Using 1.7x Teleconverter with Tamron 150-600 lens

Started 3 months ago | Discussions thread
John Sheehy
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Re: Using 1.7x Teleconverter with Tamron 150-600 lens
In reply to fotokeen, 2 months ago

fotokeen wrote:

Teleconverters are available in 1.4 , 1.7 and 2.0 multipliers . The main problem with the (assuming you would buy a good quality one) is they lose apertures . 1 ap for the 1.4 , 1.5 aps for the 1.7 , and 2 aps for the two . If you lose 2 apertures on the 7d it will not autofocus as the max ap on the lens will be smaller than f8 . The best compromise is the 1.4 which only loses one ap so autofocus will work and it will still give you a 210-840 , which I think is fantastic .

TCs multiply f-stops; they don't change apertures at all. The aperture range of the lens is the same regardless of what you attach in front of, or behind it. Apertures are measured in millimeters.

People use the terms "aperture" and "f-stop" as if they are synonymous, but they are not.

The fact is, if you stay at the same distance from the subject, and take a shot, and then take another one with a 1.4x TC, both wide open, they will both collect the same amount of light from the subject, and have approximately the same noise when the images are resized so that the subject is the same size in both! Whether or not there is light loss due to a TC depends really on context. You would have to move 1.4x as far from the subject with the 1.4x TC to actually get a stop less total light from the subject.

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