EOS Ra - Stuck/Hot Pixels with long exposures...
5
arman mohammadi wrote:
I just received my canon ra camera , during my test , i realized that there are many colorful dots on the picture while shooting with lens cap on the lens .
Hello Arman.
I have the EOS Ra. Truly "Dead" Pixels receive no charge and are black ... Your images are likely to show "stuck" pixels.
.
Whilst some may disagree, I believe it's possible to have dead pixels that are "stuck" on White and cannot be removed or fixed. But because they still return an illuminated value, some will say they are not genuinely "Dead". I would disagree if a pixel remains "White" for 4 years of shooting and appears in every single image taken with that camera. In such instances I would personally prefer to call that a Dead pixel rather than a Stuck one.
.
Doing an Auto Sensor Clean - Put your Body Cap on the camera and select the Sensor Clean option in the Menu. It doesn't hurt to do this after a session of long exposures.
.
*DEAD PIXELS:
Dead Pixels are literally defective pixels that receive no power. Usually they are black.
*STUCK PIXELS:
Stuck Pixels are unable to change color but often disappear or return to normal. They can be red, blue, green or white etc. A stuck pixel will show up in any image (whether or not a long exposure and high ISO are used). They are harder to see against similar colors or bright scenes but will show up with darker subjects. An Automatic Sensor Clean by the camera's menu options will often return a Stuck Pixel to "Normal Status" again.
*HOT PIXELS:
Usually appear with longer exposures - especially with higher ISOs. They will not show up with normal shutter speeds later but may often be visible during future long exposures. Usually Hot Pixels will appear and disappear in consecutive images. But sometimes they become Stuck Pixels. This is normal and simply an aspect of current technology that must simply be endured or tollerated.
.
Astropotography can create just the right instances for a digital camera to generate "stuck pixels" and "hot pixels". Pretty much all cameras will do this. Stuck pixels tend to stay stuck on a specific color value or tonal value. If a pixel is Dead, it will show up during normal photography with lower ISO settings and faster shutter speeds (eg while taking a portrait). Hence, a simple test (see image below) will reveal if your have dead or hot pixels...
.
EOS Ra - Here's a test picture I took with "normal" exposure times - to test that my hot pixels were gone after doing an automatic sensor clean. There were none that I could see. The dark scene with modestly normal shutter speeds would still demonstrate a dead pixel.
.
Stuck pixels / Hot pixels are normal and to be expected. I think I had about 80 stuck pixels on one of my first shots with the Ra. They disappeared after I got home and did an automatic sensor clean with the lens cap on the body. Some have returned in future sessions. Often if you compare several shots taken minutes apart, you can see the red, green and blue pixels appear and disappear over dozens or even hundreds of shots. If the same Hot Pixels show up repeatedly in exactly the same place in your Photographs, you might consider doing an Automatic Sensor Clean with the lens cap on (remove the lens for this). When the process is done, it only takes about 15 seconds or so... and then you can turn your camera off to finish the process.
.
This is a CROPPED area of one of my test images from the EOS Ra that shows stuck pixels in the center of the frame. I have placed a red square around each one. This was the first long exposure I had taken with this camera after spending a few days taking terrestrial images with it during daylight hours. I had not locked down my tripod head and the camera turned slowly on the tripos, causing the background to blur during the 20 second exposure. But the blurred background helps show the stuck pixels more easily.
.
It does get more problematic when you get a stuck pixel on your LCD screen because it will annoy you more ... fortunately, this is usually very rare and usually doesn't go away. Canon says THIS in the EOS R manual: "Although the screen and viewfinder are manufactured with very high precision technology with over 99.99% effective pixels, 0.01% or fewer of the pixels may be dead, and there may also be spots of black, red, or other colors. This is not a malfunction. They do not affect the images recorded."
.
With my old EOS 6D (which is a favorite among Astrophotographers), my first long exposures at high ISO (eg 20 seconds at ISO 2000) I was getting so many stuck pixels that it looked like snow at first glance. This was the first time I had used the camera. By doing an Automatic Sensor Clean when I got home, they disappeared. Some returned later when I was doing some similar exposures. The longer the exposure and the higher the ISO used, the more likely some pixels will get stuck.
.
As mentioned above, Dead Pixels are defective and cannot be fixed. Each pixel on your sensor has a microscopic transistor of sorts that can sometimes allow more or sometimes less power through to the pixel. The longer your exposure is, the more likely it is for that pixel to warm up and become "stuck". A short 1-second exposure isn't long enough to get a pixel to become Hot/Stuck. But a 15 or 20 second exposure often is. Shooting in cooler weather will often produce less stuck or hot pixels. Shooting for longer periods in warmer weather may produce more. If repeated automatic sensor cleaning fails to "shake" a few of the Hot Pixels, you can presumably refer to them as "Stuck",
.
This image of my EOS Ra was taken with the EOS M6. Since I needed a long exposure with a higher-than-usual ISO setting, there were a few dozen Hot Pixels and even a few "Stuck Pixels"that I needed to edit out with Photoshop. For me, that's easy enough but a Dark Frame Subtraction would offer a faster method for others.
.
Taking a "Dark Frame" during imaging sessions is one way to subtract any stuck pixels. The Dark Frame exposure needs to be taken at the same ISO and same Exposure Time as your full color image/s to ensure any stuck or hot pixels are subtracted using any software you might care to apply. To be certain your pixels were stuck/hot and not dead....try this: During daylight hours, take a picture with a normal shutter speed (eg 1/60sec or faster) with an ISO speed of 100. Don't worry about image color etc. Take a look to see if your stuck pixels are still showing. If they're not visible then there's nothing abnormal happening with your camera.
.
Most people buying a new DSLR or Mirrorless camera will not use their camera for long exposures like we do with the EOS Ra. So they will probably never notice until a Pixel Site becomes a Dead Pixel. It's normal to get a few stuck pixels on a sensor after several years of use with a specific camera. But it can surprise people when they buy a new camera and it demonstrates some stuck pixels or hot pixels. If you're only getting a "few dots" with your test images from your Ra, you're doing very well. It will change over time as you take more long exposures... but it's normal behavior to experience this. Take your lens off, put the body cap on the Ra and do an Automatic Sensor Clean. It may map out any annoying pixels for you. I believe there's more sophisticated ways to "map out" an annoying pixels but this method is simple and requires no risk on your part since the sensor is covered the entire time by the lens cap. Your new EOS Ra camera sounds perfectly normal to me.
