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

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f-stop = focal length / aperture

With a regular TC, aperture doesn't change, but focal length does.

If your front-mounted TC changed focal length, it has to change aperture to maintain f-stop. If you apply a 2x to a 200/2.8 and want a 400/2.8, you have to have an entrance pupil on the FM TC of 400mm/2.8 = 143mm. Since the entrance pupil can't be smaller than the front element (obviously), the front element has to be that big or bigger.

--
Lee Jay
(see profile for equipment)
 
Joe Photo Lover said:
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.
Click to expand...
As far as I could tell from tests with a 85/1.8 lens, there is some loss of light with the B300, though not as much as with a rear TC, so it will not be quite 5.6. When I put it on the Tamron 70-300 lens, the images were very soft. It worked pretty well with the kit lens though (not that I would need that :)

--
Misha
 
ljfinger said:
f-stop = focal length / aperture

With a regular TC, aperture doesn't change, but focal length does.

If your front-mounted TC changed focal length, it has to change
aperture to maintain f-stop. If you apply a 2x to a 200/2.8 and
want a 400/2.8, you have to have an entrance pupil on the FM TC of
400mm/2.8 = 143mm. Since the entrance pupil can't be smaller than
the front element (obviously), the front element has to be that big
or bigger.

--
Lee Jay
(see profile for equipment)
Click to expand...
 
Jurgen Larssson said:
ljfinger said:
f-stop = focal length / aperture

With a regular TC, aperture doesn't change, but focal length does.

If your front-mounted TC changed focal length, it has to change
aperture to maintain f-stop. If you apply a 2x to a 200/2.8 and
want a 400/2.8, you have to have an entrance pupil on the FM TC of
400mm/2.8 = 143mm. Since the entrance pupil can't be smaller than
the front element (obviously), the front element has to be that big
or bigger.

--
Lee Jay
(see profile for equipment)
Click to expand...
Click to expand...
 
Jurgen Larssson said:
Jurgen Larssson said:
ljfinger said:
f-stop = focal length / aperture

With a regular TC, aperture doesn't change, but focal length does.

If your front-mounted TC changed focal length, it has to change
aperture to maintain f-stop. If you apply a 2x to a 200/2.8 and
want a 400/2.8, you have to have an entrance pupil on the FM TC of
400mm/2.8 = 143mm. Since the entrance pupil can't be smaller than
the front element (obviously), the front element has to be that big
or bigger.

--
Lee Jay
(see profile for equipment)
Click to expand...
Click to expand...
Click to expand...
 
misha said:
Joe Photo Lover said:
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.
Click to expand...
As far as I could tell from tests with a 85/1.8 lens, there is some
loss of light with the B300, though not as much as with a rear TC,
so it will not be quite 5.6. When I put it on the Tamron 70-300
lens, the images were very soft. It worked pretty well with the kit
lens though (not that I would need that :)

--
Misha
Click to expand...
 
I've been trying to get more information about Add-on lenses with SLRs and there really is not much information about there at all. I've love to get one good prime and slap some addon lenses on it in a pinch, etc.

That way my camera is really portable and I still get good optics most of the time, but when I need a wide-angle or telephoto, I can get it, etc.

There is a good website that tests these kinds of lenses, but on digicams only...

http://www.lensmateonline.com

From what I read on this website, the Tiffen 2X 43mm was the best they tested, so I purchased one for my Canon A610. I was very impressed with the results... no CA, and no discernable loss of quality. Check out my test samples:

HERE IS MY A610 ZOOMED OUT AT 35MM

http://www.stevesforums.com/forums/attachment.php?id=85625

HERE IS MY A610 ZOOMED IN AT 140MM

http://www.stevesforums.com/forums/attachment.php?id=85626

HERE IS MY A610 WITH THE TIFFEN2X LENS** AT 280MM

http://www.stevesforums.com/forums/attachment.php?id=85627

***

From what I've seen so far, I think the quality is very good. Now one poster raised the fact that some lens AF motors will be strained by putting an add-on lens, and I can see that... so perhaps manual focus would be in order. But most wide-angles are not a big and heavy, so perhaps you'd be able to use the AF, depending on the lens, etc.

What do you guys think?

Can you put a .75x or .5x lens (assuming the quality is good like this Tiffen) on a 50mm prime?
 
ohcello said:
I've been trying to get more information about Add-on lenses with
SLRs and there really is not much information about there at all.
I've love to get one good prime and slap some addon lenses on it in
a pinch, etc.

That way my camera is really portable and I still get good optics
most of the time, but when I need a wide-angle or telephoto, I can
get it, etc.

There is a good website that tests these kinds of lenses, but on
digicams only...

http://www.lensmateonline.com

From what I read on this website, the Tiffen 2X 43mm was the best
they tested, so I purchased one for my Canon A610. I was very
impressed with the results... no CA, and no discernable loss of
quality. Check out my test samples:

HERE IS MY A610 ZOOMED OUT AT 35MM

http://www.stevesforums.com/forums/attachment.php?id=85625

HERE IS MY A610 ZOOMED IN AT 140MM

http://www.stevesforums.com/forums/attachment.php?id=85626

HERE IS MY A610 WITH THE TIFFEN2X LENS** AT 280MM

http://www.stevesforums.com/forums/attachment.php?id=85627

***

From what I've seen so far, I think the quality is very good. Now
one poster raised the fact that some lens AF motors will be
strained by putting an add-on lens, and I can see that... so
perhaps manual focus would be in order. But most wide-angles are
not a big and heavy, so perhaps you'd be able to use the AF,
depending on the lens, etc.

What do you guys think?

Can you put a .75x or .5x lens (assuming the quality is good like
this Tiffen) on a 50mm prime?
Click to expand...
 
Sure you lose light... the physical aperture remains the same but the focal length increases, therefore the f/ratio goes down, and thus the image brightness decreases and therefore we get less light. This is assuming constant sensor size. I'm also assuming that by "regular TC" you mean a teleconverter mounted between the lens and the camera. If I'm missing something, please let me know...

Victor
ljfinger said:
f-stop = focal length / aperture

With a regular TC, aperture doesn't change, but focal length does.

If your front-mounted TC changed focal length, it has to change
aperture to maintain f-stop. If you apply a 2x to a 200/2.8 and
want a 400/2.8, you have to have an entrance pupil on the FM TC of
400mm/2.8 = 143mm. Since the entrance pupil can't be smaller than
the front element (obviously), the front element has to be that big
or bigger.
Click to expand...
 
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.
--



Linda~ http://sweetlight.yuku.com/forum/viewtopic/id/362
You don't take a photograph. You ask, quietly, to borrow it. Author Unknown
 
vor said:
Victor
ljfinger said:
f-stop = focal length / aperture

With a regular TC, aperture doesn't change, but focal length does.

If your front-mounted TC changed focal length, it has to change
aperture to maintain f-stop. If you apply a 2x to a 200/2.8 and
want a 400/2.8, you have to have an entrance pupil on the FM TC of
400mm/2.8 = 143mm. Since the entrance pupil can't be smaller than
the front element (obviously), the front element has to be that big
or bigger.
Click to expand...
Click to expand...
 
vor said:
Sure you lose light... the physical aperture remains the same but
the focal length increases, therefore the f/ratio goes down,
Click to expand...
Up, not down. I suspect you knew that!
vor said:
and
thus the image brightness decreases and therefore we get less
light.
Click to expand...
When I think of "losing light" I think of an ND filter. The light gets spread out by the TC, and it may vignette. But just because the light is spread out doesn't mean the light is lost. Certainly, it's lost to the sensor, so perhaps that's what people mean when they say "you lose light when you attach a TC".

The f-number goes up because the focal length goes up with spreads the existing light from the aperture thinner.

--
Lee Jay
(see profile for equipment)
 
Yeah, you can collect the light before it enters the camera lens, but then the camera wouldn't be able to focus because you've altered the location of the imaging plane. You can add a second lens element to fix that problem, but it'd make the effective focal length longer and you'd be back to the smaller effective aperture.

--
Joe

My craptacular photos: http://www.pbase.com/pyogenes/favorites

Any perceived rudeness, condescending tone, or insults are not intended, but rather the result of my inability to properly express myself with the written word.
 
Pyogenes said:
Yeah, you can collect the light before it enters the camera lens,
but then the camera wouldn't be able to focus because you've
altered the location of the imaging plane. You can add a second
lens element to fix that problem, but it'd make the effective focal
length longer and you'd be back to the smaller effective aperture.

--
Joe

My craptacular photos: http://www.pbase.com/pyogenes/favorites

Any perceived rudeness, condescending tone, or insults are not
intended, but rather the result of my inability to properly express
myself with the written word.
Click to expand...
 
ljfinger said:
vor said:
Sure you lose light... the physical aperture remains the same but
the focal length increases, therefore the f/ratio goes down,
Click to expand...
Up, not down. I suspect you knew that!
Lee Jay said:
and
thus the image brightness decreases and therefore we get less
light.
Click to expand...
When I think of "losing light" I think of an ND filter. The light
gets spread out by the TC, and it may vignette. But just because
the light is spread out doesn't mean the light is lost. Certainly,
it's lost to the sensor, so perhaps that's what people mean when
they say "you lose light when you attach a TC".

The f-number goes up because the focal length goes up with spreads
the existing light from the aperture thinner.

--
Lee Jay
(see profile for equipment)
Click to expand...
 
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