We have been using this lens for years mounted on Canon DSLRs with a crop factor of 1.6 making it effectively a macro 160mm so I sold my old macro 180mm lens. It is simply outstanding and has given us great results whether on flowers or butterflies, dragonflies or fungi. We use it almost entirely hand-held with cameras set to ISO 800 and the IS works a treat. For occasional use with an extension tube I improvise a support using anything to hand like my hat or backpack etc. There will be much less distance compression with this lens compared with the 300 and you will need to get closer for a given image size but the lens is so much more compact you will be able to react more quickly. If you only used your 300 on a tripod you will find a new freedom when using the 100 hand-held.