What is the correct Aperture to use in Time-Lapse Star Trails?

Overview

There are many articles out there which “tell” you what the correct aperture is to take star trails, but none of them shows you the difference between the different aperture ranges. I set out to take different low-light photographs with different apertures and ISO ranges with my trusty Canon 760D camera. I compiled then three photos which shows the differences between the different f-stops on the photo, and what the impact is on the colour range and amount of detail captured in the photograph.
The three areas which I covered were:
·         Comparison of f-stops on ISO 6400,
·         Comparison of f-stops on ISO 3200, and
·         Comparison of f-stops on ISO 1600
Note: I used the same image and did NOT use any image manipulation to alter the photo in any way (I just “cut-out” the relevant section of each photograph and transposed it onto one photo). I shot these in jpeg mode to ensure as well that I have one photo of each of the f-stops. These photos were taken of my home in a light polluted environment, but this will give you a good indication of what are the ideal settings to use.
 

Comparison of f-stops on ISO 6400

The mid-range f-stops were closer to my personal preference in colours, and the lower numbered f-stops produced too much light, the upper numbered f-stops produced too little light and too little star details. I used ISO 6400 (drawback is too much noise in photograph) and tungsten white balance for all the photos. The ideal range thus for colours in relation to star details were between f/8 and f/13 as seen in the next composition.

Comparison of f-stops on ISO 3200

The lower to mid-range f-stops were closer to my personal preference in colours, and the lowest numbered f-stops produced too much light, the upper numbered f-stops produced too little light (too dark) and too little star details. I used ISO 3200 and tungsten white balance for all the photos. The ideal range thus for colours in relation to star details were between f/6.3 and f/10 as seen in the next composition. 

Comparison of f-stops on ISO 1600

The lower range f-stops were closer to my personal preference in colours, and the higher numbered f-stops produced too little light and were too dark to see any star details. I used ISO 1600 and tungsten white balance for all the photos. The ideal range thus for colours in relation to star details were between f/4 (or lower) and f/7.1 as seen in the next composition.
 

Conclusion

A lot depends on your own preference for colours and amount of star details in your photographs. But when you perform the comparison between the different composite photographs then you will be able to make up your own mind as to which is better, and what kind of look you are going for in your photograph. I would recommend the following settings though:
·         ISO 6400, White Balance of Tungsten and f-stop between f/8 and f13,
·         ISO 6400, White Balance of Tungsten and f-stop between f/6.3 and f/10. and
·         ISO 6400, White Balance of Tungsten and f-stop between f/4 and f/7.1
 
Happy shooting low light photos with knowledge 🙂
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