1.7X TC- much needed

Tom Reichner wrote in post #18542577
I don't know what to say to that. . I mean, if you have been on these forums for almost 10 years, and still don't understand the impact that sensor size has on DOF, then, well ...... that's unfortunate.

Maybe this will make sense:

Shooting on a full frame sensor, and then cropping the image, is the same as shooting on a smaller sensor (all else being equal). . And we all know that the same shot with the same framing on a crop sensor has greater DOF than on a full frame sensor. . So the same thing applies to cropping in to a large image - in fact, that's why the term "crop sensor" was coined.

But this really isn't supposed to be discussion about sensor sizes - it's supposed to be about a 1.7x tele-extender. . Sorry for the detour.

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There is no contradiction here. You can think of DOF in at least those two ways: the DOF of the field of view of the entire image, and the DOF of a normalized subject. Since you, personally, always target the entire frame, then thinking in terms of the frame works out fine. People who are focal-length-limited, however, have a more direct handle on subject DOF when they consider aperture size, subject distance, and subject size.

Archibald wrote in post #18543107
That would be an exciting moment for you.

As for me, I have my doubts about any tele-extender. They give you more pixels on subject, but reduce light,

Not from the subject; only from the frame, with the same shutter speed and optical aperture. No loss there as opposed to cropping, noise-wise. For AF, losses can be very real

That's part of what it's supposed to do. No loss there. The aberrations *added* by a TC, though, are something to be considered, but they are generally small with good TCs.

THAT can be an actual problem.

How fast are your lenses? F/4 lenses generally AF pretty good with a 1.4x, unless lighting or contrast get fairly low.

As you eventually move towards mirrorless, cameras will lock accurate AF with higher open f-numbers.

John Sheehy wrote in post #19030722
There is no contradiction here. You can think of DOF in at least those two ways: the DOF of the field of view of the entire image, and the DOF of a normalized subject. Since you, personally, always target the entire frame, then thinking in terms of the frame works out fine. People who are focal-length-limited, however, have a more direct handle on subject DOF when they consider aperture size, subject distance, and subject size.

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But the DOF that really matters is not the DOF as it affects the subject itself. It is all about getting the background behind the subject and the out-of-focus surrounding context to look exactly the way you want it to - the exact amount of blur and quality of blur that sets the subject off the way you prefer.

The way the background looks is usually just as important as the way the subject itself looks. . Shooting wide, and then cropping to get the framing that you want, really messes with one's ability to precisely control the way the background is rendered. . And the way the background is rendered is of the utmost importance in bird and wildlife imagery


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Tom Reichner wrote in post #19030732
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But the DOF that really matters is not the DOF as it affects the subject itself. It is all about getting the background behind the subject and the out-of-focus surrounding context to look exactly the way you want it to - the exact amount of blur and quality of blur that sets the subject off the way you prefer.

The way the background looks is usually just as important as the way the subject itself looks. . Shooting wide, and then cropping to get the framing that you want, really messes with one's ability to precisely control the way the background is rendered. . And the way the background is rendered is of the utmost importance in bird and wildlife imagery

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That's covered by distance to focused subject.

I have no idea how I came upon this old thread. I must have clicked on something that I usually don't and found my way to the first page of this thread. Most of what I wrote today is redundant, but in fresh words.

CyberDyneSystems wrote in post #18543264
1.7x T-Cons were once quite common. Kenko, Tamron, Tokina, all had them. Nikon still sells theirs. I believe that we are seeing them pop up again in certain areas. Hassleblad has had one for some time, but boy does it cost!

You lose 1.5 stops on the Nikon.

With film cameras that had 1/2EV increments on the mechanically coupled lens aperture control ring, 1.7X teleconvertor was easy to adjust for.
With modern dSLRs what many photographers have set for 1/3EV , going to 1/2EV is not so readily accessible

Furthermore, if you put a 1.7X convertor onto a 400mm f4, you end up with 748mm f/6.8 ...but f/6.8 does not rea;;y exist in a 1/3EV f/stop setting nor a 1/2EV f/stop setting standard position...1/2EV f/6.7 is 'close enough'.