Unistellar eVscope 2 - Exposure Time versus Brightness

Introduction | Get DSO Brighter with Longer Exposure Time? | Conclusions | Links

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On this page, I will investigate whether images (or better, objects in the images) get brighter the longer you expose, that is, the longer the exposure time* is. I check this for the eVscope 2, but the results for the original should be analogeously.

*) The exposure time is 4 seconds for each image/frame; by superimposing images/frames, Enhanced Vision creates a "sum" or "accumulated image", also called "image stack", which is displayed on the screen and can be saved. By "exposure time" (or "total exposure time") I mean in the following the total time that an object was exposed (for example: 10 frames x 4 sec = 40 sec total exposure time).

Note: See page Overview of the Unistellar Pages for just that!

Introduction

Photos: My third eVscope 2 (August 22, 2022)

The Vaonis Vespera allows you to view the changes in the image stack during the observation as a fast animation. You can see that the longer you expose (that is, the more images/frames you add to the image stack), the brighter the image stack becomes. This is the behavior one would normally expect for stacking. With the eVscope (2), however, the resulting image stack did not seem to change much after a short period of time (one tester even wrote that the image gets worse again when you expose longer). I discussed this issue(?) with a star friend who also owned an eVscope, and his photos also did not get brighter with longer exposure times.

I then did another comparison between the Vespera and the eVscope 2 with exposure times of up to about 30 minutes, which confirmed this impression (Vaonis Vespera - Photo Comparison against Unistellar eVscope 2 - Part 3). Admittedly, I found the behavior of the eVscope (2) a bit "strange"...

Get Images Brighter with Longer Exposure Time?

Changes of DSO Brightness for Exposures of up to 10 Minutes

When I took the test shots for Deep Dark Technology, I exposed for a maximum of between 7 and 10 minutes and also saved intermediate results. These photos now allow you to easily see whether the brightness of the DSO changes over this period of time. To make a long story short, it does, the DSO get brighter over time. Below, I present three sample series (of 11 series) to prove this:

M 13	M 51	M 101

M 13 - Aug 21 2023 - 8 sec	M 51 - Aug 21 2023 - 16 sec	M 101 - Aug 21, 2023 - 12 sec

M 13 - Aug 21 2023 - 60 sec	M 51 - Aug 21 2023 - 60 sec	M 101 - Aug 21, 2023 - 64 sec

M 13 - Aug 21 2023 - 2 min	M 51 - Aug 21 2023 - 2 min	M 101 - Aug 21, 2023 - 2 min

M 13 - Aug 21 2023 - 3 min	M 51 - Aug 21 2023 - 3 min	M 101 - Aug 21, 2023 - 3 min

M 13 - Aug 21 2023 - 4 min

M 13 - Aug 21 2023 - 5 min	M 51 - Aug 21 2023 - 5 min	M 101 - Aug 21, 2023 - 5 min

M 13 - Aug 21 2023 - 7 min	M 51 - Aug 21 2023 - 7 min	M 101 - Aug 21, 2023 - 7 min

M 13 - Aug 21 2023 - 8 min		M 101 - Aug 21, 2023 - 8 min

	M 51 - Aug 21 2023 - 10 min	M 101 - Aug 21, 2023 - 10 min

Note: If you click on the images, display the larger versions in different tabs, and switch between the tabs, you can see the differences in brightness better!

This test demonstrates that it is worth waiting at least 10 minutes for a result before saving it (or stopping the observation). In the following, I will check, whether it is worthwhile to expose faint objects even longer.

Changes of DSO Brightness for Exposures of up to 110 Minutes

Now I was interested, of course, in whether it really has an effect, if one exposes longer than 10-15 minutes. For this, I chose M 51 and exposed the galaxy up to nearly 2 hours (110 minutes). If you save an image/frame every 2-5 minutes, you get of course a lot of "intermediate images". From the 33 photos taken during my test, I selected 22 to show here. In addition, I generated a movie with all 33 photos, with which you can see the changes of the DSO brightness. However, you can also operate the movie by hand and thus, look at individual images and see better that the DSO brightness still increases somewhat in the second hour...

So this example shows that for low-light objects it can be well worth exposing for half an hour or a full hour - and possibly even longer.


M 51 - Aug 23, 2023 - 12 sec	M 51 - Aug 23, 2023 - 64 sec	M 51 - Aug 23, 2023 - 2 min

M 51 - Aug 23, 2023 - 4 min	M 51 - Aug 23, 2023 - 6 min	M 51 - Aug 23, 2023 - 8 min

M 51 - Aug 23, 2023 - 10 min	M 51 - Aug 23, 2023 - 15 min	M 51 - Aug 23, 2023 - 20 min

M 51 - Aug 23, 2023 - 25 min	M 51 - Aug 23, 2023 - 30 min	M 51 - Aug 23, 2023 - 35 min

M 51 - Aug 23, 2023 - 40 min	M 51 - Aug 23, 2023 - 45 min	M 51 - Aug 23, 2023 - 50 min

M 51 - Aug 23, 2023 - 55 min	M 51 - Aug 23, 2023 - 60 min	M 51 - Aug 23, 2023 - 70 min

M 51 - Aug 23, 2023 - 80 min	M 51 - Aug 23, 2023 - 90 min	M 51 - Aug 23, 2023 - 100 min

M 51 - Aug 23, 2023 - 110 min		M 51 - Aug 23, 2023 - Movie

Note: If you click on the images, display the larger versions in different tabs, and switch between the tabs, you can see the differences in brightness better!

Changes of DSO Brightness for Exposures of up to 40 Minutes (M 101)

On August 25, 2023 I performed another test, for which I chose a relatively faint object, namely M 101. Originally, I wanted to expose up to 2 hours again. But clouds covered up the sky, so that I had to stop the observation after 40 minutes. Before that some clouds appeared, and M 101 did not get brighter between 32 and 40 minutes of exposure time (in fact, it got a little darker).


M 101 - Aug 25, 2023 - 12 sec	M 101 - Aug 25, 2023 - 60 sec	M 101 - Aug 25, 2023 - 2 min

M 101 - Aug 25, 2023 - 4 min	M 101 - Aug 25, 2023 - 5 min	M 101 - Aug 25, 2023 - 7 min

M 101 - Aug 25, 2023 - 8 min	M 101 - Aug 25, 2023 - 10 min	M 101 - Aug 25, 2023 - 13 min

M 101 - Aug 25, 2023 - 15 min	M 101 - Aug 25, 2023 - 17 min	M 101 - Aug 25, 2023 - 20 min

M 101 - Aug 25, 2023 - 25 min	M 101 - Aug 25, 2023 - 27 min	M 101 - Aug 25, 2023 - 30 min

M 101 - Aug 25, 2023 - 32 min	M 101 - Aug 25, 2023 - 33 min	M 101 - Aug 25, 2023 - 34 min

M 101 - Aug 25, 2023 - 35 min	M 101 - Aug 25, 2023 - 37 min	M 101 - Aug 25, 2023 - 40 min

M 101 - Aug 25, 2023 - Movie

Note: If you click on the images, display the larger versions in different tabs, and switch between the tabs, you can see the differences in brightness better!

Conclusions

In contrast to my previous experiences, I found that with app version 2.4ff DSO brightness increases the longer you expose (30, 60 minutes, and more). Thus, it may indeed be worthwhile to expose a faint DSO, such as M 51 or M 101, much longer than 10 minutes. I can only speculate about, whether the change in behavior that I observed is actually due to the Deep Dark Technology...