Sony Aps-c lense to Full Frame Conversion

[jigarpatel]

Hello Everyone,

I am aspiring astro photographer who has just stepped into this field. I own a A7 and i have bought two lenses Rokinon 12mm F2(APSC lense) and Rokinon 14mm F2.8 (Full Frame).

On my recent shoot i found out that 14mm is too good for wide angle shots but for astro photography f2.8 is not that great compared to f2.0 on 12mm .

When i use 12mm f2.0 on my sony A7 i have to activate crop sensor mode and it remove vignette around the picture not sure if it reduces the megapixel too.

1. My question is. Can we buy adapter to convert apsc sony lense to full frame lense ?

2. Which lense is better rokinon 12mm or 14mm lense ? In terms of professional astro shoot.

3. Is there a full frame lense with 12mm range and f2.0 or less ? In the same price range as rokinon lenses.

 

Thanks for your time.

 

 

Sent from my SM-G955U using Tapatalk

[Username]

You can put a negative dioptre on the 

APS-C lens to increase its FL, but

 

1. You will need an extension tube to 

focus the longer FL .

  

2. It will slow down to f/2.8.   

    

3. You won't like the IQ of the result. 

      

 

Therefor, use the 14mm f/2.8.  

   

If you don't realize that f/stops do 

not govern the exposure of point 

source subjects, you've skipped a 

chapter in your astro-photo text   

book, or skipped class that week :-)  

  

F/stops do affect exposure for 

the moon or for illuminated gas 

clouds, but exposure for point 

sources depends on diameter, 

NOT on relative diameter, of 

your optics.