<p>I have a non-motorized Newton 130/900 telescope.</p>
<p>Of course, it's hopeless to do pictures with exposure ~ 1 minute. Even 1 second is probably too much, as seen in <a href="https://astronomy.stackexchange.com/a/50707">Optimal exposure time for photography with unmotorized telescope</a>.</p>
<p>Instead of doing 1 long exposure photography of 50 seconds (which would produce star trailing), can we do:</p>
<ul>
<li><p>100 automated photos of 0.5 second exposure time (each photo on its own has few star trailing)</p>
</li>
<li><p>an algorithm can reposition each picture to compensate the movement of the earth</p>
</li>
<li><p>at the end we merge the 100 (re-aligned) pictures to get a single picture.</p>
</li>
</ul>
<p>It seems that, with this scenario, we get the same &quot;number of photons&quot; with these 100 photos, merged, as with a single 50-second-long exposure photo.</p>
<p>Is it a common practice?</p>

CC BY-SA 4.0
2024-01-26T21:50:38.247Z
You get the same number of signal photons, but also more noise.
ProfRob
CC BY-SA 4.0
2024-01-26T22:16:41.983Z
@ProfRob Yes, noise due to the realignement (btw, is it just a translation + rotation or should it be a more complex geometrical transformation, like an homography ?).  Due to what else exactly ? Do you think it is still doable ?
Basj
CC BY-SA 4.0
2024-01-26T22:45:34.960Z
You have a fixed readout noise in each picture.
ProfRob
CC BY-SA 4.0
2024-01-26T23:12:56.673Z
@ProfRob Oh right. Is it a common practice for amateur astronomers? Is there a well-known freeware for this?
Basj
CC BY-SA 4.0
2024-01-27T03:21:52.807Z
It's a great question and there are plenty of options for software to align sequential images. I am sure you'll either receive an excellent answer or three or it's possible someone might close this as duplicate of a similar question whose answers also answer your question. You can also search the [astrophotography tag in Photography SE](https://photo.stackexchange.com/questions/tagged/astrophotography) for software suggestions. And by the way, even motorized telescopes with alt/az mounts including major observatories have to deal with the fact that the FOV *rotates* about it's center over time
uhoh
CC BY-SA 4.0
2024-01-27T03:24:28.963Z
And before CCDs they had other solutions! [Did astronomers ever use photographic plate rotation along with alt-az mounts?](https://astronomy.stackexchange.com/q/47933/7982) But I digress... Anyway have a look at [Optimal exposure time for photography with unmotorized telescope](https://astronomy.stackexchange.com/q/50691/7982)
uhoh
CC BY-SA 4.0
2024-01-28T13:41:53.070Z
@Basj  Is this what you're looking for?  https://astrobackyard.com/astrophotography-image-stacking-software/
Dave Gremlin
<telescope><photography><merger>
With a non-motorized telescope, can 100 pictures of 0.5 seconds be realigned and merged to get the equivalent of a 50-second long exposure shot?
Basj
# With a non-motorized telescope, can 100 pictures of 0.5 seconds be realigned and merged to get the equivalent of a 50-second long exposure shot?

(Asked by: username_0 on 2024-01-26)

I have a non-motorized Newton 130/900 telescope.

Of course, it's hopeless to do pictures with exposure ~ 1 minute. Even 1 second is probably too much, as seen in [Optimal exposure time for photography with unmotorized telescope](https://astronomy.stackexchange.com/a/50707).

Instead of doing 1 long exposure photography of 50 seconds (which would produce star trailing), can we do:

* 100 automated photos of 0.5 second exposure time (each photo on its own has few star trailing)
* an algorithm can reposition each picture to compensate the movement of the earth
* at the end we merge the 100 (re-aligned) pictures to get a single picture.

It seems that, with this scenario, we get the same "number of photons" with these 100 photos, merged, as with a single 50-second-long exposure photo.

Is it a common practice?

**Tags:** telescope, photography, merger
> **Comments:**
> **username_1**: You get the same number of signal photons, but also more noise.  
> **username_0**: @ProfRob Yes, noise due to the realignement (btw, is it just a translation + rotation or should it be a more complex geometrical transformation, like an homography ?).  Due to what else exactly ? Do you think it is still doable ?  
> **username_1**: You have a fixed readout noise in each picture.  
> **username_0**: @ProfRob Oh right. Is it a common practice for amateur astronomers? Is there a well-known freeware for this?  
> **username_2**: It's a great question and there are plenty of options for software to align sequential images. I am sure you'll either receive an excellent answer or three or it's possible someone might close this as duplicate of a similar question whose answers also answer your question. You can also search the [astrophotography tag in Photography SE](https://photo.stackexchange.com/questions/tagged/astrophotography) for software suggestions. And by the way, even motorized telescopes with alt/az mounts including major observatories have to deal with the fact that the FOV *rotates* about it's center over time  
> **username_2**: And before CCDs they had other solutions! [Did astronomers ever use photographic plate rotation along with alt-az mounts?](https://astronomy.stackexchange.com/q/47933/7982) But I digress... Anyway have a look at [Optimal exposure time for photography with unmotorized telescope](https://astronomy.stackexchange.com/q/50691/7982)  
> **username_3**: @Basj  Is this what you're looking for?  https://astrobackyard.com/astrophotography-image-stacking-software/  

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## 0 answers

