20 votes

Why does my Canon 700D take so long processing when I take a long exposure?

To reduce the processing time for long exposures, you want to turn off Long Exposure Noise Reduction. However, you may not want to give up the benefit of LENR. Long Exposure Noise Reduction (LENR) is ...
  • 169k
10 votes
Accepted

How to prevent hot pixels?

You can't really prevent hot pixels on long exposures, you can only deal with them. For a single four minute exposure the easiest way is to use what is known as Dark Frame Subtraction. Different ...
  • 169k
10 votes
Accepted

What's the best way to deal with hot/stuck pixels in long exposure night photographs?

For exposures longer than 1 second, you can enable Long Exposure Noise Reduction (LENR). This is Canon's nomenclature for in-camera dark frame subtraction. When you take a photo the camera will expose ...
  • 169k
7 votes

Why does my Canon 700D take so long processing when I take a long exposure?

It's not actually processing for most of that extra time. It is taking a second exposure with the shutter closed, for dark frame subtraction. This removes sensor-based pattern noise. Of course, there ...
  • 140k
6 votes

How to remove hot pixels with a dark frame?

Ideally, dark frame subtraction should be done with raw images before demosaicing. Then the resulting black spot is 1 pixel, and after demosaicing it will typically be invisible in the result due to ...
  • 3,113
5 votes
Accepted

What should I look for in a camera for shooting in bulb mode for astrophotography?

Regarding Bulb Mode If you use a wired remote there is generally not a time limit regarding the length of an exposure using bulb mode with most current DSLRs. Pressing the button, halfway or fully, ...
  • 169k
5 votes
Accepted

Should I turn off in-camera long exposure noise reduction when shooting for image stacking?

Long Exposure Noise Reduction takes a dark frame of the same duration to subtract the noise from the image. That's why there is a long delay; a 30-second exposure plus a 30-second dark frame plus ...
  • 712
5 votes
Accepted

Is there any quality advantage to doing dark frame subtraction in camera?

On the quality front, in general, it will be better to do it in camera when the sensor is particularly subject to hot pixels (those that only appear stuck when heated) or when there is other heat ...
  • 32.4k
5 votes

Astrophotography exposure setting for noise reduction

The best way to deal with noise in the situation you describe is to use a form of dark frame subtraction. If your camera doesn't offer such a built in feature, take a few frames during your session ...
  • 169k
5 votes

Long exposure shots showing huge bright spot. What happened to my sensor?

I do not know that specific camera, but generally sensors will have a pattern of thermal noise which is not uniform. The "Long Exposure Noise Reduction" feature, if your camera has it, is intended to ...
  • 2,288
4 votes

Issues with dark frame subtraction: Dark frames adding "noise" and changing image color/tint

You misunderstand the purpose of dark-frame-subtraction. While it is a technique used to reduce noise, it only reduces noise that is consistently output from the sensor. Any read noise due to the ...
  • 101k
3 votes

Dark Frames for Long Exposure on a tracker?

Shoot (15 minutes) x (However many frames you want) → manually shoot one dark frame (15 minutes). You can take a manual dark frame by putting a lens cap on the lens before taking the shot. You're done....
  • 169k
3 votes
Accepted

At what exposure times do fixed pattern noise become apparent?

Shutter time is only one of many variables that affect when dark frame subtraction would be beneficial. There is no single answer to your question. Since what we call 'noise' is present in all ...
  • 169k
3 votes

Astrophotography exposure setting for noise reduction

The SLT A58 has the so-called "long exposure noise reduction" function which performs the dark frame subtraction mentioned in Micheal's Clark's answer. You should choose the shutter speed a lot less ...
  • 3,508
3 votes

How to prevent hot pixels?

I'll explain the image stacking method here. Image stacking can yield better results, you then take multiple images at lower ISO and/or expose for a shorter time. A practical way to go about this is ...
  • 3,508
3 votes

Is there any quality advantage to doing dark frame subtraction in camera?

Since there are many variables that affect the sensor read noise, taking the dark frame at the same time increases the chances that it is also taken under the same conditions as the exposed frame, ...
  • 169k
2 votes

Is there any quality advantage to doing dark frame subtraction in camera?

In order to match the type and character of noise accurately, the dark frame subtraction should be done at the same time as the exposure. So doing it in camera should yield better results.
  • 5,115
2 votes

Black level unchanged after long exposure noise reduction

Noise reduction is concerned with maximizing the Signal-to-Noise Ratio (SNR) by differentiating between actual signal and signal created by noise. With a lens cap on the camera there is no signal in ...
  • 169k
2 votes

What should I look for in a camera for shooting in bulb mode for astrophotography?

To address the "for beginners" aspect of the question, most recent-generation Olympus Micro 4/3 cameras (which are mirrorless, not technically DSLRs) have a feature called "Live Bulb" which allows you ...
2 votes

How does in camera dark frame noise reduction work?

I am confident that the exact method used by each camera manufacturer is different and company-confidential. All manufacturers have a large vested interest in getting the maximum image quality using ...
  • 712
2 votes

Issues with dark frame subtraction: Dark frames adding "noise" and changing image color/tint

Instead of reducing noise, the darkframe subtraction increased the noise- or rather, added some dark/monochrome noise. How long was your session? What was the ambient temperature? Was the camera at ...
  • 169k
2 votes

Issues with dark frame subtraction: Dark frames adding "noise" and changing image color/tint

A while back I tried some of these images and found that it was much more convenient to take a dark frame for a group of long exposures rather than sit and wait for a minute every time I took a minute ...
1 vote

Terminology - photos with lights on, lights off

I think "lit" and "natural light" are the two terms you're looking for in terms of distinguishing using lighting gear or not using lighting gear, if you don't light. A very ...
  • 49.4k
1 vote

Issues with dark frame subtraction: Dark frames adding "noise" and changing image color/tint

Try turning on in-camera darkframe subtraction instead. The designers of the camera have insight into how to best mitigate noise because they have detailed knowledge of the sensor and the noise ...
1 vote

Why does a non-linear relationship exist between noise level (of dark frame) and ISO setting

Based on inspection of your "captured dark frames and their associated statistics" and some experience in document scanner technology, it appears that between ISO 400 and 200, Canon shifted away 2 ...
1 vote

What should I look for in a camera for shooting in bulb mode for astrophotography?

Some very good answers about long exposure times, but for astrophotography I thought it was worth adding another consideration - the rotation of the earth. If you're looking for star trails (https://...
1 vote

Black level unchanged after long exposure noise reduction

There are many sources of noise in the CMOS imaging process. Fixed-pattern noise (FPN) refers to image noise caused by nonuniformity in the sensor. For example, differences in manufacturing might ...
1 vote
Accepted

Long exposure shots showing huge bright spot. What happened to my sensor?

First, let's distinguish two kinds of noise. One is temporal random noise, such as thermal noise, photon shot noise, or electron shot noise in the analog electronics. These tend to follow Poisson ...
1 vote

Why does raising ISO make image quality appear lower even though my measurements suggest it shouldn't?

In this answer ISO, shutter speed and aperture are independent parameters. 1) Yes, setting ISO to a higher number will almost always lead to better SNR - because additional analog amplification ...

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