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Old Jul 29, 2009, 1:46 PM   #1
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Default Tamron 70-300 on Sony A200

Dear All,

I recently bought the A200 (My first DSLR) and after reading a lot of online reviews took the Tamron 70-300 LD Di lens.

I have 2 queries on my gear -

1) Camera Query: Are 10 hot pixels at 20 Seconds shutter OK for an entry level DSLR?

2) I tried using the Tamron 70-300. It was quite fast in the shop (probably the shop was very well lit). During cloudy skies it tends to hunt like crazy (moving throughout the focus range) before Autofocussing. My kit lens 18-70 is comparitively fast (I could take some birds in flight photos with it). Could anyone let me know some tricks so that the AF becomes fater in Tamron and the lens does not hunt. I have bought the lens to take bird photos. Further does the UV (0) filter has any effect on AF?

Thanks a ton for your advice.

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Old Jul 29, 2009, 2:22 PM   #2
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Welcome to the forums and congrats on the A200.

20 seconds, huh? Turn on Long Exposure Noise Reduction and that should take care of it. Unless you're getting hot pixels at faster than 1 second shutter speeds, I wouldn't worry about them.

As for the Tamron's AF, for birds, set the camera to use Continuous AF and select the Center AF Point (it's more sensitive compared to the outside AF points). Then, after locking focus with a half press of the shutter button, the camera should use the other AF sensor points to track the subject.

As for UV filters, I can see where you might have AF problems using one if you get a lot of flare (or loss of contrast from flare due to light reflections in between optical elements) since the AF sensors wouldn't be able to see as well. Personally, I never use UV filters with digital.
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Old Jul 30, 2009, 12:25 AM   #3
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Thanks a lot Jim. I would try out these suggestions today evening when I reach home.

Rgds,
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Old Jul 30, 2009, 1:40 AM   #4
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Don't except miracles from the Tamron. At $160 new, it is a very good bargain, and a decent lens.

From what I have read, pretty much all Tamrons have slow AF. Don't know about their more expensive lenses.

On the other hand, I have read many horror stories about Sigma lenses and bad gears. Since I cannot afford top lenses, I will stick with Tamron and slow AF than taking chances with a Sigma (my opinion). Tamron has 6 years warranty, which they honor.

I have gotten a few hot pixels too a few times with long exposure with the identical (w/ live view) a300.
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Old Jul 30, 2009, 8:49 AM   #5
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For birds in flight, you might want to prefocus. Switch to manual focus, and focus just short of infinity. Without knowing the circumstances you're in when you shoot, it's hard for me to tell you exactly what settings to use or how to determine them. Different combinations of distance and aperture can affect the results.

You could also use AF to focus on some distant object, and then immediately switch to manual focus, thereby preserving the focus setting as determined by the AF setting. For instance, you could use AF to focus on a tree where a bird might fly out of, switch to MF, and when the bird does fly, it will be in focus.
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Old Jul 30, 2009, 2:29 PM   #6
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Quote:
Originally Posted by rsnfunky View Post
Dear All,

I recently bought the A200 (My first DSLR) and after reading a lot of online reviews took the Tamron 70-300 LD Di lens.

I have 2 queries on my gear -

1) Camera Query: Are 10 hot pixels at 20 Seconds shutter OK for an entry level DSLR?
I've read many times that with the A700, once the camera date/time goes past month end, the camera automatically writes out the dead/hot pixels the camera's sensor has auto-detected in the previous month. I can find nothing on this in the PDF version of the A700 owners manual and I'm not so sure this is true for the A200 being that it is a lower end model in the Sony line.

I recall people posting that if you advance the camera date past month end, it will force the camera to perform the auto-write. You could try this if you still see the hot pixels with a camera body that is at room temperature.

10 hot pixels seems pretty high to me unless you were using your camera in extreme heat. This can happen if you're using your camera in a manner that would keep the sensor under power for long periods or if the camera body was "heat soaked" as could happen in a bag in the back seat of your car or even in the trunk.

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Old Jul 30, 2009, 2:43 PM   #7
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The remap routine is designed to find hot pixels at typical shutter speeds (i.e., faster than 1 second). You wouldn't want it to map out pixels that are only hot on longer exposures. That's why you have a Long Exposure Noise Reduction features. ;-) It's performing a dark frame subtraction on pixels that are hotter than they should be.

Hot pixels are when photosites record a higher value (brighter) than they should, usually with longer shutter speeds. When the problem occurs at faster shutter speeds, they're considered "stuck" (always bright). Virtually all CCDs will have hot pixels in some conditions. The longer the shutter is open (and the darker the conditions since not enough photons are hitting the sensor) the more likely a photosite won't be linear in it's output when responding to light, and it will record a higher value than it should.

Temperature also impacts it (which is why you see cooling systems for sensors in digital cameras used in astronomy). The more you test for them, the more you'll likely have, especially without any light hitting the sensor.

You just don't see hot pixels with most newer cameras because of built in noise reduction to subtract them out on longer exposures, since the ones that occur at typical shutter speeds have already been mapped out at the factory. So, make sure your long exposure noise reduction is turned on. That's what it's there for (to remove hot pixels on longer exposures). It's not designed to remove the typical noise you see. It's entire purpose is to remove hot pixels on longer exposures. Hot Pixels are normal on longer exposures. Most newer cameras have a built in dark frame noise reduction system to try and locate them and map them out on longer exposures.

It works on photos taken longer than 1 second (where hot pixels usually show up). The way it works is by taking two photos. The first photo is of your subject. Then the camera automatically takes a second image using the same settings with the shutter closed. The camera then notes the positions of any hot pixels in the "dark frame" (second) exposure, and maps them out of the actual exposure. It knows where to find them because the dark frame exposure was taken at the same time, using the same settings, with the camera at the same temperature. In most cases the hot pixel locations will be the same in both images using this technique. But, the longer the exposure, the greater the chance it will miss some of them.

If you have a pixel that is always hot (bright), even on shorter exposures in good light, then it's referred to as a "Stuck" pixel. The Long Exposure NR feature won't help for that. In most cameras, when a camera develops a stuck pixel, a trip back to the manufacturer is needed. The manufacturer then updates a bad pixel table in EEPROM. When a photo is taken the image processing automatically checks the camera's bad pixel table and maps the pixel out (replaces it with values determined from adjacent pixels using sophisticated interpolation algorithms). Some cameras allow the user to perform a bad pixel map themselves (a number of Olympus models have a menu choice that calls a procedure to locate and map out bad pixels).

KM and Sony DSLR models have an undocumented feature that checks and maps out bad pixels on a monthly basis that you can force by setting the date up one month if you don't want to wait after you see a bad one. To force it, set your camera's date and time up to the last few minutes of the last day in the month. Turn it off, and wait until enough time has passed for the internal clock to change months. Turn the camera back on, take some photos, and turn it off again. Then, after you are sure the red led has gone out, turn it on and reset your date and time back to where it should be. Take some photos and see if the hot pixels are gone.

Note that this is *not* designed to remove hot pixels that occur on longer exposures (they're normal, and the long exposure noise reduction should get most of them if turned on, as it should kick in on exposures of around 1 second or longer). The remap is only designed to map out pixels that are going to be hot on typical exposures (faster shutter speeds) You don't want it remapping pixels that only show up on long expoures since the long exposure noise reduction system's entire purpose is to remove those, and you can end up with a lot of them on a long exposure without noise reduction turned on with many cameras.

If you do have some at typical shutter speeds (with the lens cap off), it's probably best to perform a remap with a warm camera to make sure it finds them all (the warmer the sensor, the more likely they'll occur, and you'll want them to be bright enough to meet the threshold the camera is looking for before it remaps them).
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Old Jul 31, 2009, 2:08 AM   #8
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Thanks guys,

The hot pixels that I found were when the camera was completely cold and just switched on. Further the Noise Reduction was on. I will retry the process with a warm camera (after taking some shots) and with NR off and recheck the correct numbers of hot pixels.

What do you think, should I get a replacement from Sony (Actually this is the replacement camera, my previous new camera had 20 hot pixels at 1 sec shutter speed).
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Old Jul 31, 2009, 6:17 AM   #9
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Quote:
Originally Posted by rsnfunky View Post
Thanks guys,

The hot pixels that I found were when the camera was completely cold and just switched on. Further the Noise Reduction was on. I will retry the process with a warm camera (after taking some shots) and with NR off and recheck the correct numbers of hot pixels.

What do you think, should I get a replacement from Sony (Actually this is the replacement camera, my previous new camera had 20 hot pixels at 1 sec shutter speed).
With long exposures, you'll get hot pixels. It's called thermal noise (though, of course, 20 hot pixels in 1 second is too many.) Many cameras that use the main image sensor for 'Live View' will actually turn themselves off when the image sensor gets too hot.

You might have to try a shorter shutter speed or a smaller aperture.
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Old Jul 31, 2009, 1:22 PM   #10
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Thanks Jim for posting the info on the remapping feature.

for rsnfunky.... if you take an exposure with the lens cap on you can run the jpeg thru a software program that will test for dead or hot pixels.

http://www.starzen.com/imaging/deadpixeltest.htm

If it is as bad as this then you have a problem:



Red arrows point to pixel clusters that show up in most images and blue arrows point to pixels that show up when the camera gets warm. All at exposures 1 second and shorter. These were from my old old Canon G1 before I retired it.

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