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Question about TC's
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Jul 29, 2014 09:42:39   #
oldtool2 Loc: South Jersey
 
I know when I mount a TC, say a 1.4X, it effects focal length (400mm X 1.4 = 560mm) and the f-stop (f5.6 X 1.4 = f8, roughly).

My question is, does it also effect the ISO (ISO-400 X 1.4 = ISO-560)? I can not ever remember seeing this mentioned before. Not that it really matters that much but I am curious. Does anyone know for sure?

Jim D

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Jul 29, 2014 09:48:30   #
davidheald1942 Loc: Mars (the planet)
 
The ISO is the ISO is the ISO.
the answer is NO
ronny

oldtool2 wrote:
I know when I mount a TC, say a 1.4X, it effects focal length (400mm X 1.4 = 560mm) and the f-stop (f5.6 X 1.4 = f8, roughly).

My question is, does it also effect the ISO (ISO-400 X 1.4 = ISO-560)? I can not ever remember seeing this mentioned before. Not that it really matters that much but I am curious. Does anyone know for sure?

Jim D

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Jul 29, 2014 09:48:50   #
fotohouse Loc: Northern Illinois
 
No, The ISO is not affected by a TC, just focal length, aperture, and image quality.

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Jul 29, 2014 10:04:22   #
Db7423 Loc: Pittsburgh, PA
 
Ditto. ;)

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Jul 29, 2014 10:08:36   #
oldtool2 Loc: South Jersey
 
I didn't think so but was not sure. You would think it would be though.

Thanks for the quick answers.

Jim D

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Jul 29, 2014 10:11:39   #
ecobin Loc: Paoli, PA
 
The ISO indicates the sensitivity of the sensor to light. It can only be changed electronically within the camera. The lens and any filter used do not affect sensor sensitivity.

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Jul 29, 2014 11:05:33   #
davidrb Loc: Half way there on the 45th Parallel
 
oldtool2 wrote:
I know when I mount a TC, say a 1.4X, it effects focal length (400mm X 1.4 = 560mm) and the f-stop (f5.6 X 1.4 = f8, roughly).

My question is, does it also effect the ISO (ISO-400 X 1.4 = ISO-560)? I can not ever remember seeing this mentioned before. Not that it really matters that much but I am curious. Does anyone know for sure?

Jim D


Teleconverters effect the amount of light the sensor sees, regardless of any formula. How can that NOT effect ISO?

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Jul 29, 2014 11:42:43   #
oldtool2 Loc: South Jersey
 
davidrb wrote:
Teleconverters effect the amount of light the sensor sees, regardless of any formula. How can that NOT effect ISO?


davidrb,

You would think it would. This is something I had never seen discussed here before, which is why I am asking. Again, it doesn't matter, what is is, but would like to know

Jim D

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Jul 29, 2014 11:47:31   #
fotohouse Loc: Northern Illinois
 
davidrb wrote:
Teleconverters effect the amount of light the sensor sees, regardless of any formula. How can that NOT effect ISO?


ISO is sensor sensitivity and controlled by the electronics of the camera, it is the same as film speed if you ever shot film.

The lower available light is due to the reduction in the relative aperture size due to the TC used. Try this, adjust your aperture to wide open (2.8 for me) without a TC. Now add a 2X TC, the max aperture available will now be f5.6.

Now if you wish to use the same settings (provided you were not already wide open on the aperture) say f.11 at 125th sec and ISO 100 and you add a 1.4TC then you can adjust to f.11 at 125th and ISO 200.

It all depends on what part of the triangle you want to adjust to compensate.

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Jul 29, 2014 12:04:51   #
MT Shooter Loc: Montana
 
davidrb wrote:
Teleconverters effect the amount of light the sensor sees, regardless of any formula. How can that NOT effect ISO?


The sensor has nothing to do with the lens. The effect the lens has on ISO needs via TC light reduction has already been addressed via the loss of one stop of light (F5.6 to F8).

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Jul 30, 2014 00:59:46   #
BHC Loc: Strawberry Valley, JF, USA
 
davidrb wrote:
Teleconverters effect the amount of light the sensor sees, regardless of any formula. How can that NOT effect ISO?

ISO is a factor of the sensitivity of the sensor to light and is not affected by the amount of light striking it.

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Jul 30, 2014 05:56:03   #
Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)
 
oldtool2 wrote:
I know when I mount a TC, say a 1.4X, it effects focal length (400mm X 1.4 = 560mm) and the f-stop (f5.6 X 1.4 = f8, roughly).

My question is, does it also effect the ISO (ISO-400 X 1.4 = ISO-560)? I can not ever remember seeing this mentioned before. Not that it really matters that much but I am curious. Does anyone know for sure?

Jim D


No.

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Jul 30, 2014 09:01:17   #
zigipha Loc: north nj
 
Is the reduction in F stop a reflection of the reduction in light, or does it also increase the DoF (as would be expected if i icrase F stop from 5.6 to 8)?

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Jul 30, 2014 09:14:43   #
jcboy3
 
oldtool2 wrote:
I know when I mount a TC, say a 1.4X, it effects focal length (400mm X 1.4 = 560mm) and the f-stop (f5.6 X 1.4 = f8, roughly).

My question is, does it also effect the ISO (ISO-400 X 1.4 = ISO-560)? I can not ever remember seeing this mentioned before. Not that it really matters that much but I am curious. Does anyone know for sure?

Jim D


The TC shifts the focal length range and aperture range of the lens by the corresponding magnification factor. It does not otherwise significantly change the exposure (ignoring any transmission loss due to extra glass).

So in your example, you want a 1/1000sec shutter speed (for stability), and suppose you have correct exposure at 400mm with 1/1000 sec, f/4, ISO 400. Then the TC-14 will increase focal length to 560mm and decrease aperture to f/5.6. The increase in focal length does not affect exposure, but the decrease in aperture does. To keep the fast shutter speed, you need to increase ISO to 560 to compensate.

On the other hand, if correct exposure at 400mm is 1/1000 sec, f/8, ISO 400, then with the TC-14 at 560mm, correct exposure is still 1/1000 sec, f/8, ISO 400.

So here's the rules:

1. Changing focal length does not change exposure

2. Changing aperture does change exposure, which is compensated by change to either shutter speed or ISO.

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Jul 30, 2014 09:24:39   #
redhogbill Loc: antelope, calif
 
oldtool2 wrote:
davidrb,

You would think it would. This is something I had never seen discussed here before, which is why I am asking. Again, it doesn't matter, what is is, but would like to know

Jim D

past threads for UHH on TC ,good luck
http://www.uglyhedgehog.com/search.jsp?q=Question+about+teleconverter&u=&s=0

:thumbup:

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