Genessi wrote:
Hi I will be at the race track with a group to photograph horses and then botanical gardens. Not sure which camera i should use for the track. I will have my 100macro, 28-135 and 100-400mm. Also what lens would be better to use between the zooms. Thank you for your input.
It will depend on the type of shots you'll be taking at the race track.
If you are shooting distant action on the track, you'll need your telephoto and the SL1 will be the better choice. As an 18MP APS-C camera, it will put a lot more "pixels on target" than the full frame camera. In other words, if you were to take the same shot with the same focal length from the same distance with both the SL1 and the 6D, then crop the full frame camera image down to match the SL1, you'll only have about 7 or 8MP left out of the 20MP full frame image. The 18MP image from the SL1 will definitely be superior for telephoto work.
On the other hand, if you are up close and personal... i.e. shooting the horses in the winner's circle, paddock or stables... your 28-135 will be a good choice and can be used on either camera.
If shooting indoors by available light, the 6D will be the better choice. It is able to produce clean images at far higher ISO than the SL1. With some care (avoid underexposure like the plague) and a bit of extra post processing (shoot RAW and apply some noise reduction), you probably won't want to use the SL1 above ISO 3200, but the 6D can probably manage ISO 12800 or even a little higher.
With either camera, for action shots you should limit the camera to the center AF point only. All the other AF points in both cameras are lower performance, single-axis type. Those are okay for sedate stuff like portraiture, but pretty much useless for anything moving.
In low light the 6D's center point is the best choice, too... it's -3 EV (moonlight) capable. The 6D's other 10 points are -1 EV rated. At best all the points in SL1, including the center one, are probably -1 EV or -0.5 EV.
So, if it were me I'd take both cameras and both zooms to the track. (The macro lens is not very likely to be needed.)
For the botanical garden you also might want both cameras and all the lenses. You'll likely use the macro lens a lot... but if shooting butterflies or anything else active you may want to put the 100mm on the SL1 so you can work from a greater distance.... or use the 100-400 on it if the longer focal lengths are needed. Again, low light conditions might call for the 6D instead.
The 28-135 isn't at all bad for close-up work, either. It focuses a whole lot faster than the macro lens. One thing to be aware of is that the 28-135 gets a little soft when it's racked all the way out to 135mm... stopping down to f8 helps with that. At other focal lengths, the 281-35 is quite capable, even wide open.
If your 100-400mm is the original push/pull version, I hope you don't have a "protection" filter on it. That particular lens goes soft when any filter... even a very high quality one... is fitted to it. A lot of 100-400mm users were surprised just how good their lens was, when they removed the filter they thought was protecting it. (From exactly what, who knows... After all, how much protection can a thin piece of glass be expected to give?.