Why are "digital" lenses so "slow"

Another quick question for this great group. I'm looking at the Canon
20D and can't quite understand why most of the lenses in the 28-80
range all seem to have a pretty slow aperature. At least compared to
my old FD lenses. I understand about the lens factor as it relates to
focal length, but does something similar happen for f-stop?

Many thanks

 

<<why most of the lenses in the 28-80
range all seem to have a pretty slow aperature... but does something similar
happen for f-stop?>>

Manufacturers know that most people buying digital cameras are amateurs who
cannot appreciate the photographic value (vs. cost) of lenses with large
maximum f/stop. There are plenty of offerings with f/2.8 though, and at
relatively affordable prices, and that's not exactly slow!

--Wilt

 

It's not a matter of "digital" or not, it's a matter of there being a market
for cheap slow consumer zooms, so the manufacturers produce cheap slow
consumer zooms. This market appeared long before dSLRs.

You should be able to find equivalent lenses for every single one of the FD
lenses in an EF mount. Fast primes are still available. (Actually, the
50/1.0 was discontinued, but my understading is that it was increadibly
expensive and poor optically.)

Design, manufacturing, materials, and coating technologies have improved a
lot since the FD days, and those improvements have largely gone into cheap
slow consumer zooms.

With the success of the Tamron 28-75/2.8 zoom, Sigma has been releasing new
f/2.8 zooms at a phenomenal rate of late, so there are more choices in the
affordable fast zoom range. As of last March, the Tamron 28-75/2.8 zoom was
(by far) the best rated consumer zoom that covers that range, but people are
saying nice things about some of the new Sigmas. (There's a Japanese book
issued every March that reviews every 35mm AF lens in production, although
they dropped the reviews of the primes in 2004, which indicates that the
market is shiftimg away from primes. Heck, I bought 4 lenses this year, and
only one was a prime, whereas I had never purchased a zoom before 2004.)

Nope. Of course, there is the fact that dSLRs do better at ISO 400 and 800
than film does, so slower lenses aren't quite so painful on a dSLR.

David J. Littleboy
Tokyo, Japan

 

They don't have to be. I'm looking at getting a Nikon Digital body
and one of the lenses I'll put on it is the f1.4 50mm Nikkor. It just
depends on your price point.


******************************************************

"The National Rifle Association has been in support of
workable, enforceable gun control legislation since its
very inception in 1871."

NRA Executive Vice President Franklin L. Orth
NRA's American Rifleman Magazine, March 1968, P. 22

 

You must be referring to Canon's midrange zooms.. I actually hadn't
noticed it before, but you are correct, the only 'fast' midrange zoom
is the EF 24-70 f/2.8

I guess 'good', 'fast' and 'zoom' isn't an easy thing to do..
The 24-70 f/2.8 is pretty fast, but It's probably the most expensive
of the lot.

If you want fast, go to a fixed focal length lens.. There you'll find
a decent selection of lenses in the f/1.x range. But of
course, don't forget the prime rule of optics... fast = $$$

 

Can you get grainless ISO 1600 shots with your old FD mount cams ?
You do need DoF .. but not that desperately .. as f/1.4 was only used in
very poor lit condition.
[ tho I dun mind having a 300mm f/1.4 ]
+ there is Photoshop ?

=bob=

 

Unless you need the shallow DOF of an ƒ 1.4 or ƒ2.

 

You mean besides the EF mount 24-70 f2.8?
There weren't many zoom lenses in the f2.8 range back in the FD range days,
either. The FD mount 35-70 was a 2.8-3.5, true, but the 28-50 was a 3.5.
The fastest "new" FD (bayonet mount as opposed to breech lock) was the 25-70
f2.8-3.5, but the 28-85 was an f4. My Kiron 28-80 was a 3.5, as was my
dad's Vivitar Series 1 and my wife's Sigma. The Canon EF mount 28-105 is a
f3.5-4.5, which matches the FD mount 35-105 f3.5-4.5.
If you're talking about third party mfrs, Tamron, Tokina and Sigma all have
current 24/28-70/80 lenses in the f2.8 range, some designed specifically for
digital cameras.
The digital crop doesn't affect aperture in anyway.

 

That's a rather broad statement, with all of the pros going to digital
output. There are no fewer EF mount zoom lenses available at f2.8 than
there were with the FD mount, check:
http://www.canon.com/camera-museum/camera/lens/f_lens.html
In fact, there are more. There were no single aperture f2.8 lenses in that
range, at least listed on the Canon site.

 

<shrug> Then you must use f/1.4 or f/2.

There is no real shortage of lenses in that range, all primes. The Canon 85
f/1.2 is particularly spectacular, for example, though it focuses *really
slow*.

I'm pretty happy with the wide range of f/2.8 zooms, and they are beginning
to become very affordable.

 

Right. Pick any two of the above.

What is most annoying of the mid-zooms is not so much the speed but the
fact that it changes through the zoom, making exposure compensation
neccesary and slowing down your response time.

Yep. Fortunately, both Sigma and Tamron make real alternatives now, staring
in the $350 range.

<snip>

 

Or faster shutter speed to stop subject motion. Even in informal snapshot
portraits, subject motion's a nastier problem than camera shake. (Note that
I didn't really intend to defend the slow cheap consumer zooms: just to
point out that they're not as much of a disaster as one might think.)

But the experience here is that the radically shallow DOF at f/2.0 and wider
is radically overvalued. Sure, the fraction-of-a-mm DOF portrait is a cool
effect, but it gets old after a while. And as long as one picks a not too
busy background, almost any f-stop will provide some amount of blurring as
long as one's subject is less than 25 or so times the (35mm equiv.) focal
length away.

According to

http://www.nikonians.org/html/resources/guides/dof/hyperfocal2.html

(which overestimates the DOF in my experience: the 0.025 mm CoC (0.016 for
dSLRs) is a bit excessive if one is looking at a dSLR image (or 4000 dpi
film scan) at 100% on the screen: a 6MP dSLR has a 0.0075mm pixel pitch,
which is probably smeared to 0.011 mm by the AA filter.)

the DOF of an 85mm portrait lens at 6 feet at f/8 is +/- 0.3 feet. That's
for 35mm, so you'd have to open up to f/5.6 with 1.6x digital at 55mm. But
that's not enough to get a whole head in focus, and that would be assuming
perfect placement of the plane of focus.

At 10 feet, with f/5.6 on a 1.6x dSLR, at f = 75mm (120mm equiv.), DOF is
+/- 0.4 feet. Still barely a head's worth of DOF.

David J. Littleboy
Tokyo, Japan

 

Ever hear of a Canon 24-70 2.8 L?

 

This is not unique to digitals. Look at most of the low to medium
priced film point&shoot cameras- lenses have about same range (in
relative focal lengths) as P&S digitals.

 

One reason that motivates manufacturers to release less-than-top-shelf
lenses is that the digital photographer can often compensate for some lens
deficiencies during post-shoot editing.

The lens is not as critical a component for many digital applications as it
was for film shots.

As Wal-Mart has demonstrated, the lowest-priced items will nearly always be
best-sellers.

 

Already pointed out by others: not true.

Manufacturers have long provided a range of quality and apertures.
Nothing to do with digital.

Not true for many photographers. And, for some, going digital has caused
them to upgrade their lens choices as they can better see the
shortcomings of the lesser quality lenses.

 

Apparent DOF is so easily controlled in a wide varity of image editors
that one can now concentrate on using the sharpest lens openings and
blur background/foreground as required.

Those big f0.95 and f1.0 lenses all date back to the days of kodak
supper X ASA 100, pushed all the way to 250. They were not sharp but
they at least captured something in "black cat in a coal bin"
situations.

Dave
East Engelwood

 

See my other note. But to reiterate, even with a 1.6x camera, the background
is blurred quite nicely by a portrait lens or anything longer at almost any
f stop. DOF goes down with the square of the focal length, so while wide
angle lenses have gobs of DOF, it doesn't take much beyond normal to get
into painfully narrow DOF.

I was knocked out when I tried some shots with the 50/1.4 at f/1.4 at ISO
1600 with the Drebel. Even at handholdable speeds it's amazingly sensitive.
A fast lens leverages the usable high ISOs into something seriously neat.

David J. Littleboy
Tokyo, Japan

 

They are not slow. All reasonable priced good zoom
lenses for SLR cameras are slow. It has nothing to do
with digital cameras.

I say - buy a 50/1.4 for your camera and you have a nice
and fast "portrait" lens for a reasonable amount of money.



/Roland

 

Well to provide perspective, I was hoping to find a fast lens for
indoor ambient light shooting in clubs. I was also thinking that
having IS in a low light environment like this would be helpful. But
it seems the best I'd be able to do is a fast fixed lens with no IS,
or a slower lens with IS.

Anyway, thanks for all the good viewpoints.