Help required for a purchase

I have a little photoshoot next month that involves moving objects in low light situations. So I need a fast lens. Must be auto focus, as I have a 50mm 1.7 manual but find it difficult to keep refocusing on moving subjects. Im on a limited budget of £300 and under. So i'm mainly looking at the DA-50 1.8 or Fa50 1.4. With £100 between the two. Which would you decide on ?

The DA 50mm f/1.8 performs slightly better, the FA f/1.4 is slightly faster. The speed difference is in reality quite small.

Personally I'd buy the f/1.8 version as it will be more useful for close ups, reversing, use on bellows, use with close up lenses, etc. In other words, you can abuse it more and maintain quality.

You don't say what it is you are shooting, but what about a fast zoom?

The Tamron 17-50 and 28-75 are both f2.8 and 2nd hand will come in around the £200/£250 for a mint version.

If you could find one for £300 there is the Sigma 24-70, again f2.8 and has rave reviews on its IQ.

Thanks John. Pretty much my first thought. Andrew I'm using it for small venue low light gig photography. I currently have f2.8 lenses and more often than not they prove to be not fast enough, without using very high iso numbers. So Im looking for the most detail and trying to cut down the noise levels

The DA f1.8 it is then!

Sat, hoping with fingers crossed for this deal in the UK...

http://www.pentaxforums.com/news/pentax-lens-deals-august-2013.html

Why not keep your eye out for a used F or FA 50mm f1.7 ... they seem to come up quite regularly for around £150 or so.

Thanks for that information Mike. I'll look into it....

Not sure if it's any good to you but SRS have a f1.4 for £210 with 12 months warranty on Ebay LINK

The da has great contrast and like the da35 has great sharpness. The 1.4 was slightly slower ti focus i guess due to a larger focus throw.