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Is there any reason to use flash in the middle of the day to photograph flowers? Yes, if you want a different look and absolute control of the time of day. You were told to photograph early in the morning and late in the afternoon to get the best light. Now, what do you do when you come across a nice flower on your walks, but the clock rounds midday?
Now imagine that the sun is on the wrong side of the flower, so all you get is a shadowed flower that does not look that nice. Give up, go home? The solution might be closer than you think, if you've got a flash with you. An external flash will turn this problem situation into exactly the type of lighting you want.
It's easier with compacts
With compact cameras this is somehow a no-brainer, because they sync their flashes, generally, with any speed you choose. But on a DSLR, the popup flash usually stops at 1/250, making it difficult to get good results, especially if you're out in the sun and the Sunny 16 rule applies. Then you have something like 1/125 at f/16 as a starting point, which is not good if you need to get rid of a distracting background.
The 1/200 flash sync limit on some cameras makes it difficult to balance the foreground with the background when there's too much light
The picture above, of a sunflower, is a good example of the limitations you will find under daylight with the sun on the wrong side of a sunflower. It was taken on a Canon EOS 600D with the EF-70-300mm L lens, and my exposure was 1/200 at f/10. The sync speed limit on the EOS 600D is 1/200 so the sky is a bit lighter that I like. As this picture is taken against the sky I had no problem with backgrounds, but if I had something behind the flower that was distracting, than I would not be able to close the aperture so much, and it would be impossible to expose the photo properly.
Create night in the peak of day
The end result is different once you enter the High Speed Sync (HSS) world
This second picture, of another sunflower in the same conditions, shows a different approach, only possible with an external flash that lets you work in High Speed Sync (HSS). This means the flash will sync with any speed above the usual 1/250. You've got to remember the light emission is weaker, but it will work for a lot of things.
In this case, I used a 420 EX Speedlite placed on top of the camera (yes, sometimes it works fine, thank you!) which let me work at 1/2500 f/4.5. There are three things to remember: effectively underexpose the sky, control the light on the flower, and be aware of your background.
The problem of having too much light or a close background you want to keep out of focus are not the only reasons to use HSpS. It can be used to create mood and to get a different look to your pictures. Controlling the amount of light let's you create night in the peak of day, and that's something that always puzzles people.
The images show the look of the same flower without and with HSS
So, by using an external flash you're not only able to solve some technical problems of exposure under intense daylight but also redefine the way your images look.
Get an extra "WOW" with external flash
If the sun is not shining or if you’re working in the shade, the popup flash can be used without much thinking (try it and see for yourself), but once you get under direct sunlight the exposure values are usually beyond what you want or need to get the best results.
Once you get the hang of it you can start to use your own sun. This picture was made in broad day light. Exposure at 1/800 at f/8.
I am a Canon user so in my case it's easy to get things rolling. Because Canon cameras read the ambient light and let you introduce flash as a separate measure. It’s rather easy to control the relation between the ambient light exposure and the flash.
I usually work in manual mode on the camera, and let the E-TTL take care of things on the flash. I just adjust FEC (or Flash Exposure Compensation) if I need to. I occasionally use manual flash control, something we can discuss about another day.
Even flowers at sunset can look different. Shot taken at 1/8000 at f/5.6.
The technique shown above is quite easy to use and can give an extra “wow" factor to your flower pictures. Try it next time you go out. If you experimented with this technique, please post your results in the comments!