I've been reading about early and late blight to see if there was anything I could have done differently this year. I read that late blight might be introduced into a field early by volunteer potatoes that come up from the previous year, but then it quickly becomes airborne like Little Minnie pointed out. Volunteer potatoes could be a factor for me, but another grower I've been commiserating with over blight doesn't grow potatoes at all, so I think it's just a bad year for us here in the Mid-Atlantic because of the wet conditions. Organic fungicides seem to have failed me this year, so I think I'll try to focus more on blight resistant varieties of tomatoes next year. If I pick Defiant tomatoes when they look ripe, they taste like supermarket tomatoes, but if I leave them on the vine until they are very ripe, they're pretty good. Certainly better than no tomatoes at all.

It was difficult to get close enough to see the spots and still focus. Hopefully, you can enlarge the linked photos enough to see what I'm talking about. Thanks, John A Here is a link that might be useful: Lemon Hab Leaf Spot

Tomatoes are heavy feeders and need lots of nutrients. You should have started feeding long ago (based on the size of the fruit in the background). You should use some water soluble fertilizer with higher amount of potash (go for 15-15-19 or 19-19-25 or some similar N-P-K ratio) and with micronutrients (Ca, Mg...). You are dealing with multiple nutrient deficiencies and your plant needs them fast (water soluble fert nutrients are readily available to plant, so i'd strongly advise you to use those). Always follow directions for use on the label, over-feeding can hurt them too. Good Luck, Djole

Doesn't look like disease. More like an environmental glitch.