Close-up Phtography with Extension Tubes.

Hello.

Could someone explain the principle behind using

--
Manoj Kummini
Graduate Student, Dept. of Mathematics, The Univ. of Kansas,
Lawrence KS 66045 USA. 38 deg 55 min N, 95 deg 14 min W.
http://www.math.ukans.edu/~kummini/index.html

Manoj Kummini wrote:

Could someone explain the principle behind using

Sorry to have posted the message before completing it.

Could someone explain the principle behind using an extension tube? I would
best like an explanation of the optics, or reference to a URL that contains
it.

Which of the following is preferable for close-up photography?
1. 50mm prime + close-up lenses + extension tube
2. 100mm prime + close-up lenses.

I am uncertain whether the question makes sense.

With regards,
Manoj.

--
Manoj Kummini
Graduate Student, Dept. of Mathematics, The Univ. of Kansas,
Lawrence KS 66045 USA. 38 deg 55 min N, 95 deg 14 min W.
http://www.math.ukans.edu/~kummini/index.html

The focus of a lens is shifted towards the lens away from infinity by
moving elements away from the film plane. Given that a lens has a finite
amount of travel designed into it for close focusing, then at some near
focus you reach a limit. An extension tube moves the overall lens further
out than its internal design had provided. So, you can focus closer.

Some prefer the longer focal length lens since it get an image without being
so close to the subject. The lens does not shield theobject from the
illuminating light as much and also gives a more pleasing perspective. When
photographing fauna, it stays further away and does not disturb the animal
as much. I use 105mm rather than 50mm; it is also a better protrait lens to
boot.

PSsquare


"Manoj Kummini" wrote in message
...
Hello.

Could someone explain the principle behind using

--
Manoj Kummini
Graduate Student, Dept. of Mathematics, The Univ. of Kansas,
Lawrence KS 66045 USA. 38 deg 55 min N, 95 deg 14 min W.
http://www.math.ukans.edu/~kummini/index.html

in article , PSsquare at
wrote on 13/11/03 3:25 pm:

Some prefer the longer focal length lens since it get an image without being
so close to the subject. The lens does not shield theobject from the
illuminating light as much and also gives a more pleasing perspective. When
photographing fauna, it stays further away and does not disturb the animal
as much. I use 105mm rather than 50mm; it is also a better protrait lens to
boot.

However, the effect of lens extension on magnification is less on a longer
lens. Moving a 50mm lens (focussed at infinity) out from the body with a
50mm extension tube will provide a 1:1 subject size to image size (on the
film) ratio. Moving a 100mm lens out by 50mm will give much less
magnification, but more working distance at a given magnification. With a
std. 50mm lens and an extension tube set (normally three different lengths),
you can do good quality images of subjects if you use a tripod (the image
circle is getting bigger as you focus closer- you lose about 2 stops at 1:1
I think, so you need longer shutter speeds at a set aperture on the lens)-
but will require static subjects. Flash becomes harder to use because the
subject is nearer the lens, so you have to have off-camera flash (else you
get the shadow of the lens over the subject), and TTL flash becomes quite
important, as it is very hard to calculate the amount of light getting
through (especially if there is a combination of close-up equipment used)

The lens will lose the ability to focus at infinity when you use extension
tubes. Close-up lenses (filter thread type) will do this too. If used with a
zoom, extension tubes require the lens to be refocused with each movement of
the zoom, which is very annoying in practice. Close-up lenses will not cause
this effect.

Filter-thread based solutions only work on lenses of the same filter thread
(or less- with a step-up ring). Extension tubes can be used on all lenses
with the same mount.

An alternative (can also be used in addition to the others) is to use a
teleconverter, which adds an enlargement factor (1.4x, 1.6x, 2x, 3x) to the
image. The image is darker (less light transmission, but infinity focus and
close focus distance are the same as without (so a f2 50mm that can give a
4.5:1 close-up ration can become a 2.25:1 100mm f4 lens with a 2x
teleconverter). There are some macro-focussing tleconverters which combine a
teleconverter and a focussing helicoid (in effect a variable extension
tube).

If you need more magnification than extension tubes can give, you can use a
bellows unit, which will be able to move the lens quite a distance from the
body.

Another way of increasing magnification is to reverse the lens, using a
special adapter ring. You can combine this with extension tubes. A 20mm
lens, reversed, on a bellows unit can give you (typically) 8x life size
magnification on film.

A negative for the filters and teleconverters are that they put more bits of
glass in the optical path, adding to image degradation. Teleconverters
magnify any lens defects, and sometimes stopping down to f16 or so is
required to get edge sharpness (or corner illumination in some cases) back
up to a similar levels to without it.

Hope that helps,

Ben

Kevin Backs wrote:
[..]
Extension tubes actually have no glass in them. The work by physically
moving the lens further from the focal plane.

Closeup lenses add more glass and therefore more flare, more
distortion, more surfaces, etc., all of which will act to reduce the
quality of the image being captured on film or sensor.

Is is *not* true that close up lenses do nessesaryly reduce the
image quality by a greater amount than extension tubes do.

Entension tubes don't add distortion,

That's not true because most of the lenses are not designed
for close up photography and because of that their performance
with extension tubes can be poor.

For example you will get a huge amount of image curvature and
astigmatism using the Canon EF 1,8/85 USM with extensions
tubes longer as 25 mm, but it does work fine with a Canon 500D
close up lens.

In other words: the decision to use close up lenses or extension
tubes depends on the lens.

but they do reduce the amount of
light that hits the film or sensor as the move the lens further from
the focal plane. (yada yada, inverse square law, blah, blah ...).

And if you are using close up lenses you will not lose light.


--
Helmut Faugel

As someone who has recently moved up from the Nikon Coolpix 4500 (which
takes wonderful macro shots), I am still low on the learning curve about
macro lenses for my Canon 10D. I have purchased two lenses thus far -- the
100-400 L and the 28-135 USM. The latter says "macro 0.5m" on the side of
the lens. I assume this means that the closest focus is 0.5 meters. Can I
use extension tubes with this lens or should I save up for a prime macro
lens and if so, which one? I have been spoiled by the close focus of the
Coolpix and would wish to get similar magnification.

Thanks.

Arlene
http://nestbox.com

I use a set of Kenko extension tubes with my Canon 28-135 USM IS
occasionally with reasonably good results, about the same quality you get
with that lens without the extension tubes. It is feasible to do macro work
with that combination. The reason I don't use it very often is that I get
better results with my Sigma 105 EX macro lens.

What you need depends on how much macro work you do and how critical you are
of your work. If you are critical enough to use a tripod, cable release and
mirror lock-up, you will see an improvement in your work by getting a
dedicated macro lens. Canon 100 USM, Sigma 105 EX and Tamron 90 SP are all
extremely sharp lenses. The Canon 100 USM is somewhat more expensive, but
you can get an accessory tripod mount that allows you to turn the camera
into portrait orientation easily while mounted on a tripod.

If I was buying again I would look at the Canon because of that feature.
(The older non-USM version that was available when I bought the Sigma did
not have a tripod mount and had no better optical quality than the cheaper
Sigma and Tamron models.)

Scott Elliot
http://www3.telus.net/selliot/

"Cate" wrote in message
k.net...
As someone who has recently moved up from the Nikon Coolpix 4500 (which
takes wonderful macro shots), I am still low on the learning curve about
macro lenses for my Canon 10D. I have purchased two lenses thus far -- the
100-400 L and the 28-135 USM. The latter says "macro 0.5m" on the side of
the lens. I assume this means that the closest focus is 0.5 meters. Can I
use extension tubes with this lens or should I save up for a prime macro
lens and if so, which one? I have been spoiled by the close focus of the
Coolpix and would wish to get similar magnification.

Thanks.

Arlene
http://nestbox.com

Helmut Faugel wrote:

For example you will get a huge amount of image curvature and
astigmatism using the Canon EF 1,8/85 USM with extensions
tubes longer as 25 mm, but it does work fine with a Canon 500D
close up lens.

In other words: the decision to use close up lenses or extension
tubes depends on the lens.

I read in a few articles on the WWW that a combination of extension tubes,
teleconverters and close-up filters can be used to achieve magnification.
Has someone used teleconverters and close-up filters together? Is there a
book / WWW article that describes the optics behind using these together?

Manoj.

--
Manoj Kummini
Graduate Student, Dept. of Mathematics, The Univ. of Kansas,
Lawrence KS 66045 USA. 38 deg 55 min N, 95 deg 14 min W.
http://www.math.ukans.edu/~kummini/index.html

"...
Is there a
book / WWW article that describes the optics behind using these together?
...."

For starters ... try John Shaw's Closeups in Nature

Paperback: 144 pages ; Dimensions (in inches): 0.38 x 11.03 x 8.29
Publisher: Amphoto; (October 1987)
ISBN: 0817440526






"Manoj Kummini" wrote in message
...
Helmut Faugel wrote:

For example you will get a huge amount of image curvature and
astigmatism using the Canon EF 1,8/85 USM with extensions
tubes longer as 25 mm, but it does work fine with a Canon 500D
close up lens.

In other words: the decision to use close up lenses or extension
tubes depends on the lens.

I read in a few articles on the WWW that a combination of extension tubes,
teleconverters and close-up filters can be used to achieve magnification.
Has someone used teleconverters and close-up filters together? Is there a
book / WWW article that describes the optics behind using these together?

Manoj.

--
Manoj Kummini
Graduate Student, Dept. of Mathematics, The Univ. of Kansas,
Lawrence KS 66045 USA. 38 deg 55 min N, 95 deg 14 min W.
http://www.math.ukans.edu/~kummini/index.html

Cate wrote

As someone who has recently moved up from the Nikon Coolpix 4500 (which
takes wonderful macro shots), I am still low on the learning curve about
macro lenses for my Canon 10D. I have purchased two lenses thus far -- the
100-400 L and the 28-135 USM. The latter says "macro 0.5m" on the side of
the lens. I assume this means that the closest focus is 0.5 meters. Can I
use extension tubes with this lens or should I save up for a prime macro
lens and if so, which one? I have been spoiled by the close focus of the
Coolpix and would wish to get similar magnification.


I've used extension rings on the 100-400 for shooting insects and
butterflies with good results. It's very convenient to be able to shoot from
a long enough distance so that the subject does not get disturbed. With the
full three ring Kenko set, at 400 mm the subject can be more than two feet
away from the front lens, and a two inch wide subject still fills the whole
screen. It is however a quite heavy piece of equipment. But when shooting
insects handheld I'm usually close to the ground anyway, so there is often
some rock or similar that can be used to steady the camera.