Which L Mount lens for Astro

[c18rch]

I’m looking at upgrading my current lens. I’m currently running a Sigma 16mm F1.4 on a Panasonic S5II. When I bought the lens I wanted something fast for Astro but also didn’t really understand the effect of having a APS-C lens on a full frame camera. It also fit my budget at the time.

Now I’m looking at a Sigma 20 or 24mm F1.4 FF. I would go for the 14mm if I can find one at the right price, but a bit beyond my budget atm.

Are there any better options out there? I only really want it as an Astro lens.

What’s the difference realistically between the DN and HSM on a mirrorless camera?

 

[Box Brownie]

Just one observation......

APS-C sensor lenses are designed explicitly for that size sensor!
You can use a full frame lens on a crop sensor body but, if you find one that will fit, an APS-C lens on a full frame body does not provide an "image circle" big enough to cover the sensor. In other words you will see an extreme vignette on the image

PS in Canon speak
EF lenses will fit both full frame & crop bodies
But EF-S lenses will not physically fit a full frame dSLR body for two reasons:-
The mount is not oriented to fit the same way for EOS contacts to marry up.
The rear element of the lens will obstruct the movement of the mirror.

NB I stand to be corrected and learn if the Panny S5ii differs in the above regard ?

 

[c18rch]

The sigma 16mm fits the Panasonic, and the camera has a crop mode. I’ve used it to get some decent pictures (by my standards) without any real vignetting.

What I didn’t appreciate when I got the lens is that I’m only using part of the sensor, so I feel like a true full frame lens will get better images. More sesnor, more light captured, but that’s the gist of my question. Is that how it really works?