ADVISE NEEDED ON 2ND HAND PURCHASE.......

Hi everyone,
I need some advise, yesterday i posed the question of whether or not to REPLACE my 85mm 1.8 with a more flexible zoom ie. Tamron 28-75 or Sigma 17-70...

I have now decided [with some encouragement from this forum] to keep the 85mm and add another.

I have found a sigma 17-70 in my local area [Sydney] the seller has told me it is AS new, hardly used, he wants $400.00 AUS for it.

I am not sure what they are worth 2nd hand but I thought this might be a good place to start.

Also this maybe a silly question but I would rather ask it than later wish I had of......What am I veiwing on a 1.6 crop [10D] with my kit 28-90 lense???

Sorry it's a little long but thanks for reading..

Did some research at local stores..
Tamron 17-50 - AUS $700 approx.
sigma - AUS $500 -$549
So 2nd hand - $400 looks like a fair price to pay..

Just need to decide if the constant 2.8 apeture of the Tamron is worth it ?
It will be used mainly for childrens portrait and close ups...

errm, portrait length is really from about 70-100 mm. so your new addition will partially accomplish your goal considering if you have a crop camera.

Just to clarify: On a FF that is...

Thanks for the response
I know what your saying, just not 100% sure on a decision yet

I'e got the Sigma 17-70mm, and I wouldn't dream of allowing it to replace my 85mm f/1.8...

Simple ... 28*1.6 - 90*1.6,
so it will give you the field of view of a 44.8 - 144 mm lens on full frame 35 mm film camera.
The 17-70 is equivalent to a 27-112 lens on film, so it will roughly give you what you saw in the viewfinder of your film camera with your 28-90 lens (a bit longer, actually).

Best regards,
Andy