MR14EX underexposing

<p>I have a MR14EX ring light that I am mating to a Canon EF100/2.8 macro and EOS10d body.<br>

I set the body to manual, 1/125 at f16 for decent DOF at ISO 100 to do intra-oral dental images and ETTL on the flash.<br>

The exposures come out consistently 1 to 1-1/2 stops UNDEREXPOSED.<br>

I have to do flash compensation +1 or more to get decent exposures.<br>

Is this normal with this flash?</p>

<p>Do the teeth occupy most of the image? I'm guessing these teeth are off-white and maybe 1 to 1-1/2 stops brighter than medium toned. Like a white wedding dress, white sand beach or snow field it will be underexposed since metering is calibrated for scenes that average to medium. Whenever I shoot predominately light colored subjects I have to dial in +FEC or EC. Dark voids or black suits are the opposite and need -FEC/EC.</p>

<p>I use the MR-14EX for botanical work, and, as with other Canon flashes, it is often necessary to compensate a bit for the lightness or darkness of the subject, as PF says. More recent camera bodies than the 10D may be a bit smarter at getting it right first time, but are not infallible.</p>

I also use the MR-14 for dental images but on a 7D and this combo seems to meter very well. I'm thinking the older body

just doesn't meter as accurately. I would recommend you get your assistant to "pose" for you and find the correct manual

flash setting for the shutter speed and aperture you want to use. The best part about dental photography is that the

subject and working distance change very little. That means you can pick an aperture for good focus depth, pick a

shutter speed that syncs and compensate manually on the flash, then use those settings almost exclusively. If you do

need to alter your "go-to" settings, you can compensate with a quick change of shutter speed or flash power.

<p>Now that I think about it, when I owned a 10D (2003!) I recall riding FEC like a madman. When I upgraded to a 5D in 2005 I was happy flash metering needed less user intervention.</p>

<p>Try setting the flash metering mode to Average instead of Evaluative</p>

<p>All good points.<br>

I had the camera metering mode set to partial center weighted average which in shooting light objects would influence the exposure.. I may switch to spot metering, take a reading and add 1 1/2 compensation on the flash as I have done to confirm this. But usually teeth arent pure white so didnt think it would influence the metering as much as it did. <br>

Thanks for all your help.</p><div></div>

<p>I had the 10d in the closet gathering dust. I didnt think I needed to upgrade to more current model as sensor rez really isnt a factor in the application. Metering is another story however, but if I can get around it by FEC Im ok with it. I just didnt know if the flash itself was faulty on ETTL metering</p>

<blockquote>

<p>I had the camera metering mode set to partial center weighted average which in shooting light objects would influence the exposure.</p>

</blockquote>

<p>That means only a small circle--about 10%--in the center of the image is actually metered, i.e., the off-white or light yellow teeth. If you metered the entire scene in Evaluative it would take into consideration the medium and dark portions of the frame and render a better exposure.<br /> <br /> If you do use spot metering, you will need to meter a medium toned area of the mouth, e.g., lips or gum, to get a reasonable exposure. If you spot meter the light colored teeth it will read 1 to 2 stops dark (remember, meters are calibrated to an average distribution of medium tones). In my chrome shooting days I used to spot meter medium toned objects in the same light as my light colored subject to get a good exposure. If my subject was light colored, I opened up 1 to 2 stops from the reading. Now I mainly use Evaluative and can estimate FEC/EC before shooting, based on the tonality of the subject.</p>

<p>When I shot repetitive subjects--same flash, distance and exposure--it's easier to leave all the flash and camera settings preset to taste on manual. If you get a patient with super white teeth, open up a half stop. Otherwise, why toil with auto exposure and overrides?</p>

<p>ignore... </p>

<p>This isn't about camera exposure metering. You're shooting manual anyways. Try changing the flash metering mode.</p>

<p>+1 using manual flash not TTL<br>

If you use TTL I think you can not compare before and after a bleaching, exposure will be averaged, if you use manual exposure then the light will always be the same and if colors are different is because subject is different not because you metered in a dry or in a wet teeth.</p>

<p>I recomend this parameters with full frame camera (for AACD requirements)</p>

<p>for 1:1 magnification (eg. incisors), ISO 200, F/29, manual flash power at 1/4<br>

for 1:2 magnification (eg. full smile, upper or lower arch, retracted views), ISO 200, F/20, manual flash power at 1/4<br>

for 1:10 magnification (eg. full face portrait), ISO 200, F/6.3, manual flash power at 1/4</p>

<p>Open 1/3 of stop if using a mirror (for occusal or lateral views)<br>

This way you only have to change aperture when changing magnifications.</p>

<p>To obtain those "magnifications" (viewed area) with a APS-C sensor you can not use the scale on the lens (those are for full frame), with 100 F2.8 USM Macro (not the last one that has IS, burt the previous one) the prefocused distances for a cropped sensor are:</p>

<p>1:10 at 5 feet<br>

1:2 at the dot of 0.49<br>

1:1 at the 3 of 0.35</p>

<p>Hope it helps<br>

Regards</p>

<p> </p>

<p>Thank you Jorge,<br>

Very good information, thanks for taking the time to post.<br>

Bob</p>