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Sigma 20mm 1.4 review at Lenstip
- Thread starter dmanthree
- Start date
PBR Streetgang
Forum Enthusiast
+1. :-(
S
SushiEater
Guest
I am very, very itchy.
dmanthree
Forum Pro
That is a weak spot. Shame, too.
epozar
Senior Member
And no filters.
man4mopar
Forum Enthusiast
Looking at his full frame star pictures in the sample part they look pretty decent. The corners do have some minor issues with the stars. I am weighing that against the two stops faster than F2.8.
In F2.8 there are good coma performers such as the Tamron 15-30 F2.8, Nikkor 14-24 F2.8 and Rokinon 14mm F2.8 for landscape astro. They all have t-stop in the 3.0 range, not sure what the Sigma 20mm F1.4 but likely around 1.7 to 2.0 which is a lot more light at a given ISO and shutter speed. Might be worth dealing with some coma in the corners, majority of the center is pretty clean from my view.
Compared to the Nikkor 20mm 1.8 I think the Sigma fairs similar to it at 1.4 as far as coma which I think is impressive. Lenstip did rate the Nikkor low and the Sigma medium but they look very similar to me.
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Camera Nikon D7100, Lenses Nikon 18-140mm,Sigma 8-16mm, Tamron 70-200 VC, Sigma 18-35mm
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NancyP
Veteran Member
Designing an ultra-wide-angle lens without coma at f/1.4 would be very difficult. Even Zeiss hasn't managed it, and their price point is $5,000.00, not under $1,000.00.
NancyP
Veteran Member
Zeiss 21mm f/2.8 Distagon ZE/ZF (now re-packaged as "Milvus") has low coma wide open. But that's 4-fold less light than the Sigma provides.
dmanthree
Forum Pro
Uh, I have both a Samyang 14mm f/2.8 and a Samyang 24mm f/1.4 that are more-or-less coma-free for only ~$300 and ~$500, respectively. Neither lens is perfect by the entire complement of optical metrics that together define the performance envelope of a lens, but they are right in the important aspects for the intended application.
So it's obviously not a matter of difficulty-for-cost.
That's not to bash Zeiss. They are chasing different things than just coma. But to claim that it can't be done for the price is to be ignorant of what has already been done.
A non-filter mountable super-fast wide/UWA is obviously not speaking to general landscapers, but astrophotographers. But an (possibly *the most*) important aspect for astrophotographers is coma control, which Sigma did not focus on enough to pursue other ends (such as incredible center resolution). But that's the sort of bragging rights that comes secondary to an image exhibiting coma.
man4mopar
Forum Enthusiast
The 14mm F2.8 does a great job as do a few others Nikkor 14-24mm, Tamron 15-30 are the other two I know of.
The Samyang 24 F1.4 is not coma free. Here it is compared to the Sigma 20mm F1.4
Here is the Samyang 14mm and Tamron 15-30mm Both doing great with coma at F2.8.
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Camera Nikon D7100, Lenses Nikon 18-140mm,Sigma 8-16mm, Tamron 70-200 VC, Sigma 18-35mm
CyclopSIEU
Member
So I wrote a post elsewhere about this.The 14mm F2.8 does a great job as do a few others Nikkor 14-24mm, Tamron 15-30 are the other two I know of.
The Samyang 24 F1.4 is not coma free. Here it is compared to the Sigma 20mm F1.4
Basically, I had in the past called Lenstip as being full of sh*t about this. This is because Lenstip's test results runs in opposition to many other testimonials (both online and personal) and my own observations (being an owner) as to the coma-free nature of the Samyang 24mm f/1.4. It was chosen explicitly toward this end, costs be damned. I mean, I had pre-ordered the Sigma 20mm Art the night of its announcement on the promise of coma-free UWA astro, costs be damned.
Here is a 100% crop of a corner with the Samyang 24mm f/1.4.
http://www.dpreview.com/forums/post/56628005
I mean, if somebody who tests lenses (i.e. borrows it, tests it, returns it) says one thing totally at-odds with your extensive experience with something you personally own and know (i.e. each posted astro shot is probably 10+ similar shots at different exposures, slight framing differences and ISOs), you are going to be livid about the perceived blatant lies.
Only recently, with the Sigma 20mm f/1.4 test they did, have I gained insight into the reality of what might be happening.
It should have been obvious to us all, but Lenstip DOES NOT normally test for coma in the same way that would be relevant to any of us. That guy is located in the middle of Warsaw (read: large-city light pollution) and does not get out to shoot astro for every lens he tests. What you see is some sort of red laser.
(I too use a constant-on red laser for stealthy night photography focus assist. That's a long, different story.)
From an experimental perspective, a controlled light source (such as a laser) is better by virtue of being much more reproduce-able than a natural light source. But any grasp of the nature of optical aberrations (i.e. the inability to bring different wavelengths of light back into the same focal point) will tell you that a laser (by definition an intense, coherent light source of a single wavelength) should give you totally different results than from starlight (by definition a weak light source of many different wavelengths).
Looking at both the Sigma 20mm f/1.4's red laser "coma" test and the actual astrophotography coma test, you can see that the manifestations are totally different. The laser shows none of the classical coma "wings". The actual astro shows the wings.
In other words, Lenstip's "coma" test is probably only relevant to coma as produced from a red laser light source. If you so overexpose your actual astro so that the red component of the the starlight approximates the intensity of the laser and hence produces the sort of observable aberration as shown by the laser test... chances are the sky itself is so highly exposed that the aberration is obscured.
This is how I think the differing observations can be reconciled assuming honesty is being attempted by all parties (probably), competency is equally present (maybe), and similar lens qualities are had by all (uhhhhh...). It does also mean that the Lenstip laser "coma" test is meaningless to most everyone's actual usage.
The Tamron 15-30mm is seen to exhibit classical coma "wings" in the course of actual astrophotography in a thread on this very page:Here is the Samyang 14mm and Tamron 15-30mm Both doing great with coma at F2.8.
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www.dpreview.com
(see upper left corner)
And others have noted the same elsewhere. The latter is why I gave up on it and opted for the Canon EF 16-35mm f/4L IS USM in my profile. All this is further evidence that Lenstip's laser "coma" test is meaningless except for shooting, um... lasers.
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epozar
Senior Member
Well this image is not relevant being 30sec long (e.g "streaky"), maybe even decentered.
When has a "improper" 30s exposure produced wings that a "proper" 20s exposure didn't?*
And here:
http://www.the-digital-picture.com/Reviews/Tamron-15-30mm-f-2.8-Di-VC-USD-Lens.aspx
You can see the coma much like the "not relevant" 30s exposure.
It should be noted that Roger Cicala (of Lensrentals fame) is their collaborator... so they know what they're doing. This was one of the reviews that made me give up on dreams of a one-lens UWA solution. The Tamron 15-30mm f/2.8 was in contention to be just that had it been as good as the Samyang in terms of coma.
* In another thread about coma, a 20s exposure of mine that was pointed away from the poles produced a bit of streaking in one corner. In that thread, somebody claimed that the minimal amount of streaking obscured whatever coma might be there. This is the opposite ("too much exposure obscures coma") to your claim ("too much exposure manifests coma"). Ironic, isn't it?
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epozar
Senior Member
Yep, I too use 10 seconds exposure for stars.
IMO, those star "dots" at TDP are perfectly acceptable.
What does that matter to the issue of coma?
Your standards are obviously more accommodating when it comes to this lens, because you seem to be okay with the purple tails on the brightest stars. (This is the upper right corner of the frame.)
I would call this an acceptable compromise for being a zoom lens, but somewhat removed from perfect* and less than what the Samyang primes can-do/have-done. If one could only only carry one UWA (or can only afford one), this would be a good compromise as a jack-of-all-trades.
* TDP says, in their words, "There is some coma present in these examples, but the stars still look like stars – not flying saucers." In other words, somewhat removed from "perfect".
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epozar
Senior Member
You are talking about 14/2.8 lens? Or?
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