I've just bought a Sigma 105mm OS HSM after using a Raynox macro adapter for a while. I couldn't use the on camera flash with the Raynox because of the working distance/lens shadow. I was pleasantly surprised to find that it works with the Sigma. I've got it looking OK(ish) for some things by adjusting the flash compensation but it's still too harsh for some stuff, especially flowers and foliage. I've not used it for insects but I suspect it will be the same. How can I soften It? Or do I need to get an external flash for more options?