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

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Jurgen Larssson

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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
 
A few ideas:

1) Anything on the front of the lens is by necessity going to be much larger than something on the back of the lens. In addition, the filter ring isn't made to hold that much weigt/mass -- see the cantelevar that is requird under the Tcon 300 for example

2) The front filter element of lens are all different sizes, hence you'd need a different TC for each leans with a different filter ring size.

3) Quality will generally be lower unless it's something with very very high quality optics which leads back to #1 and #2 above.

4) As a result of of 1, 2, and 3, cost is higher than an equivalent behind the lens TC.
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...
 
Jay Bean said:
1) Anything on the front of the lens is by necessity going to be
much larger than something on the back of the lens. In addition,
the filter ring isn't made to hold that much weigt/mass -- see the
cantelevar that is requird under the Tcon 300 for example

2) The front filter element of lens are all different sizes, hence
you'd need a different TC for each leans with a different filter
ring size.

3) Quality will generally be lower unless it's something with very
very high quality optics which leads back to #1 and #2 above.

4) As a result of of 1, 2, and 3, cost is higher than an equivalent
behind the lens TC.
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...
Click to expand...
 
Jurgen Larssson said:
Jay Bean said:
1) Anything on the front of the lens is by necessity going to be
much larger than something on the back of the lens. In addition,
the filter ring isn't made to hold that much weigt/mass -- see the
cantelevar that is requird under the Tcon 300 for example

2) The front filter element of lens are all different sizes, hence
you'd need a different TC for each leans with a different filter
ring size.

3) Quality will generally be lower unless it's something with very
very high quality optics which leads back to #1 and #2 above.

4) As a result of of 1, 2, and 3, cost is higher than an equivalent
behind the lens TC.
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...
Click to expand...
Click to expand...
 
If cost is no object it won't necessarily be worse, but it costs a LOT more to make a high quality optic 4 inches in diameter than a similar quality optic 1.5 inches in diameter (about the size of the rear mounted TCs).
 
Honestly, I'm not sure. The reasons already mentioned sound good to me. Camera manufacturers have been designing optics for a century now. It's hard for me to believe that an idea like this would be passed over if it were truly better than behind the lens tc's. If they are in fact, as you claim, substantially better than behind the lens tc's, there must be some large drawback (size, weight, cost, difficulty to produce). It seems the market is there for it, since the market clearly exists for behind the lens tc's, so it would seem logical that there is some major limiting factor.
 
ajkessler said:
Honestly, I'm not sure. The reasons already mentioned sound good
to me. Camera manufacturers have been designing optics for a
century now. It's hard for me to believe that an idea like this
would be passed over if it were truly better than behind the lens
tc's. If they are in fact, as you claim, substantially better than
behind the lens tc's, there must be some large drawback (size,
weight, cost, difficulty to produce). It seems the market is there
for it, since the market clearly exists for behind the lens tc's,
so it would seem logical that there is some major limiting factor.
Click to expand...
 
--

--------------------
  • Caterpillar
'Always in the process of changing, growing, and transforming.'
 
Yes they are popular for compact cams. Not too expensive either, though they suffer mightily in the quality of image they produce. I use to use one on my old Olympus. Great for what it did, but IQ wise, horrible vignetting, very soft, dramatic fringing...
 
--
Lee Jay
(see profile for equipment)
 
if they are the lens experts, they should be able to come up with more than the 500d lens element. I used to use the tele's on my sony, and it worked great, plus a wide angle on the front. But they did not autofocus from my lenses. [I'll get them out and try it again, it was a long time ago]

my point was if they could be so great, and so easily made, why havn't they. Canon could make a ton of money.
--



Linda~ http://sweetlight.yuku.com/forum/viewtopic/id/362
You don't take a photograph. You ask, quietly, to borrow it. Author Unknown
 
It is the successor (new name mainly?) to the Olympus B-300 which I own and have been very happy with. I used this mostly with my Canon Pro90 IS and it gave me an equivalent of 629mm. It was convenient because it was 58mm and screwed directly onto the camera lens. The drawback was that you lost some of the wider end of your zoom and it did vignette but those weren't serious problems. You get a circular image that you can crop a bit if necessary to make a rectangle. IQ was darn good for a 2.6 mega pixel rig.

With my 70-300mm IS lens on an XT, I should get an equivalent of 816mm at f5.6. Cool! One of these days I will try it. I don't use this TC much because of one gripe.

My gripe is that I can't find a rear lens cap that fits the TC making it awkward to bring along.

Anyone know where I can get one?
 
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