slow down, everybody here likes to spend your money for you
you've JUST got the studio light kit so how about waiting a while and getting some mileage on it to work out what you NEED.
if you've only got £200 then you can't afford to waste it
24-105 F4 L IS costs £600, so no chance
Zoom will be useful as you have limited space to work in as there's a limit to how far back you can stand to get the composition. So that counts against longer length primes too. Remember you can always make a cheap long lens by walking forwards with a shorter lens
. A 50mm prime will be good for head and shoulder stuff, and the nifty fifty (50mm f1.8 Mk2) from kerso is a bargain, is really sharp and opens to 1.8 if needed (but best sharpness at f2.5 onwards and the bokeh is of limited appeal because its only got 5 aperture blades and so you get pentagonal blobs from any out of focus bright spots)
For full body shots I wouldn't be surprised if you are already working in the 18-28mm range of your kit lens. 28mm will see you near to pressed with your back against the far wall which limits the compositional flexibility. Remember also that zooms tend to be a bit soft at the extremities of their zoom range, so for quality you dont want to be on a lens' limit.
Have a look at the exif, what lengths are you really shooting at?
also consider, you'll be wanting shallow depth of field capability so you can lose the background, even if it is a plain backdrop, so you need wide apertures and f4 becomes limiting, you may want to consider f2.8 or even better. All lens are relatively soft at full wide open aperture, so for quality again you dont want to be on a lens' limit.
without spending a fortune its tough. If you want perfection start saving for the ef-s 17-55 f2.8 IS at £600
For now, why not just keep going with that kit lens, but make sure you play to its strengths and you should get some good results. Try to work at f5.6 or f8, and try not to wind it all the way out to 18mm but limit yourself to say 22mm at the wide end to avoid it going soft. You've got controlled conditions with your studio so a couple of dozen test shots will nail the best settings.
If you really must spend money to have a "better" lens for full body and head&shoulder portraits, without spending big money, then the new kit 18-55 IS is being reported to be very sharp, or maybe a Tamron 17-50 f2.8 which would give you more scope with big aperture for shallow depth of field. Go have a browse through the reviews, starting at
www.photozone.de and the prices are on
http://www.camerapricebuster.co.uk/cat5.html (including sigma & tamron)
anyway why do you think your 18-55 kit lens is bad?
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