Olympus What does adding focal length mean?

Discussion in 'Olympus' started by Freedom, Oct 28, 2003.

1. FreedomGuest

I can get an Olympus C-210 Teleconverter. It multiplies focal length by
1.9x.

What does that mean in laymen terms? (like if I was shooting a 4 foot tall
object from 20 feet away?)

How much more "zoom in" will I get?

Regards,

Jeff

Freedom, Oct 28, 2003

2. Rob WildGuest

As I understand it, the focal length multiplier is exactly that - ie:
For the 1.9, multiply your focal length on the lens by that amount.

eg: if you are using a 24-80mm lens, adding the teleconverter would give
you an effective focal length of 45-152 mm, and you will generally lose
about 2 stops. A 100mm lens will become a 190mm lens, also losing about
2 stops.

cheers

Rob

Rob Wild, Oct 28, 2003

3. FreedomGuest

Losing a stop means what? Also, can it be put into a real life example with
a distance and size of object?

Regards,

Jeff

Freedom, Oct 28, 2003
4. Charlie DilksGuest

You don't get more "zoom." a teleconverter like the C-210 must be used
at or very near the maximum focal length of the camera's zoom lens or
you will get vignetting. In the example of the 24 - 80 lens given above
the effective focal length will be 152mm. You might be able to back off
a tiny bit, but not much.

Since it's a teleconverter and not a teleextender, there will be very
little light fall-off. The C-210 isn't a very large diameter so there
will be some, but the B-300 and TCON-17 converters which give 1.7x have
no measurable light fall-off..

Charlie Dilks, Oct 28, 2003
5. Charlie DilksGuest

Losing a stop means a halving of the light; ie. going from f 5.6 to f 8.
As to your original question, a 1.9x teleconverter would make a 4 foot
pole look 7.6 feet tall at the same distance.

Charlie Dilks, Oct 28, 2003
6. Rob WildGuest

Correct (basic) exposure is determined by three factors:
Film Speed (ISO or ASA)
Aperature (F/#)
Shutter Speed (1/250th sec)

The difference between each measurement is 1 stop. Each stop of
difference means that there is either double (going up) or half (going
down) as much light hitting the film/sensor

ie:
ISO 100 +1 stop = ISO 200 (twice as fast or sensitive)
F/11 +1 stop = F8 (F8 is a larger aperature, so it lets in more light)
1/125 +1 stop = 1/250th sec (twice as fact

Hence in my previous post whereby you may lose about 2 stops, the
teleconverter may alter the correct exposure calculation as follows:

(Without) E(exposure) = ISO200 @ F/11 @ 1/125th sec
(With) E(exposure) = ISO200 @ F/11 @ 1/30th sec (OR)
(With) E(exposure) = ISO200 @ F/5.6 @ 1/125th sec.

Real-life example...

(A guess) Am shooting at a person 12ft away with a 80mm lens. I will
most likely see the person's head, shoulders, maybe most of their torso.
Adding the teleconverter, same person, same distance away, with an
effective focal length of 152mm, the person's head is likely to fill the
frame. I may be able to get in a shoulding, depending on composition,
but the head will be predominant in the frame.

cheers

Rob

Rob Wild, Oct 28, 2003
7. Rob WildGuest

Charlie Dilks wrote:
Charlie,

Pardon my ignorance, but what is the difference between a teleconverter
and a teleextender? I also thought that it was a general rule-of-thumb
that there was a light falloff equiv to the focal length multiplier?

cheers

Rob

Rob Wild, Oct 28, 2003
8. Charlie DilksGuest

A teleconverter goes on the front of the lens. A teleextender goes
between the lens and camera. With a TE there is an equivalent light
falloff. With a TE it depends on the diameter. With the huge diameter of
the b-300 and TCON-17 relative to the lenses they're mounted on there is
no light falloff.

"Oly claims that the B-300 requires no exposure correction on the IS-3,
and the same appears to be true on the digital side."
From:

Charlie Dilks, Oct 28, 2003
9. Charlie DilksGuest

I meant, "With a TC (teleconverter) it depends on the diameter, not TE..

Charlie Dilks, Oct 28, 2003
10. Rob WildGuest

Many thanks Charlie,

have not actually seen one of those before - have only seen the ones for
between lens & camera - ie: Canon's 1.4x & 2x.

cheers

Rob

Rob Wild, Oct 28, 2003
11. Andrey TarasevichGuest

You won't loose any stops with "Olympus type" teleconverter - a
teleconverter that attaches to the front of the lens. The trade off is
that with this type of teleconverter you cannot change the focal length
of the main lens, meaning that it should always stay at its maximum
focal length.

The "traditional" teleconverter that goes between the lens and the body
lets you use the entire range of focal lengths if the main lens, but you
have to pay for this convenience with lost stops.

Andrey Tarasevich, Oct 28, 2003
12. William GrahamGuest

This sounds great to me......You just screw it onto the front of your lens
like a filter, and it increases the focal length without making the lens any
slower? - Sounds like something every manufacturer should sell as an
auxilliary to all their long lenses.....It must distort the image in some
way, or everyone would use them.....A 100mm Nikor f2.8 sells for under \$100
(E type) A 200mm f2.8 Nikor sells for over \$500....But I can get this simply
by adding one of these magic filters........And, (I suppose) you could stack
two or more of them........

William Graham, Oct 28, 2003
13. Andrey TarasevichGuest

Well, you should probably suggest that to the manufacturers.
Of course it must, as any teleconverter. The lens was designed to
perform best without it. There's no way to achieve the optimal result
under these circumstances.
It would be interesting to know where you got the idea that a cheap
100mm lens with a teleconverter can perform as well as a dedicated 200mm
lens. Sounds like you have a great experience with "magic" teleconverters.

As for calling "external" teleconverters "filters" and suggesting to
"stack" them... you obviously have never seen one.

Andrey Tarasevich, Oct 28, 2003
14. Per NordenbergGuest

There is also another trade off - putting a [frontmounted] teleconverter in front
of your lens means close focus will be affected, much in the same way as lens
speed is affected with a "traditional" teleextender/-converter that is inserted
between the lens and the camera body.

Regards,

Per Nordenberg

Per Nordenberg, Oct 28, 2003
15. Per NordenbergGuest

This is because frontmounted teleconverters (unlike those traditional converters
that goes between the lens and the camera) are working according to the 'Galileo
telescope principle'.

Regards,

Per Nordenberg

Per Nordenberg, Oct 28, 2003