light loss with extension tube

I am new to SLR. I want to know if there is any light loss using extension tube. I know teleconverter does.

thanks

nick

"When you double the length the light has to travel you will have a two
stop loss. This means if you add a 50mm extension tube on your 50mm
lens, you would have to open up two stops. Or, your meter reading
should go from 1/60 @ F-8 to 1/60 @ F-4."

now te question is how much light loss by using the ex-25?

nick

--
http://www.australianimage.com.au

what is the distance from the lens mount on the camera to the sensor? Does ex-25 double this distance?

Light loss is generally caused by something interfering with the light, like glass. With a teleconverter, you lose one stop with a 1.4x and two with a 2x.

With an extension tube, there's nothing but a hole; even though the light has to travel a little further to reach the sensor, there's nothing to interfere along the way, so you retain the maximum f stop.

I actually tested this just then with the 50mm, to see if there were any variations. There were none.

Cheers

Ray

--
http://www.australianimage.com.au

when you add the extension tube. you are extending the entrance pupil outward. so the same aperture size but at a longer distance from the sensor, this reduces light. The same principle for the teleconverter. The glass has no effect on the light loss. the transmittance of multi-coated glasses should be higher than 98%. glass just cause degradation to image quality (whatsoever the amount).

nick

OzRay said:

Light loss is generally caused by something interfering with the
light, like glass. With a teleconverter, you lose one stop with a
1.4x and two with a 2x.

With an extension tube, there's nothing but a hole; even though the
light has to travel a little further to reach the sensor, there's
nothing to interfere along the way, so you retain the maximum f
stop.

I actually tested this just then with the 50mm, to see if there
were any variations. There were none.

Cheers

Ray

--
http://www.australianimage.com.au

Click to expand...

digital initiatives said:

when you add the extension tube. you are extending the entrance
pupil outward. so the same aperture size but at a longer distance
from the sensor, this reduces light. The same principle for the
teleconverter. The glass has no effect on the light loss. the
transmittance of multi-coated glasses should be higher than 98%.
glass just cause degradation to image quality (whatsoever the
amount).

Click to expand...

When I put on my telconverter, I lose one stop, when I put on my extension tube I lose nothing. Go figure?

Cheers

Ray

--
http://www.australianimage.com.au

OzRay said:

Light loss is generally caused by something interfering with the
light, like glass. With a teleconverter, you lose one stop with a
1.4x and two with a 2x.

With an extension tube, there's nothing but a hole; even though the
light has to travel a little further to reach the sensor, there's
nothing to interfere along the way, so you retain the maximum f
stop.

Click to expand...

Aren't you forgetting the inverse square law? The aperture at the entrance and exit sides of the extension tubes may be the same, but the longer distance traveled by the light means it spreads out farther, thus effectively reducing its intensity.

--
'And only the stump, or fishy part of him remained'

http://www2.gol.com/users/nhavens
A Contemplative Companion to Fujino Township

1. If what you and digital are saying would be true, it would mean that the light fall-off would be true outside of a lens. In other words, every time you backed up 50 cm from a window the light would fall off 50%.

2. Hold up a light meter to a light source, check the reading. Back up twice the distance measure it again.

3. If what you said was correct, the light would fall of drastically as the lens was extended from near focus to infinity. It doesn't.

4. When someone who has been around as long as Oz tells you something pause before saying he is wrong and check your facts. Especially when he says he checked it with a meter to be sure to be sure. He just might know what he is talking about. (Even if he is an Aussie.)
Richard

Richard Pavek said:

1. If what you and digital are saying would be true, it would mean
that the light fall-off would be true outside of a lens. In other
words, every time you backed up 50 cm from a window the light would
fall off 50%.
2. Hold up a light meter to a light source, check the reading. Back
up twice the distance measure it again.
3. If what you said was correct, the light would fall of
drastically as the lens was extended from near focus to infinity.
It doesn't.

Click to expand...

Yes, but that's because the "aperture" in your example iis equivalent to the entire sky! It remains huge in relation to the insignificant distance you're backing up.
Okay, I may be wildly wrong someplace, but here's my assumption:

The maximum f-stop of a lens is the ratio of the length to the diameter of the aperture. If the aperture remains constant (as it does in extension tubes), while the distance increases (as it does in extension tubes), the effective f-stop changes.

Example: A "50mm f2 lens" means the aperture is effectively 25mm. If I add a 50mm extension tube, the focal length is now 100 mm, which means that the maximum f-stop is now 100/25= f4

I don't have the Oly extension tube in question, so I don't know how long they are, or what their exposure factor is, but there must be some compensation involved, or Oly has found a way to break the laws of physics. ^o^

--
'And only the stump, or fishy part of him remained'

http://www2.gol.com/users/nhavens
A Contemplative Companion to Fujino Township

Sorry, I misread your statement--the example of a window is similar, but not exactly the same as the one I was using. A better example than the window would be using what would happen if you used the light meter through different lengths of pipe. Add more pipe and the light level falls off accordingly. If the window example doesn't work the same, it's because of the presence of ambient light bounced around inside the room and reentering the lens.

As far as extending the barrel when focusing, it may cause some light fall off, but I would assume that has to do with the actual mechanism used for moving the internal elements; again, a better example is the use of an extendable zoom lens, where the elements spread apart when zooming, resulting in the common phenomenon of multiple f-stops over the zooming range.

--
'And only the stump, or fishy part of him remained'

http://www2.gol.com/users/nhavens
A Contemplative Companion to Fujino Township

We can throw theories around all we want, but what really matters is what we see through the viewfinder...maybe Oly found a way to change the laws of physics (no matter what Scottie from Star Trek says).

OzRay has tested both the teleconverter and the extender tube...doing a search on Google has stated that while the teleconverter does lose a stop, there's nothing out there that says the tube does.

Yes the distance the lens is away from the sensor should darken it (the E-300's viewfinder is proof of that with all the twist and turns the image has to take before getting to the eye), maybe because of the smaller physical focal length this isn't an issue.

can you show me your test result?

nick

OzRay said:

digital initiatives said:

when you add the extension tube. you are extending the entrance
pupil outward. so the same aperture size but at a longer distance
from the sensor, this reduces light. The same principle for the
teleconverter. The glass has no effect on the light loss. the
transmittance of multi-coated glasses should be higher than 98%.
glass just cause degradation to image quality (whatsoever the
amount).

Click to expand...

When I put on my telconverter, I lose one stop, when I put on my
extension tube I lose nothing. Go figure?

Cheers

Ray

--
http://www.australianimage.com.au

Click to expand...

If you increase the distance between the lens and the sensor ( ence the image of the subject is bigger), there is loss of light. NO DUBT HERE.
And the more the distance, the bigger the subject, the more loss of light!
Regards
--
(equipment in profile)

stefano-italy

digital initiatives said:

can you show me your test result?

Click to expand...

In a meaningful way? Not really.

• If I put say the 50mm lens on my E1 and open it to max aperture, I get f2.0.

• If I add the EX-25 to the lens and open up to max aperture, I get f2.0.

• If I add the EC-14 to the lens and open up to max aperture, I get f2.8.

• Unfortunately, if I add both, the camera gives me no reading.

If I wanted to lie, I could just as easily fake EXIF info, so there's no point in showing photos.

Once upon a time I probably could have explained the physics/optics behind this, but it's now a distant memory; also, nowadays I'm less concerned with theory and more interested in practice.

Cheers

Ray

--
http://www.australianimage.com.au

Hi Richard,

The inverse law holds. It is a law of classical physics and can't be altered by any means.

Richard Pavek said:

1. If what you and digital are saying would be true, it would mean
that the light fall-off would be true outside of a lens. In other
words, every time you backed up 50 cm from a window the light would
fall off 50%.

Click to expand...

OK, I just put on my Expodisc and my E-1 meter gave me 1/60 second at 1 meter from a 1.5x1.5 meter window (no lights inside) and backing off to 2 meters from the window, using the same aperture (f/2.0), the E-1 gave me 1/15 second as exposure time. That is four times longer than 1/60 second. This is exactly in accordance with the inverse quare law.

Richard Pavek said:

2. Hold up a light meter to a light source, check the reading. Back
up twice the distance measure it again.

Click to expand...

OK, I did that as well with the same method as above but the window was exchanged to a small spotligh. Same result as before.

Richard Pavek said:

3. If what you said was correct, the light would fall of
drastically as the lens was extended from near focus to infinity.
It doesn't.

Click to expand...

You are right - and there must be a good physical explanation. Most likely, there are more factors (in addition to the inverse square law) to take into account that has to do with the effective focal length and aperture as Hokuto implied. Just let me (and others with a background in physics) think about it for a while and we will be able to explain it - physically.

Richard Pavek said:

4. When someone who has been around as long as Oz tells you
something pause before saying he is wrong and check your facts.
Especially when he says he checked it with a meter to be sure to be
sure. He just might know what he is talking about.

Click to expand...

You are right Richard. However, I think it is refreshing with someone novice contesting the established guys. I have seen very knowledgeable professors having been proven wrong by their own students many times.

Richard Pavek said:

(Even if he is an Aussie.)

Click to expand...

Oh, that will be tough to accept. ;-)

Cheers, Jens

--
Everything is possible - miracles are just a bit harder

Mike_PEAT said:

We can throw theories around all we want, but what really matters
is what we see through the viewfinder...

Click to expand...

Mike is right... unless talking about the theories matters more than the photography ;-).

I only have two Oly lenses and use the EX25 occasionally on the 50-200. From actually using the EX25 I have to concur with OzRay. Checking the lens readouts with and without the extension tube gave identical readings. At least in good light photographing insects. With slide copying, there were other more pressing concerns such as light source etc. Light fall off simply wasn't an issue.

You really are working extremely close to the subject (at least with the 50-200). Using the EX25 with the 50-200 provides such narrow DOF and focussing range that worrying about a theoretical amount of light fall-off is a non-issue. Yes I know that when using bellows and even macro lenses, one is supposed to think about light fall off but with digital, you can use the LCD (as a guide, not for all out accuracy) and adjust exposure compensation if required.

As another comparison, I used to use the Canon x1.4 and x2 tele convertor either side of an extension tube to get extra reach with my 500/4 IS. The viewfinder readings gave the expected light fall off that you'd expect from the convertors but didn't appear to add any extra. There were other things to think about with this combination.

jebir said:

jebir said:

3. If what you said was correct, the light would fall of
drastically as the lens was extended from near focus to infinity.
It doesn't.

Click to expand...

You are right - and there must be a good physical explanation. Most
likely, there are more factors (in addition to the inverse square
law) to take into account that has to do with the effective focal
length and aperture as Hokuto implied. Just let me (and others with
a background in physics) think about it for a while and we will be
able to explain it - physically.

Click to expand...

Lens design itself is complicated, and the 50mm seems quite complicated for lens of its size (11 elements). Since focal length is measured from the optical center of the lens, I'm wondering if there's a way the movement of the elments inside the lens could be designed to counteract any physical change in length that occurs with extension during focusing, leaving the theoretical focal length unchanged?

--no physicist here, just thinking outloud.

--
'And only the stump, or fishy part of him remained'

http://www2.gol.com/users/nhavens
A Contemplative Companion to Fujino Township

Okay, science, theory and all else aside. I spent over 10 years doing military, industrial and medical photography. While I can't remember all the exact scientific terminology, I remember the measurements made.

1.) There is a light loss, due merely to the extension. (expansion of light patterns over a larger area.)
2.) The light loss varies according to focal length and amount of extension.

3.) The light loss of a 25mm extension tube is not signifcant at focal lengths above 50mm but it is measurable if you know what you are doing. At longer focal lengths it becomes increasingly less noticable.

How to measure, if you must:

• select a subject of consistent texture and color. an 18% neutral grey card works great.
• Use lighting that will not change, i.e. two photo floods.
• Without the extender and with the lens focused at infinity, take a manual meter reading. Note carelfully because you must be able to read to a tolerance of at least .25 F stop.

--- NOTE: the card subject will not be in focus, it doesn't need to be, you just need a starting constant and to eliminate variables, infinity is the best one. (yes this means use manual focus).

remove the lens, add the extender replace the lens. Keep everything else exactly the same. Take a new reading. At 50mm your light loss should be about .5 stop. At longer focal lengths it decreases proporationatly, depending on focal lengths.

• Be forewarned that most in camera light meters are not consistent beyond .25 stop. If you are not careful, the meter itself can introduce additional variances. Therefore repeat the test until you can get three constants within .25 stops.

You can also measure this with the macros lenses (which have greater built in extension.) without even using the extension tube but the conditions still must be controlled to do so.

In reality, Yes, there is light loss. No it is not a factor with a 25mm extension tube under most normal conditions with most lenses. If you stack tubes (creating further extension) or attempt to use it with wide focal lengths it will become a problem.

--
Denver David
My photos at:
http://eaglesnest.smugmug.com
http://www.pbase.com/brdavid/
http://homepage.mac.com/brdavid/

...there is light loss.

I was thinking about reduction in effective aperture, which doesn't occur, but there is in fact a necessity to adjust exposure, if you add an extension tube.

A typical figure might be 1/20sec @ f2 with EC-14 and 1/40sec @f2 without. Just tested this with the 50mm once again.

I need to stop and think about what the question is actually asking, before making a response.

Cheers

Ray

--
http://www.australianimage.com.au