#1  
Old 29-07-2010, 09:43 AM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Macro flash overexposure problem.

I am the brand new owner of a 100mm f2.8L macro lens and the MT24-EX twin lite macro flash and a 5DMK II.

I am so used to photography without a flash. Now I have this option to light my subjects up close without a flimsy pop-up casting a shadow over the lens.

Let me paint my question.

I set up a blade of grass with a water drop on it. I use aperture priority and let the camera work out the shutter speed for the correct exposure. I take a shot and it is exposed correctly. Do I even need a flash?

Next shot, I turn the flash on and try again. WAAAYYY overexposed. Do I drop the power of the flash, put on a diffuser, or drop the shutter speed or raise the aperture value or all of the above?

Again, it there is enough natural light about, do I even need a flash? Is macro photography best done with a flash or is it subject to the available ambient light?

Baz.
Reply With Quote
  #2  
Old 29-07-2010, 09:49 AM
luigi
Registered User

luigi is offline
 
Join Date: Jun 2010
Posts: 438
Check the flash exposure compensation on the camera AND the flash. If you have the flash at 0 but the camera at +2 the shot will be overflashed and it's hard to notice that is happening.

2nd idea shot in AV mode so the flash acts as fill light letting the camera expose the background. In M or P the flash acts as the main light source.

Hope it helps
Reply With Quote
  #3  
Old 29-07-2010, 10:20 AM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,584
Quote:
Originally Posted by bloodhound31 View Post
Is macro photography best done with a flash or is it subject to the available ambient light?
Ambient light is good if you've got enough of it. If you're using small apertures to get DOF then ambient light may not be sufficient, especially if you also need fast shutter speeds to stop motion.

Cheers,
Rick.
Reply With Quote
  #4  
Old 29-07-2010, 10:50 AM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Thanks guys.
Reply With Quote
  #5  
Old 29-07-2010, 10:54 AM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,846
The exposure is a balancing act, and you really want to use the flash as fill light only unless you want to end up with black backgrounds (which can be effective sometimes, don't get me wrong).

My first comment would be that using Av mode on the camera and ETTL for the flash, you really are relying on the camera to guess what exposure you are after. You don't know what you're going to get. Considering this, it shouldn't surprise you that you're getting overexposed subjects.

Av mode, you choose the aperture and ISO but the camera chooses shutter speed. What if the speed it chooses is too slow and you end up with motion blur? Yes, the flash will freeze motion to a certain extent, but not so much if you're only using it as fill. Moreso if it's the only source of light and you want black BG.

Can't recommend enough that you use full Manual mode for camera exposure. Take control of your exposures, especially if it's going to be an income for you. You'll end up with more "keepers", because you are dictating how you want the image to end up, not letting the camera guess it for you.

Yes, you can successfully use Av mode, but IMO it just throws in a variable that I don't want.

What I do is set camera to M mode, dial in what aperture I want (usually f/11 for up to 1:1 magnification macros), set a shutter speed around 1/200, then check the exposure and set the ISO to give me around the correct exposure. You don't need to have the subject all lined up and ready to shoot to do this, just point at what the background will be. You don't even need to be focused. And you don't need to have the exposure spot on, you might leave it underexposed by a stop or so. This will allow for some variation in ambient light, allow the subject to be better lit than the background, yet still not have that black background look. And it makes the flash not work as hard, so less power, so quicker recycyling and longer battery life, and less chance of harsh light.

I do limit the ISO though. You don't want it to be too high to control noise. Typically ISO 400, maybe 800, no higher. If you're getting up to 800, you can always drop the shutter speed back down to 1/100 instead.

So now your camera is set, time for flash. I've started using full manual flash lately as well, but might be easier for you to get used to ETTL first. If you have FEC set to zero, and the camera exposure set to underexpose by around one stop, the flash might expose the subject correctly depending on what metering mode you've used. Maybe try centre-weighted if your subject in in the middle. It may be slightly overexposed, so you just dial down the FEC to say -2/3 usually does it. It's a bit of trial and error, and every shot will be different. But you get the idea.

Finally - diffusion. If you're using ETTL flash, adding a diffuser won't change any of the above process because the flash will compensate and light loss that the diffuser takes from you. But the bare MT-24EX flash can be pretty harsh, so I do recommend doing something about diffusing it, and I've previously posted links for you on how to do that, and also about macro flash photography as well.

If there's enough ambient light around, do you even need flash? Personal taste. Probably not, but personally I always use if for fill. Controls the contrast a bit better, not as harsh. You can take out bright sunny highlights that you often get off shiny insects.

Opening up aperture? I wouldn't. Even at f/11 your depth of field is razor thin, opening it up only makes it thinner. Use the ISO, to a point as mentioned above.

Sorry about the long read. Hope it all makes sense.
Reply With Quote
  #6  
Old 29-07-2010, 11:09 AM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Troy, I can always count on you for a thorough and understandable explanation. Thanks so much mate, I will be practicing this all week!

I will lacky-band a couple of paper towels over my flash heads too.

Thanks yet again mate.

Baz.
Reply With Quote
  #7  
Old 29-07-2010, 11:19 AM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,846
I dunno much about astro, dunno much about portraits, dunno much about landscapes, dunno much in general. Macro I know a little, and the above is pretty much all of it.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 03:33 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement