Hi Helen,
Thanks for your response. What would be a good temp for color portraits (what CRI)? They sell another version that is rated at 4100K.
As far as film, for b&w using ISO 400 wouldn't be a problem. Although, when I start doing color work films I'm interested in using are ISO 160.
I would like to have the ability to stop down a little more, so I could have the head in focus if possible. The other thing is, I believe since these lights are fluorescent, I can have them somewhat closer to the subject because they are suppose to produce less heat.
Thanks for your help.
Regards,
Martin
Most of your questions have already been answered, but I'll chip in anyway.
CRI (Colour Rendering Index) is not an easy property to draw hard-and-fast conclusions about. It is determined by comparing the appearance of eight semi-saturated colour patches in the light under test and in incandescent light of the same CCT (Correlated Colour Temperature). CRI is an average value across the spectrum, and it doesn't tell you how well any particular colour will be reproduced. Some colours could be better than others.
However, CRI is a moderately good guide to how well the spikes have been smoothed out. The higher the CRI, the more smoothing there is. Tubes with a CRI of 85 are used for photography, particularly with tungsten-balanced tubes (eg Osram/Sylvania Studioline tubes, as used in Gyoury lights). Video/digital tends to cope a little better than film when the CRI is marginal. Daylight-balanced tubes are available with CRIs of 90 and over, and these are usually good for film and video/digital.
The colour balance (CCT) is a different issue from the CRI, as already pointed out. You'll be better off with tubes with near daylight balance, in general.
The rough numbers I gave should indicate that it is going to be difficult getting plenty of depth of field at a workable shutter speed with just two 105 W lamps. Though it is worth knowing about, flicker shouldn't be an issue. The self-ballasted lamps that you are considering usually have electronic ballasts that work at a much higher frequency than line frequency. The larger of the lamps you gave the link to are definitely self-ballasted with electronic ballasts.
Banks of Osram/Sylvania Studioline Daylight 55 W tubes can be turned into good soft sources for portraiture without diffusion being necessary. Those tubes are quite widely used for photography.
If you decide on flash, I'd consider getting old Dyna-Lite D series packs and heads, or something like that, from eBay.
Best,
Helen