Do I have a bad CMOS sensor on my Xsi?

I use my Xsi/450d primarily for astrophotography (of the most amatuer kind).

I have noticed that after a few exposures of between 1 and 3 minutes that some subsequent shots have a green band at the bottom of the frame. It always looks the same and it doesn't matter whether the camera is riding piggy-back on my telescope (EFS lens on) or attached to the scope with a "T" ring for prime focus photography (shooting using the telescope as a super telephoto lens).

I use Live View and the LCD alot to focus and review frames and to time exposures although I do turn the brightness way down most of the time.

Do I have a bad sensor or is this a heat issue from the LCD or elsewhere?

Here's an ugly image (nearly full moon and a shaky mount) but it illustrates what I'm talking about:

LabHappy said:

I use my Xsi/450d primarily for astrophotography (of the most amatuer
kind).

I have noticed that after a few exposures of between 1 and 3 minutes
that some subsequent shots have a green band at the bottom of the
frame. It always looks the same and it doesn't matter whether the
camera is riding piggy-back on my telescope (EFS lens on) or attached
to the scope with a "T" ring for prime focus photography (shooting
using the telescope as a super telephoto lens).

I use Live View and the LCD alot to focus and review frames and to
time exposures although I do turn the brightness way down most of the
time.

Do I have a bad sensor or is this a heat issue from the LCD or
elsewhere?

Here's an ugly image (nearly full moon and a shaky mount) but it
illustrates what I'm talking about:

--

Click to expand...

--I have taken night pictures with XSi from 30 sec to 1/2 hour or more & have never seen anything like that . It sure doesnt look right. This was about a 1/2 hr exposure with XSi.



This was abt 1.5 hr with the 40D.



Brian Schneider

Thanks Brian. The photo I included is only a 1 minute exposure. I've emailed the same question and photo (most like that I throw out) to Canon customer service so we'll see what gives, but your response suggests to me that my camera has a problem and it's only a month old. Right now I'm running an experiment by taking a bunch of long exposures with the lens cap on to see if I see the same thing. The frames may be too dark to tell but it's worth a shot.

ETA: Here is what I just got from Canon in an email reply (which has been very timely I might add):

"Please try disabling the custom functions and shooting again. The
functions do help, but try disabling them to ensure that somehow the

processing isn't causing the issue. If you do still see the green tint, unfortunately, the camera will need to be sent to a service center. It
is common to experience some noise when using high ISOs and long
exposures, but what you experience isn't normal. We apologize for this
inconvenience."

They are referring to the long exposure and high ISO noise reduction settings.

I'll try it but I seriously doubt those settings have anything to do with the issue.

To start, I see from your profile that you are located in Nevada. Is it fairly warm where you are shooting? Have you tried using LENR, and if so, does it remove this problem? Second, how much Live View are you using? It can really heat up the sensor, so you should limit its use. For astrophotography, you should only need to use it a little bit to focus the image, and then a few times throughout the night to check/adjust your focus.

I had a similar problem with green bands on my 1Ds Mark II, and its been reported on the 1D Mark II as well. In my case, using LENR removed the bands, and after a lot of time with Canon, they indicated that this is something that they are aware of, and its because I was outside the standard design envelope for the sensor.

Anyway, I suggest that you start with trying this with LENR on and off and see if that makes it go away. You can do test images inside in a really dark room (but with some light). You don't want the test images totally black.

If you can't make the green band go away at all, then your camera does have a problem, and you will have to send it back.

Jeff
--
http://www.pbase.com/jhapeman ; http://www.digitalhapeman.com

Jeff,

Thanks for the input.

I have been using both Long Exposure and High ISO noise reduction. Canon suggested I turn these off and try shooting again so I'm going to put the camera on a tripod (the moon's nearly full so no use getting the scope out) and doing some long exposure experimentation with the NR off.

My experiment with the lens cap on did yield a result but I had to peg the brightness in post processing to make it reasonably visible (see below). It follows exactly the same pattern as I've seen.
--

Hi there,
I also use my xsi for astro shots and I sometimes see this to a lesser degree.

This may be a long shot but could this be the effect of stray light coming in through the viewfinder? If you use your laptop next to your telescope-camera setup, the screen could glow into the cam!?
What lens did you use for that shot? ISO? And why so little color?

Astrophoto feels like the ultimate frontier of photography!

DTurcotte said:

Hi there,
I also use my xsi for astro shots and I sometimes see this to a
lesser degree.
This may be a long shot but could this be the effect of stray light
coming in through the viewfinder? If you use your laptop next to your
telescope-camera setup, the screen could glow into the cam!?
What lens did you use for that shot? ISO? And why so little color?

Astrophoto feels like the ultimate frontier of photography!

Click to expand...

--The mirror is up during exposure so light cant get thru that way
Brian Schneider

Brian D. Schneider said:

--The mirror is up during exposure so light cant get thru that way

Click to expand...

The mirror is only half-silvered so light passes through it. It's why Canon gives you the little viewfinder-cover thingy to use when your eye is not covering the viewfinder.

--
JerryG

See my galleries at:
http://www.pbase.com/jerryg1

DTurcotte said:

Hi there,
I also use my xsi for astro shots and I sometimes see this to a
lesser degree.
This may be a long shot but could this be the effect of stray light
coming in through the viewfinder? If you use your laptop next to your
telescope-camera setup, the screen could glow into the cam!?
What lens did you use for that shot? ISO? And why so little color?

Astrophoto feels like the ultimate frontier of photography!

Click to expand...

The green band appears without regard to external light sources with the camera piggy back on the telescope as well as using the scope as a lens, on a tripod with its EF-S 18-55 IS lens, or just sitting on a table (as in my lens cap on experiment). This is definately a CMOS sensor issue.

I typically shoot 800 ISO. The above shot is washed out because there was a nearly full moon in the same quadrant as the target (The Swan Nebula - M17). It was bright enough to read out and all that moonlight can create an atmospheric haze on longer exposures (moonlight pollution).

Although it was really bright out last night, I played around with some shots (this time with LENR and high ISO NR turned off) and I think that made things worse. I got the banding on a 30 second exposure and I've never seen that before.

The camera actually will take really nice photos. You never see any of this in daylight shots or dusk shots, but although I have a shaky equatorial mounted 8-inch LX200 telescope, I aspire to improve that situation and take more deep sky images like the one below of the Lagoon Nebula (M8). That image is the result of several 1 minute exposures stacked with Deep Sky Stacker and then tweaked in Photoshop to bring out hidden detail.

The mirror is only half-silvered to let light pass through to the submirror that feeds light to the AF sensors. When the mirror flips up the submirror also flips up, and thus all light coming through the viewfinder is effectively blocked.

The viewfinder-cover thingy is only used to avoid light coming through the viewfinder from affecting the light-metering. It is not needed while the image is taken.

JerryG1 said:

Brian D. Schneider said:

--The mirror is up during exposure so light cant get thru that way

Click to expand...

The mirror is only half-silvered so light passes through it. It's
why Canon gives you the little viewfinder-cover thingy to use when
your eye is not covering the viewfinder.

--
JerryG

See my galleries at:
http://www.pbase.com/jerryg1

Click to expand...

--
Slowly learning to use the 450D and and the Canon G6.
Public pictures at http://debra.zenfolio.com/ .

LabHappy said:

My experiment with the lens cap on did yield a result but I had to
peg the brightness in post processing to make it reasonably visible
(see below). It follows exactly the same pattern as I've seen.

Click to expand...

The picture below looks like a classic example of AMP glow. This is when the camera interal amplifier gets warm/hot and starts effecting the CMOS sensor.

A dark frame subtraction would remove the amp glow.

Amp glow gets worse with longer exposes and higher ambient temperature. I am not sure if you have too much amp glow going on or not.

LabHappy said:

Click to expand...

--
CityLights
http://www.pbase.com/citylights
.

CityLights said:

CityLights said:

My experiment with the lens cap on did yield a result but I had to
peg the brightness in post processing to make it reasonably visible
(see below). It follows exactly the same pattern as I've seen.

Click to expand...

The picture below looks like a classic example of AMP glow. This is
when the camera interal amplifier gets warm/hot and starts effecting
the CMOS sensor.

A dark frame subtraction would remove the amp glow.

Amp glow gets worse with longer exposes and higher ambient
temperature. I am not sure if you have too much amp glow going on or
not.

--

Click to expand...

CityLights said:

CityLights
http://www.pbase.com/citylights
.

Click to expand...

Citylights:

That's one thought I had originally or rather I thought it might be from using the LCD too much. It's probably been in the high 50s/low 60s recently when I've been shooting at night. The temp when I took that particular photo with the lens cap on was probably in the 70s (afternoon indoors).

LabHappy said:

That's one thought I had originally or rather I thought it might be
from using the LCD too much. It's probably been in the high 50s/low
60s recently when I've been shooting at night. The temp when I took
that particular photo with the lens cap on was probably in the 70s
(afternoon indoors).

Click to expand...

Low temperatures are good for less noise and less amp glow. I have not seen amp glow much in my cameras, but when I did it was on 2 minute exposures when I was taking pictures in over 90 deg F temperatures.

--
CityLights
http://www.pbase.com/citylights
.

n/t
--
JerryG

See my galleries at:
http://www.pbase.com/jerryg1

Ok, after doing some further reading on this subject (forgive me I'm a noob with regards to DSLRs), I agree that Amp glow is what I'm seeing in the lower left corner and I'll take a wild guess and hypothesize that the greenish band is actually the camera trying to compensate for the glow.

I guess the question is really; Is what I am seeing normal and I should just learn to live with it (it doesn't appear on every shot) or should I send it back to Canon to be repaired?

Brian's photos above suggest that what I have isn't normal or acceptable and I should probably ship the camera body in for repair.

Any comments?

LabHappy said:

I guess the question is really; Is what I am seeing normal and I
should just learn to live with it (it doesn't appear on every shot)
or should I send it back to Canon to be repaired?
Any comments?

Click to expand...

I don't know where the line is between "normal" and "bad" amp glow. You should not see it for normal shooting. If you do a lot of long exposures you will see some as the amplifier heats up.

I wish I could be more specific.

--
CityLights
http://www.pbase.com/citylights
.

LabHappy said:

Ok, after doing some further reading on this subject (forgive me I'm
a noob with regards to DSLRs), I agree that Amp glow is what I'm
seeing in the lower left corner and I'll take a wild guess and
hypothesize that the greenish band is actually the camera trying to
compensate for the glow.

I guess the question is really; Is what I am seeing normal and I
should just learn to live with it (it doesn't appear on every shot)
or should I send it back to Canon to be repaired?

Brian's photos above suggest that what I have isn't normal or
acceptable and I should probably ship the camera body in for repair.

Any comments?
--

Click to expand...

--My pictures were taken in much cooler weather than yours, that might explain the difference?
Brian Schneider

What ISO were you shooting at Brian?

I'm guessing a low ISO and a fairly stopped down aperture so you could get the star trails without overexposing ground objects or getting too much sky glow. Light pollution is actually significant where I live because of Reno to the north and outdoor lighting in my town. It ain't Manhattan or LA by any stretch, but it's still significant.

Thanks guys.

LabHappy said:

What ISO were you shooting at Brian?

I'm guessing a low ISO and a fairly stopped down aperture so you
could get the star trails without overexposing ground objects or
getting too much sky glow. Light pollution is actually significant
where I live because of Reno to the north and outdoor lighting in my
town. It ain't Manhattan or LA by any stretch, but it's still
significant.

Thanks guys.
--

Click to expand...

--It was ISO 100 f4. Temp was around 18c. Since then I have been using the stacking method. This one was 39 - 2 minute exposures at ISO 200. using this method you dont pick up so much sky colour & noise is far less.



Brian Schneider

It's not hard to tell which way is north in that photo Brian. The stacking really brings out the trails!

As a further experiment, I took the shot below to see if any amp glow showed up. Once again, the full moon is not your friend if you are trying to image stars, but for my purposes it served.

ISO 100, f22, 33 minute exposure with temps in the 60s and minimal use of the LCD. LENR set to Auto and High ISO NR set to On.

No evidence of any amp glow whatsoever. A moonless night would make the star trails pop much better and my back yard doesn't make the most interesting backdrop.

I'll have to further experiment with a range of ISO settings. These photos are time consuming because if the exposure is half an hour, the camera takes an equal length of time processing the image but at least you can watch TV while it's all going on.