Up until a few years ago, the idea of an 800mm lens fixed at f/11 would never have been considered a possibility. This is because DSLRs simply won’t work with a lens at a minimum f/11 aperture as it can’t let enough light into the AF sensor for the AF to function properly.
In fact, only the top-end DSLRs like the Canon EOS-1D Mark III will autofocus at f/8 - but, for example, if you’re using a Canon EF 100-400mm at f/5.6 with a 2x extender, so are shooting at f/11, the AF won’t work.
But thanks to the more advanced AF in the latest Canon EOS R system mirrorless cameras, and their Electronic Viewfinder which brightens your view of scenes you’re shooting even at narrow apertures, an f/11 fixed aperture lens will focus and work just fine!
This has enabled Canon to make the RF 600mm and 800mm F11 IS STM super telephoto prime lenses offering you double the reach at half the price!
It’s this narrow f/11 aperture that’s enabled Canon to make these lenses smaller, lighter and cheaper – and the relatively compact RF 800mm is impressively light and easy to shoot handheld, without any worries about arm ache usable associated with using such long lenses.
The Canon RF 800mm f/11 IS STM weighs only 1260g and is 352mm when fully extended, and only 282mm when stowed.
An 800mm prime might seem unwieldy, at double the reach most of us have experienced, plus without any way to zoom out, but you soon get used to what distance to set up to frame up your chosen subject. Just bear in mind that the closest focusing distance is 6 metres!
Having an 800mm super-duper telephoto lightweight lens started as a very exciting proposition, I pictured myself taking amazing frame-filling shots of distant wildlife with ease!
However, while the RF 800mm offers some attractive advantages, there are also some distinct disadvantages when you start using the lens in different scenarios.
With both the RF 600mm and 800mm lenses, only the central area of the screen is usable for AF so you have to make sure your subject is central in the frame. This is okay, though, as you can crop your images later to position subjects to one side of the frame for a better composition.
Also, when a lens is fixed at only f/11, note AF won’t be as fast or responsive as a lens at f/5.6 or f/2.8, as f/11 is 2-stops ‘darker’ than f/5.6, and 4-stops ‘darker’ than f/2.8.
I also wouldn’t normally choose to shoot at f/11 when using a telephoto for wildlife or sports, as I want to blur the background and would usually shoot wide open around f/5.6, f/4 or even f/2.8 at around 400mm.
However, using an R6 at f/11 at 800mm is a unique proposition, and f/11 at 800mm is fine for blurring backgrounds – as long as your subject has a clean backdrop without close distractions in the frame behind it - eg a bird on a fence post with a hedge or grass 50 yards away.
But a bird in a tree with branches around, or squirrel on a forest floor, then the backgrounds look very messy and not blurred enough at f/11 compared to if you were using a wider aperture.
Then there’s the impact f/11 has on your shutter speeds. Remember that f/11 is 2-stops slower than f/5.6, and a full 4-stops slower than f/2.8. This means the resulting slower shutter speeds shooting at f/11 is a big issue if you’re not shooting in bright sunshine.
You don’t need to worry about requiring a shutter speed of 1/800 sec or faster for the 800mm focal length, thanks to the lens IS, and IBIS in latest EOS cameras which overcomes camera shake issues.
But light levels will restrict what you can shoot with the RF 800mm at f/11. For example, in sunshine at f/11 and ISO3200 on the R6, we had a lovely super-fast shutter speed of 1/4000 sec - ideal for freezing the even the most skittish little birds.
However, when we were using the RF 800mm and shooting on darker winter days, or in low-light inside darker forests, things went slowly pear-shaped. The RF 800mm forces you to whack up the ISO in an attempt to get faster shutter speeds.
But even shooting at ISO6400, I was only getting shutter speeds averaging between 1/50 sec and 1/100 sec in daylight in the woods, which weren't fast enough to freeze the birds and squirrels I'd set out to photograph!
Fixed at f/11, I frustratingly stuck trying to shoot at 1/40 sec. If I had an aperture of f/5.6 available, I would be shooting at 1/160 sec, or this would increase to a far more manageable 1/320 on an f/4 telephoto lens, or even faster at 1/640 sec on a top-pro f/2.8 lens.
I resorted to an ugly ISO of 12800 just to shoot at 1/160 sec. You can get away with higher ISOs of 3200 and 6400 on cameras like the R6 without horrendous noise, but resorting to ISO12800 is when you start seeing a noticeable loss in image quality.
But what about the fancy in-camera IBIS and lens IS, can we just use that to get sharp shots of everything? Well, although both lenses have IS with the RF 800mm producing 4-stops of IS, and the RF 600mm offering 5-stops IS – and the IS on the lenses also works with IBIS on the R5 and R6 – stablization only helps if you’re shooting static subjects.
Stabilization will overcome slower shutter speeds and still allow you to shoot handheld to beat any camera shake stuff, but it’s no use whatsoever when – as well be most cases with these RF lenses - you’re looking to shoot quick wildlife or action sports, when only faster shutter speeds will capture sharp shots.
So, the RF 800mm isn’t without its limitations. However, I’m pleased to say I did find the perfect subject for a mega 800mm telephoto focal length at f/11! The RF 800mm is almost purpose built for the bigger, brighter, faraway moon!
At night I could comfortably shoot at f/11 - the aperture I would choose anyway for the moon - and for the brightly-lit moon I could achieve 1/250sec at only ISO800! If you didn’t know, you need a shutter speed of 1/250 or faster for sharp moon shots, because both the moon and earth are rotating.
The detail in the moon’s craters was incredible, and I captured some of my best-ever moon photos. The above image is only very slightly cropped in too.