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Canon A70 Problems With Pixels in Pictures

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emcd

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I have started to see problems in pictures that I have taken with flash on and aperture priority set at 5.6. There are hexagon pixels showing up in the pictures - particularly when there is black in the subject area. I exchanged my camera for another one and I continue to see the problem. I am wondering if this is a weakness in the A70.

Look at the yellow circled parts of these pictures: Click on the thumbnail to see the picture and click on the picture again to enlarge it. These hexagon pixels are not in the same place from picture to picture.

http://www.sendpix.com/albums/03051420/2053550000000d38d98ef42f730b6658871b128c43d57/

Has anybody else seen this? Is there a solution?

Thanks,
emcd
 
The hexagonal spots are out-of-focus reflections of the flash from dust or other particulates in the air. They are a common problem with small digital cameras, whose short focal length results in large depth of focus. The hexagonal shape comes from the shape of the aperture/shutter. They have been discussed in detail in several threads on this forum...
--
Dave Gard
http://www.pbase.com/gard
 
Thanks for your reply. I am wondering if I select a different aperture, if the spots would not occur as often.

Regards,
emcd
 
I have an a70 too and have seen this from time to time. The Canon user manual says this is a reflection from dust but I think it looks like internal lens reflections. The hexagonal shape is probably the lens diaphragm opening (sets the aperture), and the concentric circles the lens elelments.

Anyway there's apparently nothing you can do except to try again from a different angle.

Bob Resnikoff
emcd said:
I have started to see problems in pictures that I have taken with
flash on and aperture priority set at 5.6. There are hexagon
pixels showing up in the pictures - particularly when there is
black in the subject area. I exchanged my camera for another one
and I continue to see the problem. I am wondering if this is a
weakness in the A70.

Look at the yellow circled parts of these pictures: Click on the
thumbnail to see the picture and click on the picture again to
enlarge it. These hexagon pixels are not in the same place from
picture to picture.

http://www.sendpix.com/albums/03051420/2053550000000d38d98ef42f730b6658871b128c43d57/

Has anybody else seen this? Is there a solution?

Thanks,
emcd
Click to expand...
 
I think the common "white ghosts" that people see are reflections from particulates (dust, bugs, snow) in the air (or in one case that I remember, water).

It is very common for out of focus specular highlights to exhibit the shape of the aperture or diaphragm... it has to do with diffraction and optics. This can cause them to look like little hexagons in many cameras. I used to use a 500 mm mirror telephoto with my film SLR, and it had a secondary mirror that obstructed 30% of the main aperture. With it, out of focus specular highlights looked like little rings of light, or bright donuts.

I have wondered about the concentric appearance of the hexagonal highlights myself. On a thread several weeks ago, I commented on it, and suggested that it might result from the way the camera is using a single diaphragm for both aperture control and shutter. Perhaps the diaphragm opens and closes in small increments or steps? Don't recall that there were any replies to that speculation...
--
Dave Gard
http://www.pbase.com/gard
 
emcd said:
I have started to see problems in pictures that I have taken with
flash on and aperture priority set at 5.6. There are hexagon
pixels showing up in the pictures - particularly when there is
black in the subject area. I exchanged my camera for another one
and I continue to see the problem. I am wondering if this is a
weakness in the A70.

Look at the yellow circled parts of these pictures: Click on the
thumbnail to see the picture and click on the picture again to
enlarge it. These hexagon pixels are not in the same place from
picture to picture.

http://www.sendpix.com/albums/03051420/2053550000000d38d98ef42f730b6658871b128c43d57/

Has anybody else seen this? Is there a solution?

Thanks,
emcd
Click to expand...
 
This is caused by out of focus dust spots in the air directly in front of the camera. The dust may be so small that you can't even notice it with the naked eye, but it's there nonetheless.

You'll find this happening fairly rarely (in my experience with my A70 it's only happened maybe twice). The only fix is to get the flash off camera (away from the axis of the lens). You can use any slave flash with the A70 to achieve this, but you must use the camera in manual mode so it doesn't do a pre-flash.

Sincerely, Bob the Printer
 
Donald Lam wrote:

I have seen circular spots or blobs in a G2. These are perfect circles with well defined edges. They are different in size and opacity. Sometimes, mutiple circles occur in the same picture. Some of these circles overlap each other. They are most visible in dark areas. I doubt if they were due to out of focus specks of dust because of their large diameters. Canon has requested to send the camera back to their factory service center for repair. According to their customer service rep, their techs had readjusted the image processor. No technical details or explanation were given why these circles occurred and how adjusting the image processor would correct the problem. I will retest the camera when I get it back.

Don
Donald Lam said:
emcd said:
I have started to see problems in pictures that I have taken with
flash on and aperture priority set at 5.6. There are hexagon
pixels showing up in the pictures - particularly when there is
black in the subject area. I exchanged my camera for another one
and I continue to see the problem. I am wondering if this is a
weakness in the A70.

Look at the yellow circled parts of these pictures: Click on the
thumbnail to see the picture and click on the picture again to
enlarge it. These hexagon pixels are not in the same place from
picture to picture.

http://www.sendpix.com/albums/03051420/2053550000000d38d98ef42f730b6658871b128c43d57/

Has anybody else seen this? Is there a solution?

Thanks,
emcd
Click to expand...
Click to expand...
 
Dave,

I did some additional investigation too which I think validates the internal reflections hypothesis: look directly into the lens and you'll see that the concentric circles you see in the white blobs are right in front of you in the lens. Additionally, if you get a loupe and press the shutter while looking through the lens with the loupe, you can see the hexagonal diaphragm blades (this is hard because the aperture is very small and you cut out most of the light when the loupe is covering the lens).

Since what we're seeing in the blobs is a picture of the front of the lens, it must be a reflection from the inside of the front element which is probably triggered by the light entering at a specific angle.

Bob Resnikoff
David Gard said:
I did a little test, to demonstrate the appearance of out-of-focus
dust spots reflecting from the on-board flash... see:

http://www.pbase.com/gard/dust_devils

--
Dave Gard
http://www.pbase.com/gard
Click to expand...
 
Dave,

I examined your before and after images in detail, and although they appear at first to be identical (except for the blobs) there is either a slight positional difference or flash output difference. You can see this if you look at the reflective square on the quilt to the right of the guitar. The pattern of the reflection is not the same in the two images. If it's a position shift, then maybe that's why there are internal reflections in one and not the other.

Bob
David Gard said:
I did a little test, to demonstrate the appearance of out-of-focus
dust spots reflecting from the on-board flash... see:

http://www.pbase.com/gard/dust_devils

--
Dave Gard
http://www.pbase.com/gard
Click to expand...
 
Bob Resnikoff said:
Dave,

I examined your before and after images in detail, and although
they appear at first to be identical (except for the blobs) there
is either a slight positional difference or flash output
difference. You can see this if you look at the reflective square
on the quilt to the right of the guitar. The pattern of the
reflection is not the same in the two images. If it's a position
shift, then maybe that's why there are internal reflections in one
and not the other.
Click to expand...
Better be sure to use a tripod if you're posting to this group! :)
 
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