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Why the aversion of front mounted TCs? They are better.

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netgarden said:
I had no problems with one on my sony V1, but could not get it to
focus on the canon dslr. I put it away thinking they just aren't
compatible, but I may get it out again and try it. But so far it
seemed to confuse the camera whereas at the connection end they are
mostly fine.
Click to expand...
It's not confused, it just can't get enough extension to make it to infinity. I know I had to use a tube when I put my TCON-14B on my 135/2, but I don't remember which one right now, (and I'm not even sure which box of not-currently-used camera stuff my TCON is hiding in.)
 
ljfinger said:
Roger Krueger said:
...you weren't taping Next Gen, were you? (ewwwww!)
Click to expand...
I think TnG was way better than TOC, in just about every way.
Lee Jay said:
Babylon 5 was head-and-shoulders better than all of the
shiny-happy-plastic-world later Treks. Yeah, Patrick Stewart was an
impressive Captain, but most of the stories were as limp as
week-old lettuce.
Click to expand...
B5 had the best long-term story by far. Some of the episodes were
a bit weak, however, as was some of the acting and technical
production. TnG had a very weak long-term story but I thought many
of the episodes (but not all) were stronger than those of B5.

B5 was a one-shot and we're lucky they got to film all 5 seasons.
It was a pleasure to watch when it was on 5 times a week, and
in-order from start to finish.

--
Lee Jay
(see profile for equipment)
Click to expand...
 
Jurgen Larssson said:
ljfinger said:
Roger Krueger said:
...you weren't taping Next Gen, were you? (ewwwww!)
Click to expand...
I think TnG was way better than TOC, in just about every way.
Jurgen Larssson said:
Babylon 5 was head-and-shoulders better than all of the
shiny-happy-plastic-world later Treks. Yeah, Patrick Stewart was an
impressive Captain, but most of the stories were as limp as
week-old lettuce.
Click to expand...
B5 had the best long-term story by far. Some of the episodes were
a bit weak, however, as was some of the acting and technical
production. TnG had a very weak long-term story but I thought many
of the episodes (but not all) were stronger than those of B5.

B5 was a one-shot and we're lucky they got to film all 5 seasons.
It was a pleasure to watch when it was on 5 times a week, and
in-order from start to finish.

--
Lee Jay
(see profile for equipment)
Click to expand...
Click to expand...
 
Jurgen Larssson said:
With a front mounted TC you gather and focus more light
so you won't lose any stops of light when exlarging 2x-3x.
Click to expand...
Wrong. Totally and utterly wrong. You have to apply the laws of optics, the first and important one here is the law that governs the amount of light that passes through your lens.

To get a 300mm f/4.0 lens your entry pupil (as aproximated by your front element) has to have a diameter of 75mm. Add a 2x regular SLR teleconverter and your lens will be a 600mm f/8 as you haven't changed the size of the entry pupil.

To attach a 75mm diameter teleconverter would do the same (if it were perfect, but big lenses are harder to get right, so big losses are already incurred). To not loose lens speed (going from 300mm f/4 to 600mm f/4) your front element size now has be 150mm - something you really wouldn't want. It's not as if the lens is only using the center of the front element, it's using the whole diameter to gather the light coming from your subject onto the focal plane! Reduce the relative size of the gathering area and you loose lens speed.
--
regards
Karl Günter Wünsch
Visit my gallery at
http://www.fotocommunity.de/pc/pc/mypics/461808
 
Roger Krueger said:
For a small format change it may still use all of the front element
because there probably wasn't enough front element for full
illumination wide open at its intended format. But put a 4x5 lens
on a 2/3rds sensor and you definitely won't use all of the front
element.
Click to expand...
This is not correct and you can prove it to yourself without even taking a picture. As long as the sensor (any size) is in the focal plane, it uses all of the lens diameter. If you remember your basic ray tracing, you can take a light ray from an object that is dead center in the field of view and trace it to the edge of the objective (front element). It will then go through the center of the lens at the aperture and finally be focused to the center of the sensor in the focal plane. That means at the center of the image. You are using all of the front element for image formation at the center of the picture.

This can also be proven in a more sophisticated way by calculating the point spread function of a point source in the center of the field of view. You have to integrate over the full aperture to get the correct answer. If you assume only the central area of the lens is used and integrate over that aperture function, you will get the wrong result.
Roger Krueger said:
Roger Krueger said:
A lot of people seem to think that a smaller sensor only looks
through the center of the lens elements. That is just flat wrong.
Click to expand...
Click to expand...
And that is correct.

Darrell
http://members.aol.com/pixbydg/still/life.html
 
Karl Günter Wünsch said:
Jurgen Larssson said:
With a front mounted TC you gather and focus more light
so you won't lose any stops of light when exlarging 2x-3x.
Click to expand...
Wrong. Totally and utterly wrong. You have to apply the laws of
optics, the first and important one here is the law that governs
the amount of light that passes through your lens.
To get a 300mm f/4.0 lens your entry pupil (as aproximated by your
front element) has to have a diameter of 75mm. Add a 2x regular SLR
teleconverter and your lens will be a 600mm f/8 as you haven't
changed the size of the entry pupil.
To attach a 75mm diameter teleconverter would do the same (if it
were perfect, but big lenses are harder to get right, so big losses
are already incurred). To not loose lens speed (going from 300mm
f/4 to 600mm f/4) your front element size now has be 150mm -
something you really wouldn't want. It's not as if the lens is only
using the center of the front element, it's using the whole
diameter to gather the light coming from your subject onto the
focal plane! Reduce the relative size of the gathering area and you
loose lens speed.
--
regards
Karl Günter Wünsch
Visit my gallery at
http://www.fotocommunity.de/pc/pc/mypics/461808
Click to expand...
 
Jurgen Larssson said:
With a front mounted TC you gather and focus more light
so you won't lose any stops of light when exlarging 2x-3x.

Easy to remove/flip up

In theory you could make a 70-200 2.8 IS into a 70-200 1.8 IS
using a front mounted TC just gathering more light.

Or a 140-400 2.8 IS

Or a 210-600 2.8 IS

Are there really no applications for this?

---

Look at Tcon 17 and Tcon 300.
You can mount them on regular SLR lenses with step rings.
At 200 mm you only use the center of the lens anyhow.
It'll work, and won't weigh much more.

Any tests?

F
Click to expand...
 
Daniella said:
In comparison to my Tamron 1.4c, the Tcon 17 is just plain
horrible. I still have it but would not use that on a coke bottle.
Click to expand...
I'm surprised you would say such a thing. The Tcon 17 is a very good, well-corrected attachment lens. I suspect you had a bad mismatch with the lens you were using it on.

I don't use the Tcon17, but I use a Raynox teleconverter and it produces better results by far than I get with a Barlow type 1.4x teleconverter. All converter optics have the potential for bad mismatches.

Here's the sample I posted with the Raynox:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=21548557

Darrell
http://members.aol.com/pixbydg/still/life.html
 
But you wouldn't with the price, the weight and the quality of the converter if there were compromises to be made due to weight and price. It would cost in about the same as a decent 600mm lens as the converter basically is such a lens...
--
regards
Karl Günter Wünsch
Visit my gallery at
http://www.fotocommunity.de/pc/pc/mypics/461808
 
About as useful as your other thoughts. Stop posting in single sentences and respond properly outside the title!

I really think you should visit your nearest university library, go to the physics department and check out a book on optics 101. After you read and understood what the lens equation is and how a lens is focused then you can call again. Until then happy reading!
--
regards
Karl Günter Wünsch
Visit my gallery at
http://www.fotocommunity.de/pc/pc/mypics/461808
 
Darrell Spreen said:
Daniella said:
In comparison to my Tamron 1.4c, the Tcon 17 is just plain
horrible. I still have it but would not use that on a coke bottle.
Click to expand...
I'm surprised you would say such a thing. The Tcon 17 is a very
good, well-corrected attachment lens. I suspect you had a bad
mismatch with the lens you were using it on.
Click to expand...
it has bad image quality, chromatic aberation etc..

you can post some 100% crop of it if you have better experience. I thought I still had mine but I don't. I think I sold it on ebay. can't remember.
Member said:
I don't use the Tcon17, but I use a Raynox teleconverter and it
produces better results by far than I get with a Barlow type 1.4x
teleconverter. All converter optics have the potential for bad
mismatches.
Click to expand...
lets just say that it was a bad mismatch with all my lenses.
Member said:
Here's the sample I posted with the Raynox:
Click to expand...
that's a web size image, post a 100% crop wide open maybe? and of a subject with possible CA problem. then you will see what I am talking about.

--



http://www.pbase.com/zylen

'Never argue with an idiot, they drag you down to their level and beat you with experience'
 
no, not any more. I searched for it and I cannot find it. all I have is an empty box. So not sure if it is in California (I am now in Canada for the winter) or if I sold it.

I quickly got a Tamron 1.4x and 2x and that was like day and night, so I never used the Tcon after that.

--



http://www.pbase.com/zylen

'Never argue with an idiot, they drag you down to their level and beat you with experience'
 
Someone has seemingly invented a program to ask what look to be reasonable questions, but miss the meaning on the answers, and get people like me to waste their time. It was launched most successfully by the OP!
 
Karl Günter Wünsch said:
About as useful as your other thoughts. Stop posting in single
sentences and respond properly outside the title!
I really think you should visit your nearest university library, go
to the physics department and check out a book on optics 101. After
you read and understood what the lens equation is and how a lens is
focused then you can call again. Until then happy reading!
--
regards
Karl Günter Wünsch
Visit my gallery at
http://www.fotocommunity.de/pc/pc/mypics/461808
Click to expand...
 
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