Canon 85 1.8 > or < than Sigma 17-70 OS + Nifty Fifty

Hello all, I'm breaking the lurker / research role and asking for a bit of advice from you all.

I shoot with a Canon 30D - mostly my daughter and newly born son, some travel / vacation, and I have done a few weddings ( with *gasp* a 18-55 kit - not the IS versions! ). I have, obviously, the kit 18-55 that came with my body and also a 85mm 1.8

Obviously the 85 rocks as far as sharpness, but I certainly find that it is a bit long for many of the shots that I take. Given that, I have used it to take about 38% of my shots when looking at my exif data over the last 5 years.

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I have the sigma 17-70 OS and the nifty, I like them both. The 17-70 is a great travel lens, and the nifty works just fine indoors (though can still be a tad long in some situations, but definitely better than the 85).

Personally I quite like the 85mm focal length on crop, but if its not what you need, then replace it.

Would you say that you used the 85mm 38% of the time because that's what you wanted or because that's what you had? Some people don't like to swap lenses. The 18-55 doesn't have the best reputation for IQ either, so perhaps you kept the 85mm on for IQ and compromised by backing up.

I had the 18-55mm IS and 50mm 1.8 until I got the Canon 17-55. I usually stopped the 50mm down to f/2.2 or 2.8 and didn't feel like I needed it anymore with the 17-55. I found 50mm to be long indoors, but that obviously depends on how large your rooms are. If you sold both lenses, and put the money for the 50mm towards a lens, you might be able to get the Sigma 17-50. You'd obviously be losing some range, but you'd also have a constant f/2.8 lens with OS. If you find that most of your shots are outdoors, then the slower lens might not matter as much. If you're chasing your kids around the park, the Sigma 17-50 probably won't be long enough.

What is your budget? What does the graph of apertures look like? If my assumption is right, you shoot wide open a lot. If so, that chart to me screams 24-70/2.8, or 28-75/2.8. Maybe even the 24-105. Keep the 18-55 for when you want go wide or better yet pick up a used 18-55IS for that.

I would try the Canon 50 f/1.8 for around $100 and see how much you like or use that lens and focal length before going through and selling the 85. Also if you want a great indoor lens the Sigma 30 f/1.4 has alot of followers here.
The Sigma 17-50 f/2.8 OS is a great sharp lens as well, but may not have the reach you are looking for in a lens.

I own a Sigma 50 f/1.4 and can honestly say the ability to shoot at f/2 and knowing I can get sharp pics without using flash is one less thing to worry about indoors. So if you had a Sigma 30 f/1.4 and opened up to f/2 you should get simular results. Whereas the Sigma 17-70 2.8 may not be as sharp wide open at f/2.8. So if you had to shoot at f/4 for razor sharp images you are losing 2 full stops of lights when shooting. I do realize the OS feature will help shooting handheld at slower shutter speeds but it won't help a lens that isn't sharp when wide open.

I replaced my kits lens with the Sigma 17-70 OS HSM DC and love it. Great lens!