I'm very close to purchasing a Nikon D40 - my first SLR. My interest
is birds and wildlife so a high zoom is essential.
A long focal length is what you need. "High zoom" might
be that, or might not be.
My questions are:
1. Will a 300mm lens and a 1.7x teleconverter give me 510mm zoom?
Yes. And added to that, the Nikon D40 has a 1.5 crop
factor, so this is equivalent to a 765mm lense on a 35mm
SLR.
There is no such thing as a long enough lense for
birding, but that's certainly a good start.
2. What "optical zoom" number is this equiv. to? (I'm used to a
generous 15x on my Fuji bridge camera)
Wellllll... Usually that means the ratio of the longest
focal length to the shortest focal length, but it also
can mean the focal length compared to a "normal" lense.
"Normal" for a 35mm camera is about 45mm, so perhaps
that is a 17x lense? Or, if "Normal" is considered 50mm
it would be 15x.
3. Will autofocus still work?
Depends on the widest f/stop for your 300mm lense, and
on the loss through the 1.7x telextender. If your 300mm
is an f/2.8, it will likely continue to work fine
(assuming almost a 2 stop loss in the telextender). If
your 300mm is an f/6.3, it probably will have a hard
time with autofocus. (That is much the same as saying
that if your 300mm is expensive it will work, but might
not if you are looking at an economy class model.)
4. Would I be better off getting a super zoom lens in the first place
(though this option looks VERY expensive)?
Of course it would be better. All that money buys
_something_!
Be gentle with me - I'm new to photography.
If you *really* want to get it right, Nikon has the lense
for you: 600mm f/4, with VR, and it only costs $7000.
But it *will* work with a D40.
You might want to reconsider the D40 though, because as
the lowest end of the Nikon DSLR line, it simply doesn't
have some of the features you might need in the future.
And working with manual focus lenses is one of the
missing features.
An option to consider is whether you want to go with a
more expensive camera so that you can use less expensive
lenses, or stick with a less expensive camera that will
only work with the more expensive lenses. For example,
the D200, D2x, D300, D3 models will work with virtually
any 600mm or 800mm lense you can find in a Nikon mount,
including old manual focus models.
It happens that I live in a place famous for birds, but
it is also flat and treeless and a 600mm lense won't get
close enough to many birds here by about half. So I use
a D2x and an old 800mm manual focus lense made by Canon
30 years ago. (With a 1.6x telextender and the 1.5 crop
factor, that amounts to the same as a 1920mm lense on a
35mm camera. It *still* isn't long enough!)
But the penalty in using a MF lense is that I'll
probably _never_ get a good shot of a bird just after
taking to flight. It is just impossible to focus a
monster like that fast enough. To get that, those $7000
Nikon beasts are the only way go...