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next PZ lens test report - Sigma 14mm f/1.8 DG HSM ART
#51
Quote:No, I didn't test at infinity but at f/1.8 there was quite some field curvature anyway. Even in the theoretical event that the lens is better at infinity, the field curvature would hit astro-photographers.
 

I was going to ask about that as well. The charts at f/1.8 don't look that great - I was wondering if the image periphery would be better at longer focus distances (sometimes lenses aren't as good close up). Unfortunately in the sample image section all the wide open ones are close-ups and all the near-infinity shots are stopped down. In any case, it is more likely than not that the issues are real and apply to infinity focus too, but then I would have to wonder why others rave about the lens for astro...
#52
Quote:It does well with that night sky.
 

That's what I hear, yes. Just pointing out that "no subject ever needs sharp corners at f/1.8" is a rather flawed argument when applied to a lens like this one...
#53
I think you misunderstood me, GoldRingNikkor,  Wink

 

I think, it's literally impossible to get a 14 mm lens with that aperture at the same time doing extraordinary things with test charts at test chart distance and doing well wide open at infinity. Like you said, night sky is one of the fields for it - and unfortunately, if you check it's corners, sharpness is there, but coma as well (butterflies instead of pin points).

 

All I was saying is that for these kind of lenses it's tough to find subjects with a flat field which need to be shot wide open.

#54
A fast ultrawide lens that is dead sharp in the corners at 50mp doesn't exist.


Your best bets will be the Otus 28mm f/1.4 ( not really wide ) or the Leica Summilux 21mm f/1.4 ( on Sony Alpha ).


Even then - these lenses will still have lots of vignetting at f/1.4.


Alternatively - go down with your megapixel requirements.
#55
    Star shots are all about wide apertures and limited time exposures (20 secs or less without a astro-mount), so the Sigma is going to be seriously looked at by astro-shooters....corners and all!

 

   My Samyang was back-focusing so much, I thought I was getting pre "big-bang" exposures......black frames.....it was clear to me that I was back focusing beyond the formation of the universe.....big league stuff huh?

 

   I spent many hours daydreaming about my breakthrough and was already preparing for the scientific world's reception of my "White papers".......explaining this time/distance fabric situation with all the appropriate calculations of how to find the exact plane of focus in order to capture the actual glorious moment of the"Big Bang" itself .....

 

      Sat back,eyes closed, gin+tonic in hand, bathing in my newly discovered eureka moment, the world was finally my oyster,.... then.... I looked up to notice that I had forgotten to remove the lens-cap....

 

 

     It was at this point I decided to write a thesis on over-active neurons and the lifetime of confusion they had caused me!

       

Dave's clichés
#56
At high resolution there are already visible startracks at 20 sec. 

 

It's the question if a star tracker and a less fast lens (but well corrected) might be the better idea for static milky way shots. In your otherwise great picture the corners are also notshowing pointy stars but some stripes. For example, an Irix 15/2.4 has an adjustable infinity hard-stop, costs less than 1000 bucks, so a bit of money is left for getting a star tracker.

 

The question is also, if - except some star tracking experts and lens nerds - will complain about these things if the see a beautifully composed picture with a milky way no on usually sees with bare eyes at our light polluted night skies?

 

I think, the Sigma is meant for more than only milky way shots - it's sort of good for these kind of stuff, but less good than specialized gear. However, that specialized gear doesn't help much with wide angle wide open shots. The bokeh is very neat and I really love the lens for this kind of things. If I were "only "in milky way shots, I'd look for something else.

#57
     You asked what subject is on a flat plane to the corners.....astro photography is just that!

  

  I think you will find the most of the star deformations are caused by the maximum exposure of around 20 seconds, 10-15 secs is the point at which stars start to make trails ....which are always worse in the corners.

Dave's clichés
#58
Please stop giving general time values which are incorrect unless you name the sensor resolution. The higher that is, the shorter the time has to be, if the camera is static looking towads the sky. And instead standing on a "planet that's revolving, revolving at 900 mph" according to monty Python's scientifically accurate galactical song. Calling our galaxy a flat plane is pretty bold, too  Tongue

 

There's infinity, infinite infinity and your Samyang giving it a fourth dimension touch.

 

I wonder who will be waiting for us somewhere at infnity, waiting with a giant text board. Oh, and you don't think I will try to find coma stars in your tiny picture?

 

The funny thing with the Sigma is, there are some coma stars in the corners. But not all stars in the corners show coma.  :blink:

#59
I just got a nice parcel back from Sigma Switzerland.

 

Last week on Monday I sent them 4 lenses to check - their Swiss guarantee includes one free check per year. For some it was the first time to make the travel. One got the front ring replaced (for free), the others were checked and the 14/1.8 needs to go again to replace broken and glued lens hood against a new one coming from Japan - but I didn't want to leave the lens there for 3 weeks.

 

Now I'm again thinking about closing the 85/1.4 gap with a Sigma - or go the Tamron way this time.  -_-

  


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