Advice on wideangle?

I'm after a wide angle lens for my Pentax K-r. I know a bit about photography but still learning. I've been looking at either the Sigma 10-20mm F4-5.6 EX DC HSM or the Sigma 10-20mm F3.5 EX DC HSM

I know the difference between the lenses are their apertures. But what difference does that really make between these two? I know aperture is how much light is let in and relates to depth of field too.

But unless I've got the wrong end of the stick (which I must have) - the lack of aperture range on the first one can be made up by the length of time the shutter is open? Why buy a lens without a limited apeture - purely to get less blur in the background and quicker nightime photos? Or am I looking at this totally wrong?

Any help and your advice is much appreciated!

I use the 10-20mm F4-5.6 great lens I find no real difference just the f stop and a smaller chip APS but both have fast autofocus and Hyper-Sonic Motor just like it says in link you put on
i love my lens i dont do landscapes with out it
go for 10-20mm F4-5.6 EX DC HSM you cant go wrong
i hope that helps

Firstly - in my view - either version - good choice.

My Sigma 10-20 is my most used lens and delivers stunning IQ. I have the 4-5.6 version.

In reality - and every day use - I doubt you would notice a great deal of difference between the 2 versions. In theory - the 3.5 version should be slightly better in low light. Some prefer a fixed aperture - on this lens - to me it makes little/no difference.

You are correct - longer exposure would/ should compensate for the aperture difference - to some extent but low light long exposure needs a tripod

The reality - is most of your use will be around f8 or f11 in any case - so they should perform similarly.

If you can get the 3.5 for about the same price as the 4-5.6 - then it should be considered as it is the newer model. If there is big price gap - the 4-5.6 is a fantastic lens. Another price consideration is the 4-5.6 is a 77mm filter thread whereas the 3.5 is an 82mm thread - therefore filters for the 3.5 are more expensive than for the 4-5.6

Hope this helps and am sure others will have different opinions

Carl

Ditto on all counts

John

I had the 10-20 for a while- I found my best shots were taken at 14mm + as the perspective at the wide end renders large things in the distance quite small, for landscapes the 15mm ltd or DA14mm would be worth consideration.

The extra width of the Sigma is very good for tight spaces though, and I actually used it most when shooting video indoors.

I concur - The older and cheaper F4-5.6 model is still a great lens. I love mine.

The Sigma is a very good lens but I would also have a look at the Pentax 12-24. Second hand ones ( or the identical Sansung version) can be had for quite reasonable prices. I think you will be more than happy with any of the above .

Be careful too - the 4-5.6 isn't HSM in Pentax mount. To be honest, on a wide lens that doesn't really matter, since it's so easy to use hyperfocal focussing and forget about actually focussing the lens at all!

I've previously owned the older Sigma 10-20 but much prefer my current DA12-24, sharper corner to corner than my previous Sigma

Simon

I prefer the DA12-24 to the older Sigma 10-20 (not tried the new one.) I agree the Pentax lens is a little sharper, has a more even exposure across the frame and has great bokeh.
Don't forget though the Sigma 8-16mm which is extremely good and does have HSM. It's not a fish-eye either.

John