{"id":13592,"date":"2018-05-24T12:21:59","date_gmt":"2018-05-24T11:21:59","guid":{"rendered":"https:\/\/phillipreeve.net\/blog\/?p=13592"},"modified":"2024-04-21T14:06:13","modified_gmt":"2024-04-21T13:06:13","slug":"review-sony-fe-100-f-2-8-stf-gm-oss-lens","status":"publish","type":"post","link":"https:\/\/phillipreeve.net\/blog\/review-sony-fe-100-f-2-8-stf-gm-oss-lens\/","title":{"rendered":"Review: Sony FE 100 f\/2.8 STF GM OSS Lens"},"content":{"rendered":"

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Introduction:<\/h3>\n

The Sony FE 100 f\/2.8 STF GM OSS lens is a lens that I purchased some time ago not really knowing what to expect. I had read about the lens, of course, but frankly I found that it took me some time to get an understanding of how best to use this lens. I think it is a very fine optic with excellent sharpness and anextraordinarily smooth quality of bokeh, however, it is also a lens that imposes a steeper than normal learning curve.\u00a0 It has a distinctive look in some situations that seems to be polarizing in the photo community.\u00a0 With use, I have come to like this lens very much and don’t plan on parting with mine anytime soon.\u00a0 In this review, I will attempt to explain why I like it and also some of its quirks so that prospective buyers might have a better idea about what to expect.<\/p>\n

A few samples:<\/h3>\n
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F2.8<\/figcaption><\/figure>\n
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F2.8<\/figcaption><\/figure>\n
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F2.8<\/figcaption><\/figure>\n

 <\/p>\n

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F2.8<\/figcaption><\/figure>\n

<\/p>\n

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F2.8<\/figcaption><\/figure>\n
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F2.8<\/figcaption><\/figure>\n

Most of the samples in this article are available in higher resolution here:\u00a0http:\/\/www.pbase.com\/luvwine\/gm_100_stf_<\/a><\/p>\n

Specifications<\/h1>\n\n\n\n\n\n\n\n\n\n\n
Diameter<\/td>\n85 mm<\/td>\n<\/tr>\n
Length<\/td>\n118 mm<\/td>\n<\/tr>\n
Filter Thread<\/td>\n72 mm<\/td>\n<\/tr>\n
Weight<\/td>\n700 g<\/td>\n<\/tr>\n
Max. Magnification<\/td>\n\u00a01:4<\/td>\n<\/tr>\n
Close Focusing Distance from the sensor<\/td>\n\u00a057 cm<\/td>\n<\/tr>\n
Number of aperture blades<\/td>\n\u00a011<\/td>\n<\/tr>\n
Elements\/ Groups<\/td>\n\u00a014\/10<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Handling<\/h3>\n

Physically, the lens is of moderate size though larger than one might expect given its focal length and modest maximum aperture of F2.8 (more on that below).\u00a0 It has a 72mm filter thread which is considerably larger than say the Loxia 85\/2.4 filter thread of only 52mm.\u00a0 However, it is not terribly dense–weighing noticeably less in the hand than say the GM 85\/1.4.\u00a0 Doubtless some of the size is due to the evident desire to make the bokeh as pleasing as possible.\u00a0 Here is a picture with, from left to right, the Loxia 50\/2, Voigtlander 65\/2 apo-lanthar, Sony GM 85\/1.4, and the Sony 100 STF on the right.<\/p>\n

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The lens is equipped with an aperture ring (which one can de-click for silent operation) which is marked with the T-Stops (light transmission) as opposed to the F Stops.\u00a0 F2.8 corresponds with T5.6, which is wide open.\u00a0 The apodization filter accounts for two full stops of light loss at F2.8.\u00a0 However, the effect diminishes as one stops down and by F8, there is no further effect from the filter and aperture and T-stop values are equivalent.\u00a0 Note that the exif information displays the T-Stop value.\u00a0 This is indicated on the lens barrel markings.\u00a0 Additionally, typical for G Master lenses, it has a programmable button\u00a0 which is useful for programming custom functions like eye AF.\u00a0 Also, the lens has switches for both AF\/MF and lens optical stabilization on or off.\u00a0 Finally, there is a mechanical ring that changes the focusing range from close range\u00a0 (.57 meter to 1.0 meter) to longer range (1 meter to infinity).\u00a0 This is not merely an autofocus range indicator, but an actual mechanical alteration that allows the lens to focus in the indicated range only.\u00a0 The lens body is dust and weather sealed.\u00a0 In all, it is ergonomically a pleasure to use.<\/p>\n

Focusing<\/h3>\n

The manual focus barrel is focus by wire, but while slightly less pleasing to use than the best mechanical manual focus lenses, it is still more than adequate.\u00a0 Autofocus is not very snappy, but is adequately fast and accurate though best in good light.\u00a0 The apodization filter (see below) does make this lens less than ideal to use in darker conditions.\u00a0 At wide open (F2.8), there is only the same amount of light transmission as at F5.6.\u00a0 Thus, one’s available light is cut by 75% wide open.<\/p>\n

The Apodization filter<\/h3>\n

What makes the GM 100 STF lens unique in the current range of Sony FE mount lenses, is the presence of a built in apodization filter.\u00a0 This filter is a clear glass filter in the center that progressively darkens like a neutral density filter farther away from center.\u00a0 The fact that there is no darkening close to center explains why, as one stops down, the filter’s effect diminishes. By F8, it has no effect as the light is traveling through the unmodified glass.<\/p>\n

The effect of the apodization filter is greatest wide open at F2.8 (T.5.6).\u00a0 The filter makes bokeh balls darker towards their outer edge\u00a0 and greatly softens bokeh generally to something like a gaussian blur.\u00a0 There are no hard edges and the quality of bokeh is remarkable.\u00a0 While the quantity of bokeh is exceeded by faster lenses, the bokeh that is produced is remarkably smooth.<\/p>\n

The filter also has other effects.\u00a0 While nominal aperture is F2.8, the depth of field is roughly equivalent to an F4 lens. This has the happy effect of giving one more depth of field for subjects like\u00a0 faces to be in focus, yet having a lovely quality of background blur.\u00a0 The amount of blur is of course greater the closer one is to the subject and, since the lens closes quite closely, the lens is extremely capable for quasi macro shot such as flower shots.\u00a0 It is very good at isolating flowers in busy backgrounds and smoothing out what otherwise might be a distracting background and enabling pleasing compositions where other lenses might struggle.<\/p>\n

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F2.8<\/figcaption><\/figure>\n

Optical Performance<\/h3>\n

Sony’s published MTF graphs are theoretical and do not take diffraction effects into account.\u00a0 Therefore, I will not quote them here but they do show a very high degree of optical performance.\u00a0 In my testing, I have indeed found sharpness to be excellent across the frame even from wide open.\u00a0 Stopping down does improve corner performance somewhat but the difference is subtle and one must truly pixel peep in order to see any improvement.\u00a0 Unless I am using the lens for landscape or want a less smooth bokeh or need the depth of field, I always shoot the lens wide open so as to maximize the bokeh smoothing character of the lens.<\/p>\n

The lens seems designed for portraiture and quasi macro shooting and its overall look is just about ideal for these applications.\u00a0 The lens is not as high in contrast as say the Zeiss Batis 135 or Loxia line of lenses, however, its sharpness is comparable with these lenses and, of course, one can add contrast in post to a certain degree.\u00a0 While its sharpness certainly makes it suitable for landscape use, it would not normally be my first choice for that application.\u00a0 Nevertheless, I decided to test it at infinity against a very fine zoom (C\/Y 100-300) where the zoom is about at its best (100mm).\u00a0 I also decided to test it against the Batis 135 for close up sharpness.<\/p>\n

Infinity Sharpness testing<\/h3>\n

I compared the GM 100 with the older Zeiss (C\/Y) 100-300 zoom at 100mm.\u00a0 The zoom is very good indeed at 100mm and as we will see, it is a fairly close comparison between these two lenses in this application.\u00a0 Shots were on tripod, remote release, manual focus with focus in the center of the image on a distant building using my Sony A7riii.<\/p>\n

The scene:<\/p>\n

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Note the Zeiss is slightly longer at its 100mm setting than the Sony.\u00a0 Midfield 100% crops wide open:<\/p>\n

<\/div>\n

Left GM STF Right Zeiss<\/p>\n

Now at F8:<\/p>\n

<\/div>\n

Left GM STF right Zeiss<\/p>\n

Now the corner crops first wide open:<\/p>\n

<\/div>\n

Left GM STF Right Zeiss<\/p>\n

Here at F8:<\/p>\n

<\/div>\n

Left GM STF Right Zeiss<\/p>\n

My copy of the Zeiss\u00a0 improves in the corner at F11, so here it is for comparison:<\/p>\n

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Zeiss 100-300 at F11<\/figcaption><\/figure>\n

I did not include the center crops as there is little between the two lenses in the center with the Zeiss having a bit more native contrast but no sharpness advantage to either lens.\u00a0 In the midfield crops, we see fairly similar performance with the Zeiss arguably stronger wide open but no difference once stopped down.\u00a0 In the extreme corner, the Sony is clearly better at wide open and retains its advantage until F8 with the Zeiss only catching up at F11.<\/p>\n

What this test told me was that both lenses are more than up to the task for landscape applications.\u00a0 I do favor the zoom due to flexibility of focal length, but if one has the Sony GM 100, it will certainly work well for landscape or cityscape applications and is commendably sharp from wide open even into the corners.<\/p>\n

Close Focus ability<\/h3>\n

The Sony GM 100 focuses quite closely at a native maximum magnification of 1:4.\u00a0 Here is as close as I can get a $100 bill in the picture at minimum focus distance:<\/p>\n

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F7.1<\/figcaption><\/figure>\n

One can easily enhance the close focus ability by adding a close up filter to the lens.\u00a0 I use the Canon 500D close up lens for that purpose and see little to no noticeable degradation of quality.\u00a0 Here is how the $100 note looks with the 500D in place:<\/p>\n

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GM 100 STF with Canon 500D<\/figcaption><\/figure>\n

For comparison’s sake, here is the same subject at minimum focusing distance with the Voigtlander 65\/2 apo-lanthar (a macro lens that focuses to 1:2):<\/p>\n

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CV 65\/2 apo at F5.6<\/figcaption><\/figure>\n

The CV natively still has higher magnification, but the GM 100 STF gets nearly as close as the CV 65 when the 500D close up filter is in place and has the advantage of autofocus and in-lens optical stabilitzation.\u00a0 The GM 100 STF thus is a convenient and high quality choice for quasi macro applications.\u00a0 Of course, the CV 65 is a superb lens (even better corrected)\u00a0 and affixing a close up lens or extension tubes makes for macro capability the STF 100 cannot begin to equal.<\/p>\n

Close Focus Sharpness testing<\/h3>\n

Here I compare the Sony STF 100 with the Zeiss Batis 135.\u00a0 The Batis 135 is perhaps the sharpest lens currently made for Sony E mount (with the possible exception of the CV 65\/2 apo-lanthar).\u00a0 The Batis does not focus quite as closely as the Sony (1:5.3 instead of 1:4).\u00a0 So here I identically framed the $100 bill as closely as I could manage and the scene thus looks like this:<\/p>\n

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Batis 135<\/figcaption><\/figure>\n

Here are 100% crops close to the center and then in the upper left corner.\u00a0 They are unsharpened and unprocessed other than color temperature correction and adding the same amount of exposure to each. \u00a0 I will compare wide open and then at F 5.6.<\/p>\n

Center at F2.8:<\/p>\n

<\/div>\n

Left GM STF Right Batis<\/p>\n

Center at F5.6:<\/p>\n

<\/div>\n

Left GM STF right Batis<\/p>\n

Here are the corner crops, first wide open:<\/p>\n

<\/div>\n

Left GM STF Right Batis<\/p>\n

Now at F5.6:<\/p>\n

<\/div>\n

Left GM STF right Batis<\/p>\n

Here the Zeiss’ slightly greater native contrast is evident.\u00a0 The difference in this regard is greatest in the corner and wide open but is present in every case.\u00a0 However, there appears to my eyes very little difference in the ability to resolve fine details.\u00a0 There is a bit more detail in this test in the Sony at F2.8 in the corner than the Batis, but this is minor and could be due to several factors.\u00a0 At F5.6 there is no sharpness advantage to the Sony nor is there on center at F2.8.\u00a0 These are very different lenses with different strengths but both are clearly very sharp lenses at\u00a0 close distance.\u00a0 Finally, the lenses do exhibit a rather different color palette here with the Zeiss lens corner crops going much more toward blue.\u00a0 Both lenses were separately white balanced on this shot using a white balance card.\u00a0 The color to my eyes is a bit more accurate on the Sony but I don’t want to draw any conclusions from this difference as this is only one test.<\/p>\n

Flare Resistsance<\/h3>\n

Telephoto lenses in general have a harder time with flare resistance than wide angle lenses due to the larger size of the sun should it appear in or adjacent to the frame.\u00a0 Flare resistance in the Sony GM 100 STF is good though not excellent.\u00a0 One will notice some veiling flare and even some ghosting in images where the sun is prominent in the frame.\u00a0 However, you usually have to work at it.\u00a0 Here is an example of some ghosting see the green blobs in the lower right corner:<\/p>\n

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F2.8 (T5.6)<\/figcaption><\/figure>\n

However, that was an image where I was deliberately trying to provoke flare.\u00a0 Here is a more common example where I was shooting a sunset.\u00a0 A later picture in this sequence is the last of the samples at the end of the article.\u00a0 Here, the sun was higher in the sky and the lens produced flare as seen here:<\/p>\n

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F8<\/figcaption><\/figure>\n

There is some veiling flare and a bit of ghosting at the bottom of the frame, but the image is still quite acceptable to me.<\/p>\n

Vignetting and Distortion<\/h3>\n

There is very little vignetting.\u00a0 It is noticeable if you look for it wide open, but is very minor at -.5 EV in the corners\u00a0 according to DxO mark.\u00a0 Distortion is pincushion but is fairly modest at .4%.\u00a0 The lens has a Lightroom profile that corrects these minor issues.\u00a0 I have never had cause to worry about these shortcomings perhaps because in my usage with this lens the vast majority of my images are flowers, portrait, or general use and not architecture.<\/p>\n

Travel Use<\/h3>\n

This lens is not an ideal travel companion lens to me.\u00a0 While it is not overly heavy and is moderate in size, it has relatively poor performance in low light situations due to its apodization filter taking away 75% of the available light.\u00a0 T5.6 wide open means it will struggle in dark conditions.\u00a0 Thus, in a travel bag of limited size, this lens does not make the cut.<\/p>\n

Portrait Use<\/h3>\n

What can I say?\u00a0 This lens is a great portrait lens to me so long as there is adequate light. It takes full advantage of eye autofocus on Sony bodies, its apodization filter makes backgrounds pleasing and results in greater than normal depth of field while still producing wonderful bokeh. It is very sharp, and has a rendering that is ideally suited to portrait work.\u00a0 However, it does have some limitations and its look is quite different from other lenses.\u00a0 Given the lesser quantity of blur compared to faster lenses, one has to be more careful to compose shots with a pleasing background.\u00a0 This is especially true for full body portraits.\u00a0 Tight head shots will result in as much background blur as you could want, but if you are farther from the subject, you have to be very aware of the background as it will be more visible than with faster lenses shooting at wide apertures.<\/p>\n

Here are a couple of pictures that show some differences in look between the Sony GM 85 and the GM 100 STF.\u00a0 The area to look at of course is the background:<\/p>\n

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85 GM at F1.8<\/figcaption><\/figure>\n
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Sony GM 85 at F2.8<\/figcaption><\/figure>\n
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Sony GM 100 F2.8 (T5.6)<\/figcaption><\/figure>\n

So above you see the 85 GM at F1.8 and then at F2.8.\u00a0 If you look at the pictures at the larger size, you will see that the GM 85 has prominent bokeh balls in the background.\u00a0 NOw, the GM 85 is one of the finest portrait lenses money can buy, however, in some circumstances the bokeh balls can be distracting.\u00a0 In the GM 100 STF picture above , bokeh balls are not really noticeable as such–they simply melt int the background.\u00a0 The GM produces much more quantity of blur at F1.8, but the bokeh balls are distinctly noticeable.\u00a0 In the F2.8 picture with the GM 85, the bokeh balls are smaller, but still quite distinct.\u00a0 Some will prefer the STF 100 here, some will prefer the GM 85, but the look is certainly different.<\/p>\n

However, care is needed in choosing backgrounds with the STF 100.\u00a0 There are circumstances where, to me, the background can look a bit wonky.\u00a0 Here is one such example from early in my time owning the lens.\u00a0 Here, both the GM 100 STF and the GM 85\/1.4 are wide open:<\/p>\n

<\/div>\n

Left GM 85 Right GM STF 100<\/p>\n

For me, in the above example, I like the greater amount of bokeh softening the busy background in the above example of the GM 85 at F1.4 more than the STF 100 where the background gives a busier and more distracting appearance.\u00a0 This is not so much a failing of the apodization filter as a limitation of the amount of blur the F2.8(T5.6) lens can produce compared to the F1.4 of the GM 85.\u00a0 Some care and experience are needed in the use of the STF lens.\u00a0 In some cases, the bokeh can take on a “too perfect” or “plasticky” appearance to some observers or simply fail to adequately smooth a busy background as in the above example.\u00a0 I personally find having both the STF and one or more conventional portrait lenses in the bag the best approach.<\/p>\n

The differences between the look of other portrait lenses and the STF often diminishes in tight portraits—particularly with somewhat distant backgrounds.\u00a0 Here are two similar portraits:<\/p>\n

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Zeiss Batis 135 at F2.8<\/figcaption><\/figure>\n
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Sony GM 100 STF at F2.8 (T5.6)<\/figcaption><\/figure>\n

This is not a perfect comparison, of course, as the STF shot was from closer to the subject, but one can see that the background blur of the Batis 135 starts to resemble that of the STF (or vice versa) since due to background distance, both lenses are creating a large quantity of blur and thus the qualitative differences are lessened.<\/p>\n

It takes a lot of practice seeing how this lens differs from “normal” lenses.\u00a0 In many cases, the differences are not that striking.\u00a0 In some instances, they are hugely different.\u00a0 One’s expectations and even one’s taste will be challenged as the STF produces images that are different from what we as photographers have come to expect.\u00a0 To me, the STF produces portrait images that are quite lovely and often very natural in appearance as here:<\/p>\n

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Sony 100 GM F2.8 (T5.6)<\/figcaption><\/figure>\n

or here:<\/p>\n

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Sony GM 100 STF at F2.8 (T5.6)<\/figcaption><\/figure>\n

or popping out from a distant yet still discernible background as here:<\/p>\n

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Sony GM 100 STF F2.8 (T5.6)<\/figcaption><\/figure>\n

 <\/p>\n

It is simply a remarkable portrait lens.\u00a0 I find myself reaching for the STF often as a first choice though I will also carry my GM 85 or longer lenses. In low light I always favor the GM 85, but in good light, I lean toward the STF 100.<\/p>\n

Bokeh<\/h3>\n

In some ways, this whole article is about Bokeh.\u00a0 It is the quality of the STF’s bokeh that makes it unique.<\/p>\n

Here is a bokeh comparison I did between the GM 85, STF 100, and Batis 135.\u00a0 It is not perfect, but may help give some idea of the different character of these lenses:<\/p>\n

GM 85 first<\/p>\n