New 20D needs lenses

[nick c]

Musty wrote:

> "nick c" <n-chen@comcast.net> wrote in message
> news:ppYBd.319660$HA.316505@attbi_s01...
>

>>Musty wrote:
>>

>>>"Chuck" <nospammm@no_spam.com> wrote in message
>>>news:3385vsF3rlj6cU1@individual.net...
>>>
>>>
>>>>>Have you considered the EF-S IS 17-85mm f/4-5.6 ?
>>>>
>>>>anothier piece of crap... avoid that lens at all cost !
>>>>
>>>>Get the 17-40 L or the 24-70 L instead of the toy above
>>>>
>>>>
>>>
>>>
>>>What an insightful analysis "piece of crap". Have you used the 17-85?
>>>
>>>There are quite a few users that have both the 17-40 L and the 17-85 and

>
> can
>

>>>attest that the 17-85 takes same quality as the L. Keep in mind that the
>>>17-40L is an "affordable L" being in the $650 range. The EF-S being

>
> about
>

>>>$100 cheaper. What you get with the EF-S ofcourse is the much larger

>
> range
>

>>>and the IS - not to mention the size and weight, making it possibly the
>>>best walk-around lens for the 20D.
>>>
>>>Do you have any images to back up your claims? Like I said, there have

>
> quite
>

>>>a few posts on r.p.d from users who own both lenses and "piece of crap"

>
> is
>

>>>not what they are saying. I also own L-glass and can tell you that the
>>>17-85mm is an excellent and versatile performer.
>>>
>>>Just another basher...
>>>
>>>Any posts from owners of the 17-85mm would be appreciated here. Even

>
> more
>

>>>important, any owners of both lenses (17-40 L and 17-85).
>>>
>>>

>>
>>I have both Canon lenses (17-85 and 17-40) in addition to the 28-135 and
>>I'm very pleased with them. AFAIC, these are keeper lenses. The 17-85
>>lens is ideal with my 20D camera. I use the 17-40 and the 28-135 with my
>>1D MkII and I pleased with the results from using those lenses with 1D
>>MkII camera. I intend getting the 24-70 F-28L and either the 70-200 F-4L
>>or 70-200 F2.8L lens. I like the 70-200 F-2.8L lens but I also like the
>>weight of the 70-200 F-4L lens.
>>
>>nick

>
>
> Thankyou for your post. Its good to hear from people that have actually
> experienced these lenses. I am happy with my 17-85, except that it is a
> little on the soft side at 17mm. Do you see the same phenomenon? How does
> you 17-40 f/4L compare at the wide end? Do you feel that the L is sharper?

Musty, don't be too concerned about the 17-85 lens seemingly being a
little on the soft side at 17mm. The lens is a very good lens. I do my
own computer processing and I have yet to find a problem with the use of
this lens.

I had the 17-40MM F4L lens before I bought the 17-85 lens IS lens and
yet I still bought the 17-85mm lens and I'm quite happy having both lenses.

>
> Regarding the 70-200 f/4L it is a very practical lens due to its weight.
> Also I have yet to read a negative or "average" review of that lens. I have
> read even some posts of users who sold their IS or f/2.8 versions and bough
> the f/4L instead just because of the weight and the images were just as good
> (obviously IS would help a lot, but price is quite high).

When I bought my 1D MkII, I used both the 16-35 F2.8L and the 17-40 F4L
lenses and I found the 17-40 F4L lens to be better than the 16-35 F2.8L
lens. I did not like the noticeable distortion of the 16-35mm F2.8L lens
at 16mm. I had reservations about not getting a fast lens because I have
always bought fast lenses but the 17-40mm F4L is a super lens and I no
longer have any reservations about the lens not being a fast lens.

nick

>
> Musty.
>
>

[paul]

Musty wrote:

> "leo" <someone@somewhere.net> wrote in message
>
> Ofcourse f/2.8 will also give very shallow
> DOP for portraits and other isolation shots.

Pardon my butting in with ignorant comments but I just realized that a
fast lense (or ability to simulate with high ISO) gives both the ability
to get narrow or deep DOF. Am I understanding this correctly?

I'm still trying to grasp all the possibilities.

[Musty]

"paul" <paul@not.net> wrote in message
news:iL-dnV_ygNfMSkXcRVn-hQ@speakeasy.net...

> Musty wrote:
>

> > "leo" <someone@somewhere.net> wrote in message
> >
> > Ofcourse f/2.8 will also give very shallow
> > DOP for portraits and other isolation shots.

>
> Pardon my butting in with ignorant comments but I just realized that a
> fast lense (or ability to simulate with high ISO) gives both the ability
> to get narrow or deep DOF. Am I understanding this correctly?
>
> I'm still trying to grasp all the possibilities.

Deep DOF uses small apertures (high f number), so this is correct. A fast
lens has the advantage that it gives you shallower DOF due to larger
apertures. Having a small aperture, is not any issue with most lenses I
imagine (all you need is f/22). So in essence a "fast" lense provides a
wider range of depth of field. Also keep in mind that DOF is a function of
focal length so the smaller the focal length (eg 17mm vs 28mm) will give you
larger DOF.

[paul]

Musty wrote:

> "paul" <paul@not.net> wrote in message
> news:iL-dnV_ygNfMSkXcRVn-hQ@speakeasy.net...
>

>>Musty wrote:
>>
>>

>>>"leo" <someone@somewhere.net> wrote in message
>>>
>>>Ofcourse f/2.8 will also give very shallow
>>>DOP for portraits and other isolation shots.

>>
>>Pardon my butting in with ignorant comments but I just realized that a
>>fast lense (or ability to simulate with high ISO) gives both the ability
>>to get narrow or deep DOF. Am I understanding this correctly?
>>
>>I'm still trying to grasp all the possibilities.

>
>
> Deep DOF uses small apertures (high f number), so this is correct. A fast
> lens has the advantage that it gives you shallower DOF due to larger
> apertures. Having a small aperture, is not any issue with most lenses I
> imagine (all you need is f/22). So in essence a "fast" lense provides a
> wider range of depth of field. Also keep in mind that DOF is a function of
> focal length so the smaller the focal length (eg 17mm vs 28mm) will give you
> larger DOF.

OK so a telephoto lense limits your depth of field. So if I'm shooting
macro, I would want a short lense right? But Telephoto enlarges things
so it counteracts that benefit in terms of DOF. So if I used a wide
angle lense (short?) that would mean I'd have to be be 1/2 inch from my
flower but I could have decent depth of field vesus sitting 2 feet away
with a telephoto lense.

Am I getting the general idea? What goes into an ideal macro lense?

[Musty]

"paul" <paul@not.net> wrote in message
news:146dneY8bbQHQEXcRVn-vw@speakeasy.net...

> Musty wrote:
>

> > "paul" <paul@not.net> wrote in message
> > news:iL-dnV_ygNfMSkXcRVn-hQ@speakeasy.net...
> >

> >>Musty wrote:
> >>
> >>
> >>>"leo" <someone@somewhere.net> wrote in message
> >>>
> >>>Ofcourse f/2.8 will also give very shallow
> >>>DOP for portraits and other isolation shots.
> >>
> >>Pardon my butting in with ignorant comments but I just realized that a
> >>fast lense (or ability to simulate with high ISO) gives both the ability
> >>to get narrow or deep DOF. Am I understanding this correctly?
> >>
> >>I'm still trying to grasp all the possibilities.

> >
> >
> > Deep DOF uses small apertures (high f number), so this is correct. A

fast

> > lens has the advantage that it gives you shallower DOF due to larger
> > apertures. Having a small aperture, is not any issue with most lenses I
> > imagine (all you need is f/22). So in essence a "fast" lense provides a
> > wider range of depth of field. Also keep in mind that DOF is a function

of

> > focal length so the smaller the focal length (eg 17mm vs 28mm) will give

you

> > larger DOF.

>
>
> OK so a telephoto lense limits your depth of field. So if I'm shooting
> macro, I would want a short lense right? But Telephoto enlarges things
> so it counteracts that benefit in terms of DOF. So if I used a wide
> angle lense (short?) that would mean I'd have to be be 1/2 inch from my
> flower but I could have decent depth of field vesus sitting 2 feet away
> with a telephoto lense.
>
> Am I getting the general idea? What goes into an ideal macro lense?

I am not an expert on macro photography, but I dont believe you need a great
DOF for macro shots. For example compare two scenarios:

1) Shooting a landscape where you want to capture maybe several miles of
distance - here you will need massive DOF

2) Shooting a flower macro more where you want to have "acceptable" focus
probably over an inch or two - This is not a large DOF, its a tiny DOF

So generally macro shooting is done not with wide lenses (since you want to
magnify and limit DOF). If you look at Canon EF lenses that are designated
"macro" here are some examples:

EF 180mm F3.5L macro
EF 65mm F3.5L macro
EF 100mm F2.8 macro
EF 50mm f2.5 macro

So you can see that focal length is not wide by any means (50 to 180mm). The
main features of a macro lens would be as follows (I would think):
- Long enough focal length to "magnify" the subject
- Large aperture (small f) to limit DOF (you want to focus that one flower
or insect)
- Small focusing distance (eg the 50mm can focus as close as 23cm) which
would give awesome magnification with 50mm focal length.

Thanks
Musty.

[Ken]

"paul" <paul@not.net> wrote in message news:146dneY8bbQHQEXcRVn-vw@speakeasy.net...

> > Deep DOF uses small apertures (high f number), so this is correct. A fast
> > lens has the advantage that it gives you shallower DOF due to larger
> > apertures. Having a small aperture, is not any issue with most lenses I
> > imagine (all you need is f/22). So in essence a "fast" lense provides a
> > wider range of depth of field. Also keep in mind that DOF is a function of
> > focal length so the smaller the focal length (eg 17mm vs 28mm) will give you
> > larger DOF.

>
>
> OK so a telephoto lense limits your depth of field. So if I'm shooting
> macro, I would want a short lense right? But Telephoto enlarges things
> so it counteracts that benefit in terms of DOF. So if I used a wide
> angle lense (short?) that would mean I'd have to be be 1/2 inch from my
> flower but I could have decent depth of field vesus sitting 2 feet away
> with a telephoto lense.
>
> Am I getting the general idea? What goes into an ideal macro lense?

Don't confuse telephoto/wide angle lenses with DOF characteristics. For a good
explanation see - [url]http://luminous-landscape.com/tutorials/dof2.shtml[/url]

[Frank ess]

Musty wrote:

> "paul" <paul@not.net> wrote in message
> news:146dneY8bbQHQEXcRVn-vw@speakeasy.net...

>> Musty wrote:
>>

>>> "paul" <paul@not.net> wrote in message
>>> news:iL-dnV_ygNfMSkXcRVn-hQ@speakeasy.net...
>>>
>>>> Musty wrote:
>>>>
>>>>
>>>>> "leo" <someone@somewhere.net> wrote in message
>>>>>
>>>>> Ofcourse f/2.8 will also give very shallow
>>>>> DOP for portraits and other isolation shots.
>>>>
>>>> Pardon my butting in with ignorant comments but I just realized
>>>> that a fast lense (or ability to simulate with high ISO) gives
>>>> both the ability to get narrow or deep DOF. Am I understanding
>>>> this correctly?
>>>>
>>>> I'm still trying to grasp all the possibilities.
>>>
>>>
>>> Deep DOF uses small apertures (high f number), so this is correct.
>>> A fast lens has the advantage that it gives you shallower DOF due
>>> to larger apertures. Having a small aperture, is not any issue with
>>> most lenses I imagine (all you need is f/22). So in essence a
>>> "fast" lense provides a wider range of depth of field. Also keep in
>>> mind that DOF is a function of focal length so the smaller the
>>> focal length (eg 17mm vs 28mm) will give you larger DOF.

>>
>>
>> OK so a telephoto lense limits your depth of field. So if I'm
>> shooting macro, I would want a short lense right? But Telephoto
>> enlarges things
>> so it counteracts that benefit in terms of DOF. So if I used a wide
>> angle lense (short?) that would mean I'd have to be be 1/2 inch from
>> my flower but I could have decent depth of field vesus sitting 2
>> feet away with a telephoto lense.
>>
>> Am I getting the general idea? What goes into an ideal macro lense?

>
> I am not an expert on macro photography, but I dont believe you need
> a great DOF for macro shots. For example compare two scenarios:
>
> 1) Shooting a landscape where you want to capture maybe several miles
> of distance - here you will need massive DOF
>
> 2) Shooting a flower macro more where you want to have "acceptable"
> focus probably over an inch or two - This is not a large DOF, its a
> tiny DOF
>
> So generally macro shooting is done not with wide lenses (since you
> want to magnify and limit DOF). If you look at Canon EF lenses that
> are designated "macro" here are some examples:
>
> EF 180mm F3.5L macro
> EF 65mm F3.5L macro
> EF 100mm F2.8 macro
> EF 50mm f2.5 macro
>
> So you can see that focal length is not wide by any means (50 to
> 180mm). The main features of a macro lens would be as follows (I
> would think):
> - Long enough focal length to "magnify" the subject
> - Large aperture (small f) to limit DOF (you want to focus that one
> flower or insect)
> - Small focusing distance (eg the 50mm can focus as close as 23cm)
> which would give awesome magnification with 50mm focal length.
>

At macro scales, lighting can be a major consideration: unless you are
otherwise equipped, common solutions are more easily applied with larger
lens-to-subject distances.


--
Frank ess

[paul]

Ken wrote:

>>
>>OK so a telephoto lense limits your depth of field. So if I'm shooting
>>macro, I would want a short lense right? But Telephoto enlarges things
>>so it counteracts that benefit in terms of DOF. So if I used a wide
>>angle lense (short?) that would mean I'd have to be be 1/2 inch from my
>>flower but I could have decent depth of field vesus sitting 2 feet away
>>with a telephoto lense.
>>
>>Am I getting the general idea? What goes into an ideal macro lense?

>
>
> Don't confuse telephoto/wide angle lenses with DOF characteristics. For a good
> explanation see - [url]http://luminous-landscape.com/tutorials/dof2.shtml[/url]

Excellent explanation. However, under limited lighting, the wide angle
should be able to use a smaller aperture (higher f-stop) and get better
DOF. Or 'apparent DOF' I'm not sure because the distances &
magnification are different.

[paul]

Musty wrote:

> "paul" <paul@not.net> wrote in message
> news:146dneY8bbQHQEXcRVn-vw@speakeasy.net...

>>
>>OK so a telephoto lense limits your depth of field. So if I'm shooting
>>macro, I would want a short lense right? But Telephoto enlarges things
>>so it counteracts that benefit in terms of DOF. So if I used a wide
>>angle lense (short?) that would mean I'd have to be be 1/2 inch from my
>>flower but I could have decent depth of field vesus sitting 2 feet away
>>with a telephoto lense.
>>
>>Am I getting the general idea? What goes into an ideal macro lense?

>
>
> I am not an expert on macro photography, but I dont believe you need a great
> DOF for macro shots. For example compare two scenarios:
>
> 1) Shooting a landscape where you want to capture maybe several miles of
> distance - here you will need massive DOF
>
> 2) Shooting a flower macro more where you want to have "acceptable" focus
> probably over an inch or two - This is not a large DOF, its a tiny DOF

I'm not sure but the relative DOF issues are a problem with macro.
Usually you end up only getting a 1/2-inch slice of focused flower in
the middle.

>
> So generally macro shooting is done not with wide lenses (since you want to
> magnify and limit DOF). If you look at Canon EF lenses that are designated
> "macro" here are some examples:
>
> EF 180mm F3.5L macro
> EF 65mm F3.5L macro
> EF 100mm F2.8 macro
> EF 50mm f2.5 macro
>
> So you can see that focal length is not wide by any means (50 to 180mm). The
> main features of a macro lens would be as follows (I would think):
> - Long enough focal length to "magnify" the subject
> - Large aperture (small f) to limit DOF (you want to focus that one flower
> or insect)
> - Small focusing distance (eg the 50mm can focus as close as 23cm) which
> would give awesome magnification with 50mm focal length.

I don't understand what allows you to get close.

[Jeremy Nixon]

paul <paul@not.net> 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.

--
Jeremy | [email]jeremy@exit109.com[/email]

[paul]

Jeremy Nixon wrote:

> paul <paul@not.net> 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.

[Jeremy Nixon]

paul <paul@not.net> wrote:

> 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.

It doesn't make a difference to your exposure settings; if you need a
setting of 1/60 at f/8, you'll need that regardless of focal length.
f/8 is a different size at different focal lengths, freeing you from
needing to worry about adjusting your exposure according to focal
length.

--
Jeremy | [email]jeremy@exit109.com[/email]

[paul]

Jeremy Nixon wrote:

> paul <paul@not.net> wrote:
>
>

>>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.

>
>
> It doesn't make a difference to your exposure settings; if you need a
> setting of 1/60 at f/8, you'll need that regardless of focal length.
> f/8 is a different size at different focal lengths, freeing you from
> needing to worry about adjusting your exposure according to focal
> length.

Maybe we are talking about something different. If I zoom in from 28mm
to 200mm & stand back to get the same frame, I need to lower the f-stop
from 8 to 4.6 at the same speed (minimum to hand-hold), plus now I need
an even faster speed since I've magnified the shake.

Or since I'm talking about framing the same shot maybe it doesn't
matter. I just tested & I think it makes a difference. I get to use a
higher f10 at 28mm & therefore have more depth of field. I think.

So for macros I'd do best with a shorter lense that allows me to get a
few inches away from the subject than a telephoto lense a foot & a half
away. Unless there is some other factor or I'm otherwise confused.

[John Francis]

In article <9Z6dnen1N6kkAkTcRVn-vg@speakeasy.net>, paul <paul@not.net> wrote:

>Jeremy Nixon wrote:
>

>> paul <paul@not.net> wrote:
>>
>>

>>>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.

>>
>>
>> It doesn't make a difference to your exposure settings; if you need a
>> setting of 1/60 at f/8, you'll need that regardless of focal length.
>> f/8 is a different size at different focal lengths, freeing you from
>> needing to worry about adjusting your exposure according to focal
>> length.

>
>
>Maybe we are talking about something different. If I zoom in from 28mm
>to 200mm & stand back to get the same frame, I need to lower the f-stop
>from 8 to 4.6 at the same speed . . .

No you don't. If the object you're trying to photograph is correctly
exposed at f/5.6 in the 200mm shot, it will be correctly exposed at f/5.6
in the 28mm shot.

If you're using some form of center-weighted or multi-segment metering,
though, it's quite possible that the extra field of view of the wide
angle lens is getting more sky in the background (even if the foreground
objects are framed correctly), and this can make the camera suggest f/8
for the aperture.

Try using a spot meter (or an incident meter) instead of an averaging meter.

[Jeremy Nixon]

paul <paul@not.net> wrote:

> Maybe we are talking about something different. If I zoom in from 28mm
> to 200mm & stand back to get the same frame, I need to lower the f-stop
> from 8 to 4.6 at the same speed (minimum to hand-hold),

You shouldn't, if it's the same scene, especially with the same framing.
If the background is fooling the light meter in one version vs. the other
(because the wide angle is getting more sky in there, for instance) then
you may actually need to compensate for that.

> Or since I'm talking about framing the same shot maybe it doesn't
> matter. I just tested & I think it makes a difference. I get to use a
> higher f10 at 28mm & therefore have more depth of field. I think.

Don't trust the meter... it lies.

It's probably changing the recommended exposure due to different light
in the background. At wide angle it may be drastically underexposing
the shot due to backlight.

--
Jeremy | [email]jeremy@exit109.com[/email]

[Musty]

"paul" <paul@not.net> wrote in message
news:9Z6dnen1N6kkAkTcRVn-vg@speakeasy.net...

> Jeremy Nixon wrote:
>

> > paul <paul@not.net> wrote:
> >
> >

> >>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.

> >
> >
> > It doesn't make a difference to your exposure settings; if you need a
> > setting of 1/60 at f/8, you'll need that regardless of focal length.
> > f/8 is a different size at different focal lengths, freeing you from
> > needing to worry about adjusting your exposure according to focal
> > length.

>
>
> Maybe we are talking about something different. If I zoom in from 28mm
> to 200mm & stand back to get the same frame, I need to lower the f-stop
> from 8 to 4.6 at the same speed (minimum to hand-hold), plus now I need
> an even faster speed since I've magnified the shake.
>
> Or since I'm talking about framing the same shot maybe it doesn't
> matter. I just tested & I think it makes a difference. I get to use a
> higher f10 at 28mm & therefore have more depth of field. I think.
>
> So for macros I'd do best with a shorter lense that allows me to get a
> few inches away from the subject than a telephoto lense a foot & a half
> away. Unless there is some other factor or I'm otherwise confused.

That is not always practical. For example an insect might get scared and fly
or run off if you are too close, so a more tele-style macro lens is handy
when getting close to the subject may not be possible or practical (eg a
dangerous scorpion). This is why Canon offers both a wider (but not "wide")
and tele macro lenses. Even if you can get REALLY close, nothing beats a bit
of tele to get very detailed close ups. Consider those insect photographs
where they take the shot of just the eye.

[Wolfgang Weisselberg]

John Francis <johnf@panix.com> wrote:

> If the object you're trying to photograph is correctly
> exposed at f/5.6 in the 200mm shot, it will be correctly exposed at f/5.6
> in the 28mm shot.

True.

However, if you use different lens systems, and one of them has
_many_ more lenses than the other one, you may find _slight_
differences in brightness due to lens transmissivity.

Assuming a 20 lens glass, with 0.5% loss at each glass-glass or
glass-air border, you'll have 0.995^40 == 0.818 == 81.8% of the
light left (i.e. about 1/3rd stop less) compared to an ideal lens.

-Wolfgang

[John Francis]

In article <nj8pa2-95n.ln1@ID-52418.user.berlin.de>,
Wolfgang Weisselberg <ozcvgtt02@sneakemail.com> wrote:

>John Francis <johnf@panix.com> wrote:
>

>> If the object you're trying to photograph is correctly
>> exposed at f/5.6 in the 200mm shot, it will be correctly exposed at f/5.6
>> in the 28mm shot.

>
>True.
>
>However, if you use different lens systems, and one of them has
>_many_ more lenses than the other one, you may find _slight_
>differences in brightness due to lens transmissivity.
>
>Assuming a 20 lens glass, with 0.5% loss at each glass-glass or
>glass-air border, you'll have 0.995^40 == 0.818 == 81.8% of the
>light left (i.e. about 1/3rd stop less) compared to an ideal lens.

If you're using lenses with that many elements, you'll probably
have rather less than 0.5% loss at any surface. The most I've
got in my personal selection is 18 elements in 16 groups, for a
total of 34 surfaces. But some of those elements are coated,
and I'd be surprised to find total losses as high as 15%.

On the other end of the scale, I don't have any lenses with less
than seven elements, although there is a lens I'd consider that
only has five elements. So the difference is more likely to be
at most 25 air-glass or glass-glass surfaces. I'd consider it
astonishing if there was as much as one sixth of a stop difference,
which is for all practical purposes almost undetectable.

[Wolfgang Weisselberg]

John Francis <johnf@panix.com> wrote:

> Wolfgang Weisselberg <ozcvgtt02@sneakemail.com> wrote:

>>John Francis <johnf@panix.com> wrote:

>>> If the object you're trying to photograph is correctly
>>> exposed at f/5.6 in the 200mm shot, it will be correctly exposed at f/5.6
>>> in the 28mm shot.

>>Assuming a 20 lens glass, with 0.5% loss at each glass-glass or
>>glass-air border, you'll have 0.995^40 == 0.818 == 81.8% of the
>>light left (i.e. about 1/3rd stop less) compared to an ideal lens.

> If you're using lenses with that many elements, you'll probably
> have rather less than 0.5% loss at any surface.

Hopefully! But you also get loss with each mm of glass that the
light has pass through.

> The most I've
> got in my personal selection is 18 elements in 16 groups, for a
> total of 34 surfaces.

34? I must be dumb today ... I don't get that number.

I counter with a few more elements. Lots of _heavy_ glass.
Don't drop it! :-)

> But some of those elements are coated,
> and I'd be surprised to find total losses as high as 15%.

We are talking about 1/100 loss of light on a lens -- I'd thought
that quite realistic.

> On the other end of the scale, I don't have any lenses with less
> than seven elements, although there is a lens I'd consider that
> only has five elements. So the difference is more likely to be
> at most 25 air-glass or glass-glass surfaces.

Just for kicks:
Canon's EF 35mm f/2 has 5 elements, the EF 70-200 IS L USM has
23. (18 elements == 36 surfaces difference).

If you go overboard, add a 1.4 and 2.0 converter (and better
use a high-end body, if you want any autofocus at f/8), for
5 and 7 additional elements, for a 30 elements (60 surfaces)
worst case difference.

> I'd consider it
> astonishing if there was as much as one sixth of a stop difference,
> which is for all practical purposes almost undetectable.

Canon seems to feel different, at least for TV cameras:
[url]http://www.canon-europe.com/TV-Products/News/CinePrimeReview.asp?ComponentID=34223&SourcePageID =33108[/url]
| F-stop aperture marks are based on a theoretical mathematical
| formula which when transferred to different lenses can
| sometimes be inaccurate up to a full f-stop error.

| This inaccuracy is actually much more likely with zoom
| lenses as they have a more complex series of different glass
| elements that move around inside to give the different focal
| lengths. These glass elements can combine together to decrease
| the actual transmission factor of the light passing through the
| lens quite considerably at different focal lengths.

[url]http://www.medito.com/htdocs/dcforum/DCForumID64/6.html[/url]
says about a lens: "also about 1/3 stop less transmission as is
typical for zooms".

Look at [url]http://medfmt.8k.com/mf/fast.html[/url] (search for
transmission) or [url]http://medfmt.8k.com/third/primes.html[/url]
for some more info.

And here
[url]http://www.rugift.com/photocameras/mto_11_ca_lens_for_canon_eos.htm[/url]
an actual transmission factor is listed as (no worse than) 0.77,
aka loosing no more than 23% of the light (on an 1000mm f/10
*mirror* lens). That would be about 1/2 stop ...

-Wolfgang

[John Francis]

In article <sglra2-4hg.ln1@ID-52418.user.berlin.de>,
Wolfgang Weisselberg <ozcvgtt02@sneakemail.com> wrote:

>John Francis <johnf@panix.com> wrote:
>

>> The most I've
>> got in my personal selection is 18 elements in 16 groups, for a
>> total of 34 surfaces.

>
>34? I must be dumb today ... I don't get that number.

Consider a very simple example; two elements in one group.
That's 3 surfaces; one air/glass, one glass/glass, and one glass/air.

>> I'd consider it
>> astonishing if there was as much as one sixth of a stop difference,
>> which is for all practical purposes almost undetectable.

>
>Canon seems to feel different, at least for TV cameras:
>
>| This inaccuracy is actually much more likely with zoom
>| lenses as they have a more complex series of different glass
>| elements that move around inside to give the different focal
>| lengths. These glass elements can combine together to decrease
>| the actual transmission factor of the light passing through the
>| lens quite considerably at different focal lengths.

Ah, but those Canon TV cameras have an astonishing zoom range;
something around 100:1 It's not exactly surprising that at
some part of that range some of the light doesn't manage to
get through all the elements, but ends up in the sidewalls.
(It's also hard to understand how surface-to-surface losses
could be dependent on just where the element is in the path)

>
>[url]http://www.medito.com/htdocs/dcforum/DCForumID64/6.html[/url]
>says about a lens: "also about 1/3 stop less transmission as is
>typical for zooms".

Again, that's not because of surface losses; it's because even
those constant-aperture zooms sometimes manage to paint the
inner walls of the lens barrel with some of the light that
should really be passed on through the optical chain.

>Look at [url]http://medfmt.8k.com/mf/fast.html[/url] (search for
>transmission) or [url]http://medfmt.8k.com/third/primes.html[/url]
>for some more info.

Again, talking about light falloff in the corners; an artifact
of the way the cross-section of the light beam is restricted
by the geometry of the lens, especially at very wide apertures.

>And here
> [url]http://www.rugift.com/photocameras/mto_11_ca_lens_for_canon_eos.htm[/url]
>an actual transmission factor is listed as (no worse than) 0.77,
>aka loosing no more than 23% of the light (on an 1000mm f/10
>*mirror* lens). That would be about 1/2 stop ...

Hard to tell, but this too could be talking about the same issue.
It's certainly not going to be talking about surface-to-surface
transmission losses; this is, after all, a mirror "lens". My
guess is that what it is talking about is really falloff; with
no aperture control, you're always using the lens at full aperture.