1.7x extender - just me, or would this be a great product?

[kubelik]

so everyone knows by now that Canon has refreshed its telephoto extender lineup with the 1.4x III and the 2.0x III.  they're really great (even without having the chance to use them on the lenses they're really designed for, the series-II super teles) ... but as I mull over a future purchase of either 300 f/2.8 or the 500 f/4 (many years in the future), I started wondering:

the gap between the 1.4x and 2.0x is pretty significant.  if you were to say purchase a 300 f/2.8 with the intent of using extenders to increase its reach, you end up with the following focal lengths: 300, 420, and 600.  the gap between 300 and 420 is pretty minor, but the gap between 420 and 600 is huge.  a 1.7x would bridge that perfectly, giving you the option of also creating a 510mm f/5 lens.

is that just me, or would that be awesome?  I would totally shell out another $500 for a 1.7x extender of the quality of the new series-III extenders, and I'm curious to see if others would as well.

even on the new 70-200, the gap between the 1.4x and 2x is significant.  you're stuck with either a not-so-long 280mm f/4, or a long-ish but slow-ish 400mm f/5.6.  I've found myself shooting a bunch in the mid-300mm range but stuck at a f/5.6 max aperture, which kind of sucked, and probably slowed down AF speed quite a bit as well.  a 1.7x would make the 70-200 into a 120-340mm f/5 lens, which would be great for a number of mid-telephoto applications.

[TexPhoto]

I know the Nikon side of the house loves the 1.7x they have, any many recommend it as the only teleconverter you need.

I have a 400mm f2.8 and both the 1.4X and 2.0X converters (version 2).  I find I almost never use the 1.4X converter.  The gain is not worth the drop in quality.  For me 1.7X might be just the ticket, but would replace my 2X, not add to my collection.

[Mt Spokane Photography]

I use my 7D as a 1.6 extender and that works great.  However, the 5D MK II has better IQ if I have a long enough lens.

My 1D MK III with a 1.4X TC was approx equivalent to a 1.7 extender and worked well that way, so 1.7 is a useful value - if you can autofocus.

I suspect that the drawback is the inability to autofocus when a 1.7 is used with a f/3.5 or  f/4 lens, since that f/4 would be about f/6.8.  This would result in lots of confused and disappointed people who bought it, and then discovered that they needed a f/3.3 lens aperture to autofocus.

The Canon autofocus system is pretty well geared and calculated to work with 1.4 on non pro bodies and f/4 or larger apertures, and with the 2X on pro bodies with f/4 or larger apertures.

[kubelik]

I suspect that the drawback is the inability to autofocus when a 1.7 is used with a f/3.5 or  f/4 lens, since that f/4 would be about f/6.8.  This would result in lots of confused and disappointed people who bought it, and then discovered that they needed a f/3.3 lens aperture to autofocus.

I don't think that's any different than what people face with the 2X extender ... canon and retailers are usually pretty clear that it doesn't work with every lens. 

I know for myself, I'd definitely use a 300 f/2.8 with 1.7x over a 500 f/4.  and, it'd be great for full framers to get an APS-C crop equivalent without having to lug a second body around (although the price of purchase on these teleconverters is pretty much like buying another body)

I know the Nikon side of the house loves the 1.7x they have, any many recommend it as the only teleconverter you need.

I have a 400mm f2.8 and both the 1.4X and 2.0X converters (version 2).  I find I almost never use the 1.4X converter.  The gain is not worth the drop in quality.  For me 1.7X might be just the ticket, but would replace my 2X, not add to my collection.

I didn't realize Nikon offered a 1.7x, but that makes me more hopeful that Canon will come out with one.  if such a large photo company felt like a 1.7x was a good idea ... clearly I'm not alone in wanting something for that niche

[Mt Spokane Photography]

Kalimar did sell a now discontinued 1.7X TC for EOS autofocus lenses.  I don't know if it had a decent quality, but there are occasionally a few on the used market. 

There is one currently available on craigslist in Vancover BC for $30.

http://vancouver.en.craigslist.ca/van/pho/2562227354.html

If you live near Vancover, or if they will mail it to you, it might be interesting to try.  Certainly cheap enough.

I'm very doubtful that you would want it for a 300mm f/2.8 lens except to play with.

[recon photography]

Canon should make 1.6x converter better IQ and it would make full frame lens lengths in crop frame camera lens lengths

[Mt Spokane Photography]

Canon should make 1.6x converter better IQ and it would make full frame lens lengths in crop frame camera lens lengths

I think you are suggesting that a 1.6X TC on a FF camera would give the same or similar field of view as a crop camera. 

However, I'd buy a 1.4X TC that would autofocus with my f/4 lenses rather than a 1.6X that would not. 
Actually, I just bought a crop camera (7D) to use where I need the longer reach with my lenses, and the IQ is better than my 5D MK II with a TC, autofocus works, and is much faster.  You lose a lot when using a TC.

[TexPhoto]

I really can't see using a 1.7X converter and wishing I had a 1.6X.  Kind of a wash at that point and better image quality?  Yes, obviously we'd like better IQ with any of the current and future TCs

And a 5dII +7D Combo vs teleconverters?  Hells yea, I already have that and it's awesome. I think the combo is so much better than owning a single 1D4.  I also do occasionally add the 2X converter to my 400 and the 7D for a 1280mm equivalent:

That 747 is 5 miles away.

[Lawliet]

Using both Canon and Nikon: I actually have  a TC1,7
It is about the least used piece in my collection. 
 
Regarding the spacing: a TC1,4 and TC2 narrow the FOV by the same degree. The jumps in focal length have to be seen as relative changes, not absolutes! Also with the mandatory disabled AF at certain apertures those 1,5stops of loss don't go well with Canons system.
Also keeping in mind how good the TC2III works with the current teles I don't see that much net gain from slightly less magnification, that TC1,7 performs actually worse then a current TC2.

[akiskev]

A theoretical question.
Which combo is better iq-wise?
1. 7D+300mm 2.8L
2. 5DmkII+Extender 2.0X III+300mm 2.8L

We know which is better at AF, but what about image quality? 

[ehud.eshet]

the gap between 300 and 420 is pretty minor, but the gap between 420 and 600 is huge.

Mathematically (and in terms of angle of view) 1.4 * 1.4 = 2.0.
In other words: the gap between 1.0 and 1.4 is identical to the gap between 1.4 and 2.0.

The 2.0x extender only extends the 1.4x extender in 1.4.

[neuroanatomist]

A theoretical question.
Which combo is better iq-wise?
1. 7D+300mm 2.8L
2. 5DmkII+Extender 2.0X III+300mm 2.8L

We know which is better at AF, but what about image quality? 

7D + bare lens would better, theoretically.  Empirically, on TDP you can compare the above scenario with the 200mm f/2L IS (instead of the 300/2.8 ), and the 1DsIII instead of the 5DII.  The 7D + bare 200/2 beats the 1DsIII + 200/2 + 2x III across the frame.  With the 1.4x III, the 1DsIII is slightly better in the center, but loses away from the center. 

[kubelik]

the gap between 300 and 420 is pretty minor, but the gap between 420 and 600 is huge.

Mathematically (and in terms of angle of view) 1.4 * 1.4 = 2.0.
In other words: the gap between 1.0 and 1.4 is identical to the gap between 1.4 and 2.0.

The 2.0x extender only extends the 1.4x extender in 1.4.

I know that's the case from a numerical standpoint.  but when you're shooting in the field, there's a much bigger difference in terms of how you use the lens between 420 and 600 than there is between 300 and 420.  I feel like the mid-200 range up to the low 400 range pretty much gets you very similar types of shots of a very similar range of subject matter.  going up to 500mm or 600mm changes that pretty dramatically, in terms of what you can shoot and how you shoot it.

[TexPhoto]

I was talking to a photgrapher once who told me he had a 28-70 Lens, and an 80-200, both pro quality.  I asked if he was going to aquire other lenses and he said he was pretty happy with what he had, exept for that gap between 70 and 80.  I thought I'd heard him wrong, but he insisted, that is where the weakness in his lens collection was.  And even said, "what if I need a 75mm?"  I said what if you needed a 14mm or an 800?  He said "what for?"

Anyway I realized at that point that people have different ideas about these things.  I tend to be a broad stroke person, and some people are really detail oriented.