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01-03-2013, 09:10 AM   #1
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Need help picking a prime low light lens - good autofocus

I have a Pentax K100D. I have two young daughters that I take photos of inside the house. I've been using my manual 50mm f2 for taking indoor shots, but I'm not very good at focusing quickly - particularly when the girls are moving around etc. Maybe I'm just trying to squeeze too much of the low light capabilities and having it wide open at f2 making it difficult to focus. But I'm wondering if there's a fast lens that has a great autofocus. I was looking at the FA 50mm 1.7 and the DA 50mm 1.8. I also looked at the FA 50mm 1.4, but I've read that you need a hood for that one - not a big deal I guess, but I like the idea of a small lens. I'm trying to stay less than $300 but would entertain more expensive option. I'd also be using it outside as an all-around lens. I'm just a amateur so I don't need anything fancy. Also not sure how much the autofocus is more about my camera or the lens. I wish we had a place around here to rent lenses. I'm in Salem, OR.

thanks

01-03-2013, 09:27 AM   #2
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Unfortunately there is no lens that can help the K100D perform in low light. I would save up for a used K5 with kit/ WR lens.
My $0.02.

Last edited by Ex Finn.; 01-03-2013 at 09:33 AM.
01-03-2013, 09:36 AM   #3
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QuoteOriginally posted by schnur07 Quote
I wish we had a place around here to rent lenses
You can rent here. CameraLensRental.com - Your online source for lens rentals and camera rentals
01-03-2013, 09:36 AM   #4
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Low-Light, Fast A/F?

Hello Schnur07, Welcome to the Forum!
The first lens that came to mind after reading your post is the DA 35mm f/2.4 AL.
For about $200 USD new, (about $150-170 used) you will have a tack-sharp, fast A/F normal-view prime that will serve you well as a walk-around, street, candid and landscape lens. It is very small, light and a bargain to boot!
Here's the PF lens reviews;
SMC Pentax-DA 35mm F2.4 AL Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database
And for more info and lots of sample photos, check out the "Plastic Fantastic" thread.
I believe it will work as well on your K100D as well as any modern lens, for even faster A/F, you would have to upgrade the camera body.
FWIW, the FASTEST and most accurate A/F I've ever seen on a Pentax lens isn't a prime, but the F 35-70 f/3.5-4.5 zoom. While it lacks the great low-light capability of a prime, in all other respects it is a fine all-purpose zoom with a "Macro" (close-focusing, actually) function at the 70mm end. About $50.00 USD on eBay or other online sellers.
Both these lenses use a 49mm filter/hood size, a near-standard Pentax size. Saves quite a bit of money and space in accessories like CPL's and hoods!
JMO,
Ron


Last edited by rbefly; 01-03-2013 at 09:45 AM.
01-03-2013, 09:40 AM   #5
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Generally, the autofocus performance lies within the camera more than the lens. The lens is important for transmitting the light (and also a good quality image signal) to the autofocus sensor, but it is the autofocus sensor's job to interpret the data and perform the calculations.

I would say getting a DA 35 F2.4, a FA 50 F1.7, or the new DA 50 F1.8 would be a good investment regardless - and they may perform well on your K100D in indoor shooting. Just be aware that the majority of the focusing performance lies within the camera.
01-03-2013, 06:00 PM   #6
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I appreciate all the replies. Regarding the camera body being the biggest drive for focus, and maybe specifically the 100d, is it a matter of a fast auto focus, an accurate auto focus or both? I'm ok with it not being quite as fast. I just hate when I'm using my manual f2 and get my daughter's toy in their hand in focus instead of their face - or maybe their ear. Or if they move a little bit and then I have to manually refocus. Seems like autofocus would be a huge upgrade from my poor manual focus skills.
01-03-2013, 08:09 PM - 1 Like   #7
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I have lots of experience chasing my kids with a K100D. I came to terms with shooting at 3200 -- in B&W it's "grain", not "noise", right?

For a long time I used an FA 50/1.4. Terrific little len, and super cheap for the image quality you get.
01-03-2013, 08:11 PM   #8
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QuoteOriginally posted by schnur07 Quote
I appreciate all the replies. Regarding the camera body being the biggest drive for focus, and maybe specifically the 100d, is it a matter of a fast auto focus, an accurate auto focus or both? I'm ok with it not being quite as fast. I just hate when I'm using my manual f2 and get my daughter's toy in their hand in focus instead of their face - or maybe their ear. Or if they move a little bit and then I have to manually refocus. Seems like autofocus would be a huge upgrade from my poor manual focus skills.
It sounds as if you have a manual focusing issue rather than a camera issue. In your position I would get an AF lens and see how that goes before upgrading the body. New DA35 or new/second-hand FA50 (either 1.4 or 1.7, doesn't matter) sound like possible routes to go.

01-03-2013, 08:57 PM   #9
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QuoteOriginally posted by schnur07 Quote
I'm using my manual f2 and get my daughter's toy in their hand in focus instead of their face
At f1:2 your depth of field is pretty unforgiving for pictures of moving kids.
This is where a newer body with good high ISO performance and more advanced AF engine would come in handy. You could shoot at f4 or 5.6 for better DOF coverage, yielding more keepers.

I took around 40k shots with my K100D before giving it to my daughter. It always was and still is accurate in AF, given good light. In poor light it would take several tries to get a lock and half of the time it just could not do it.
Rent a K5 and a AF lens you think you would like for a week, and go from there.

Cheers.

Last edited by Ex Finn.; 01-03-2013 at 09:13 PM.
01-04-2013, 02:29 AM   #10
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For chasing kids indoors, I would also go for a 35mm lens. I haven't used a DA35 but own an FA35/f2.0 that focuses quite fast (and is tack-sharp) with a K10D and K5IIS. A fast 50 is okay but inside the house it might be a bit long at times.
01-04-2013, 09:57 PM   #11
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I think I'm leaning toward the FA/F 50mm 1.7. I'll just have to patient to find one. Right now I only see two on E bay. One is about $250, the other looks like it's in poor shape. I didn't see anything on the marketplace. I think part of my manual focus issues relate to me wearing glasses - in addition to my limited experience. But I'm thinking I should go back to wearing contacts for my photography hobby. Part of it is me pushing the lens to a very limited DOF making it tricky to get the spot on focus I want.

Also can someone help explain when people reviewing lenses talk about them being soft wide open. Read one blog that sort of debunked this saying it's a focus problem and not a soft problem. The blog showed a photo of a pop can with a 50mm 1.4 wide open and it looked plenty sharp.
01-07-2013, 05:25 PM   #12
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QuoteOriginally posted by rbefly Quote
Hello Schnur07, Welcome to the Forum!
The first lens that came to mind after reading your post is the DA 35mm f/2.4 AL.
For about $200 USD new, (about $150-170 used) you will have a tack-sharp, fast A/F normal-view prime that will serve you well as a walk-around, street, candid and landscape lens. It is very small, light and a bargain to boot!
Here's the PF lens reviews;
SMC Pentax-DA 35mm F2.4 AL Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database
And for more info and lots of sample photos, check out the "Plastic Fantastic" thread.
I believe it will work as well on your K100D as well as any modern lens, for even faster A/F, you would have to upgrade the camera body.
FWIW, the FASTEST and most accurate A/F I've ever seen on a Pentax lens isn't a prime, but the F 35-70 f/3.5-4.5 zoom. While it lacks the great low-light capability of a prime, in all other respects it is a fine all-purpose zoom with a "Macro" (close-focusing, actually) function at the 70mm end. About $50.00 USD on eBay or other online sellers.
Both these lenses use a 49mm filter/hood size, a near-standard Pentax size. Saves quite a bit of money and space in accessories like CPL's and hoods!
JMO,
Ron
+1 for the DA 35 F2.4. ...and it wont break your wallet. I have that and the Pentax-F 50mm F1.7 (which I was able to find a mint copy of). Good luck
01-07-2013, 05:34 PM   #13
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QuoteOriginally posted by schnur07 Quote
I have a Pentax K100D. I have two young daughters that I take photos of inside the house. I've been using my manual 50mm f2 for taking indoor shots, but I'm not very good at focusing quickly - particularly when the girls are moving around etc. Maybe I'm just trying to squeeze too much of the low light capabilities and having it wide open at f2 making it difficult to focus. But I'm wondering if there's a fast lens that has a great autofocus. I was looking at the FA 50mm 1.7 and the DA 50mm 1.8. I also looked at the FA 50mm 1.4, but I've read that you need a hood for that one - not a big deal I guess, but I like the idea of a small lens. I'm trying to stay less than $300 but would entertain more expensive option. I'd also be using it outside as an all-around lens. I'm just a amateur so I don't need anything fancy. Also not sure how much the autofocus is more about my camera or the lens. I wish we had a place around here to rent lenses. I'm in Salem, OR.

thanks
+1 for the DA 35 F2.4. Still, at the risk of stating the obvious - for fast action shots without a lot of light, nothing beats using an external tilt/swivel flash.
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