Working distance with Macro and TC 1.4

I'm going to get a macro lens in the near future, and have a couple of questions. I tried searching different forums, and couldn't find an answer. If I add a 1.4x TC to a Macro lens, what does that do to the working distance. I.E. does it extend the working distance by 1.4x for the same magnification, or just increase the magnification. Also what is the working distance on a 1.6 crop camera. I'm assuming the reported WD for a macro is on a FF, or 35mm camera, so is the WD to go to 1:1 already longer on a 1.6 crop camera? Thanks for your help

Working distance has nothing to do with the camera or sensor size, it's all dependent on the lens itself. Having used Canon TCs I know that they do not change the minimum close focus distance nor do they change the focus point. That is, if I focus on something with my lens, then insert the TC, I will still be focused on that point. The TC just magnifies by 140%. I would imagine that's the same with other brands of TCs.

In a sense, though, a TC will decrease the working distance... A lens's reported close focus distance is measured from the sensor. You'd have to subtract the length of the lens and the hood to get what I would consider the working distance, which I consider to be from the front edge of the hood to the focus point. Since a TC has length it pushes out the lens and hood, thus reducing the working distance by an inch or whatever.

Kind of what I was thinking, Thanks for the confirmation

Well guys, it's not quite that easy. The killer combo is the Canon 180mm macro f/3.5L lens and TC. It is the only Canon macro that accepts Canon TC. The normal close focus of this lens is 25cm from lens front, or 48cm from sensor plane. With the Canon 1.4xTC in place:

1. Yes, the max magnification is 1.4x, or 140% life size at the lens' close focus limit. Thus, you can back off and achieve 1x reproduction at distances slightly farther than the close focus limit. Good for bugs and snakes.

2. You do lose auto focus below 0.8 meter, because in effect the f/3.5 lens with TC becomes an f/5.0. We manually focus most times, but with a TC, you will manual focus ALL the time at close and farther distances. I do not know behavior of Sigma 150mm and Sigma TC or Tamron, but I imagine they are similar.

2. The real challenge is the EFFECTIVE f/stop from light loss. When you are close-focused you lose 2 f/stops of light. [Less with new generation of internal floating element macro lenses like the Canon 180 and 100mm, like 1 1/3 stops, but lets not split hair.]
So, when using an f/2.8 macro lens with a 1.4x TC, the lens is now an effective f/4 lens. If you are at close focus, that lens is an f/8! It's dark in there. So, bring plenty of flash power and supplemental light to use a macro with a TC! I always carry a small flashlight and sometimes use it to aid focusing.

Have fun. Jack

I don't understand either of your #2 statements, Jack. Why do you lose 2 stops of light when you are close focused? I've never noticed any difference on my macro lens when focusing and then getting closer...

Jack's first #2 statement must be assuming a camera that loses AF before f/5.6. Any of the Canon DSLRs should maintain AF through a reported f/5.6 (or better in the case of the 1D series).
Statement #2 #2, well, if you're computing exposure based on an external meter, your actual aperture at 1:1 is 2 stop worse than it is at "normal" focussing distances. For normal work, lens extension doesn't affect aperture values markedly, but at close-up distances the extra extension has to be allowed for. The effective aperture calculation for a lens is aperture=i/(entry pupil); where 1/f=1/i +1/o and i= lens-image distance, o = lens-object distance, f = focal length.The marked aperture is just a special case where f = i. At normal ranges, i is very close to f, so the change is negligible. In close, at life size i is twice f, so a 50 mm lens would have an i of 100 mm. With the 20 mm (f/2.5) entry pupil, at life size, 100/20 = 5, so effective aperture is f/5, for a loss of 2 stops (f/2.5-f/3.5-f/5). With internal, TTL, metering you don't need to worry about this, and the change isn't abrupt so you won't generally notice a change in light levels as you move in, but it's happening. That's why at very high magnifications you get a very dark viewing screen. But this won't directly affect AF. It won't cut off unless the lens reports an aperture change as it focusses closer (please! my brain hurts at the feedback circuit that would need!), but it will start to "hunt" as the light falls off.

Scottes - You don't see it but SLR TTL meter does & TC 1.4x

Scottes:
We photographers do lose f/stops at magnification. Camera lens f/stops are designed for infinity focus. As magnification increases [distances get close] the actual aperture (aka, effective f/stop) becomes darker. The classic formula was 2 f/stops at 1x reproduction.

We don't "see" it because camera TTL meter "sees" it for us. What we thus "experience" is f/stop-shutter speed challenges.
E.g., A scene set at f/8 that a TTL camera meters as a normal exposure of 1/200 with a regular lens, is metered as 1/50 with a macro at close focus. You don't "see it" but you "experience it". Can you hold a 100mm lens at 1/50? I can't. We experience it, as lower shutter speed or lower f/stop macro challenges, requiring tripods.

The Canon 180mm macro f/3.5L is an amazing optic. Because it has more than 1 floating element, it only loses 1 1/3 f/stops at 1x reproduction instead of 2 f/stops. That is why macro shooters who know are never concerned that it is f/3.5 instead of f/2.8 lens.
I forgot to put this in my Working Distance STICKY at the top of the lens forum that Moderator CDS put there.
Add this to its extraordinary low diffraction at high f/stops, contrast. It's a great lens for tripod work.

Jon
When you add the Canon 1.4x TC to the Canon 180mm macro lens, you lose auto focus with ALL Canon bodies at distances under 0.8m. It's a known mechanical "feature" of the specific combination and has nothing to do with Series 1 or other bodies autofocus f/stop sensitivity limits. Canon explains this to 180mm macro owners because they know that lens and the 1.4x TC are a beloved combination.

Is all this clear as mud? Sometimes I am not to good at explaining.

A plea to Sigma 150mm Macro Users:
I am curious how the Sigma 150mm macro f/2.8 behaves with a Sigma 1.4 TC. This combo is far cheaper than the $1,600 I have in my Canon 180mm macro and Canon 1.4x TC. On its own that Sigma 150 macro is an EXCELLENT lens, especially for the money. I've used it. I don't like most Sigma "me-too" lenses, but their 150mm macro [and 100-300 and 120-300 lenses] are special.

Jack

Oh, I understood what you were saying, I just didn't understand [I]why[/i.] Jon's math was the answer to that question, and now I understand. Well, I'll understand it tomorrow, since I'm too darned tired right now.