Canon 100-400 IS and TCs

[John Sheehy]

There have been a lot of discussions that mentioned the 100-400 IS, and how sharp or soft it is, depending on who you ask.  The discussion of TCs used with it gets even more complex, as some people compare it at the pixel level to a shot without the TC; perhaps some people aren't achieving focus because the lens isn't designed to focus that critically, or are using taped or less-pinned TCs for AF.  Maybe the lenses vary from copy to copy quite a bit.

Here is mine, TC'ed to a virtual max.

Quoted from the pbase notes:

100% crop of a pepsi can taken at ISO 1600, under-exposed by about 1 stop, on a Canon 20D, with a 100-400 IS zoom at 400mm with 2 Kenko Pro 300 1.4x TCs plus a Tamron SP 2x TC stacked, for focal length of about 1600mm (probably really about 1400-1500mm, with all the exaggeration typical in TCs and lenses). Hand-held, 1/400s, f/32 (one stop down from the maximum f/22 with this combo).

Converted in ACR, sharpening default 25%, USM applied to top half of crop in PS - 250%, 0.8px, thrshld 7.

Here's the image:



Is this as good, better, or worse than what you'd expect from your copy with 4x magnification?

Do you think that shooting without a TC and using 400% resampling could achieve this?  I don't even think the AA filter could allow that, with *any* lens.

[Ray]

John,
It looks impressive, but unless you post another crop from an image of the same general scene without teleconverters, at say f11 and 1/1600th sec, we can't be sure can we?  

[John Sheehy]

John,
It looks impressive, but unless you post another crop from an image of the same general scene without teleconverters, at say f11 and 1/1600th sec, we can't be sure can we? 
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I never take my first TC off of the camera in the field, unless I'm switching to a wide-angle for evening scenics or night shooting.  Don't need the dust.

I'm not a big fan of such comparisons, because it is impossible to achieve exactly the same focus in all shots.  The idea here is that this is the best that the system is capable of.  I was just fooling around at the end of the beach, because after my long walk over gravel and kelp, there were no birds.  I just took a few shots that I would normally delete on the scene, but I zoomed in and noticed that this shot was especially sharp and stable for the combo.  All the shots with less TCs of the same subject were softer, due to wind or tremors or poor focus.

It is mathematically and technologically impossible for a shot taken without the TCs, to be this sharp (relatively, of course) with 400% resampling.  Even a sharp B&W graphic with 100% pixel-to-pixel contrast will be much softer resampled to 400%.  Even downsampled to 50%, this image is about as sharp at the pixel level as you usually see, which means that the lens itself is outresolving the sensor/AA system by at least a factor of two.

The point I am really trying to make is that the lens is a bit sharper than people make it out to be.  Perhaps there are a lot of bad copies; perhaps a lens is sharp but focus is not being achieved.  And, of course, the lens is a little slow by itself, so you can run out of light easily and wind up using it wide open.  To me, the bigger issue with this lens and TCs is not sharpness, but bokeh.  The bokeh becomes more donut-like and brighter at the edges, the more TCs you put on it., especially wide-open.  Some shots need some blur of the OOF areas to have relaxed-looking backgrounds.

[Ray]

More amazing to me is that you could take a hand-held shot with all those TCs and the 20D crop factor, at just 1/400th sec. A 400th is my minimum shutter speed for a tack sharp hand-held shot at 400mm (effectively 640mm) using IS and my 20D.

[Ray]

I see I made a slight slip of the mind. That should be a 640mm equivalent with a 400mm lens on a 20D.

John, so you used two 1.4x converters plus a 2x converter pluse a 1.6x sensor converter on a 400mm lens? By my calculation that gives you the equivalent of a 2560mm focal length in 35mm terms. And the above image was a hand-held shot?

Even the 1/FL shutter speed guidline for an 8x12' print would be 1/2500th sec exposure. Take into consideration the 2 stop advantage of IS and that brings you to a minimum of 1/600th. But the 1/FL rule tends to break down for long telephotos and extreme wide-angle lenses. You can't expect to get a sharp image with a 24mm IS lens using 1/6th sec exposure, and I suspect you wouldn't normally get a sharp image using a 2500mm lens at 1/600th sec.

Have you been practising Yoga breathing exercises?  

[John Sheehy]

More amazing to me is that you could take a hand-held shot with all those TCs and the 20D crop factor, at just 1/400th sec. A 400th is my minimum shutter speed for a tack sharp hand-held shot at 400mm (effectively 560mm) using IS and my 20D.
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640mm effectively, don't you mean?

Well, I don't always achieve that.  That's one reason I often take a lot of shots, even of a static subject in marginal lighting; I may need 1/640 or 1/800 to achieve it more consistently.  I bought the 17-55/2.8 IS for my 20D and was hoping to get shots at 1/2s and 1/3s at 17mm, and to my surprise, I can get them sometimes at 55mm, too, tack sharp.  At other times, I get (non-subject) blur at 1/5 at the 17mm end.

[John Sheehy]

I see I made a slight slip of the mind. That should be a 640mm equivalent with a 400mm lens on a 20D.

John, so you used two 1.4x converters plus a 2x converter pluse a 1.6x sensor converter on a 400mm lens? By my calculation that gives you the equivalent of a 2560mm focal length in 35mm terms. And the above image was a hand-held shot?

Yes.

Even the 1/FL shutter speed guidline for an 8x12' print would be 1/2500th sec exposure. Take into consideration the 2 stop advantage of IS and that brings you to a minimum of 1/600th. But the 1/FL rule tends to break down for long telephotos and extreme wide-angle lenses.

I don't know about that; I think it depends on how you hold the camera.  For a telephoto, I hold the camera in the grip with my right hand, and by the focus ring and the body next to the focus ring cradled in the left hand.  At that magnification, you are forced to learn to steady the lens for the sake of your own immediate view, a feedback you do not get with WA lenses, as they look steady no matter how much you shake when holding them.  Now, if you held the long telephoto th same way you hold a small lens, it will easily shake as it pivots from one end in your hands, and you can never get the control you would get holding the lens with one hand near the end.

For WA, I don't see the rule breaking down, except if your shooting something close.  The "rule" is really about a subject at or close to infinity.  Close subjects need faster shutter speeds, as magnification is the real reason for necessary shutter speeds; it just so happens that at infinity magnification is proportional to FL.

You can't expect to get a sharp image with a 24mm IS lens using 1/6th sec exposure,

Why not?

and I suspect you wouldn't normally get a sharp image using a 2500mm lens at 1/600th sec.

1/640 is more reliable than 400, but 800 is the guarantor, IMO.

Have you been practising Yoga breathing exercises? 
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No, but I did consciously relax for the shot, something that is harder to do when shooting flitting little birds.

[Ray]

Why not?

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I don't know. That's the way it seems to be. (And I'm not sufferening from Parkinson's).

The Canon 24-105 IS, a later generation of IS technology, is supposed to provide a 3 stop advantage. Using the 1/FL guide, I figured I should be able get a reasonably sharp result at 1/3rd sec at 24mm. Not so. Even 1/13th is a bit dicey, which is just a one stop advantage from the IS. A 13th sec at 100mm (a 3 stop advantage from IS) is just as dicey.

[spidermike]

At that magnification, you are forced to learn to steady the lens for the sake of your own immediate view, a feedback you do not get with WA lenses, as they look steady no matter how much you shake when holding them. 

That reminds me of documentaries about micro surgeons who seem to be able to stitch together nerve cells without special gear to hold the forceps and needles (even though they are available). Becuase of the magnifications they work at they apparently learn to hold their hands more steady than would generally be expected.