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So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
Sorry if I get that backwards) which is a fine enough lens, but it
goes from f3.5 -> f6.3. It's not a huge lens by any stretch.

What I am wonder is why such a lens can't be made that is either 2.8
straight through or has an at least lower f-stop throughout (say 2.8
-> 4).

I have the Nikon coffee thermos (i.e. their 70-200/2.8 lens) which in
comparison is huge, so I am assuming that size of the lens is a factor.

My reasoning goes something like the size of the lens is needed for
the f-stop to be so low at higher zoom distance, but the bigger the
lens, the higher the lowest zoom becomes (which is why it's 70-200 and
not 18-200).

Could anyone shed some light on this?

--
Sandman[.net]

In article <>,
Alfred Molon <> wrote:

> In article <mr->, Sandman
> says...
> > So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
> > Sorry if I get that backwards) which is a fine enough lens, but it
> > goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
> >
> > What I am wonder is why such a lens can't be made that is either 2.8
> > straight through or has an at least lower f-stop throughout (say 2.8
> > -> 4).
> >
> > I have the Nikon coffee thermos (i.e. their 70-200/2.8 lens) which in
> > comparison is huge, so I am assuming that size of the lens is a factor.
> >
> > My reasoning goes something like the size of the lens is needed for
> > the f-stop to be so low at higher zoom distance, but the bigger the
> > lens, the higher the lowest zoom becomes (which is why it's 70-200 and
> > not 18-200).
> >
> > Could anyone shed some light on this?
>
> I'm not a lens expert, but obviously an 18-200 lens with such apertures
> would be very big and heavy and probably also quite expensive.

That's what I'm assuming, the question I meant to ask was "why?". I
mean, what is it that makes it big and/or expensive?

> Maybe pros wouldn't buy it because of the not to great optical quality,
> and non-pros would not buy it because of the size, weight and cost.

Sigma has a 200-500/2.8 lens which is *HUGE* and has it's own battery
to power it:

<http://www.digital2u.co.uk/images/200-500.jpg>

I'm assuming that this is for a reason, I was just curious about the
particulars.


--
Sandman[.net]

On Sun, 10 Jul 2011 22:10:20 +0200, Sandman <> wrote:

>In article <>,
> Alfred Molon <> wrote:
>
>> In article <mr->, Sandman
>> says...
>> > So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
>> > Sorry if I get that backwards) which is a fine enough lens, but it
>> > goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
>> >
>> > What I am wonder is why such a lens can't be made that is either 2.8
>> > straight through or has an at least lower f-stop throughout (say 2.8
>> > -> 4).
>> >
>> > I have the Nikon coffee thermos (i.e. their 70-200/2.8 lens) which in
>> > comparison is huge, so I am assuming that size of the lens is a factor.
>> >
>> > My reasoning goes something like the size of the lens is needed for
>> > the f-stop to be so low at higher zoom distance, but the bigger the
>> > lens, the higher the lowest zoom becomes (which is why it's 70-200 and
>> > not 18-200).
>> >
>> > Could anyone shed some light on this?
>>
>> I'm not a lens expert, but obviously an 18-200 lens with such apertures
>> would be very big and heavy and probably also quite expensive.
>
>That's what I'm assuming, the question I meant to ask was "why?". I
>mean, what is it that makes it big and/or expensive?
>
>> Maybe pros wouldn't buy it because of the not to great optical quality,
>> and non-pros would not buy it because of the size, weight and cost.
>
>Sigma has a 200-500/2.8 lens which is *HUGE* and has it's own battery
>to power it:
>
><http://www.digital2u.co.uk/images/200-500.jpg>
>
>I'm assuming that this is for a reason, I was just curious about the
>particulars.


F number is focal length over diameter.

So, for /f 2.0 with 300 mm lens, the diameter would be 150 mm, or
about 6 inches.

Lots of other things to consider, this is just a very simple example.

On 10/07/2011 2:11 PM, Sandman wrote:
>
> So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
> Sorry if I get that backwards) which is a fine enough lens, but it
> goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
>
It would be 28~300mm on the FX body, on a DX (APS-C) it acts like a
42~450mm. They could make it a straight 28~300/2.8 constant. It would
need a 120mm lenscap, and would weigh around 3-4 kg 6-10 lbs.

On 10/07/2011 4:30 PM, charles wrote:
> On Sun, 10 Jul 2011 22:10:20 +0200, Sandman<> wrote:
>
>
> F number is focal length over diameter.
>
> So, for /f 2.0 with 300 mm lens, the diameter would be 150 mm, or
> about 6 inches.
>
That is pure math, a 300mm f:2. Nikon did make a special order 300/2
that used a 160mm filter, so about 6% bigger in diameter than math to
compensate for light loss.

Mike

Sandman <> wrote:
>So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
>Sorry if I get that backwards) which is a fine enough lens, but it
>goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
>
>What I am wonder is why such a lens can't be made that is either 2.8
>straight through or has an at least lower f-stop throughout (say 2.8
>-> 4).
>
>I have the Nikon coffee thermos (i.e. their 70-200/2.8 lens) which in
>comparison is huge, so I am assuming that size of the lens is a factor.
>
>My reasoning goes something like the size of the lens is needed for
>the f-stop to be so low at higher zoom distance, but the bigger the
>lens, the higher the lowest zoom becomes (which is why it's 70-200 and
>not 18-200).
>
>Could anyone shed some light on this?


It simply isn't possible to make a good, wide aperture 11X zoom lens
at an affordable price. You can thank the laws of physics for that.

11X zoom lenses are best avoided. Period.

In article <>, Bruce
<> wrote:

> >So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
> >Sorry if I get that backwards) which is a fine enough lens, but it
> >goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
> >
> >What I am wonder is why such a lens can't be made that is either 2.8
> >straight through or has an at least lower f-stop throughout (say 2.8
> >-> 4).
>
> It simply isn't possible to make a good, wide aperture 11X zoom lens
> at an affordable price. You can thank the laws of physics for that.

that's why they're not wide aperture, but rather f/4-5.6 or so.

> 11X zoom lenses are best avoided. Period.

nonsense.

"nospam" <> wrote in message
news:110720111620492354%...
> In article <>, Bruce
> <> wrote:
>
>> >So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
>> >Sorry if I get that backwards) which is a fine enough lens, but it
>> >goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
>> >
>> >What I am wonder is why such a lens can't be made that is either 2.8
>> >straight through or has an at least lower f-stop throughout (say 2.8
>> >-> 4).
>>
>> It simply isn't possible to make a good, wide aperture 11X zoom lens
>> at an affordable price. You can thank the laws of physics for that.
>
> that's why they're not wide aperture, but rather f/4-5.6 or so.
>
>> 11X zoom lenses are best avoided. Period.
>
> nonsense.

For some it may be true. The rest of us will make our choices according
to our own needs. There are plenty of times when the 11X zoom is the best
tool for the job, as you imply.

Cheers,
David

"David J Taylor" <david-> wrote:
>"nospam" <> wrote in message
>news:110720111620492354%.. .
>> In article <>, Bruce
>> <> wrote:
>>
>>> >So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
>>> >Sorry if I get that backwards) which is a fine enough lens, but it
>>> >goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
>>> >
>>> >What I am wonder is why such a lens can't be made that is either 2.8
>>> >straight through or has an at least lower f-stop throughout (say 2.8
>>> >-> 4).
>>>
>>> It simply isn't possible to make a good, wide aperture 11X zoom lens
>>> at an affordable price. You can thank the laws of physics for that.
>>
>> that's why they're not wide aperture, but rather f/4-5.6 or so.
>>
>>> 11X zoom lenses are best avoided. Period.
>>
>> nonsense.
>
>For some it may be true. The rest of us will make our choices according
>to our own needs. There are plenty of times when the 11X zoom is the best
>tool for the job, as you imply.


Self-justifying nonsense. No-one "needs" an 11X junk zoom.

There is never any situation when an 11X zoom can be "the best tool
for the job". It is always the worst tool for any job.

An 11X zoom is a choice only for undiscerning camera owners who don't
care about image quality - people who bought interchangeable-lens
cameras (why?) but are just too darn lazy to change lenses.

"Bruce" <> wrote in message
news:...
> "David J Taylor" <david-> wrote:
>>"nospam" <> wrote in message
>>news:110720111620492354%. ..
>>> In article <>, Bruce
>>> <> wrote:
>>>
>>>> >So I have this Tamron 28-300 (which is 18-200 on a FX body, right?
>>>> >Sorry if I get that backwards) which is a fine enough lens, but it
>>>> >goes from f3.5 -> f6.3. It's not a huge lens by any stretch.
>>>> >
>>>> >What I am wonder is why such a lens can't be made that is either 2.8
>>>> >straight through or has an at least lower f-stop throughout (say 2.8
>>>> >-> 4).
>>>>
>>>> It simply isn't possible to make a good, wide aperture 11X zoom lens
>>>> at an affordable price. You can thank the laws of physics for that.
>>>
>>> that's why they're not wide aperture, but rather f/4-5.6 or so.
>>>
>>>> 11X zoom lenses are best avoided. Period.
>>>
>>> nonsense.
>>
>>For some it may be true. The rest of us will make our choices according
>>to our own needs. There are plenty of times when the 11X zoom is the best
>>tool for the job, as you imply.
>
>
> Self-justifying nonsense. No-one "needs" an 11X junk zoom.
>
> There is never any situation when an 11X zoom can be "the best tool
> for the job". It is always the worst tool for any job.
>
> An 11X zoom is a choice only for undiscerning camera owners who don't
> care about image quality - people who bought interchangeable-lens
> cameras (why?) but are just too darn lazy to change lenses.

Still nonsense.