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11-11-2007, 05:07 AM   #1
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f2.8 v's f4 in lowish light

Hi all!
i'm new, to the forum and photography in general, so if any of my questions are obvious or stupid, please be gentle.

i've decided on getting a K10D body, but am still undecided on lens(s)

the two main frontronners are the DA 16-45 f4 and the Sigma 17-70 f2.8-4.5
i realise these are two that are a common source of indecision and i have read many posts about them.

specifically i'm wondering about lower light. how much difference the f2.8 will make.
i'm mainly interested in family gatherings and so on. inside, with lights on, but no flash.

also, at what focal length do you lose the f2.8?

or, should i forget it and plan to get a fast prime for these situtations?

thanks for any opinions or suggestions

11-11-2007, 05:49 AM   #2
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I don't have the sigma so I can't comment other than I have seen some incredible photos taken with this lens.

I chose the 16-45 and find it a superb lens, very sharp and nice colours and contrast.
I think if you are after lowlight though the difference between F2.8 & F4 isn't huge and I would be more inclined to recommend the FA 50mm F1.4 for those indoor lowlight occasions and using the 16-45 in better light situations.

What you really have to decide though is do you need the reach of the Sigma lens at 70mm plus don't forget the Sigma is only F2.8 at 17mm and 70mm is F4.5.
11-11-2007, 05:50 AM   #3
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QuoteOriginally posted by Bob83 Quote
specifically i'm wondering about lower light. how much difference the f2.8 will make.
i'm mainly interested in family gatherings and so on. inside, with lights on, but no flash.
Exactly half, because 4 is one stop slower than 2.8.

Since 2.8 happens to be right on the edge for fast enough shutter speeds at ISO 1600 in typical indoor lighting, that one stop can really hurt.
11-11-2007, 05:56 AM   #4
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For the type of shooting you indicated I'd suggest the FA35 f2 or if the rooms you are going to shoot in are large enough then the FA 50 f1.4. Both are much faster and with a higher ISO in low light you'll be able to shoot without a flash most of the time. F2.8 vs F4 is 1 full stop and can make a huge difference in whether you can hand hold a shot or have to use a flash or tripod. The table below shows the differences. The 50mm will give you 3 stops and is a great lens for many reasons. I don't own the Sigma as I find the variable aperture zooms frustrating. It might handle a shot at the wide end then be too slow to take the same scene when zoomed in. Usually they switch to the slower speed at about 30% from wide.

Also a fast prime will always give you sharper images and often with better colour characteristics than a zoom. The only exception to that might be DA* series zooms that are almost as good as most primes.

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11-14-2007, 03:25 AM   #5
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Thanks everyone for your reply's.

I'm still uncertain about which general use lens to get, but for the low light i think i will go for a prime. i was looking at the FA 50mm f1.4, but i think i would like a wider one.
i went into a local store and tested the FOV at several focal lengths, and 50mm is a bit narrow for the size rooms i'm likely to use it in.

i think i'll wait till i get my camera and take notice what focal length's i actually use most before outlaying on a prime.
11-14-2007, 03:57 AM   #6
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Doesn't Sigma make something like a 30/1.8? Might be something to consider.
11-14-2007, 03:58 AM   #7
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QuoteOriginally posted by Bob83 Quote
...
and 50mm is a bit narrow for the size rooms i'm likely to use it in...
FA35/2 is quite good for indoor use, but it is already discontinued in Australia.
11-14-2007, 05:08 AM   #8
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Mike is right. Sigma does make a 30mm f1.8 which by most reports is a good lens. And I love my FA35mm f2. Sigma also makes a 20mm f1.8 but that's getting expensive for family shooting.
FA 35 f2's still show up on Ebay and KEH, B&W etc fairly regularly since it was only dropped this past year. Expect to pay $450+ for a used Pentax FA20mm f2.

11-14-2007, 05:26 AM   #9
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I've got the Sigma. Here's the max aperture/focal length info:

F2.8 - 17mm
F3.5 - 23mm (i.e. the max aperture is F3.5 from 23mm onwards)
F4.0 - 37mm
F4.5 - 70mm

So basically at focal lengths under 37mm, the Sigma is faster than the Pentax; the Sigma is also F4 all the way up to 70mm, where it's F4.5
11-14-2007, 05:43 AM   #10
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QuoteOriginally posted by Peter Zack Quote
Mike is right. Sigma does make a 30mm f1.8 which by most reports is a good lens.
They make a 20/1.8, 24/1.8, 28/1.8 and 30/1.4. The 30/1.4 is a digital only lens (designed for APS-C) while the rest are full-frame lenses so they can be used with DSLR or film.
11-22-2007, 08:34 PM   #11
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I was hoping that someone could post some pics which illustrate the differences in low light conditions between f4, f2.8, and if possible f/1.4. I am also pretty new to photography and a working example showing the differences would definitely help provide useful information in future lens purchases.

Peter, could you also explain the chart you recently posted? TIA.
11-23-2007, 02:23 AM   #12
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QuoteOriginally posted by weaponx525 Quote
I was hoping that someone could post some pics which illustrate the differences in low light conditions between f4, f2.8, and if possible f/1.4.
Hi all!

yes, some comparison pics would be great if anyone has the time.

Also, i just picked up my new K10D
I ended up getting the DA 16-45mm.

suddenly i realise just how crappy my old camera was. and thats with the pentax in the green mode with everything on default.

I also am starting to realise how much i don't know.
the learning curve will be steep, but fun.

the idea of a fast prime has been shelved for the short term. i think i need to learn the camera etc a bit better first. i don't want to spend the money until i have a better idea of what i will use.
sounds depressingly restrained doesn't it? i guess the LBA is still in early stages

Thanks
11-23-2007, 03:03 AM   #13
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QuoteOriginally posted by Bob83 Quote
... i guess the LBA is still in early stages
Don't worry, it's incurable.
11-23-2007, 04:38 AM   #14
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Congratulations on your new purchase!. F4 inside is not too bad, you just need to improvise a little. Rather than try and hand hold the camera inside look around the bar for something you can rest it on...ive used bottle tops and upturned glasses (empty of course!) with success. You have an ultrawide so theres little chance of you missing any of the action. As you said its all about having fun while you learn.
11-28-2007, 05:16 AM   #15
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Hi!

first outing with the new camera.
a nearby town here has some caves. they have feature lighting, but still fairly dim.

i don't have a tripod yet, so this image is handheld, and of course srunk quite a bit to make it more practical on the forum.
I hope the quality is good enough for effective feedback from anyone who's interested.

noise was noticable, as i couldn't seem to get anything usable without iso1600
but that may just be my inexperience.

Any suggestions on technique improvements.

ISO 1600, 19mm, f4, 1/10sec
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