact same subjects with same condition. If it's
> not the lens problem, then I think the only difference is the size of
> the lens. The problem is I don't know for sure which one is the cause.
> From what you saying, it seems that it is possible that the 50-200 can
> cause more flash firing than 18-55 does, right?

I'm saying that an f/4 lens won't let in as much light as an f/3.5 lens,
making it more difficult for the autofocus system to work.

In article <1hlidac.x0zhlj1i7c5y9N%0m>, 0m
(Paul Mitchum) wrote:

> I'm saying that an f/4 lens won't let in as much light as an f/3.5 lens,
> making it more difficult for the autofocus system to work.

Paul-

The kit lens that came with my *ist DS, has an f/3.5-f/5.6 aperture. In
other words, it is f/5.6 at the telephoto end.

I suspect Roy may have hit the nail on the head by suggesting the large
50-200mm lens was physically blocking the flash beam. Even with the kit
lens, the DS instruction manual (page 49) says to remove the lens hood.
It also has a table of lens-flash compatibility (page 151) but the
50-200mm lens is not listed.

That table also assumes the lens hood has been removed. It is possible
the 50-200mm lens is too big even without a hood.

Fred