Canon Gets 300mm Creative

[neuroanatomist]

I still have yet to see a soul use an extender out in the field.

I guess you must take pictures in a really small field.

 

[kaihp]

The sweet spot for integrated teleconverters is the 400mm f2.8. With a 1.4 it's close to a 600/f4 and with a 2x it's a 800/f5.6. You get a small lens package, that is light and easly to lug about (compared with the 600/4) and the 400/2.8 has a much closer MFD which some times helps.

The EF 200-400mm is anything but light and easy to lug around. But then I have only rented a 600mm once for a specific event (Red Bull Diving Cup) a couple of years ago.

If I keep using the 200-400 for a period of time, I always get pleasantly surprised at how short, light and handy the EF 300mm f/2.8L feels when I pick it up. And it pairs beautifully with the 2x TC (contrary to most other lenses).

 

[neonlight]

(for example, a 400/2.8 is letting in a lot more light than a 100/2.8 because it has a much larger entrance pupil, but with both lenses set to f/2.8 the exposure will be the same).

But the 400 is collecting light from a narrower field of view. So for a uniform field illumination the f- number works: the 100/2.8 is collecting light over a larger angle.

 

[juststeve]

My original point seems to have been missed. While the lens patent is for 295 mm or so, the optics of the lens are crammed into a length of 184 mm, with the exception of what appears to be the insertable filter. That is very compact. Those hunks of glass still need to be 70 mm or so from the image plane but that is what makes the insertable tele converter possible. It seems to me to make the lens optics that compact will take some special optical trickery, like diffractive optics. If you go to the actual patent you will see other 300/2.8 lens designs which are much more like the EF 300/2.8 ii. The glass in those designs is spread out much more the length of the lens. But an insertable tele converter would not be possible.

 

[neuroanatomist]

But the 400 is collecting light from a narrower field of view. So for a uniform field illumination the f- number works: the 100/2.8 is collecting light over a larger angle.

Yes, that was the point.

 

[neuroanatomist]

My original point seems to have been missed. While the lens patent is for 295 mm or so, the optics of the lens are crammed into a length of 184 mm, with the exception of what appears to be the insertable filter. That is very compact. Those hunks of glass still need to be 70 mm or so from the image plane but that is what makes the insertable tele converter possible. It seems to me to make the lens optics that compact will take some special optical trickery, like diffractive optics. If you go to the actual patent you will see other 300/2.8 lens designs which are much more like the EF 300/2.8 ii. The glass in those designs is spread out much more the length of the lens. But an insertable tele converter would not be possible.

This is the patent diagram aligned with the EF 300/2.8 block diagram at the front element, with the front element diameters matched.



There's about the same amount of glass in the rearward groups (behind the aperture stop). Stronger converging lenses in front of the aperture stop in the patent enable the rearward groups (and the aperture stop itself) to be shifted forward, essentially relocating the empty space that is in front of the aperture in the EF 300/2.8 II to the back. That, combined with the extra space because the patented design is longer (and remember that the flange distance is 24 mm shorter with RF), allow room for the TC elements to drop in. No special optical trickery required.

 

[Canis Lupus]

I would rather see an RF 500 or 600 f4 with inbuilt extender, as the Nikon Nikkor Z 600mm f/4 TC VR S. Canon should have had this a long time ago, and one reason I would have choosen Nikon today, if I had started at scratch. To just flip in and out the tc is very different from changing a separate TC in field. I guess the quality could gain some steps too.

​

 

[juststeve]

Neuro, great you matched the front element diameters. Had that thought but too many other things on the agenda. To my eye there is more curvature to the EF lens front cell, but there is one more element, 8 vs. 7, in the patent lens. The section behind the diaphragm is interesting with more, 10 vs 8, elements but thinner, lighter looking elements. Also, seems to be less curvature to the patent lens elements. And, lastly, my estimate of distance of filter to image plane is a wee bit over 37 mm, which I believe is enough to allow use of the present tele converters.

 

[Richard CR]

Neuro, great you matched the front element diameters. Had that thought but too many other things on the agenda. To my eye there is more curvature to the EF lens front cell, but there is one more element, 8 vs. 7, in the patent lens. The section behind the diaphragm is interesting with more, 10 vs 8, elements but thinner, lighter looking elements. Also, seems to be less curvature to the patent lens elements. And, lastly, my estimate of distance of filter to image plane is a wee bit over 37 mm, which I believe is enough to allow use of the present tele converters.

you can't take the embodiment diagrams to that level of scale. They are only there to show the rough approximation.