[Brightcolours]

Yes, Dave, I would have to try before I buy!


As an aside, I believe that the 20MP (full frame) camera is not diffraction limited until about f/13, so for that camera, if I am right, it would not be absurd to expect sharpness.  And I was serious that the aperture stopping down can effect sharpness.  

Now about my fantasy...I have used the 70D, and you have been using the D500, both of which are APS-C, though I had to deal with a tougher 1.6x versus your 1.5x.  I used my 70D for Macro quite a bit at f/11 and didn't seem any the worse for it.  I know in theory there should be diffraction, but since it was often necessary for a sufficient DOF I had to use it.  Therefore I am not expecting it to be unusable with a telephoto.

Still, I would, in reality, want to go back to 20mp.  I can always do some shooting at f/11 with the 90D, but now that I think of it...I have been mostly shooting wide open.  If you can call F/5.6 wide, that is!

The truth that is sinking in, is that I am hooked.  I think I might actually want an RF camera!  Maybe not now.  But soon!

-Mac

Clearly diffraction limited past f4 (center sharpness drops). On 21mp.
But as Klaus has pointed out, 600mm will often be atmosphere limited at the usual long distance usage, limiting the impact of diffraction softening (or rather, masking it).

[Arthur Macmillan]

Yes, Dave, I would have to try before I buy!


As an aside, I believe that the 20MP (full frame) camera is not diffraction limited until about f/13, so for that camera, if I am right, it would not be absurd to expect sharpness.  And I was serious that the aperture stopping down can effect sharpness.  

Now about my fantasy...I have used the 70D, and you have been using the D500, both of which are APS-C, though I had to deal with a tougher 1.6x versus your 1.5x.  I used my 70D for Macro quite a bit at f/11 and didn't seem any the worse for it.  I know in theory there should be diffraction, but since it was often necessary for a sufficient DOF I had to use it.  Therefore I am not expecting it to be unusable with a telephoto.

Still, I would, in reality, want to go back to 20mp.  I can always do some shooting at f/11 with the 90D, but now that I think of it...I have been mostly shooting wide open.  If you can call F/5.6 wide, that is!

The truth that is sinking in, is that I am hooked.  I think I might actually want an RF camera!  Maybe not now.  But soon!

-Mac

Clearly diffraction limited past f4 (center sharpness drops). On 21mp.
But as Klaus has pointed out, 600mm will often be atmosphere limited at the usual long distance usage, limiting the impact of diffraction softening (or rather, masking it).

BC- There is a lot of information there.  The second to weakest center performance is wide open.  the best corner and edge performance is at f/5.6, f/8, and f/11.  All I am saying is that I have had very acceptable results shooting at f/11 with a 70D.  Some lenses lenses are better than others in this respect.  But I don't find it impossible to believe that a prime lens could perform well regardless of the fact that the APS-C sensor is diffraction limited because of the small pixels on the sensor.  As I said I don't believe a the full frame 20mp sensor would be effected at all at f/11, and on the 45mp sensor the lens will probably be OK as well...until it is compared to a lens 15x the price.

What remains to be seen is how well these lenses perform.  That probably depends more on build and design quality.  I mean how well does Canon want a cheap lens to perform? 

The funny thing is I think the lens design is more important than the DLA.  I have done macros with the 6MP Canon D60 DSLR.  Even then, f/11 seemed to be the point at which the image is still acceptable, and f/16 starts being a little soft.  I haven't seen the situation change all the way through the 20mp 70D.  For macros f/11 was the best for me.  I haven't done much or any macro with the 90D, because I am shooting birds these days.  But it will happen...I admit I expect to see things change.  But who knows?

-Mac

---

Dave, Sorry I was slow on the uptake.

I do understand the resistance to the growing size of lenses. But the irony here is that while traditionally small lenses keep getting larger, there are a lot of super telephoto options that are getting smaller. All of Canon's Mark iii supers are significantly lighter. The 600 and 800 F/11s and the even the 200mm zoom lens which now extends.

I did not find the bokeh so bad at first because I was admiring the bird itself, and remembering your advice to get as low as possible for such shots. Then you may not have a bokeh problem at all, and you are still getting a beautiful bird and maybe a blurred background. The photo actually made me want to see what the lens could do. The RF L lenses seem to be at a very high level. Hell, just crop the picture, apply a little Gaussian Blur selectively if it still bothers you.

But, like I said, I do think maybe I missed the point of the original post. It seems the Canon takes a lot of hits around here sometimes. It makes me oversensitive.

I became intensly interested in lenses because in the early days D60 (not 60D), 300D, 400D things were changeing fast. The price of a lens did not always corrospond to its abilities. I've always wanted a cheap lens that can perform, and wondered if an L lens was really as superior as they say. And more recently the question has included does a lens have to be the size of a house to be any good. I have several L lenses now. I like them. But so far have avoided replacing traditionally smaller lenses for huge ones.

I guess until I take the "brick plunge" I won't know for sure! No bricks here!

-Mac

[Klaus]

The RF 600/800 will be perfectly fine on the R6. On the R you may spot some softness. More so on the R5. So it all depends.
The RF 600/800 are not targeting high-end users anyway. These are just "affordable" (non-L) options - surely meant to lure away users from APS-C/MFT.
Most will also use these lenses without a tripod at ISO 800+ and combined with air diffusion diffraction may be the least of your issues then.

This is also a lesson from the Leica 100-400mm. At 400mm f/6.3 (aka 800mm f/12.6) you are already beyond the verge of what can be used handheld in an "enjoyable" way.
I wouldn't really recommend the RF 800mm unless you already know what you are up to (and the RF 600 is also attractive due to its more efficient IS).

[davidmanze]

-Mac

Dave, Sorry I was slow on the uptake.



Let's forget bricks

  Rent before you've spent is my recommendation! ........ new lenses .... new bodies ...... you're looking at around three grand ..... and you've already spent out on the 90D ..... that way for the cost of a weeks hire you can see if it works out for you .....

..... advice is cheap ..... cameras and lenses aren't!