I have been using a single light for my ‘I am an Ironman’ portraits – when possible my Elinchrom Quadra with a 1 meter softbox and a speedlight with an Lastolite Ezybox softbox when travelling. The flash is the key light and I am metering off this using a flashmeter.
The amount of fill depends upon the available ambient daylight – I have been trying to avoid tungsten lights. For the fill to be effective I need to keep the key light within a stop or so of the fill. Most times this has been possible but on a couple of occasions I have had to accept a slightly darker background. I do not want to open up beyond f8 so that the depth of field is sufficient to keep most of the face of the subject sharp. (I am using a Hasselblad 503cm with an 80mm lens and a Phase One P45+ back). One of the consequences of this is that the colour balance of the images has varied quite a bit depending on the amount of ambient fill and the nature of the light.
Whilst I am happy to accept that the background lighting will vary, I obviously want the skin tones of the subjects to be to a consistent and realistic standard. I have decided to use a device called Colorchecker Pro to assist with this. This tool has a grid of squares with different colours and tones. In particular it has a set of squares for portrait photography, ranging from cool to neutral to warm tones. By taking a test photograph of the setup for each portrait with the Colorchecker Pro in the frame, it is possible to ensure a consistent white balance for each portrait. This is effected by clicking Lightroom‘s white balance eyedropper tool on the same square of the Colorchecker Pro each time. The photographs below show the effect of using the tool on the neutral setting.
Test series of portraits without adjustments
Test portrait series with WB adjusted using neutral setting
As can be seen the adjusted images have a bluer tone. In practice I plan to use a slightly warmer setting for the skintones.
A further technical challenge I have been dealing with is achieving focusing accuracy with the Hasselblad and the P45+ back. My aim is always to use the subjects eyes as my point of focus. The resolution of the P45+ back us so good that unless the eyes of the subject are absolutely in focus then when the images are displayed at 100 percent the lack of sharpness is very apparent. The sensitivity of this is far greater than I had anticipated and my ability to achieve accurate focusing is not assisted by my relatively poor eyesight. I have now decided to use a piece of string with knots at 1 foot intervals to get an exact distance for the subjects eyes….primitive but very effective!
A final technical problem with the Phase One back arises because the back does not have an anti-alias filter. The consequence of this that with certain clothing materials some images show Moire defects. Because of this and the focus problems I have adopted the practice of checking the output from the shoot at intervals throughout the session. This also offers an opportunity to sit down with the subject to review how the portraits are shaping up. If there are severe Moire problems it might be necessary to ask the subject to wear alternative clothing or to try to adjust the lighting to avoid the problem….not hit this one yet!!
photo-graph 
CliveW
April 11, 2012
What focussing screen do you have? Mine is has a split screen circle in the middle with a microprism collar and my eyes are completely screwed but I don’t have a problem with focussing using the built in magnifier.
Keith Greenough
April 11, 2012
Hi Clive
yes I have an Acute-Matte split screen. The main problem is my relative inexperience with focusing on Hasselblad’s. Another challenge is the fact that the digital back is an older one and the preview screen on the back is not very high resolution so some things look pretty sharp on the back but when blown up to 100% on the computer they very occasionally look a little soft. I think with film one would never pixel peep in the same way as one is tempted to do with digital. The whole issue is also complicated by the fact that I am using relatively old Hassie CF lenses and an old 503cm…the resolution of these lenses is possibly not able to match the capability of the digital back and there is always the risk that the lens/camera set up may backfocus….
CliveW
April 11, 2012
I’ve got CF lenses, I don’t think there’s a problem with their performance. One thing I noticed many many years ago when moving from shooting solely on Nikon to the Hasselblad for the first time was that the Hasselblad lenses didn’t have the same ‘snap’ as the NIkon lenses, the transmission of tonal gradation was ‘smoother’ and of course the grain wasn’t playing such a big modifying effect. Taken together they gave the impression that the Hasselblad lenses weren’t as apparently sharp as the Nikon lenses. I had to readjust my expectations to appreciate the different rendering that the Hasselblad lenses gave. Of course you may be correct that there is some error in the focussing paths caused by say the mounting of the back, the positioning of the mirror, or indeed the focussing screen. You need to run some careful test to eliminate the possibilties.