New 20D needs lenses

Excellent explanation. However, under limited lighting, the wide angle
should be able to use a smaller aperture (higher f-stop) and get better
DOF.

Why? If the lighting is the same, the exposure will be the same regardless
of whether the lens is wide angle.

Without a tripod, you can get sharper shots under the same lighting
conditions with wider lenses. To consider an extereme example, at
f/30, a 300mm lens will give you nothing but blur hand-held, while a
35mm lens will give most people a crystal clear shot.

-Joel

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Excellent explanation. However, under limited lighting, the wide angle
should be able to use a smaller aperture (higher f-stop) and get better
DOF.

Why? If the lighting is the same, the exposure will be the same regardless
of whether the lens is wide angle.

OK so maybe I'm not understanding. I'm just thinking that wide angle has
a larger piece of glass so it lets in more light but I don't know.

This is also generally true, but the consequences of this optical fact
are that telephotos lenses tend to be slower, while wide-angle lenses
tend to be faster. An f/3.5 300mm lens is expensive, while an f/3.5
28mm lens is cheap.

As for idential f-stops at different focal lengths, see my last post.

-Joel

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In message ,
(Dr. Joel M. Hoffman) wrote:

Has anyone really looked at the quality of the digital sensor on the
dSLR's to determine at what point buying better glass doesn't make any
difference? The 28-135 IS is a great lens for what it does.

Better glass is always better, unless your camera is lacking an
anti-aliasing filter, like the Sigmas SDs and the Kodak 14MP cameras.

Even if the camera's pixel spacing and AA filter play an important role
in limiting resolution, a better lens will give better pixel-to-pixel
contrast as well as truer overall contrast.
--


John P Sheehy

In message ,
(Dr. Joel M. Hoffman) wrote:

Others here have shown that 1600 (and 3200) are digital manipulations
of 800,

Not exactly. I said that the Canon 10D, 300D, and 20D, when set to
"1600", are actually internally amplifying for 800, and doubling the RAW
values upon output.

"3200" on the 10D and 20D is digitally manipulated 1600-level
amplification. So what you get is this:

ISO GAIN MULTIPLIER

100 1x 1x
200 2x 1x
400 4x 1x
800 8x 1x
1600 8x 2x
3200 16x 2x

so if you shoot raw, there's no point in setting the ISO
higher than 800. (Still, 800 is pretty high, especially when you
consider how grainy most 800 ISO film is.)

If you shoot 1600, you might as well shoot at 800 with -1 exposure
compensation, because you get an extra stop of headroom (of course,
flash compensation needs to be equally offset, if flash is used). On
the 10D (and possibly, the 300D as well, but I haven't really tested any
300D files), an additional benefit is that you avoid the ridiculous
stripes of even numbers that have been offset by 1 to give some odd
numbers in the data; perhaps to fool histograms. I have blurred dark
frames at ISOs 1600 and 3200 from the 10D, and they show distinct zones
of darker and lighter areas due to this striping when
histogram-equalized. The 20D gives even RAW numbers throughout the
image at ISOs 1600 and 3200.

The amount of gain available at "ISO 3200" on these cameras can not be
accomplished with the camera set to ISO 800, so "3200" is not as
redundant and useless as "1600". In my experience, images shot at
"3200" are cleaner looking than ISO 800 images under-exposed by 2 stops.

IMO, Canon went too digital-minded in trying to create a smooth
transition in image quality from one ISO to the next.

Had they used pure amplifaction all the way through the range, image
quality would have deteriorated very rapidly as you went to 1600 and
3200, so they limit the deterioration by using some math, but they could
have done 11x amplification for ISO 1600, with 1.45x scaling
instructions in the RAW data for the converters, and we would probably
have an ISO 1600 worth using. Or, they could do that for the casual
user, and have a custom function to turn on literal amplification for
more technical users who see through the numbers.
--


John P Sheehy

In message ,
(Dr. Joel M. Hoffman) wrote:

This is also generally true, but the consequences of this optical fact
are that telephotos lenses tend to be slower, while wide-angle lenses
tend to be faster. An f/3.5 300mm lens is expensive, while an f/3.5
28mm lens is cheap.

That's only moderately wide, though. When you start going wider than
that, the lenses start getting slower again, at a given price point.
Most of the affordable fast lenses you see are in the 50 to 100 mm
range.
--


John P Sheehy

On Mon, 17 Jan 2005 17:14:16 GMT, (Dr. Joel M. Hoffman) wrote:

Excellent explanation. However, under limited lighting, the wide angle
should be able to use a smaller aperture (higher f-stop) and get better
DOF.

Why? If the lighting is the same, the exposure will be the same regardless
of whether the lens is wide angle.

OK so maybe I'm not understanding. I'm just thinking that wide angle has
a larger piece of glass so it lets in more light but I don't know.

This is also generally true, but the consequences of this optical fact
are that telephotos lenses tend to be slower, while wide-angle lenses
tend to be faster. An f/3.5 300mm lens is expensive, while an f/3.5
28mm lens is cheap.

Is this a roughly-right way of looking at it:

The aperture of a 28mm f/1.0 lens will be 28mm.

The aperture of a 300mm f/10 lens will be 30mm.

Therefore, in some crude way, the amount of glass (and therefore, roughly,
the cost) will be comparable.

The aperture of a 300mm f/2.8 lens will be about 100mm and will therefore
need pieces of glass at least three times the diameter of the two examples
above. This would be _at least_ 9x the cost (the area is squared),
probably more because the lens elements will be thicker, and probably need
better machining.

Regards,
Graham Holden (g-holden AT dircon DOT co DOT uk)
--
There are 10 types of people in the world;
those that understand binary and those that don't.

Graham Holden wrote:


Is this a roughly-right way of looking at it:

The aperture of a 28mm f/1.0 lens will be 28mm.

The aperture of a 300mm f/10 lens will be 30mm.

Therefore, in some crude way, the amount of glass (and therefore, roughly,
the cost) will be comparable.

The aperture of a 300mm f/2.8 lens will be about 100mm and will therefore
need pieces of glass at least three times the diameter of the two examples
above. This would be _at least_ 9x the cost (the area is squared),
probably more because the lens elements will be thicker, and probably need
better machining.

I won't research prices to see the correlation, but that is roughly right.
Further, of course, is the volume effect. As the prices of these longer/faster
lenses go up, there is less market, less volume so the price is pushed up even
further. A Canon 1200mm f/5.6 is over $118,000. I believe you can negotiate a
price break if you order 3 or more.



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