Backlit images on SX60 HS with high ISO and long exposures.

Garrett

11

« on: 20 / July / 2022, 18:31:00 »

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Hi, everyone!

Recently I bought an used camera - SX60HS, and decided to shoot some night sky.
Unfortunately, all the shots with ISO 3200 and 1 minute exposure had a flaw - they have a backlit area on the right side. The image is attached.
I tried to shoot some photos with lens cap on, but this backlit area is still present. It starts showing even with exposure around 30 seconds.
The issue appears only while CHDK is enabled, because it looks like with native allowed settings the camera seems to be not sensitive enough to capture this issue.

So, my questions are:
1. Does anyone else has this issue?
2. It seems to be caused by the LED indicator. Is there a way to disable it using CHDK?

Thank you in advance.

IMG_2235.JPG (1399.94 kB, 2304x1728 - viewed 25 times.)
Model:Canon PowerShot SX60 HS Software Used:GIMP 2.10.18 Exposure Time:600/10 seconds F Number:F/6.5 ISO Speed:3200 Date Taken:2022:07:21 00:05:28 Metering Mode:Pattern Flash Mode:Flash did not fire; compulsory flash mode Focal Length:247 mm Color Space:sRGB

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waterwingz

12140

Re: Backlit images on SX60 HS with high ISO and long exposures.

« Reply #1 on: 20 / July / 2022, 20:17:42 »

Google "amp glow"

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Garrett

11

Re: Backlit images on SX60 HS with high ISO and long exposures.

« Reply #2 on: 21 / July / 2022, 00:13:24 »

Waterwingz, thank you. This is the first time I encountered such issue.
However still the question #1 persists. Maybe I just should sell this camera and buy another one, that doesn't have such issue.

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blackhole

942
A590IS 101b

Re: Backlit images on SX60 HS with high ISO and long exposures.

« Reply #3 on: 21 / July / 2022, 00:38:29 »

Quote from: Garrett on 21 / July / 2022, 00:13:24

Waterwingz, thank you. This is the first time I encountered such issue.
However still the question #1 persists. Maybe I just should sell this camera and buy another one, that doesn't have such issue.

Every camera suffers from this on long exposures, buying another camera will not change anything.
Google "dark frame subtraction" and learn how to deal with this problem.
If you only use jpg files, the camera can do it for you, in the chdk menu set the "Dark Frame Subtraction" option to ON.
You can reduce the "amp glow" if you use a shorter exposure time and a lower ISO, Tv 60 and ISO 3200 are extreme settings for the tiny sensor in the SX60HS camera.
Much more expensive dslr cameras suffer much less from this issue.

« Last Edit: 21 / July / 2022, 00:55:01 by blackhole »

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http://astrofoto.pondi.hr

Garrett

11

Re: Backlit images on SX60 HS with high ISO and long exposures.

« Reply #4 on: 21 / July / 2022, 03:40:50 »

Blackhole, let me disagree.
I made a lot of photos even with 3 minutes of exposure on much older and cheaper SX520HS, but didn't encounter such an issue, so that's why it surprised me that much.
Also, never saw this on my EOS 7D.
So, I'd still like to learn more about experience of other users. Whether it happens to all SX60 HS, or some cameras behave better than others.

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reyalp

14118

Re: Backlit images on SX60 HS with high ISO and long exposures.

« Reply #5 on: 22 / July / 2022, 00:03:20 »

Quote from: Garrett on 21 / July / 2022, 03:40:50

I made a lot of photos even with 3 minutes of exposure on much older and cheaper SX520HS, but didn't encounter such an issue, so that's why it surprised me that much.

SX520 and SX60 are actually the same era (both released in 2014) and possibly even the same sensor (both 1/2.3 inch 16 MP BSI CMOS), so I'd expect them to suffer similarly.

However, if you haven't explicitly used dark frame control, one possibility is that the Canon auto dark frame behavior is different between these models. If dark frame is being used, it should be obvious since a 3 minute exposure will take 6 minutes to complete, with camera displaying "busy" while it does the dark frame.

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So, I'd still like to learn more about experience of other users. Whether it happens to all SX60 HS, or some cameras behave better than others.

I don't have SX60, but amp glow is common on these cameras, and looks exactly like the image you've posted. I'm pretty sure I've seen people post about it for SX60 specifically before.

There can be significant variation between models. My experience is generally that it is much more pronounced on cameras released before somewhere around 2012, but I certainly haven't tested every model. I'm not surprised to see it on a 1 minute, IS3200 exposure.

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Garrett

11

Re: Backlit images on SX60 HS with high ISO and long exposures.

« Reply #6 on: 22 / July / 2022, 20:09:05 »

Reyalp, now, that was really helpful!
The thing you mentioned about the dark frame behavior forced me to check the settings. I did not configure it myself, but it looks like the CHDK build I installed years ago onto SX520 had dark frame subtraction set to "auto" by default. That's why I never saw the glow. And SX60 had it disabled.

As for the exposure time difference I thought it was related to processors (like, old DIGIC 4+ in SX520 has to spend additional 100% of the time to handle the image, while newer DIGIC 6 in SX60 gives me the result immediately).

Well, once more thank you to everyone who replied here. The mystery is solved.

I'm a bit sad that I'll have to spend a bit more time to get an acceptable photos using RAW, but at least I know that I wasn't fooled when I bought the camera.

Oh, and fun fact.
Dark frame substraction suddenly stopped working when I tried to switch to "on" for my SX520. It worked only when set to "auto". Later I will try to update my CHDK and will report the bug to corresponding thread if it persists.

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reyalp

14118

Re: Backlit images on SX60 HS with high ISO and long exposures.

« Reply #7 on: 22 / July / 2022, 23:38:23 »

Quote from: Garrett on 22 / July / 2022, 20:09:05

I'm a bit sad that I'll have to spend a bit more time to get an acceptable photos using RAW, but at least I know that I wasn't fooled when I bought the camera.

FWIW, Canon dark frame subtraction works fine with raw, it just requires 2x the exposure time to shoot.
A workflow with separate dark frames can be better for astrophotography, especially if you are taking a lot of frames, but it's not required.

FWIW, I wrote this script https://chdk.fandom.com/wiki/Lua/Scripts:_Fixed_Exposure_Intervalometer for astrophotography, which allows the creation of stand-alone dark frames.

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Dark frame substraction suddenly stopped working when I tried to switch to "on" for my SX520. It worked only when set to "auto". Later I will try to update my CHDK and will report the bug to corresponding thread if it persists.

Definitely let us know if "on" doesn't work in the current autobuilds. Note that it could be affected by shooting mode (M, Tv, Auto etc) or other settings.

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