Tuesday, April 07, 2009

PSF Variations in 50mm f/1.4

Talk about Coma and Astygmatism..... I tried out the 50mm prime lens to do some astro-photo work at f/1.2 when camping at Nickel Creek in the Redwoods. It was super-bright. Lots of light made it to the focal-plane, but the aberrations were pretty damn severe. The field dependence was really strong - stars near the center were true points but out in the corners they were "butterflies". But it makes for pretty pictures.

The wide angle:
Stars from various parts of the field. The corners were the worst....


Blogger Jesse said...

Was it f/1.4 or f/1.2? Big difference. Also, usually when using the low f-number regime you are typically taking a picture with perspective rather than something flat like the sky. Then, the low depth of field kicks in and the corners are going to be out of focus anyway.

Only in situations like this, or if you take pictures of walls does the "soft" corners (aka coma/astyg.) really cause problems. The other thing is that these soft corners go away by F/4.0 or so. Google dpreview and find the lens review for the Pentax (or Canon/Nikon as they are similar), there is a sweet ass applet showing these things.

6:40 AM  
Blogger Jesse said...

Oh yeah, and I do actually see some color spreading in my corners at F1.4 where there are distinct lines or point sources in the fuzz.

6:42 AM  
Blogger brian harrington said...

coma? astygmatism? aberrations? more like god butterflies, generally referred to as goderflies

1:21 PM  
Blogger geekedout said...

i believe it's f/1.4 though my lens sometimes shows 1.2 when i'm focused close using the manual aperture ring.... never really figured out why.

4:16 PM  
Blogger brian harrington said...

never really figured out why? looks like someone is desperate for a spiritual explanation. acknowledge me, or i will strike down upon thee with great vengeance and furious anger those who seek to poison and destroy my brothers, and YOU WILL KNOW I AM THE LORD, when i put snakes on your plane.

7:37 AM  

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