Using extension tubes?

I have never used extension tubes and would appreciate feedback on
some questions I have about it.


1. As I understand it the use of extension tubes is mainly used to
convert normal and telephoto lenses to macro lenses -- is that
correct?


2. If I were to add a 25mm tube (Canon EF 25 II) between my camera
(Canon 1Dm2) and a 300mm lens (Canon EF 300mm /4.0) what would the
effect be on: minimum focus distance, image size, image brightness
(EV), camera function (AE/AF)?


3. What effect does using different tube lengths have?


Thanks,

Brian

1. Absolutely correct.
2. With the EF300/4, your magnification will be between 0.24 (close focus)
and 0.09 (infinity focus*), with focus distances of between 1661 and 3925.
(Information sourced from
http://www.bobatkins.com/photography/eosfaq/closeup.htm)

Now, as you will see from that site, you will get more magnification when
using lower focal length lenses. I have been using the 50/1.8 with the Kenko
tubes (much cheaper than teh Canon jobs, and as there is no glass, they are
the same optical quality - they also feel very secure when holding a
70-200/2.8. However Kenko tubes will not work with EF-S lenses, only the new
Canon mkII extenders do.)

Anyway, here are some samples with tubes:
http://planeguy.mine.nu/pictures/?gallery=6

I also, have more images in my other galleries:
http://planeguy.mine.nu/pictures/

Hope this helps.

Extension tubes do exactly what you do when focusing a lens. They just do
more of it.

This may not be obvious with some modern lenses, but if you look at an older
camera, you'll see that in order to focus closer, the lens moves forward.
Extension tubes allow you to move it even farther forward, thus focusing
even closer.

From: Brian Stirling

I have never used extension tubes and would appreciate feedback on
some questions I have about it.

I recommend the latest John Shaw book on nature photography, which has a
chapter on using extension tubes and close up lenses on longer lenses like you
mention.

1. As I understand it the use of extension tubes is mainly used to
convert normal and telephoto lenses to macro lenses -- is that
correct?

Just lets you focus closer ... you don't actually get to "macro" range with a
long lens without a LOT of extension.

2. If I were to add a 25mm tube (Canon EF 25 II) between my camera
(Canon 1Dm2) and a 300mm lens (Canon EF 300mm /4.0) what would the
effect be on: minimum focus distance, image size

You gain about two feet or so in close focus distance. For a full frame camera
(ie, film or the 1Ds) with the non-IS 300 f/4 L the image size goes from .13x
to .24x where 1x is life-size. I think the IS version has a closer min focus
distance (5 ft instead of 8.2 ft, something like that) so would have a slightly
higher magnification with the IS lens. There's probably an added conversion
factor in there somewhere for the 1.3x "crop factor" of the Mark II ...

image brightness (EV)

You lose a fraction of an f/stop, which the meter will take care of
automatically.

camera function (AE/AF)?

Everything works fine with the Canon gear until the effective aperture is below
f/5.6 with the consumer bodies and f/8 with the Pro bodies like your Mark II.
I think some of the Nikon gear won't AF or do some other things with various
combos of extension tubes but the Canon stuff mates seamlessly.

3. What effect does using different tube lengths have?

The basic idea is to get life-size image magnification you need to add
extension equivalent to the focal length of the lens. So a 300 mm focussed at
infinity would need 300 mm (6 inches) of extension tubes for life-size. As you
turn the helicoid to close-focus the lens you pick up some of this but you'll
still probably need say 275 mm ... so 25 mm isn't buying you much with a lens
this long. We've used as much as 100 mm in extension and it starts to feel
pretty springy and flimsy, especially if the lens and/or body is 3 lbs or so.
With a light lens it's not too bad though.

On the other hand with a 24 mm lens a 25 mm tube gets you beyond 1:1 even at
infinity focus ...

You might also look at the 77 mm 500D close up lens attachment. We have the
300 f/4 and sometimes use either the 500D or various combinations of tubes for
closer focussing but it's easier to work like this with a zoom lens like the
70-200 f/2.8 L, and if you really need macro the 180 L is a great lens, my wife
has one that she uses all the time. Basically we use the extension tubes
mainly on long lenses to gain another 2-3 ft of close focus range, like say
with the 500 f/4 to bring it in to about 12.5 ft instead of 15 ft min for small
birds, or with a 100 mm or 180 mm macro to go beyond 1:1.

Bill

From: Brian Stirling

I have never used extension tubes and would appreciate feedback on
some questions I have about it.

I recommend the latest John Shaw book on nature photography, which has a
chapter on using extension tubes and close up lenses on longer lenses like you
mention.

1. As I understand it the use of extension tubes is mainly used to
convert normal and telephoto lenses to macro lenses -- is that
correct?

Just lets you focus closer ... you don't actually get to "macro" range with a
long lens without a LOT of extension.

2. If I were to add a 25mm tube (Canon EF 25 II) between my camera
(Canon 1Dm2) and a 300mm lens (Canon EF 300mm /4.0) what would the
effect be on: minimum focus distance, image size

You gain about two feet or so in close focus distance. For a full frame camera
(ie, film or the 1Ds) with the non-IS 300 f/4 L the image size goes from .13x
to .24x where 1x is life-size. I think the IS version has a closer min focus
distance (5 ft instead of 8.2 ft, something like that) so would have a slightly
higher magnification with the IS lens. There's probably an added conversion
factor in there somewhere for the 1.3x "crop factor" of the Mark II ...

image brightness (EV)

You lose a fraction of an f/stop, which the meter will take care of
automatically.

camera function (AE/AF)?

Everything works fine with the Canon gear until the effective aperture is below
f/5.6 with the consumer bodies and f/8 with the Pro bodies like your Mark II.
I think some of the Nikon gear won't AF or do some other things with various
combos of extension tubes but the Canon stuff mates seamlessly.

3. What effect does using different tube lengths have?

The basic idea is to get life-size image magnification you need to add
extension equivalent to the focal length of the lens. So a 300 mm focussed at
infinity would need 300 mm (6 inches) of extension tubes for life-size. As you
turn the helicoid to close-focus the lens you pick up some of this but you'll
still probably need say 275 mm ... so 25 mm isn't buying you much with a lens
this long. We've used as much as 100 mm in extension and it starts to feel
pretty springy and flimsy, especially if the lens and/or body is 3 lbs or so.
With a light lens it's not too bad though.

On the other hand with a 24 mm lens a 25 mm tube gets you beyond 1:1 even at
infinity focus ...

You might also look at the 77 mm 500D close up lens attachment. We have the
300 f/4 and sometimes use either the 500D or various combinations of tubes for
closer focussing but it's easier to work like this with a zoom lens like the
70-200 f/2.8 L, and if you really need macro the 180 L is a great lens, my wife
has one that she uses all the time. Basically we use the extension tubes
mainly on long lenses to gain another 2-3 ft of close focus range, like say
with the 500 f/4 to bring it in to about 12.5 ft instead of 15 ft min for small
birds, or with a 100 mm or 180 mm macro to go beyond 1:1.

Bill

In message ,
dy (Bill Hilton) wrote:

You might also look at the 77 mm 500D close up lens attachment. We have the
300 f/4 and sometimes use either the 500D or various combinations of tubes for
closer focussing but it's easier to work like this with a zoom lens like the
70-200 f/2.8 L, and if you really need macro the 180 L is a great lens, my wife
has one that she uses all the time. Basically we use the extension tubes
mainly on long lenses to gain another 2-3 ft of close focus range, like say
with the 500 f/4 to bring it in to about 12.5 ft instead of 15 ft min for small
birds, or with a 100 mm or 180 mm macro to go beyond 1:1.

It's really wild, the way a zoom that has the same minimum focusing
distance over its full range of 5 feet might have a range of 6 inches to
4 feet with extenders in place.
--


John P Sheehy

In message ,
dy (Bill Hilton) wrote:

You might also look at the 77 mm 500D close up lens attachment. We have the
300 f/4 and sometimes use either the 500D or various combinations of tubes for
closer focussing but it's easier to work like this with a zoom lens like the
70-200 f/2.8 L, and if you really need macro the 180 L is a great lens, my wife
has one that she uses all the time. Basically we use the extension tubes
mainly on long lenses to gain another 2-3 ft of close focus range, like say
with the 500 f/4 to bring it in to about 12.5 ft instead of 15 ft min for small
birds, or with a 100 mm or 180 mm macro to go beyond 1:1.

It's really wild, the way a zoom that has the same minimum focusing
distance over its full range of 5 feet might have a range of 6 inches to
4 feet with extenders in place.
--


John P Sheehy

Brian Stirling wrote:

3. What effect does using different tube lengths have?

In "macro mode" it's usually easier to work in terms of magnification
than distance. If your lens has a maximum magnification of Mmax, and
you extend it by 'e', then the maximum extended magnification is
simple: Mmax + e/f, f = focal length.

The EF 300/4 IS is actually rather nice for macro work alone, or in
concert with the 2x teleconverter (manual focus required at f/8 with
gumby bodies like a 10D). It's Mmax is 0.25 (min distance is 1.5m),
or 0.5 with the 2x converter.

Brian Stirling wrote:

3. What effect does using different tube lengths have?

In "macro mode" it's usually easier to work in terms of magnification
than distance. If your lens has a maximum magnification of Mmax, and
you extend it by 'e', then the maximum extended magnification is
simple: Mmax + e/f, f = focal length.

The EF 300/4 IS is actually rather nice for macro work alone, or in
concert with the 2x teleconverter (manual focus required at f/8 with
gumby bodies like a 10D). It's Mmax is 0.25 (min distance is 1.5m),
or 0.5 with the 2x converter.

To focus closer you need to increase the distance from the optical centre of
the lens to the film/ccd.
So adding a tube allows you to focus closer and stops you from focussing to
infinity.

You will see most effect on shorter lenses as the length of the tube is a
higher proportion of the focal length.

For the light dropoff:
'bellows factor' = extension squared divided by focal length squared
(extension = focal length plus tube)

50mm lens with 25mm extension, BF=(75x75)/(50x50)=2.25
(increase exposure by 2.25x or just over 1 stop)

50mm lens with 50mm extension, BF=(100x100)/(50x50)=4
(increase exposure by 4x or 2 stops)

50mm lens with 100mm extension, BF=(150x150)/(50x50)=9
(increase exposure by 9x or just over 3 stops)

Exposure Factor 1x 1.4x 2x 2.8x 4x 5.6x 8x 11x 16x
Loss in Stops 0 0 .5 1 1.5 2 2.5 3 3.5 4
(might have to TAB this yourself)

Another way to look at it:
BF = (Magnification +1) squared. At 1:1 you have (1+1) sq = 4x, 2:1 (2+1)sq
= 9x etc

In camera metering with 'auto' tubes negates you having to calc any of this,
but it's handy to know what the relationship is.
If you're using a hand-held meter, or manual flash, then the formulae become
more useful...

Cheers, Jason (remove ... to reply)
Video & Gaming: http://gadgetaus.com