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11-25-2012, 10:10 AM   #1
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Blurriness? Low light help, lens repair, and fast lens question

Hi everyone!

I've been enjoying my navy Pentax K-x for a year and a half now, and I still feel like there is so much to learn to use my camera well. I lurked and read hundreds of pages here in this forum (Thank you for your shared wisdom) before making the purchase of a K-x and a MIJ early silver 43mm (serial 7333) and 77mm. I was convinced by some of the members that it would do me well to start off learning photography on primes, and I reasoned that I could always sell my primes back at reasonable prices if I couldn't get the knack of it. But after using the kit lens and these 2 primes for these 2 years, I came up with some questions that I couldn't find an answer to:

1. How can you tell if a lens is a good copy or not (blurry)? I bought my K-x and 43mm used, and it seems like a lot of the pictures I take are a little blurry. I'm not sure whether it's because the lens is at fault, or if there's a front/back focus problem (and I think a K-x isn't like the K-5 with adjustments), or if it's the K-x problem. =( Or, it could be that I like taking the pictures at F1.9-2.8, so the depth of field is thinner and therefore it's harder to get the right area in focus. =( And if there is a possibility of a problem, should I send it into repair? I have a low serial 43mm, which is supposed to have the special blue coating and I heard I might lose that coating if it's repaired....

2. In low light, am I supposed to use a lower F stop? Sure, I can use f4 on my 43mm, but it sort of defeats the purpose of having those extra 2 stops, and my kit lens can do the same f stop. However, with a lower f stop, the DOF is again thinner and makes it harder to get a good shot. I know I can up the iso or lower the shutter speed, but at 1/30 shutter speed, many pictures are still sort of dark and needs a high iso. =(

I just recently was asked to shoot some pictures for a school catalog, and they wanted me to do some room shots. However, as it was a little dark, I couldn't use a low f stop or else the depth would be too narrow. But with f8 or f11, it was really dark and I needed to up the iso to even see the whole room (it's about a 150 feet long room) But an iso of 1600 is pretty grainy in my opinion. How would you have solved this? I shot in RAW and I still couldn't overcome the graininess.

Thank you for your help! I love my camera but having problems with low light and blurriness have marred my enthusiasm a bit. =( Your advice would be greatly appreciated. I'm sure I have more questions but these are the ones I remembered.

11-25-2012, 10:31 AM   #2
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QuoteQuote:
I just recently was asked to shoot some pictures for a school catalog, and they wanted me to do some room shots. However, as it was a little dark, I couldn't use a low f stop or else the depth would be too narrow. But with f8 or f11, it was really dark and I needed to up the iso to even see the whole room (it's about a 150 feet long room) But an iso of 1600 is pretty grainy in my opinion. How would you have solved this? I shot in RAW and I still couldn't overcome the graininess.
Get a tripod. Make a long exposure at ISO 100.
11-25-2012, 10:37 AM   #3
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QuoteOriginally posted by Byakko Quote
How can you tell if a lens is a good copy or not (blurry)?
With a controlled test, on a tripod using a proper target. Here is a link to a review of test targets: Fixing Front and Back Focus - Introduction - PentaxForums.com You can use homemade targets if you do not want to purchase one but the methodology is the same. Normally if you have a bad copy of a lens or if there is a auto-focus error the error will be consistent. All images taken under similar conditions will be off by the same amount. If you are getting some good and some bad, then it is most likely technique not the camera or lens.

One other thought because it has happened to me. If you are using the SR (shake reduction) feature you must wait until it locks in indicated by the green hand lighting up. If you shoot before that happens you often get blurry pictures caused by the SR system.

QuoteOriginally posted by Byakko Quote
In low light, am I supposed to use a lower F stop?
By lower you mean smaller number? Smaller number means a bigger hole for the light. So yes, that is one way to handle lower light but there is no free lunch. As you noted lower f/stops means smaller depth of focus. So in many cases the aperture is not as useful to increase light because you need a particular f/stop to get the depth of focus you need.

So in your example you need f/8 or f/11 to get the whole room in focus. But there is not enough light. This means you can either use a tripod with a remote so you can use very slow shutter speeds, or you can add light using strobes or whatever other method is available. You could also up the ISO but realistically (as you discovered) that is not a good solution because it lowers the image quality.

What I would have done in your situation is use a tripod, lowest ISO you can get (100 I think on k-x), set exposure compensation up by maybe a half stop, camera in Av mode, aperture set at f/11, used a remote and 2 second delay so I did not have to touch the camera and the delay helps minimize shutter vibration. Then I would have shot several variations with slightly different exposure compensation. I like to over expose just a little as it reduces the noise in the shadows. Too much though and you blow out the highlights so you have to be careful.
11-25-2012, 11:15 AM   #4
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I also have the K-x with fast lenses. You are correct, a large aperture will give less dof, but it depends on factors such as focal length and distance to subject too. There is an online dof calculator that helps to understand this: Online Depth of Field Calculator

Perhaps you could post some pics to show us your concerns.

11-25-2012, 01:21 PM   #5
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Echoing using a tripod. I find the fact you had grain at ISO1600 kind of odd - my K-x was usable up to and beyond that point provided I had at least some sort of even light source going on.

This is 1/90 seconds @ ISO 3200 using a cheap Sigma 70-300mm zoom wide open at f/4.5. Unless you zoom in and start peeping at it at 100%, the grain is negligible - and this was about as dark as you could get. I was shooting at a county fair after dark from about 300 feet away in the bleachers overlooking the racetrack where the stage was set up. The slight fuzziness is due to my handholding the thing and shooting lower then what my focal length was.


11-25-2012, 05:04 PM   #6
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The tripod suggestions are good, just make sure that SR is off when the camera is on a tripod. The system will try to compensate for movement that isn't there, so it will add shake instead of reducing it. The SR is automatically shut off if you use the 2 second delay. That's what I do, because when you forget to turn the SR back on, you can take a lot of shots before you remember, but you'll notice the first time you forget to switch off the 2 second delay.

The idea behind the tests above is to eliminate any of the other causes of a blurry photo except part of the autofocus system. That's where the camera says "focus here" and the lens focuses in a different spot. It's not always the most likely problem. Other possibilities:
Subject motion - while the shutter was open, the subject moved. Flowers in the wind, a kid, a playful dog or a fast car might need a faster shutter speed.

Camera motion - while the shutter was open, the camera moved. Usually this is unintentional, often bad technique. With your 43mm lens, you need good technique for a shutter speed less than 1/100 sec. Someone with good technique and SR might get a good shot at 1/10 sec.

Perfect AF on the wrong thing - autofocus is nowhere near as smart as Picasa or some other software with face detection. It only sees an edge with contrast. AF might see a brick behind the most beautiful person in the world and focus on that brick, and be working exactly as it was designed. Your job is to know that, watch for it and adjust as necessary.

Small depth of field - anything outside the depth of field is going to be soft, that's just how it works. Subjects that aren't flat can have parts in focus and parts that aren't.

Terrible lenses - not many lenses are that terrible, but some have trouble, especially at the edge of their settings (wide open, at either the end of the zoom, etc.).

With some experience, you can look at the settings used for a photo and the photo itself and figure out what went wrong. I find that most of the time, I did something wrong.

BTW, a repair shouldn't harm your lens coatings at all.
11-25-2012, 08:08 PM   #7
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Thank you for your replies! A little bit more clarification, the room had the students and the teacher in it, so a tripod + long exposure wouldn't have worked since it would cause all the people to be blurry. So I needed a long DOF and ability to stop motion, or a short DOF which leads into my next question that I remembered:

1. Is it possible for the AF points to be off? I have it on single point most of the time, but it doesn't seem to be focused on it when I shoot sometimes. I tried the center spot, and some of the edge spots trying to get the middle row of students in focus, but the camera wanted to get the back wall in focus instead everytime. =( Is it because the AF spots aren't sensitive in a darkish room? I'll try to upload some of the pictures later.
11-25-2012, 10:07 PM   #8
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QuoteOriginally posted by Byakko Quote
1. Is it possible for the AF points to be off? I have it on single point most of the time, but it doesn't seem to be focused on it when I shoot sometimes. I tried the center spot, and some of the edge spots trying to get the middle row of students in focus, but the camera wanted to get the back wall in focus instead everytime. =( Is it because the AF spots aren't sensitive in a darkish room? I'll try to upload some of the pictures later.
As a general rule, the darker the area you're shooting, the more craptastic AF is going to be. You'll hit a point where its simply easier to manual focus then to trust the camera to lock where and how you want it to.

If you're shooting from a good distance you're probably going to have a somewhat wide depth of field to play with anyhow so you can find a decent focus then flip over to manual provided everyone you're shooting is staying in the same general location.

11-25-2012, 10:58 PM   #9
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You should post a few photos to show us what you think is unacceptable
11-26-2012, 01:13 PM   #10
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I think you might be using too small an aperture (larger f number) in your 150 ft. room. I plugged some numbers into a depth of field calculator and for 43mm, f4 seems like it would work OK. That would give you two or three stops more light than f8 or f11, so you could change ISO from 1600 to 200 or 400. The lens should be sharp enough at f4, so it's just a question of where the focus is and whether the depth of field calculator is correct.

It looks like the distance scale on the FA43 shows 8 meters. You could just try setting the focus ring between the 8 and the infinity mark.
11-27-2012, 06:07 PM   #11
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One other thing - you mention "graininess" at ISO 1600. What you are seeing is actually digital noise. Are you using any noise reduction? How are you processing your RAW files. Most programs have some form of noise reduction. You can purchase software that will do even more for a reasonable price. ISO 1600 should be perfectly usable with the K-X.
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