Choice of first lens for bird photography

[parthas]

With a cropped sensor mirrorless camera from canon R series, if I have to choose between canon RF 100-400mm f/5.6-8 IS USM and canon RF 600mm f/11 IS STM as my first lense for bird photography, which lense should I choose and why so?

[Tronhard]

Hi and welcome to the forum:
Much depends on your budget, since the 100-500 is an L lens with an appropriate price tag, while the 600mm is fixed FL, and not an L lens.  Obviously, the latter is not a zoom so you don't have that benefit, but the optics of the 100-500 speak to the cost - they are fabulous.  The stabilization is superior, the lens is much faster and give you more choices for control of DoF.  It is heavier but that is for the quality of the build, which is also weather resistant, which the 600 is not.
Frankly, they are chalk and cheese, so the main reason someone would be likely to compare them is for the price benefit of the 600mm.

[jrhoffman75]

OP is comparing the non-L 100-400mm lens with the 600mm lens.

The zoom maxes at 400mm with f/8 aperture; only one stop faster than the 600mm lens.

If max FL is the goal I would recommend the 600mm. Perhaps a little more noise, but less cropping necessary for same resulting size of subject - more pixels per pigeon. Most current noise reduction tools do a great job.

However, as you (Trevor) stated - if less than 400mm or 600mm is required then only the zoom fits that need.

[kvbarkley]

I am going to through a curve in here and suggest one of the Tamron or Sigma 150-600's. Zooms are nice to have for this, so this will cover all the focal lengths you want and go out to 600mm.

[kvbarkley]

I should point out that the disadvantage of this method is the fact that you need the EF to RF adapter.

Another curve is the new RF 200 to 800 zoom for about $2000.

[shadowsports · Accepted solution]

The guys have all made great points.  Think about how you will use your camera most.  Are you going to sit somewhere stationary or be walking around?  If you will be walking around, I'd suggest the RF 100-400.  If you plan to sit with a tripod, the RF 600. (between these two)

[John_SD]

"Are you going to sit somewhere stationary or be walking around?  If you will be walking around, I'd suggest the RF 100-400."

I agree. I believe this is the correct answer, particularly as it relates to a 600mm lens. Personally, I am just not cut out for sitting hours and hours or days on end waiting for an interesting bird to photograph. However, I greatly admire the superb photos these people produce. I am more of a walk-around guy and take my shots of pelicans and such at the coast. Even a crappy kit lens, such as my 24-105mm F4-7.1 IS STM, can be usable for larger birds. 

[Tronhard]

Oops!  I swear I read 100-500...  

As always, much depends on budget, shooting conditions and intended output.  Add to that the weight factor and there are always pro's and con's to be considered..

Given the OP is using a crop sensor camera, it makes sense to see the performance of the lenses in their equivalent values for FoV and Aperture, as these are significant.  To get those, one multiplies the FL and aperture by 1.6, so the lenses will capture significantly different FoV and be quite a bit darker.   Like @KVBarkley, I think the Sigma 150-600c deserves to be considered, both for its FL and its relatively fast apertures.

Lens                                     Equivalent FL              Equivalent Aperture
100-400 f/5.6 - 8                   160 - 640 mm                    f/9 - 12.8
600mm f/11                            960 mm                            f/17.6
Sigma 150-600 f/5 - 6.3        240-960 mm                     f/8 - 10

For birds, which I shoot a lot of in NZ, I would definitely go for the Sigma (or the Tamron Equivalent) for the flexibility of being able to change the FoV, and it is the best performer in terms of aperture.   Yes, one needs an adapter, but the lens works fine if one is careful about settings with the R7 in particular: turn off lens image stabilization if it on a tripod, use spot focus and animal eye tracking, and don't use high speed electronic shutter.
I have posted examples of images of birds, taken with the Sigma Here on the R5 with Gannets and Here with the R6.   I have had no issues with the R5, R6 and R6MkII so far.

That said, the Sigma is going to be the heaviest, so that has to be taken into account. I'm 71 and I have no issue carrying the lens with my bodies and battery grips for extended periods - but I do weights to make sure I can.

[parthas]

Will cropped sensor affect the aperture? I read somewhere that cropped sensor only changes the effective focus length.

[Tronhard]

Read this article - What is equivalence and why should I care Digital Photography Review and the following video, although references about changes in focal length are incorrect.  The focal length of a lens does not change, the Field of View does  Also see my article on the subject:   Equivalence