EF 300mm f/4 L IS USM vs RF 100-400mm on R7

[cadde]

I have an EF 300mm f/4 that I haven't used a lot, partly because I got busy with other things and wasn't using my camera that much at the time, and partly because I realized it didn't have the reach I needed for one of my main interests (wildlife/birds). I wound up finding a good deal on a sigma 150-600 and got that, and the 300 has just sat in the closet.

A couple of weeks ago I bought an R7 (body only) to replace my t7i with the intent of just using my EF/EFS lenses on it , but so far the eye tracking with the EF lenses isn't as good as I'd hoped, though I haven't had time to get out with it much since I got it, so it's been very little testing, but I've been thinking about getting an RF lens and maybe selling the 300mm to fund it.

I got a usb dock for the sigma to try some settings that are supposed to help with eye tracking on it, and I'm going to try out the 300mm on the R7 this weekend, but I was wondering if there's any reason I'd be better off hanging on to the 300mm rather than getting the RF lens?

[p4pictures]

One big advantage of the EF 300mm f/4L IS USM over the excellent RF 100-40mm F5.6-8 IS USM is the faster aperture lets more light in to the camera. AF systems work better when they get more light in my experience and since the AF is carried out while the aperture is fully open that would be  +2-stops more at 300mm for the old EF lens vs the RF 100-400mm. 

I'm surprised you find the eye tracking performance not as expected, as that differs to my own experience. At the moment all my telephoto lenses are EF models, I have EF 70-200mm f/2.8L IS II USM and EF 100-400mm f/4.5-5.6L IS II USM. I have compared them with native RF lenses including the RF 100-400mm F5.6-8 and RF 100-500mm F4.5-7.1 and found no difference in AF tracking or eye detection capability. One other benefit for me of the EF lenses is that I can use a 1.4x Extender Mk III with them for a bit more reach and that makes them more flexible for me than the similar RF models. 

If your Sigma 150-600mm is the contemporary model then they do focus a little slower than the Canon brand lenses. Certainly when I have compared a Sigma 150-600mm contemporary lens with the EF 100-400mm in the past it was noticeable how much quicker the Canon lens could focus and lock on to a subject. 

[ebiggs1]

I own the ef 300mm f4L lens and I love it. At f4 it is a good deal faster.  The 300mm f4L is one of just a very few lenses I recommend use of the 1.4x tel-con. Yes, it gives up some IQ which is expected but still on par with any of the 100-400mm zooms, IMHO, of course.

I have the Sigma Sport 150-600mm and I don't notice any slower AF with it. I do notice some with the C version. Perhaps a tad bit, but not really, with the Tamron 150-600mm G2 model. BTW, I consider the Tamron G2 the best of the 150-600mm super zooms on the market today.

However, all that said I would still advise anyone with an R series camera to invest in RF lenses.

[Waddizzle]

The EF 300mm f/4L IS USM is an excellent lens on a DSLR.  If I were using it on an R series body with the 2nd Generation of Dual Pixel AF, then I would not try to use any of the advanced tracking features like eye, animal, and vehicle recognition and tracking.  

[p4pictures]

I'm a little confused as to why you say not to use the advanced AF ability such as subject and eye tracking of the latest EOS R-series models when using old lenses?

My own experience is that older EF lenses work well with the latest EOS R-series models and I've had no trouble with using people, animal, vehicle tracking with eye / spot detection enabled. 

[wq9nsc]

One other advantage of the 300 f4, in addition to wider aperture, is in general a prime will have faster focus acquisition than a "zoom" of the same basic quality.  It isn't a night and day difference in most cases but it is noticeable.

I am leaving shortly to shoot a daytime soccer match and I will be using an EF 200-400 f4 with integrated 1.4X extender on one body.  For a bright daylight game, the versatility of the 200-400 f4 extender provides some benefits over the EF 400 f2.8 I use for most sports but the very slight difference in focus acquisition when changing from a close to a far target requires me to slightly modify my typical event strategy and it does put a little more pressure on the photographer.  The 400 f2.8 has incredibly fast focus performance on a 1DX III body and it has saved me more than once when I didn't properly anticipate action on the field, the 200-400 is excellent but like any high end zoom its performance doesn't quite match a prime.

So while you are deciding, pay attention to focus acquisition time on a suddenly appearing target which will favor the 300 f4.

Rodger