waegwan Loc: Mae Won Li

I have one. It is super sharp and versatile. It should serve you well. A 300 is nice but more prone to camera shake.

pithydoug Loc: Catskill Mountains, NY

If you shooting with an APS-C camera you 200 is really 300.

Psergel Loc: New Mexico

I was just kind of joking around about the extender given that it was a 100-4000 lens.

imagemeister Loc: mid east Florida

With 1.4X takes you to 280mm. - but more prone to camera movement/blur as mentioned.

amfoto1 Loc: San Jose, Calif. USA

You didn't mention what camera you are using...

For equestrian action I mostly use APS-C cameras (I use full frame only for portraits or extra low light)... So all that follows assumes a crop sensor camera.

On APS-C (7DII, 7D, 50D, etc.) I use the 70-200/4L IS a lot and it's an excellent lens. It often is plenty for equestrian events, but I do usually pair it with a longer lens on a second camera (300/2.8L IS or 300/4L IS... and 100-400L II more recently). I rarely need longer than 300mm, but a race course is a lot larger than the arenas I usually shoot, so a lens that reaches 400mm or a 1.4X along with a 300mm might be helpful at times. However, the longer focal lengths can be problematic if there's a lot of dust in the air or other atmospheric conditions that will degrade images. There's not much you can do about that, except use a shorter focal length, position yourself closer and/or wait for your subjects to come closer.

70-200/4L (either the IS or the non-IS version) is reasonably compact and not too heavy. As noted, it doesn't come with a tripod mounting ring, but one is available (Note: There are third party rings that are about 1/3 the price of the Canon ring. Some are even cheaper, but be careful... the real cheapies are often plastic and break easily. Spend more for the metal ones. They must be a good fit, too.... when you see how they work you'll understand why).

I wouldn't want to be out at a harness race with a 300mm prime alone. That would be great for some shots, but really limit your photo options to a pretty narrow and specific distance range. A zoom would be better for a variety of distances.

The original 100-400L is more versatile and a quite good lens, too.... so long as you don't put a "protection" filter on it. That particular lens seems to not play well with filters.... images seem to go "soft" when even a very high quality filter is added to it. I've been shooting with the 100-400L Mark II recently and really like it, but it's a whole lot more money than you seem to want to spend.

I haven't personally used the 70-300L IS, but know a lot of folks who use it and really like it. It's a fairly ideal range for equestrian events. I also know someone very successfully using the far smaller and lighter 70-300 "DO", but it's priced similarly to the L. Actually, the 70-300 IS USM (non-L) can be very useful too... it's just not as well sealed against dust and moisture and is more plasticky, so might not be as durable as the L-series.

All the above are USM lenses, which you'll need for fast focus and good tracking of moving subjects.

I've used a Canon Mark II 1.4X on the 300/4 (and 300/2.8), but not on any of the zooms. It doesn't effect the speed of focus on the 300/4 very noticeably so long as light is reasonably good, and image quality is still quite good. The zooms take a bigger hit of image quality with a teleconverter, compared to the primes. Keep in mind that most Canon cameras can autofocus an f4 lens with a 1.4X on it... but cannot AF an f5.6 lens with a 1.4X (which the 70-300 and 100-400 zooms are, at their longer focal lengths). Only a few Canon cameras (80D, 7DII, 5DIII, 5DS, 1D-series) can AF an f5.6 + 1.4X. Forget about 2X on any of these (I have one and only use it on 300/2.8).

The Kenko 1.4X seem a very good alternative to the more expensive Canon 1.4X. Kenko makes two: the more expensive "Pro 300" and a less expensive "MC-4". Both are quite good. The Pro 300 has better sharpness across the entire frame and would be a better choice with a full frame camera. The MC-4 is at least as sharp at the center, but loses some in the corners... still might work great on a crop-sensor camera that's not "seeing" those corners anyway. The current "DGX" Kenko have full electronic compatibility with the lenses and cameras, while the older "DG" didn't "report" to the camera in the same way (but might be useful when exceeding the f5.6 or f8-combo limitation, since the camera will not know the TC is there and will still try to autofocus... though likely more slowly and needing good light to do so).

I haven't used and can't compare the Tamron or Sigma 1.4X.... some of them seem pretty good, too.

Speaking of which, Sigma has offered 120-400mm OS and 150-500mm OS lenses in the past... now discontinued but widely available used for reasonable prices.

Finally, I agree with a previous post.... if at all possible get the IS version. Yes it's more expensive. And, for high speed shutter shooting such as you'll likely be doing at a harness race, the stabilization isn't as necessary. However, it can be very helpful at other times and makes the lens just that much more versatile. Canon's IS... especially on telephotos 70mm and longer... was one of the top reasons I switched to Canon in 2001 when they were the only manufacturer offering it. Now I simply wouldn't want to be without it on longer telephoto primes and zooms. Sigma OS and Tamron VC are similarly useful. (And Sigma HSM, Tamron USD offer similar AF performance to Canon USM.)

Have fun shopping!

amfoto1 Loc: San Jose, Calif. USA

No, it's not.

200mm is still 200mm...

On a Canon APS-C camera a 200mm lens acts like a 320mm lens would on a so-called full frame camera.

But even that's pretty meaningless if someone has never used a full frame camera at all..... has only ever used an APS-C.

amfoto1 Loc: San Jose, Calif. USA

That can be offset to a large extent with IS (or OS or VC).

Older style stabilization such as on the Canon 300/4L IS or original 70-200/2.8L IS or original 100-400L (push/pull) gives 2 to 3 stops worth of assistance.

Newer type stabilization such as on the 70-200/4L IS, 70-200/2.8L IS II, 100-400L II gives 3 to 4 stops worth of assistance.

Note: Personally I'd avoid the Canon 300/4L non-IS simply because it's a fairly old lens and might be difficult to get serviced, if needed. It was superseded by the current IS version in 1997... so any copy of the non-IS version would nearly 20 years old... at best... and might be as much as 25 years old, since it was introduced in 1991.

markngolf Loc: Bridgewater, NJ

While I don't have the f/4 (I have the f/2.8 II) I think it is a terrific choice, particularly since you will be shooting outdoors, f/4 should be fine. Canon L lenses are fantastic. (my opinion).
Mark

imagemeister Loc: mid east Florida

Surely you JOKE !

The non-IS version is selling NEW right now ........and, IMO is sharper ( when proper shutter speeds and support/techniques are used) and less prone to malfuctions because of the lack of IS elements and controls - and therefore will last longer - as is also the case with the 300mm f4.

sirlensalot Loc: Arizona

My opinion is that it is a very versatile lens. Light to carry, sharp, easy on the budget. Have used one for more than 5 years. It is considered by many to be an entry level L lens because of the price, not the quality. For your particular purpose, I would recommend this lens. For sports, suggest foregoing the added cost of IS, and since you will be outdoors, with your several hundred dollar savings, pick up a $30 monopod, and a maybe a CP or ND filter. I have used this one for sports, portraits, and weddings. $599 new, $500 factory refurbed, $450 average used on ebay, although have seen one or more for as little as $350 used, advertised in excellent condition.
Also, for the purpose you posted you may want to look at the Canon 300/4 non-IS used for the same or less than the 70-200 used (ebay). Just guessing not knowing what distance you are shooting from. You can pick up an after market lens collar for about $20. You will need one for the 300mm.

imagemeister Loc: mid east Florida

TriX Loc: Raleigh, NC

I'm a firm believer in IS and love the lenses I own that have it for relatively still subjects, but I would point out that depending on your shutter speed for the type of shooting you're doing (harness racing), it may be a non-issue. I haven't personally shot this sport, but my thought is that a beginning shutter speed of 1/250th (or maybe 1/500th light allowing) would be a good starting point unless you're good at smooth panning and want to see the blur of the wheels and hoves. if that's your main or only use for the lens, then the extra $400 for IS might be better spent on a longer or faster zoom. Btw, you could add a 1.4x teleconverter to the 70-200 if you find it "too short" and perhaps still utilize autofocus depending on the particular body you use. Also, one very real advantage of the f4 over the 2.8 is that it's half the weight, while the 70-300 is about half way in between.

CHG_CANON Loc: the Windy City

As others have already said, this lens is an excellent lens with some limitations in length and lowlight usage. I use mine regularly when I want a smaller & lighter package than others that are IS enabled and heavier. If budget is an issue, look at pricing at KEH.com. I see your 1V listed, some of favorite film shots come from my 70-200 mounted on my 1V. There's longer lenses as well as models with IS, but this model is powerful without the weight and expense and cost.

Dr.CalebRodriguez

Of course if you are shooting at a fast enough shutter speed the IS should not be an issue.

Rbode Loc: Ft lauderdale, Fla

Here's a Kenko compatibility list if you consider a extender.

http://www.kenkoglobal.com/pdf/TELEPLUS_DGX_series_CompatibilityList.pdf