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Newbie requesting a little help

Rokinon 135mm f/2.0 ED UMC M45 Messier Objects Open Cluster Deep Sky
3 replies•147 views
Johnathan Allison avatar
Johnathan Allison avatar
Hello,

For the past few weeks I've been using a Seestar S50 and have been loving it. I am very new to the hobby and have recently acquired a Sky Watcher Star Adventurer GTI and the Rokinon 135 for my Canon SL2. 

Last night was my first light with the new system. My target was M45. 

At the end of the night I noticed that the brighter stars had these star burst like spikes coming off of it. I did NOT use a mask to assist with focus. 

Settings used were:
Exposure: 60 Sec
ISO: 800
F8 (thinking this could be my issue)

I like the look, but I would like to know why it happened. 

Engaging
Nooa Jutila avatar
Nooa Jutila avatar
It's because of the aperture blades within the lens. They cause diffraction spikes.
Well Written
Dan H. M. avatar
Dan H. M. avatar
Yes, it’s because you shot at f/8. Every lens will show diffraction spikes when the iris is contracted at all. 

side note, but f/8 basically ruins the purpose of the Rokinon which is to be an ultra-fast astrograph. I wouldn’t go any higher than f/2.8.
Concise
Johnathan Allison avatar
Johnathan Allison avatar
Dan H. M.:
Yes, it’s because you shot at f/8. Every lens will show diffraction spikes when the iris is contracted at all. 

side note, but f/8 basically ruins the purpose of the Rokinon which is to be an ultra-fast astrograph. I wouldn’t go any higher than f/2.8.

Yeah I had no idea that I was shooting at f/8 lol. Rookie mistake. In the excitement of getting set up and running I overlooked a few things.