View Single Post
  #19  
Old 17-12-2018, 05:33 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 17,877
Quote:
Originally Posted by Astrofriend View Post
Hi,

I made two new pages where I compare the stars from the Pentax lens and the Sigma lens. It's from center and the extreme corner. It's interesting to study these photos, in some cases the old Pentax non APO looks sharper then the more modern Sigma APO lens. And the Pentax is at full aperture (f/2.8) and the Sigma is stopped down to f/4.

Have a look at page 7 and 8:
http://www.astrofriend.eu/astronomy/...vs-pentax.html

What I know the Sigma APO 150 mm f/2.8 is very good, even for astrophotography when stopped down one step.

/Lars
You can't compare one lens at F2.8 and the other at F4. All lens are better stopped down so the Sigma is made to look better. Even at F4 its showing a lot of coma. I prefer the Pentax. Its also showing star colour whereas the Sigma has all stars as white which of course they aren't.

The Pentax does show some chromatic aberration with those magenta rings around the brighter stars so you can either stop that down to F4 to help there or use the chromatic aberration slider in Lightroom to get rid of it.

Greg.
Reply With Quote