DJDiver

These were all shot at Tracey Arm on an Allen Marine tour with a 100-400 mm lens on a full frame DSLR.  Mostly used it at 400mm.  I've since replaced the gear with a mirrorless full frame body and a 100-500mm lens, which would have been even better for that little extra reach.  Keep in mind the weight of your gear since you'll probably be hand-holding it.  There's not a lot of room for a tripod on the boat.  Make sure you take some foul weather gear (rain jacket and pants, gloves, hat, etc) so you can stay outside on the deck.  Shooting from inside through the windows just won't cut it.

This clip was shot with a GoPro while I was scuba diving.  You can see the effect of having a red filter on the camera.  If you are only snorkeling, though, you really won't need a filter as you'll be on or close to the surface, so the colors won't be washed out.  

My new GoPro 8 arrives tomorrow!  I'm replacing my 3+, so I'm sure that the upgrades will be a vast improvement.  Looking forward to trying it out in Botswana next month, and on a Fiji cruise in January.

There's absolutely no time to change lenses or add the 1.4xTC on the whale watching trip.... when it happens, the action is fast and random.  If you don't have the right lens already there, you'll miss it.  I used my 100-400 mm lens exclusively.  I tried to remember to have it at 100mm in between action, just in case a whale breached or dove close to the boat (we had a bubble-net feeding pod surface right next to us once).  Then, practice quickly zooming in if the action is further out.  It's also easier to find the whale in your viewfinder if you are zoomed out a bit.  I brought a second camera body with a 70-200mm lens, but never used it.

We have done several whale tours as well as lots of African safaris.  I shoot with a Canon 5DM4 and Canon 1DX, but I think the 70D can do this as well:  Manual shutter speed and f-stop, with auto ISO and, when needed, exposure compensation.

Shutter speed is typically the limiting factor for getting sharp photos of fast moving critters.  I try to stay at 1/2000 or even faster since you never know when or where the action will occur - - so you have the movement of the boat, the whale and yourself to contend with.  Choose an f stop based on the desired depth of field, but I usually start around f/8.  Use exposure compensation when needed. 

This one was taken at 1/2500, f/8, ISO 2500

The Canon 100 - 400 mm L f/4-f/5.6 lens is an incredible lens, but very pricey to buy ($1,700 or so).  But, you could rent it for within your budget.  It should provide all the reach you need (with your crop sensor body) to get you some great shots while whale watching.  These are some that I took with that lens on our whale watching trip out of Juneau last year.