Showing posts with label Lenses. Show all posts
Showing posts with label Lenses. Show all posts

Monday, December 16, 2019

The World's Best Camera Lens Focal Length Comparison Tool

camera lens focal length composite
17 to 600mm all in one shot.
There are tons of camera lens focal length simulator tools out there online today. They use varying degrees of sophistication in order to simulate the views offered by various lenses' focal lengths. Unfortunately, one important bit of information is often missing: scale. Sure, it's nice to play around with the fancy interactive simulators, zooming in and out in order to see what various focal lengths will look like but, without knowing scale, there is always a question of what a lens will do in a given situation, especially when shooting at long distances.

Recently, I was questioning how much I would gain by going over the 300mm in focal length offered by my Sigma 100-300 f4, which is, coincidentally, where most camera lenses commonly available at non-specialty retailers (think Best Buy or any other big box store that sells camera stuff) max out. In most basic form, lenses that go to 300mm (and typically start at 70/75mm) are a dime a dozen and can often be bought new for less than $200. Second hand, they can be had much cheaper. Want to go longer? Well, the price goes up a lot, which begs the question: are those extra millimeters worth the money?

As an example, let's look at Nikon and Canon, the world's largest interchangeable lens camera manufacturers.

Currently (December, 2019) Nikon's cheapest zoom lens maxing out at 300mm and usable on both sub and full frame models is the 70-300 f4-5.6G, which is selling for $170. Canon's closest comparable offering is the 75-300 f4-5.6 III model that sells for $180. Both lenses are easily in reach for someone who's willing to drop $500 for an entry-level camera kit.

Want more reach? Well, for an extra 100mm the price goes up-a lot!

Moving up to a zoom lens that maxes out at 400mm, there are a pair of 100-400mm lenses from third-party manufacturers Sigma and Tamron that have MSRPs of $800. Is that extra 100mm worth the extra $600? Well, ignoring the other factors that should go into making a lens purchase (optical performance, AF capabilities, build quality, weather-resistance, warranty), the jump in reach from 300 to 400mm really isn't all that much. How about 600mm? Both Sigma and Tamron make such optics, which provide a noticeable jump in reach, but which cost $1300 and $1400, respectively.

Think that's expensive? Keep reading.
Want to stick to name brand but keep roughly the same focal range? Well, you're looking at $2100 for Nikon's 80-400mm and $2200 for Canon's 100-400mm model. Paradoxically, Nikon makes a 200-500mm lens and sells it for a 'mere' $1400, which is perhaps the cost of losing 120mm of range (and a lot of flexibility) on the short end.

As for me, not seeing a focal length simulator anywhere that had known scales for both size and distance, I decided to create one for myself.

To start with, I knew that I had a way to get up to an equivalent 600mm focal length. To start, I would begin with my Sigma 100-300f4, the longest AF lens I currently own. On top of that, I also own a 200 f4 Ai Micro Nikkor, an old MF gem produced from the late 70s to early 80s before being updated to an Ai-s version. Having a native magnification ratio of 1:2, I bought a 2x teleconverter in order to boost my magnification to full 1:1 life size and the current standard for macro optics. 200mm doubled with the teleconverter becomes 400mm, which I could then take to 600mm by using the 1.5x crop DX mode available on my D700.

Focal lengths figured, I needed something to shoot. Walking down my driveway, I realized the answer was in front of me in both my street and the stop sign at the end of it. The standard American stop sign is 750mm (roughly 29 ½ inches) across, and there was one staring right back at me. As for finding distance, I was lucky in that my street is concrete with expansion joints cut at regular intervals. Measuring one section of street in feet and multiplying that times the number of sections all the way to the end resulted in a length of approximately 950 feet (290 meters), give or take a few feet.

Everything figured, I shot at 300, 400, and 600mm and then looked at everything on the camera. Realizing this was a good sequence, I decided to fill in the rest of the focal lengths offered by the rest of my other optics, which go all the way back to 17mm.

To use the gallery below, simply click on any of the pictures to open the gallery in a filmstrip view, then use the wheel on your mouse to scroll through the pictures, all of which have the focal length displayed in the upper left. Yes, this is nowhere near as sophisticated as most of the other lens focal length simulators out there but, on the other hand, it may be the only one on the web with known size and distance scales.

Oh yes, back to the 'are the extra millimeters worth the money' question. 300 vs 400mm? If you need to go long, skip the 400mm rip-offs as there's clearly not enough gain to justify the $600 premium over a 300mm optic for anyone on anything resembling a budget. Spend a little time and save a ton of cash by cropping your photos in the camera or on the computer as today's 20+Mp cameras have more than enough resolution to do so. If you really need reach via optics, go big or go home as there's nothing that can touch those zooms maxing out at 600mm from Sigma and Tamron and, as the pictures show, there is a ton of gain from 300 to 600mm. Yes, $1300-1400 is not cheap but it's a lot cheaper than buying a $800 lens that goes to 400mm, realizing that it's not enough, going back and dropping another $1400 on a lens that goes to 600mm, and then hoping to recoup as much as possible from your 400mm mistake.

Still not long enough for you? Well, it looks like you'll have to attach an astronomical telescope to your camera and use it an a lens.

In the end, though, only you can decide what's right for your specific needs.





Believe it or not, this 50mm shot is close to the field of view for most humans.








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Saturday, November 9, 2019

The Many Tokina 28-70 Lenses and How to Identify Them (With Pictures)

different versions of the Tokina 28-70 lens
What version of the Tokina 28-70 is this? Read on to find out!
From the late 1980s to the mid 2000s, Tokina made a total of 4 constant f2.8 lenses with the 28-70mm focal range. Unfortunately, it can be hard for a would-be buyer to identify each version because many original sources were on paper (think photography magazines before the Internet) and are long gone and, being out of production for roughly 15 years, most contemporary online documentation has also disappeared.

That, plus adding online buy/sell websites like Ebay and Craigslist and now social media platforms, only adds to the confusion as many people do not know the variations of these lenses and will merely sell the lens along the lines of something like 'Tokina 28-70 f2.8.'

So, what are the variations and how to identify them?



1. Smooth finish. 2. Distance scale window. 3. Zoom ring wider than focus ring.
1st Generation: Tokina 28-70 f2.8 AT-X (1988-1994)
The first generation of Tokina 28-70 f2.8 is the easiest to identify as it is the only one that features a recessed distance scale window rather than painted on markings. Another easy identifier is that this is also the only version that does not feature the now-standard Tokina AF/MF clutch mechanism that involves moving the focus ring back and forth, so there will be no AF/MF markings anywhere on the barrel. To switch mode, flip a switch on the lens (for versions with built-in motors) or flip the switch on your camera (versions with a mechanical drive linkage). On top of that, this is the only version that features a zoom ring that is wider than the focus ring and the only version that accepts a 72mm filter. Finish is smooth.



1. Zoom ring now wider than focus ring. 2. AF/MF on barrel. 3. Smooth finish.
2nd Generation: Tokina 28-70 f2.6-2.8 ATX-PRO (1994-1997)
The second generation was the first based off the optical design Tokina bought from the French company Angenieux that would serve as the basis for the rest of the 28-70 line. This was the first 28-70 version to feature the AF/MF clutch, so look for AF/MF markings on the barrel. Unfortunately, in its early incarnation, switching focus mode meant rotating the ring while pulling/pushing on it in order to find the window where the clutch engaged and the ring moved. On top of that, one needed to flip the AF/MF switch on either the camera or the lens itself (depending on whether the lens has a built-in motor or is focused via mechanical linkage powered by the camera), depending on your manufacturer. Also new was the flip in width of the focus/zoom ring as the focus ring is now the larger of the two as it would remain through the remainder of the run. This version (as do the later ones) uses 77mm filters. On the front of the lens by the filter threads, there also appears the word 'Tokina.' Finish is smooth. To make things difficult, thank Tokina's marketing department. This lens was marketed in some places as being f2.6-2.8 (even though no camera will recognize f2.6) and others as a constant f2.8. No matter, the lenses are the same no matter what the markings say.

See also: My Tokina 28-70 f2.6-2.8 ATX-PRO I Review





The quickest way to tell a Tokina ATX-PRO "II" (left) from a PRO "I" (right) is the newer "II" lens' crinkle finish. The aperture ring is exclusive to Nikon versions.
Another way to tell the difference: the "II" (left) doesn't say 'Tokina' while the "I" (right) does.
3rd Generation: Tokina 28-70 f2.6-2.8 ATX-PRO II (1997-1999)
The third generation is optically unchanged from the previous 'PRO' version except for that the “II” got a 'high refraction low dispersion' (HLD) element designed to combat chromatic aberration. All other changes were cosmetic. The easiest way to spot the “II” from a “I” version is that the “II” now has a crinkle finish instead of the smooth one seen on the previous version. Another easy way to distinguish a “I” from a “II” is that that “II” version now features a bayonet mount for the hood (versus the screw-on versions for earlier lenses). As for markings, 'Tokina' has now disappeared from by where the filter threads on but, irritatingly, there is no mention of “II” anywhere on the lens even though it was marketed as such. Like the “I” version, the “II” was marketed in some places as being f2.6-2.8 and in others as a constant f2.8. No matter, the lenses are the same no matter what the markings say. The clunky 2-step mode to change AF/MF was, unfortunately, also unchanged.

Oh yes, the lens at the top of the page is the ATX-PRO II thanks to the crinkle finish.




The Tokina 28-80 f2.8 ATX-PRO.
The 28-80's internal configuration.

End of the Line
In 2000, Tokina launched its direct successor to the “II” version above in the form of a 28-80 f2.8 ATX-PRO. Keeping the low dispersion element, which it now marketed as a 'super low dispersion' (SD) element, Tokina now added a pair of aspherical elements to the new design, which remained in production into 2006. This lens also saw the return of a distance scale window rather than the cheap looking painted markings. As an innovation sure to be appreciated by many, Tokina reworked its system for switching focus mode. This lens now features the “One Touch” focus clutch, which allows for switching from AF/MF simply by pulling/pushing the ring anywhere while eliminating the need to flip any switches on the camera. It is for this ease of focus mode transition that this lens typically sells for more than the 28-70s on the used market.





Aperture ring (Nikon models only) aside, the Tokina 28-70 f2.8 ATX-PRO SV (left) is virtually identical to the 28-70 f2.6-2.8 ATX-PRO "I" (right).


 
Visually, the only way to tell these two lenses apart is to look at the lettering by the filter threads as the SV version will always identify itself as such.

 
The 28-70 f2.8 ATX-PRO internal configuration.

4th Generation: Tokina 28-70 f2.8 PRO SV (2002-2006)
Looking to tap into a lower price-point market, Tokina resurrected its 28-70 offering in 2002 as the Tokina 28-70 f2.8 ATX-PRO SV, with the 'SV' designating 'Special/Super Value' (I've seen it referred to as both). In appearance, this is most like the ATX-PRO “I” version as it abandons the crinkle finish of the “II” (and 28-80 f2.8 for that matter) in favor of the smooth used from 1988-1997. The easiest way to identify this one? The lettering by the filter threads will note the “SV” designation. As for what constituted a “special value,” it involved cost cutting. The SD and aspherical elements seen on the contemporary 28-80 f2.8 version were gone as was the “one touch” clutch as Tokina opted to resurrect its clunky 2-step version seen on the older 28-70 “I” and “II” PRO versions. Build quality also took a hit, with Tokina incorporating more composites (a fancy word for plastic) into the lens. Hey, you usually get what you pay for! Of the 4 versions of the 28-70, this is the least desirable.


Monday, October 21, 2019

A Complete List of Weather Resistant Sigma Lenses

List of weather sealed lenses Sigma markets as splash and dust proof
Sigma markets its weather sealed lenses as "dust and splash proof."

Being someone who values both high quality and saving money, I was looking for a list of weather sealed Sigma lenses. Unfortunately, I haven't succeeded in finding a concise list of such lenses anywhere. So, seeing a solution rather than a problem, I decided to compile one myself. So, if you're in the same boat I was in, here you go: a concise list of weather resistant Sigma lenses, which can not only stand up to the harshest environments, but can also save the buyer a lot of money over manufacturer optics. Know someone else you think would find this useful? Why not pass it on?
Companies are quick to tout cameras for weather-resistance. Unfortunately, what most beginning dSLR users don't know is this: there might as well be no weather sealing in the camera if it doesn't have a weather-sealed lens to go with it. Why is this? Simple: the lens/camera connection is the best avenue for unwanted junk, whether it be moisture, dust, or something else, to get into your camera. With a lens that has a rubber gasket at the mount, this problem is eliminated.

In terms of lenses, weather-sealing is one of the newer innovations for the simple reason that film cameras were nowhere near a susceptible to the elements as are today's “superior” digital versions. So, to keep their pros happy, camera makers started building additional rubber gaskets into their lenses at their most vulnerable points. Below is a complete list of Sigma lenses that are marketed as 'dust and splash proof.'

Hopefully, Sigma will have more on the way!


14 f1.8 DG HSM Art
16 f1.4 DC DN Contemporary
28 f1.4 DG HSM Art
35 f1.2 DG DN HSM Art
40 f1.4 DG HSM Art
56 f1.4 DG DN Contemporary
105 f1.4 DG HSM Art
135 f1.8 DG HSM Art
500 f4 DG OS HSM Sport


14-24 f2.8 DG HSM Art
14-24 f2.8 DG DN Art
24-70 f2.8 DG OS HSM Art
60-600 f4.5-6.3 DG OS Sport
70-200 f2.8 DG OS HSM Sport
120-300 f2.8 DG OS HSM Sport
150-600 f5-6.3 DG OS HSM Sport


A fan of Sigma Products? Well, check out the following reviews!
Sigma 24-105 f4 DG OS HSM Art
Sigma 35 f1.4 DG HSM Art
Sigma 100-300 f4 DG HSM Apo


Don't own one of these lenses yet?
Well, no worry, here's how to avoid getting caught with dirty pictures!


Want to Stay Name Brand?
Check out a complete list of weather-resistant Nikkors, too!


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Sunday, April 21, 2019

In-Depth Review: Tokina 17 f3.5 ATX-PRO

The Tokina 17 f3.5 ATX-PRO


Tech Specs

Focal Length: 17mm
Dimensions: 2.2 x 3.3 in.
Weight: 15.3.
Maximum Aperture: f3.5
Minimum Aperture: f
Diaphragm Blades:
Front Element: non-rotating, extending
Optical arrangement: 11 elements in 9 groups
Autofocus Mechanism: Mechanical drive
Closest Focus: 9.8 inches
Maximum magnification: .11x
Filter Size: 77mm

Background
It seems that with every new generation of camera lenses, opticians are able to push the extremes a little bit wider. By the arrival of the 1980s, sub 20mm was now the new standard for ultrawide SLR lenses. Of these, the Tokina 17 f3.5 was one of the most affordable. With the arrival of the AF era, Tokina created a new AF version of its 17mm f3.5 optic, the 17mm f3.5 AT-X, for 1993. The only real fault of this lens: a built-on lens hood, a bit of overkill for a lens without a protruding front element. Eventually, Tokina redid its 17mm ultrawide in 1999, keeping the optical formula the same, but redoing the cosmetics and dubbing the new model 'PRO.' AF was now controlled by the famous Tokina clutch system and the idiotic built-on hood became a thing of the past. To date, the Tokina 17mm f3.5 ATX-PRO lens being reviewed here, discontinued as of 2005 is Tokina's last ultrawide prime ever produced save for Sony.

Build Quality 5/5
Tokina is a company known for its high standards of construction and the Tokina 17 f3.5 ATX-PRO is built to the highest of standards, namely, out of solid metal. Honestly, many manufacturer lenses of today aren't built anywhere near as well as the third-party Tokina offering. Picking up the lens, it is quite heavy but this heavy construction goes a long way in inspiring confidence, showcasing that this lens is a true photographic tool and not some dinky toy. Onto the mechanics, Tokina was nice enough to include an aperture ring lock switch so that the ring can be locked at minimum aperture for use on today's cameras. In the act of focusing, the front element extends a tiny, tiny bit (maybe 2mm) but does nor rotate. The focus ring is of the variety where one must find the window to move it. To do this, simply rotate the ring while pushing forward/pulling back on it and wait for it to snap into the desired position.

Note the AF/MF ring positions.

Notice the Nikon-only AF slot screw at 5 o' clock
 

AF Performance 4/5
As with all ultrawide lenses, AF speed on the Tokina 17 f3.5 ATX-PRO is, at least on the D700, very fast and, for a mechanical drive lens, very quiet. However, as with all mechanical drive lenses, there is no full time manual focus feature as is seen on newer optics, which means that you need to manually switch from AF to MF mode. At least with Nikon, AF speed has a lot to do with the camera, so it may be slightly slower/faster on yours depending on what you have. In regards to accuracy, focus is dead-on every time. Additionally, thanks to the clutch mechanism, the focus ring doesn't spin when the AF is operating, so hold it anywhere.


Optics: 4/5
A lot goes into determining the optical quality of a lens, so let's look at them separately.

Sharpness
For a lens of such an extreme design, the Tokina 17f3.5 ATX-PRO performs very well. Straight out of the gate at f3.5, the center is razor sharp, with virtually nothing gained by stopping down. At f16, though, sharpness falls off due to diffraction limiting. Mid Frame, f3.5 is a little soft, but f5.6-f11 are all razor sharp, with diffraction again creating a softening at f16. In the corners, the lens is pretty mushy wide open but sharpens up nicely at f8, save for the extreme (emphasis on extreme) corners of the frame. F11 is also very good and, yet again, diffraction limiting sets in at f16. Overall, the best overall image quality across the frame is at f8, with nothing gained by closing up a stop to f11. Overall, not bad for such an extreme optic of mid 1990s design. On crop frame cameras, it should be pretty much razor sharp across the frame.



Vignetting
This lens vignettes noticeably when shot wide open. Stopping down to f5.6 greatly reduces the corner darkening and closing up to f8 reduces it a little more, with nothing gained past that point. If shooting on a crop camera, vignetting should be a non-issue.
.

Distortion
For a 17mm optic, distortion is very well controlled even when shooting brick walls. In real life shooting, it should go unnoticed.





Chromatic Aberration
For a company known for lenses that had false color (purple) chromatic aberrations during the time this optic was produced, the Tokina 17 f3.5 ATX-PRO does very well here. Only the biggest pixel peepers will notice anything at all at f3.5. Seriously, you have to actively look for it to see it at all even at 100%. The composite is 100% and the other image is the full uncropped shot.

Flare/Ghosting
Avoid bright lights just outside the frame as the lens will flare, thought obnoxiously. The hood doesn't help much if at all.

Value: 5/5
Simply put, this is a lens that anyone with a FX format Nikon camera should take a serious look at. Priced at around $350 on the used market, this lens is the way to go for anyone wanting a portable, ultrawide optic that won't break the bank. Simply put, nothing else comes close to the Tokina 17 f3.5 ATX-PRO in regards to price. The best part: no protruding, vulnerable front element

Competition
Simply put, there are no direct competitors for the Tokina 17 f3.5 ATX-PRO. Yes, there are wider optics out there, namely the 14mm f2.8s everyone is making, but these are comparatively large, unwieldy lenses that can never fit into a pocket and that have bulbous, flare/scratch-susceptible front elements. On top of that, all the manufacturer optics are all are priced much, much higher. Tamron used to make a 14 f2.8 but, like the manufacturer optics, it has a bulbous front element and is the build quality is greatly inferior. If one doesn't mind adding a few millimeters of focal length, there are some interesting 20mm options, Nikon's 20 f2.8 and Sigma's 20mm f1.8. Neither are built to the standards of the Tokina but the Nikon is much smaller and 2/3 stop faster and the Sigma is 2 stops faster but much larger and, according to some reviews, quite soft wide open across the frame, unlike the Tokina. In all, there are a lot of interesting ultrawide primes on the market but no single lens that can go toe-to-toe with Tokina's masterpiece.

The Ultrawide Myth
Many beginners believe (incorrectly) that an ultrawide lens like this will be just the thing for “getting it all in” the frame. Well, there's yes and no to that. Yes, you'll sweep up everything around you but, on the other hand, your point of focus will be appear to be pushed way into the distance. Long story short, this is not a landscape lens. On the other hand, if you find yourself shooting in tight quarters and constantly wishing that you could only back up more to fully capture a scene, this is the lens for you. Who is this lens for? Indoor architectural photographers and even realtors come to mind. Astrophotographers (like me) will also love this lens for its ability to capture nearly all-sky views, especially during meteor showers, without distortion. Paparazzi? Yes, even you scumbags of the photography world will benefit from this lens as its ultrawide field will allow you to just about shove your camera up a celebrity's nose and still get a full headshot. Crop frame shooters? Don't waste your money here as 17mm on your camera isn't ultrawide by any means. Get something in the 8-12mm range instead.


Conclusion: 4.5/5
The Tokina 17mm f3.5 ATX-PRO is quite a lens even before one considers its rock-bottom price point. Build quality and AF capabilities are top-notch and the optics, though not perfect, are very respectable for a lens in this class. The real shame about this lens is that it is out of production and so difficult to find. To start with, Tokina is the smallest of the major third party lens manufacturers, which means that there were less of these lenses produced than its Sigma, Tamron, and not to mention Nikon near-equivalents. Perhaps the true barometer of how good a lens is is to look for the frequency with which it appears on the used market. In the case of the Tokina 17mm, one hardly ever sees it show up, even at the big places like Adorama, B&H, and even the world's largest used photo gear dealer, KEH. Simply put, people know a good product when they get one and are reluctant to let go of it. Such is the case with this Tokina gem. Bottom line, if you have a FF camera, this is the best $300ish you can ever spend, that is if you're lucky enough to find this lens at all. 



Tokina Fan? Check Out These Reviews
Tokina 100 f2.8 ATX-PRO Macro
Tokina 80-200 f2.8 AT-X
Tokina 80-400 f4-5.6 AT-X
Tokina 28-70 f2.6-2.8 ATX-PRO



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Sunday, October 12, 2014

In-Depth Review: Sigma 24-104 f4 DG OS HSM Art

Tech Specs
Focal Length: 24-105mm
Dimensions: 4.3 x 3.5 in.
Weight: 31.2oz.
Maximum Aperture: f4
Minimum Aperture: f22
Diaphragm Blades: 9
Front Element: non-rotating, non-extending
Optical arrangement: 19 elements in 14 groups
Autofocus Mechanism: Sonic Drive
Closest Focus: 17.7 in
Maximum magnification: .22x
Filter Size: 82mm


Background

At Photokina 2012, third party photographic lens maker Sigma has reinvented its business model with a new Global Vision, whose focus is, among on other things, producing optics that can go toe-to-toe with the manufacturer products instead of serving as a poor man's alternative. To that end, Sigma has churned out a lot of drool-worthy gear in the past two years. However, there was a major hole in Sigma's revamped lineup: a fixed aperture standard zoom for full frame. Cue the lens we're reviewing here today: the Sigma 24-105 f4 DG OS HSM Art. With a long history of making fast to semi-fast fixed aperture zooms, Sigma has a lot of background in such optics and, with a new Global Vision, a stronger drive than ever to make class-leading products. So, does the 24-105 f4 OS Art deliver the goods? Well, read on to find out!






Build Quality: 5/5
The Sigma 24-105 f4 OS Art is built to the standards that were, even just a few years ago, reserved for manufacturer optics. Constructed out of Sigma's exclusive Thermally Stable Composite (TSC) material, which feels a lot like metal but whose formula is a closely-held corporate secret, the lens has a decidedly solid feel to it. In addition, the lens is inner focusing, which means that there is no moving/rotating of the front element when focusing, which is good for people who like to use polarizing filters. As for the rings, both zoom and focus rings are rubberized, highly textured, and come across as having that 'just right' balance between ease of movement and lack of slop. For some people, the dual cam inner design may be of a concern but, at least in-hand, there's no wobbling whatsoever. However, I cannot vouch for this lens when shot in harsh conditions as it not marketed as weather resistant.

Survivability

This lens is focused by a built-in motor and stabilized by electronic gyros which will die eventually. To protect your investment, buy factory new and register your warranty with Sigma, which will fix your lens for free should something go wrong during during the warranty period and for a cost out of warranty so long as parts are available.


See also: Weather Resistant Sigma Lenses






AF Performance: 5/5
Focus on the Sigma 24-105 f4 OS Art is as fast, accurate, and silent thanks to Sigma's Hypersonic Motor (HSM) technology, which is the company's version of a ring type sonic-drive AF system. As for tracking, the lens had no problems with birds in flight (see samples) on the D700. As with all ring-type AF, the lens has full time manual override, which allows for instantly overriding the AF simply by turning the focus ring, no need to flip switches. In reality, the AF/MF switch is more of an AF/AF Disable switch.



 At 24mm


 At 35,mm.
 At 50mm.
 At 70mm
At 105mm
Optics: 5/5
Sharpness (Note: on DX, consider the mid frame here to be the corner)
By looking at all the test images, a pattern emerges: the Sigma 24-105 f4 OS Art is as good as it will get right out of the gate at f4 across the focal range and frame, which means that stopping down will only increase depth of field as sharpness won't noticeably improve. Needless to say, that's a very, very good thing. For nit pickers, there is some slight softening in the corner of the frame on a FF sensor when viewed at 100%. For the non-pixel peepers out there, this will be impossible to notice in real life shooting and presentation.
Stabilizer Mechanism
The Optical Stabilization (OS) feature is different than everything reviewed here in that there is no absolute way to quantify how well it works since the amount of camera shake is determined, by and large, on the inherent steadiness of the photographer's hand and shooting technique. That said, I was easily getting steady pictures of ½ second long at 105mm. Additionally, the stabilizer is absolutely silent in operation
Vignetting
There is some shading with the Sigma 24-105 f4 OS Art wide open at f4, with it being most pronounced at 24 and 105mm. A stop down, the shading decreases dramatically and disappears by f8. At middle focal lengths, vignetting disappears by f5.6.


Distortion:
There is some distortion here, but nothing out of line as for what one can reasonably expect for such a lens.  
CA
Nil here.




Macro
While anything but a dedicated macro lens (.22x is its maximum magnification), the Sigma 24-105 f4 OS Art is still pretty good for capturing larger macro subjects, like flowers, especially with today's cameras and all of their megapixels, which allow for a lot of cropping. The above images are the full picture (albeit at a reduced resolution) with a 100% crop. 



 Flare/Ghosting
This lens is remarkably resistant to flaring.
Astrophotography
Infinity focus is not exactly infinity here, which means that you will need to fiddle with focus on a bright star with live view at full magnification.



Bokeh
With its 9-blade, rounded design, out of focus blur (bokeh) is buttery smooth.


Value: 5/5
Ah, here's the tough one as, at $900 new, the Sigma 24-105 f4 OS Art is not cheap by any means. On the other hand, when one looks at the manufacturer equivalents, this lens looks decidedly economical as the equivalents from Canon and Nikon, (Sony has no equivalent) both are a lot pricier. For both Canon and Nikon shooters, you get a dust seal at the mount on both of your camera makers' lenses (and an extra 15mm for Nikonians) but the question is this: do you plan to shoot in conditions that would warrant the rubber gasket at the mount that will add $250 and $400 to the price of the Sigma, respectively?



Competition
To put it plainly, the standard zoom lens is the most crowded segment on the market for the simple reason that such lenses are just so doggone useful. The direct competitors in the mid aperture stable from the manufacturers already addressed, there are a lot of other alternatives, too. For starters, there are the 24-70 f2.8s that are, again, made by just about everyone (Sigma makes one, too). Obviously, these lenses trade about 30mm of reach for an extra stop of aperture. The extra brightness is often offset with the cost of losing the stabilization, which often results in a wash at the checkout. The exception here: Tamron, which makes a stabilized 24-70 f2.8. Current models aside, there are out of production lenses in this focal range in both f2.8 and f4 versions, some with and other without stabilization, on the used market. Again, there's a tradeoff for that lower price: questionable support from the manufacturer. Long story short, if your old lens breaks, there may not be any parts with which to fix it, which will essentially turn your lens into an expensive paperweight.

My advice: with an AF lens (especially when paying this much), it's safer to buy new and the main consideration should be the f2.8 vs. f4.

Conclusion: 5/5
There's no doubt about it: the Sigma 24-105 OS Art is quite a lens. Sturdy build, excellent mechanics, great optics, and all at a bargain price when compared to manufacturer alternatives combine to make this lens a very attractive buy. In the end, the main consideration when buying a standard zoom comes down to this: a shorter f2.8 or a longer f4 with a stabilizer. If you decide to go with the f4 optic, there's no reason not to buy the Sigma 24-105 f4 OS Art as it really does represent a package that can cover 95% of the photographic applications of the people reading this review. Needless to say, I can't wait to see what Sigma has over the proverbial horizon!

Samples:












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