Does Teleconverter changes the angle of view?

[jemini_joseph]

Does Teleconverter changes the angle of view?

Hi guys<br>

This is a pure technical question. May be some optics expert or

physics expert can answer my question..<br><br>

 

I know 600mm lens has 4 degree, 500m has

5 degree and 400mm has 6 degree angle of view. <br><br>

I see the advantage of smaller angle view. When the subject distance

increases, the magnification with 600mm doesn't go down as much with

a 400mm. The below picture explains what I have in mind. The

difference in Magnification at 4 meter is not as big as the difference

in 8 meter. <br><br>

So if I add 1.4TC to 400mm lens it will become 560mm. Does this

reduce the angle of view

to somewhere in between 4 and 5? Or is it just like cropping?<br><br>

 

<img src="http://www.color-pictures.com/tests/angleofview.gif"><br>

Thanks in advance<br>

<a href="http://www.color-pictures.com/" target="w-

2">http://www.color-pictures.com/</a>

[alex_lofquist]

The answer to both questions is YES!

[awahlster]

When you add a teleconverter to a lens you will have a lens that will behave/have the optical chharacteristics of the foacl lenght of the origional lens multiplied by the magnification factor of the teleconverter. And the resulting loss in light transmisson

 

SO

 

a 400mm ff4.0 lens + a 1.4X becomes a 560mm f5.6

 

a 400mm f4.0 lens + a 2X becomes a 800mm f8

 

The only departure from this is the minimum focusing distance will remain the same as the lens had before adding the teleconverter.

 

The reason for the loss of light transmission is simple the focal length incresses but the apreture remains the same and the "F stop of a lens is the ratio between focal lenght and apreture opening. In the case of a teleconverter you changed one with out changing the other.

 

But specifically the way a teleconverter works is it takes the image circle formed by the lens and crops the center portion (how much is based on the magnification of the teleconverter)and then through optics rexpands the image circle to cover the film plane. SO if a lens has 100lpm resolution and you attach a 2X you will have a lens twice as long half as fast and with approx 1/2 the resolution of the origional lens.

 

Hope this helps

[pvp]

Teleconverters are intended as a low cost means of adding longer focal lengths to your lens arsenal. When you add a 2X TC to (for example) a 300mm f/2.8 lens, the resulting combination is a 600mm f/5.6 <I>in every respect.</I> The trade-off, of course, is that we have no right to expect the optical quality of our TC'd lens to equal that of a dedicated 600/5.6 lens.

[richard_cochran]

<cite>Does this reduce the angle of view to somewhere in between 4 and 5? Or is it just like cropping?</cite>

<p>

It is just like cropping, which is just like increasing

focal length. Since cropping reduces the angle of

view, a teleconverter reduces the angle of view, as well.

Assuming no linear distortion, the diagonal angle of view

of a 35mm frame is 2 * arctangent (21.6mm/f), or about

4.4 degrees for a 560mm lens. That applies regardless of

how you got the 560mm lens, whether the lens was originally

built as a 560mm lens or was obtained by setting a zoom

to a 560mm focal length, or was obtained by putting

a 1.4TC onto a 400mm lens.

[jemini_joseph]

Ok, thanks guys. Now one more question. Alex said Yes to both questions. So we will achieve the same thing with crop? I mean if I take an image using 500mm from 4meters and and 8 meters and same image using 400mm at same distances and crop it to match 500mm, will I get same size picture? I mean if I have to crop 20% of the 400mm image at 4 meter to match 500mm, it will same 20% at 8 meter too? Or does it need more cropping? Thanks again

[NetR]

>if I take an image using 500mm from 4meters and and 8 meters and same image using 400mm at same distances and crop it to match 500mm, will I get same size picture?

 

I'm not certain I understand your question. When you have cropped to get the subject the same size in both pictures, the background will be slightly different. The 400mm lens has a slightly wider angle of view and will capture a wider slice of background than the 500mm lens will.

 

Regards, Ross

[frank uhlig]

Oops, Ross,

 

if you keep your lens to subject distance the same and crop the 300mm lens picture to match that of the 600mm, you will get the same subject matter, foreground, background, size relations all the same. You do not change PERSPECTIVE from one spot. You could crop a 20mm lens shot to match the 600mm lens shot (from the same spot) and you would see the same image, completely. Of course with such cropping you will lose sharpness, see more grain etc. But the perspective from one spot never changes, length of lens does not matter.

[cham_saranasuriya]

Hi,

 

What happens to the perspective of the lens when you add a TC? I suspect it remains the same? It would be interesting find the right answer!!!!

 

Cheers

[doug herr]

The perspective does not change when you add the TC, as long as the lens-to-subject distance remains the same.

[ShunCheung]

Say you add a 2x TC to a 300mm/f2.8, it becomes a 600mm/f5.6. It is just like changing from a 300mm lens to a 600mm. The perspective doesn't change as explained by Frank's post earlier.

[jemini_joseph]

This is how I see it. <br>

<img src="http://www.color-pictures.com/tests/tc.gif"><br>

When I was talking about angle of view. Perspective is the right word it seems. Now I have to if 500mm+1.4TC behaves exactly like a 700mm lens. What I'm looking is when the distance goes up, does the magnification goes down by same rate..

[ShunCheung]

A 500mm lens + a 1.4x TC behaves like a 720mm lens simply because the combination is indeed a 720mm lens.

 

Now, with the teleconvertor on, if you decide to increase the distance between your subject and your camera (e.g. move back to farther away from the subject) such that the image of the subject on your sensor/film remains the same size as before when the camera was closer and without the TC on, your perspective has changed.

[w_t1]

correct...perspective only changes with changes of position of the camera/film to the subject