Sigma Imaging UK recently short-loaned me their 14mm f/1.8 Art lens to take out under the dark skies of Wales and see what I thought of it from an astrophotographer's viewpoint.

My aim here isn't to produce a comprehensive review of all the lenses features and specifications, the internet has plenty of them already, but to give you guys more of a user experience and to see how well it performs when it comes to photographing the night sky.

It's worth noting that this is the first time I feel like a lens has been produced with astrophotographers as the main focus. I mean, who else really needs a super wide angle lens that can open up to f/1.8? So with that in mind and considering it's up to £1700 price tag I went into this with high expectations.

If you're after a quick conclusion, this lens absolutely blew me away. The detail it resolves made the 12mp sensor of my Sony A7SII feel more like 30mp. The vignetting and distortion are both minimal and the overall 'look' of the images it produces is in my opinion stunning. That said, it wasn't quite the perfection I was (ambitiously) hoping for, but as I mentioned, my expectations were pretty high! I'll summarise the main points below before sharing my experience:

The Good

Fastest super-wide angle on the market
Incredibly sharp
Weather sealed
Colour rendition (personal point)
Overall 'look' (and another)

The Bad

Big and heavy
Price
Coma present down to f/2.8
Soft in extreme corners
Doesn't take screw on filters

Overflowing Starlit Reservoirs at the Elan Valley

Craig Goch Dam, Elan Valley   -    Sony A7SII + Sigma 14mm Art    (   f/2.2   /   25 secs   /   ISO12,800    ) — Craig Goch Dam, Elan Valley - *Sony A7SII + Sigma 14mm Art ( f/2.2 / 25 secs / ISO12,800 )*

With a night-long forecast for clear skies just before the new moon I headed to the Elan Valley in Mid Wales. A designated Dark Sky Park, it's one of the darkest places in Wales with plenty of foregroud interest to play with and home to a fantastic community of astronomers, astrophotographers, and dark sky lovers.

Photographing the Milky Way Handheld

Being the fastest super-wide angle on the market I was curious to see if I could photograph the Milky Way handheld. The wider the lens the longer handheld shutter speed you can get away with and with the f/1.8 aperture you can let a lot of light through onto the camera's sensor. Teamed up with the incredible high-ISO performance of the Sony A7SII and its built-in Steady-Shot technology (sensor stabilisation), I managed to get a couple of sharp images from 1-second exposures.

Sony A7SII + Sigma 14mm Art   ( f/1.8  /  1 sec  /   ISO51,200  /  Handheld w/ Steady Shot  ) — *Sony A7SII + Sigma 14mm Art ( f/1.8 / 1 sec / ISO51,200 / Handheld w/ Steady Shot )*

As mentioned in the vlog, I believe that the detail this lens resolves allowed me to perform some pretty aggressive noise reduction whilst maintaining a good amount of detail in the right places. Noise reduction algorithms are programed look for edges in an image and try to retain detail there, thus I feel like the noise reduction software had an easier job of targetting the right areas. But please note, this is just a personal hunch and it would take a far more scientific approach of investigating to prove this as fact.

Here's the same composition from a tripod...

Sony A7SII + Sigma 14mm Art    (   f/1.8   /   30 secs   /   ISO3200    ) — *Sony A7SII + Sigma 14mm Art ( f/1.8 / 30 secs / ISO3200 )*

Coma and astigmatism

One of the most important features of a lens to astrophotographers is how well it handles coma and astigmatism - imperfections in the corners that can make the stars look more like 'flying-saucers'. Sadly, the Sigma 14mm Art lens does suffer some coma at the wide open apertures, a little remaining down to f/2.8. This is the aperture I would personally use for most cases as it's what I'd consider acceptable.

So 'Why buy an f/1.8 lens if you're just going to use it at f/2.8?' I hear you ask. There's a few reasons:

1) Much less vignetting when stepping down the lens to f/2.8 compared to a 14mm lens with a maximum f/2.8 aperture. This also means the sensor will receive a bit more light, improving the signal-to-noise ratio a little and producing a slightly brighter overall exposure with ultimately less noise.

2) Because it's the only 14mm that can open to f/1.8! If you need it, you'll have it. Probably the most exciting use of this will be timelapses of the aurora (for times when the moon isn't out). The wider aperture will allow for shorter speeds resulting in a timelapse with a much more smoother and life-like flow to the aurora in the sped up video. In such a case, I would happily accept a bit of coma in the corners.

3) Low-light video. Again, the aurora being a great example here. Whilst I didn't test it for video myself, the lens distortion in the images was quite minimal for such a wide angle lens, so loosely assuming, there's probably no better super wide angle lens available right now for real-time videos of the aurora or meteor showers.

4) Opening the aperture to decrease noise. There will be cases where sacrificing a little coma in the corners is worth the ability to lower the ISO and produce cleaner images.

5) You can photograph the Milky Way handheld. How practical that is is up to you to decide however!

The stars in the top right of the frame exhibited coma and sagittal astigmatism down to f/2.8. The stars in the top-left were a similar story but also appeared a bit elongated. I think this is more likely to be stretching from lens distortion rather than tangential astigmatism though.

For a more scientific approach to the testing of the coma check out Adrien Mauduit's review video.

My personal conclusion is that whilst not perfect, it's an acceptable trade off for a 14mm lens that can open up to f/1.8 and especially one that resolves detail like this. For the most part I would be using f/2.8 where it's barely noticeable unless you zoom 100% and the level of coma at the wider apertures is worth the extra light.

Sharpness

One of the most impressive points of this lens is how sharp and detailed the images are. If you're not a fan of sharp images, this lens isn't for you because even wide open at f/1.8 the large center area of the frame is incredibly sharp. You need to be very cautious when adding sharpness in post, as it's quite easy to produce white halos on edges with high contrast.

*Centre of the frame @ f/1.8 is already incredibly sharp*

It's worth mentioning that even when stepped down to f/2.8 and f/4 there is still a sharpness drop off in the extreme corners. In all fairness to Sigma they've seemingly defied the laws of physics to create this lens, so expecting it to be pin sharp even into the extreme corners at wide open apertures is in hindsight asking a little too much! It's also going to take a lot more than that to take your attention away from the phenomenal detail in the other 90% of the frame anyway. And if like me you add a vignette in post it's going to be even less noticeable in the end.

At first I thought it may have been from the use of a wide aperture and the proximity of the lens to the foreground but it was noticeable in images where it definitely wasn't the case and other photographers have experienced the same. Similar to Nick Page's experience, the lens I was using also seemed to exhibit more of a loss in image quality in the left corners of the frame.

I appreciate this isn't a technical review of the sharpness of this lens at various apertures in different areas of the frame, as I mentioned there's plenty of those on the internet already, but from my experience I was continually impressed by the detail present in each new RAW file I opened.

Distortion and Vignetting

Whilst I didn't test it against a blank wall and walls with lines, the distortion and vignetting of this lens only came to my attention when I realised I hadn't noticed much of either.

When applying the lens distortion profile in Lightroom there is a minor adjustment to the extreme corners and the vignetting is also minimal, especially when stepped down to f/2.8.

To reaffirm my beliefs I managed to stitch a 4-shot panorama with ease, something both distortion and vignetting can cause great difficulty, especially with a super-wide angle lens. It's also something I would never do with the Samyang 14mm f/2.8 due to its heavy vignette and interesting mustache distortion.

Pen y Garreg Dam, Elan Valley   (   f/2.2   /   25 secs   /   ISO12,800   /   4-shot panorama   ) — *Pen y Garreg Dam, Elan Valley ( f/2.2 / 25 secs / ISO12,800 / 4-shot panorama )*

User Experience

This is a big, heavy, premium lens. Something to consider if your bag is already packing kilos and if you do a lot of long-distance or uphill hiking. My personal feeling is that it's worth carrying those extra grams for the image quality this lens delivers.

The focus ring has nice throw on it and a premium weighty feel but it does exhibit focus breathing (when trying to focus on a star it moves slightly up and down in the frame). This is something I'm not used to as a Samyang user so at first it frustrated me a little. In after thought this could possibly help you focus, as you can spend a little time eyeing up which position in its movement it's most in focus. In other words, moving the star up and down on the LCD screen as you turn the focus ring and hone in on the pin-sharp point.

The switch to turn-off autofocus was well engineered, easy to locate in the dark, and a joy to use even with gloves on. I can't comment on the auto-focus itself as it's not something you'd typically use in wide-angle astrophotography, if it even works at all.

I also reallly liked the lens cap. It doesn't have to go on in any orientation and there are no clips to keep it on but it fits snugly over the lens with a lining of felt material on the inside keeping it on nicely ("like a glove!"). This certainly adds a nice touch to the whole premium feel of this lens.

Conclusion

The Sigma 14mm f/1.8 Art lens is a beast. It's a big, heavy, expensive lens but it delivers images with phenomenal detail and sharpness and there's very little in the way of distortion or vignetting. It does exhibit a little coma and sagital astigmatism at apertures up to f/2.8 and the extreme corners are a little soft but there was always going to be a price to pay to be able to manufacture a 14mm lens with an f/1.8 aperture. Personally, I think it's a small price to pay.

Depending on your budget, the other landscape astrophotography competitiors I see for this lens are the old faithful Samyang 14mm f/2.8 and the newer and improved Samyang 14mm f/2.4 SP. It blows the former out of the water but at four times the price you would expect it to. The latter I've yet to use but I'm eager to give one a go and I'll share my experience with you all as soon as I do.

I opened the vlog by saying this was an astrophotographer's dream lens on paper and from my experience, it lives up to it too.