Question about TC's
Jul 30, 2014 09:30:08 #
zigipha wrote:
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)?
Yes, it reduces the ratio the entrance pupil to focal length, which increases dof. You have not changed the maximum aperture, but you have change the focal length, so the RATIO of the size of the entrance pupil to the focal length has changed.
a 300mm F2.8 with a 2x will become 600mm F5.6
it will have the same dof as a 600mm F5.6
Jul 30, 2014 12:34:23 #
jcboy3 wrote:
The TC shifts the focal length range and aperture ... (show quote)
Sorry, I should have said the ISO must increase by one stop to 800
Too quick on the draw on this one.
Jul 30, 2014 13:18:53 #
davidrb wrote:
Teleconverters effect the amount of light the sensor sees, regardless of any formula. How can that NOT effect ISO?
The only time the ISO will be effected by the teleconverter, is when the ISO is set to "Auto". Keep in mind YOU set the ISO when setting up the shot. (ISO 100 for a bright sunny day) YOU set the sensitivity of the sensor. Because of light loss by the converter, you may want to set the ISO higher yourself. With the converter the normal rules of exposure are in place. A wider aperture, or slower shutter speed when using the converter.
Jul 30, 2014 16:04:00 #
davidrb wrote:
Teleconverters effect the amount of light the sensor sees, regardless of any formula. How can that NOT effect ISO?
Because the ISO is a"fixed" thing, once it is set in-camera.
Lenses, converters, etc. are only effecting the amount of light that reaches the sensor, not it's "set" sensitivity!
Jul 30, 2014 19:19:46 #
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
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
Does not affect ISO directly- unless, as mentioned you have auto ISO turned on. But it will affect your exposure considerations and in that way ultimately ISO. When using a TC, you will see or perceive less apparent DOF than with the native lens because of the increased magnification.
Jul 30, 2014 19:50:50 #
imagemeister wrote:
Does not affect ISO directly- unless, as mentioned you have auto ISO turned on. But it will affect your exposure considerations and in that way ultimately ISO. When using a TC, you will see or perceive less apparent DOF than with the native lens because of the increased magnification.
DOF is a function of focal length and aperture, and is only dependent upon a TC because you can get a longer focal length with a TC. An exposure at 300mm f/8 will have the same DOF whether it was taken directly with the lens or at an original setting of 150mm f/8 with a 2x TC. Set the lens to 300mm to get a 600mm equivalent with the TC and the DOF will be narrower, but cannot be compared to the original lens if it can't get to 600mm on its own.
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