How much acquisition time should you aim for to improve image quality?

The light from celestial objects is incredibly faint. Capturing it with a smart telescope requires performing multiple long exposures and combining them through a process called stacking. The quality of the resulting image depends on the number of stacked frames, which is tied to the total acquisition time.  

When selecting a target in the Singularity app, a suggested observation time provides a baseline for achieving decent results. However, extending the observation time beyond this recommendation is often essential for producing high-quality astrophotography. In some cases, accumulating data over several nights is necessary—a process made seamless with Vaonis smart telescopes, thanks to their exclusive Multi-Night Observation feature.  

Here’s what to consider when determining the optimal acquisition time for your astrophotography project

It all comes down to noise reduction

Your smart telescope's sensor captures light from celestial objects, known as the signal. However, it also generates noise, an undesirable byproduct caused by several factors such as light pollution and the sensor’s electronic.

Since the signal from deep-space objects is so faint, it can easily be overwhelmed by noise, leading to poor image quality.  

Fortunately, the noise is randomly distributed across each individual frame, while the signal remains consistent. This is where stacking comes into play: it progressively cancels out the noise while preserving the signal.  

The quality of the final image can be expressed as a signal-to-noise ratio (SNR), which measures the clarity of the captured data. This is the primary concern in astrophotography.

The more images you stack, the less noise will affect your final image.
Less noisy images are easier to post-process, revealing more details and offer a cleaner result.

Zoomed-in view of the Fighting Dragons Nebula illustrating how extending acquisition time impacts noise reduction and detail clarity. Left-hand : 1h30, right-hand : 14h.

Understanding SNR

SNR, or Signal-to-Noise Ratio, measures how much stronger the signal is compared to the noise:

• High SNR: The signal dominates the noise, resulting in sharp, clear, and detailed images.
• Low SNR: The noise competes with the signal, blurring details and reducing image quality.

The reduction in noise achieved through stacking increases with the square root of the number of subframes:

Stacking 2 frames reduces noise by approximately 1.4 (the square root of 2).
Stacking 4 frames reduces noise by a factor of 2.
Stacking 9 frames reduces noise by 3, 16 frames by 4, 25 frames by 5, and so on.
This also applies to SNR. Since the number of captured frames is directly proportional to acquisition time, doubling the acquisition time increases the SNR by a factor of about 1.4 (the square root of 2), or by 40%.

Implications for acquisition time

Achieving a significant improvement in SNR requires a substantial increase in acquisition time.  

Smaller increments, such as increasing acquisition time by a factor of 1.5 (e.g., from 2 hours to 3 hours), yield limited benefits. For example, this would improve the SNR by only 1.22 times (the square root of 1.5), or 22%, which may not be visually noticeable in the final image.  

As a general rule of thumb, doubling the acquisition time is necessary to achieve a meaningful step in quality improvement.  

This leads to diminishing returns as acquisition time increases. While there’s no hard limit, the effort required to improve image quality grows significantly. If you’ve already captured 2 hours of data, you’ll need an additional 2 hours to see a noticeable improvement. Once you reach 4 hours, doubling that to 8 hours will be required for further enhancement.  

The total acquisition time required can escalate quickly, making it essential to weigh the potential gains against the effort involved. Some Vaonis users have achieved stunning results with 50 hours of data integration, but fortunately, excellent results can also be achieved with much less acquisition time.  

Finally, remember that to fully leverage the benefits of extensive acquisition times, post-processing is essential. By working with the raw TIFF files provided by the telescope, you can reveal the true potential of your data. In assisted observation mode, however, the difference may be barely noticeable.

Baseline Recommendations

The ideal acquisition time also depends on the type of object you're observing, your filter configuration (e.g., whether you're using a dual-band filter), and your capture mode (regular or mosaic).
The following table is not a set of strict rules, but rather general guidance to help you get started. Experience will help you find your optimal settings.

* To complete a full mosaic cycle at maximum size, a minimum of 1 to 1.5 hours is required, regardless of the final quality desired. The time needed to complete a mosaic cycle also depends on the field of view ratio and its orientation. Smaller mosaics require less time.

How to manage astrophotography projects with extensive acquisition time

Choose Your Target Wisely

To optimize the available acquisition time, select targets that are above the horizon for most of the night. It's best to focus on objects that are at least 20° above the horizon for optimal image quality.

Use Multi-Night Observation Capability

Exclusive to Vaonis smart telescopes, the Multi-night observations feature is a powerful tool for extended image acquisition. Capturing a target over multiple nights is as easy as conducting a regular observation.

Use Plan My Night

Program the observation of your target for the entire night without needing to supervise the telescope.

Aim for Consistent Sky Conditions

To optimize the results of a multi-night capture, try to choose nights with similar sky quality. For example, avoid resuming a capture started during a new moon on a night with a full moon.
If the seeing is poor on a given night, it's better to skip it rather than risk ruining a capture that started under better conditions.

Cover image : The Fighting Dragons Nebula in constellation Ara - 14 hours of data acquisition.