Lens Magnification Question

[MilesP]

Hello, I'm choosing between RF 100-400 and RF 100-500 L lenses. I am somewhat confused about something.

If I set both lenses to 400mm and take a photograph of a bird say at the same distance, the size of the bird on the final image files should be the same for both.

However, the specs say that the magnification factor for the 100-400 is greater (.41 vs .33). What relevance is this to the image I get out at the end? Is it purely what I see in the image finder when I take the photograph?

[MikeSowsun · Accepted solution]

Maximum magnification is a result of both focal length and focus distance.

The RF 100-400 has a max magnification of .41x, but only at 400mm and at a focus distance of 34.65”.                       The RF 100-500 has a max magnification of .33x, but only at 500mm and at a focus distance of 35.43”.

When both lenses are set to 400mm, and both lenses are at the same focus distance, the magnification should be roughly equal. Both in the viewfinder and in the final image.

In reality there will be some sight differences because not all stated focal lengths are exact, and there can be differences at different focus distances. (ie: focus breathing)

[kvbarkley]

Its relevance is strictly to "macro" operation. The maximum size you can get on the sensor when you have things set to, uh, get the maximum size on the sensor.. As pointed out by Mike, this has more to do with minimum focus distance.

[MilesP]

OK, thanks Mike & KV, I guess for my purposes the magnification is not really relevant. I won't be doing macro photography, mostly long distance wildlife shots. I was a bit concerned that there would be no point buying a very expensive lens if the final image at 500 was smaller than the  much cheaper 400.

However that said, I am hoping that Canon will be bringing out a 100-400 or 100-500 RF-S mount lens to go with a RF 7 camera. These should be much lighter hopefully.

[JoeySnaps]

The R7 camera is a great camera. But it's unlikely that Canon will release an RF-S lens of 100-400 or 100-500mm focal length that'll be smaller and lighter than the existing RF 100-400 lens, which is very small and very light for such a long focal length lens. It's also a very high quality lens optically and fantastically good value. It makes a brilliant match to the R7 camera, the 1.6x crop sensor increases the reach of the lens. And it's compatible with extenders, if you need even more reach.

I think it's unlikely Canon will release a long telephoto RF-S lens, they never made a long telephoto EF-S lens.

[MilesP]

Thanks Joey, Yes I fear you are probably right on this. As an owner at various times of three EF L series long lenses (2 prime and 1 zoom), I was always waiting for an EF-S L series long lens to go with my EOS 70D. It always struck me that I was carrying extra weight as only the centre bit of the lens is used on a 1.6 crop camera (I think I am correct on that). Maybe Canon think that most people with long lenses use full frame cameras.

On the specific two lenses in question, as I am used to L series, I don't think the RF 100-400 would be good enough in low light conditions for bird photography. The RF 100-500 L series would be, but is a lot heavier than my current lenses (EF 100-300 L and EF 300 L series prime with 1.4x extender). Perhaps Canon will bring out an RF 100-400 L series in the near future.

I was considering an upgrade to an EOS 90D camera which seems like a great camera, but then came across the mirrorless cameras, which seem to be the way things are going - hence looking at an R7. Maybe in the short term, I will look at an R7 with a RF-EF lens converter to use my existing lenses. Not sure what impact that would have on quality though with a converter and 1.4x extender on the 300mm prime.

[JoeySnaps]

The converter won't affect the quality of your images at all, the EF-RF converter does not have any optical elements, it's just a spacer with electrical connections to pass through the lens control and information. Your 1.4x extender will have exactly the same effect on image quality as it does when used with your current camera.

EF-S lenses and RF-S lenses are designed to project a smaller image circle than full frame lenses - they have to make a high quality image on a smaller sensor. To that end a few of the elements in the lens, typically those towards the back of the lens, can be smaller. But the size of the other elements is determined by the focal length and maximum aperture of the lens and these parameters are the same whether the lens is designed for full frame or cropped sensors.

In the DSLR world, cropped sensor cameras have a smaller reflex mirror than full frame cameras. It is therefore possible to design lenses with rear elements that protrude into the lens throat without the protrusion fouling the reflex mirror swing. This is advantageous for short focal length designs, enabling smaller, lighter, compact designs with high optical quality. Long focal length lenses don't need elements close to the sensor, so telephoto designs specifically for cropped sensor cameras are unnecessary.

The only reason that I can see for developing RF-S lenses is to take advantage of the smaller image circle to design lenses to suit - because there is no mirror box and lens elements can be as close as necessary to the sensor, whether full frame or cropped.

As to whether the RF 100-400mm f/5.6-8 lens will be good enough for bird photography in low light, this is an issue that many agonise over. However, remember that the 100-500mm f/4.5-7.1 L lens is only half a stop brighter. And what I have found is that the latest generation of sensors and in-camera image processing, in such cameras as the R7, is so good that you can get good images at very high ISO settings, and this combined with the excellent image stabilisation means that you can get decent results in dim light and small apertures. Canon have a pair of long telephotos with f/11 aperture, and some photographers have expressed the view that they're useless, others, including me, have bought one, tried it, and found it capable of fantastic results.

[FloridaDrafter]

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@MilesP wrote:

"On the specific two lenses in question, as I am used to L series, I don't think the RF 100-400 would be good enough in low light conditions for bird photography. The RF 100-500 L series would be, but is a lot heavier than my current lenses..."

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We shoot mostly birds, but also insects and flowers. Our subjects are usually in low brush under tree canopy or in the canopy, so basically very shady and when I say low light, that is what I am referring to. The RF 100-400mm does an amazing job in these conditions. Granted, we have it paired with the FF R6 and R6 mark II, and these cameras handle lower light, along with higher ISO's, extremely well. I can only assume the R7 would as well, but seeing as it is a cropper, it may not be as good at higher ISO and low light as it's big brothers. I also use the RF 100-500mm L on these two cameras, but it spends more time on the R5. I am also an L glass fan and have always used L glass, even on my Rebels. L-EF-S glass has never been on my wish list because I just never have put much stock in the 1.6 crop factor, not that I don't understand it as it has some advantages, just that I knew what to expect and just paid it no mind... It is what it is, so to speak, and as long as you get the results you want, there just isn't any reason to consider it. OK, enough rambling 🙂

To summarize: Although I use L, and I have a pile of it, my wife uses the RF 100-400 on her R6 mark II, it will hold its own in our low light situations. It's quite sharp wide open (f/8), but if you bump up ISO, you can get up in the f/11-f/16 range where it is extremely sharp. I have found that DOF isn't a problem at f/8 for most birds past 20 feet and all is in acceptable focus, from beak to tail. In the low light I have described, this lens focuses extremely fast, even with eye detect enabled, however we usually use the fine focus point (no servo). I just can't say enough about this entry level lens.

As for the RF 100-500mm L, it is probably the best super zoom that I have ever used. It is so versatile that I often use it for near macro work when shooting insects and flowers because it will focus so closely, just like the RF 100-400mm. It is a bit heavy, but not as heavy as the EF 100-400mm L II that I used on my previous cameras, like the 7D2 and 5D4. I did adapt the EF 100-400 L II when I first got the R5, but that didn't last long.

Anyway, I hope this helps. But I would seriously consider full frame for birds. I really upped my bird game going FF, but I do favor higher res (more MP) cameras like the 5D4 and R5.

EOS R6, RF 100-400mm, f/8, 1/400th, ISO 1600, at 20'.

Early Morning Light - RF 100-400.

EOS R6, RF 100-400mm, f/8, 1/500th, ISO 1000, at 40'.

Early Morning Light - RF 100-400.

EOS R6, RF 100-400mm, f/8, 1/400, ISO 1400, at 40'.

Under Heavy Canopy and Overcast Sky - RF 100-400.

EOS R5, RF 100-500mm L, f/8, 1/500th, ISO 1250, at 10'.

EOS R5 - RF 100-500mm L Under Canopy and Overcast.

Newton

[MilesP]

Wow, a lot of good points here Whiz.

From what you say, it sounds like the RF 100-400 is a really good lens, even in low light if you use higher ISO. That is something I have never really considered because of the noise, but maybe cameras have improved a lot since the days of my EOS 70D. Must up my camera skills I think.

However, I have decided to go for the RF 100-500 L. I was concerned about the weight, but when I re-calculated, it turns out the RF 100-500 L + R7 is actually a bit lighter than my current setup of EOS 70D + Battery grip and 2 batteries + EOS 70-300 L or EOS 300 L + extender. I have been using these for years without considering it too heavy. I did find my old EOS F2.8 L 300mm far too heavy, so I sold it, despite being a fantastic lens. 500mm was always my target length, but with the EOS lenses, they were far too heavy to consider.

The only question now is cropped or full-frame. I have always used a 1.6 crop so am used to that. I have always thought, without any personal evidence that a 1.6 crop would give me sharper and larger images because of the extra reach. Maybe using a good full-frame gives a better picture than a 1.6 crop even though you have to crop closer with the full-frame to get the same size bird. 

Must do some more research on that. Price may be a factor though. Some great points to consider though.

[JoeySnaps]

Just a couple of small points to add to what's already been said:

Newton's photos are fantastic!

Using a full frame lens on a crop sensor camera, you're only using the middle bit of the image circle that the lens projects onto the sensor, but you're using all of the lens, not just the middle bit. The diameter of most of the optical elements in a lens is determined by the focal length and maximum aperture of the lens, only the rearmost elements can be smaller when it's designed for a crop sensor camera.

The EF-RF converter won't affect image quality at all, your existing EF lenses will perform just as well on your new R series camera as they did on your DSLR. Any image quality difference will be down to the new sensor. Sensor design has come on leaps and bounds, especially as regards low light performance.

You will usually get better results using a crop sensor camera than you would using a full frame sensor camera and cropping the image to 1.6x to get the same field of view as you would have done if you'd taken the picture with a crop sensor camera. To give an example: the EOS R7 has a 32.5 megapixel sensor, and the older EOS R has a 30 megapixel sensor, fairly similar. But if you crop the image from an EOS R to 1.6x your resultant image will be only 12 megapixels. You've thrown away more than half of the pixels from your original image. The result won't look as good as your R7 32.5 megapixel image.

It's only worth comparing full frame to crop sensor cameras if you DON'T crop the full frame image. Then the larger pixel size and improved low light performance and dynamic range of the larger sensor show benefits. But to get the same reach you'll need longer focal length lenses.

The RF 100-500mm lens is a fantastic lens, but I hope you have deep pockets - it's not cheap. It'll be a very big leap from your EF 100-300L lens.