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Author Topic: Sony 100mm f/2.8 STF GM - what's its purpose?  (Read 9054 times)

shadowblade

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Sony 100mm f/2.8 STF GM - what's its purpose?
« on: March 27, 2018, 03:50:24 pm »

I've had the opportunity to try out the Sony 100mm f/2.8 STF GM lens over the last few days, amd can't help but get the feeling that they took a useful, if situational, technology and put it in the wrong lens.

Yes, it's a ridiculously sharp lens, with very smooth bokeh wide-open. But what is it for? Specifically, why put the STF element in a lens like this?

As a portrait lens, 100mm f/2.8 doesn't really blur the background enough. The fact that the bokeh is smooth doesn't change that. Even for head shots, or head-and-shoulders shots, where you'd often be shooting at f/4 or so for depth of field, you'd often want a longer lens for telephoto compression and increased background blur. If you're shooting in a studio or don't have a busy background to deal with, the STF is superfluous anyway.

It would seem that the STF element would have been much more useful in a 105/1.4, 135/1.8 or 200/2 lens, where the smoothness of the bokeh could be combined with adequate overall background blurring. Or in a supertelephoto lens (say, 500/4) for shooting wildlife against busy backdrops  (especially leaves or grass).

Furthermore, STF is a very situational feature. It's fantastic when you have a shot that can benefit from it (masking and applying Gaussian blur in Photoshop to achieve the same effect can be difficult and time-consuming) but, when you don't need it, it just sucks up two stops of light. Would it not be more flexible either as an element that can be swung in or out of the light path (like an inbuilt teleconverter) or, even better, as a radial GND filter, with a clear centre and dark edges, to be attached to the front of the lens or used as a drop-in filter in larger lenses?

Anyone else used it and have other thoughts on it?
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Slobodan Blagojevic

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #1 on: March 27, 2018, 04:17:59 pm »

What is STF? S%$* The F*&% Up?

Farmer

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #2 on: March 27, 2018, 07:37:40 pm »

Smooth Transition Focus.
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Phil Brown

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #3 on: March 27, 2018, 10:52:14 pm »

Smooth Transition Focus.

A quality one might hope was part of all Sony's lenses ;D

Or was there a new line coming with abrupt transition focus ?

Seriously, here in L.A. the lens of choice for fashion and high end portraiture is the Sony FE 90 Macro G OSS and I can't image any advantage to the 100 after using the 90.
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Farmer

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Phil Brown

shadowblade

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #5 on: March 28, 2018, 02:25:42 am »

A quality one might hope was part of all Sony's lenses ;D

Or was there a new line coming with abrupt transition focus ?

Seriously, here in L.A. the lens of choice for fashion and high end portraiture is the Sony FE 90 Macro G OSS and I can't image any advantage to the 100 after using the 90.

Is that in studio? I can't imagine a sharp, but relatively slow (for its focal length) lens with a reputation for somewhat harsh bokeh would be much use for outdoor portraits.

In-studio, where the background can be controlled, is a completely different matter. When you're shooting stopped down and bokeh doesn't matter, any lens will do the job and sharpness becomes the main attribute. There's a reason the Canon 24-105 f/4 kit lens is such a studio portrait staple - it's cheap (came with the camera) and does the job just fine.
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Paulo Bizarro

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #6 on: March 28, 2018, 05:38:31 am »

It's purpose is to be useful in certain situations. It is, after all, a specialized lens for particular applications.

According to Brian Smith:

"The Sony FE 100mm F2.8 STF GM OSS lens is not a low-light lens to shoot in near darkness. If you need a F1.4 lens you should buy a Sony FE 85mm F1.4 G Master. However if you’re opening the lens to F1.4 just to blow the background out of focus, you’ll get prettier backgrounds with the FE 100mm F2.8 STF GM OSS at F2.8 along with more of your subject in focus."

Full review here:

http://briansmith.com/lens-review-sony-fe-100mm-f2-8-stf-gm-oss/

shadowblade

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #7 on: March 28, 2018, 08:07:17 am »

It's purpose is to be useful in certain situations. It is, after all, a specialized lens for particular applications.

According to Brian Smith:

"The Sony FE 100mm F2.8 STF GM OSS lens is not a low-light lens to shoot in near darkness. If you need a F1.4 lens you should buy a Sony FE 85mm F1.4 G Master. However if you’re opening the lens to F1.4 just to blow the background out of focus, you’ll get prettier backgrounds with the FE 100mm F2.8 STF GM OSS at F2.8 along with more of your subject in focus."

Full review here:

http://briansmith.com/lens-review-sony-fe-100mm-f2-8-stf-gm-oss/

That's the intent. But it doesn't really do it very well.

Sure, compared to a normal lens set to 100/2.8, it produces a very smooth background. But if you're trying to blow the background out of focus, you're probably not going to be shooting at 100/2.8. You're either going to be shooting with a faster lens - say, 105/1.4 - or a longer lens - say, 200/2.8 - both of which are going to blow out the background much more than the 100/2.8, STF filter or not. The STF lens gives you smoother edges to the bokeh 'balls', but the faster/longer lenses blow out the background so much more that they generally produce better subject isolation, even if the bokeh is a bit rougher (and a 200/2.8 is going to give you the same depth of field as a 100/2.8 given the same field of view, while still blowing out the background a lot more).

It's almost frustrating that they took a feature that would be great on a portrait lens - STF - and put it on a lens whose other characteristics don't really lend themselves to that application. A 105/1.4, 135/1.8 or 200/2.0 (or even 200/2.8) with STF would be fantastic. As it is, the 100/2.8 is only marginally useful, and certainly not something I'd keep around in the kit.
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HywelPhillips

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #8 on: March 28, 2018, 08:55:38 am »

I agree. It has not really appealed to me to buy because it seems like a bit of a one-tricky Pony, but the focal length and f-stop just doesn't seem to match what I'd want to use it for.

I'd have been so much more interested in it as an 85mm f/1.8 or even f/1.4 (like the GM with the added STF filter) or a 135mm f/1.8-ish.

In fact one of those with a t-stop that's a good couple of stops down on the f-stop might add even more appeal, making it easier to use at very shallow apertures in daylight.

Now there may be very good technical reasons not to put this STF feature into a very fast lens, but I can't really think what it is. Autofocus etc. is going to be easier with more light, I'd have thought. The sad thing is that low sales of the STF might put them off from implementing the feature in other lenses, which would be a shame.

The killer reason not to buy though is that I liked people's images from the 85mm f/1.4 GM better than from the STF. I love that GM lens even though it makes a sound like a small animal in a woodchipper every time it tries to focus. Respect to Brian Smith but the people photos on his review page with the STF just aren't to my taste in rendition at all.

Cheers, Hywel


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shadowblade

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #9 on: March 28, 2018, 09:48:20 am »

Now there may be very good technical reasons not to put this STF feature into a very fast lens, but I can't really think what it is. Autofocus etc. is going to be easier with more light, I'd have thought. The sad thing is that low sales of the STF might put them off from implementing the feature in other lenses, which would be a shame.

You could produce the effect by putting a circular GND filter on the lens (clear in the middle, dark on the edges). After all, that's effectively what the STF filter does - just at a different point in the light path. It would then also be removable, so you can turn the effect on and off.

Have you seen how you can change the shape of bokeh just by putting a lens cap with a hole in it on the front of a lens? Make a star-shaped hole and you get star-shaped bokeh balls; make a heart-shaped hole and you get heart-shaped bokeh balls. You'd get the same effect if you put a circular GND in front of it - the bokeh balls would be full-strength in the middle, fading away to nothing on the edges, just like the filter. Which is exactly what the STF filter in the lens does.

Of course, I don't think anyone makes a filter like that...
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Rob C

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #10 on: March 28, 2018, 10:12:05 am »

FWIW I wouldn't use anything shorter than 135mm for headshots. That would bring the camera to about 5ft-6ft from the person. A 105mm was okay(ish) for half-lengths, but as you know, fashion can also make its point via distortion. Just look at some 60s/70s fashion work to see for yourself. Jeanloup Sieff made a lot of use of 21mm on Leica. Personally, I never used wider than 35mm with models even during the 60s/70s.



The shot above was with a 4/200 Nikkor, on HP3, probably wide open, but the distorted overall shape is because the file is made from copying an encapsulated calendar page tacked to a flat board; I couldn't go full on to it because the reflections off the plastic were too bad, even with a polarising filter.

I don't think greater lens quality would have added anything and might, indeed, have taken away a lot of the roughness that fitted in with the rest of the calendar's "peasant lass" theme.

(Some more of that calendar appears in the first gallery of my website, if anyone cares; you can see why a certain roughness was de rigueur.)

Rob

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #11 on: March 28, 2018, 10:19:16 am »

That's the intent. But it doesn't really do it very well.
you can always get current Sony's 135/2.8 STF (A-mount , MF)... you are not using those to shoot sport/action, so MF will do... there are few AF STF lenses (Sony 100/2.8 FF and Fuji 56/1.2 APS-C come to mind as the only 2) - the rest are MF AFAIK
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Jim Kasson

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #12 on: March 28, 2018, 11:06:29 am »

You could produce the effect by putting a circular GND filter on the lens (clear in the middle, dark on the edges). After all, that's effectively what the STF filter does - just at a different point in the light path. It would then also be removable, so you can turn the effect on and off.

I printed such a (crude) filter to see what would happen, and compared it on the Zeiss 135/2 Apo Sonnar to my Sony 135 apodized lens. It didn't produce anywhere near the same effect. There's a reason that diaphragms aren't in the front of lenses.

Jim

Jim Kasson

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #13 on: March 28, 2018, 11:07:47 am »

A quality one might hope was part of all Sony's lenses ;D

Or was there a new line coming with abrupt transition focus ?

Seriously, here in L.A. the lens of choice for fashion and high end portraiture is the Sony FE 90 Macro G OSS and I can't image any advantage to the 100 after using the 90.

It's an apodized lens.

https://en.wikipedia.org/wiki/Apodization

Jim

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #14 on: March 28, 2018, 03:37:14 pm »

I love using fast lenses wide open to take pics where almost nothing is in focus, but for portraits I prefer to stop down a little for a better-defined face. On the Sonys my current fav lenses for this are a 1937 Zeiss 85/2 Sonnar at ~f/2.8 or an early '60s Nikkor 105/2.5 at f/2.8 or even down a little more depending on locale and lighting. Both rangefinder lenses, used via the same adapter. For a flatter rendering an '80s Zeiss 200/3.5 at ~f/4 or a Leitz 180/4 Elmar from the same period do the job.

-Dave-
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Farmer

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #15 on: March 28, 2018, 07:11:08 pm »

Yeah I think there's a reason Minolta originally produced it at 135mm and that lens was always loved.  That would be a better length for the current one.
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Phil Brown

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #16 on: March 28, 2018, 09:11:17 pm »

It's an apodized lens.

https://en.wikipedia.org/wiki/Apodization

Jim

I was being facetious. I'm quite familiar with the Minolta STF innovation that Sony uses.
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shadowblade

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #17 on: March 28, 2018, 11:06:27 pm »

I love using fast lenses wide open to take pics where almost nothing is in focus, but for portraits I prefer to stop down a little for a better-defined face. On the Sonys my current fav lenses for this are a 1937 Zeiss 85/2 Sonnar at ~f/2.8 or an early '60s Nikkor 105/2.5 at f/2.8 or even down a little more depending on locale and lighting. Both rangefinder lenses, used via the same adapter. For a flatter rendering an '80s Zeiss 200/3.5 at ~f/4 or a Leitz 180/4 Elmar from the same period do the job.

-Dave-

That's what I'm getting at - you want as much of the face to be in focus as possible, but still want the ability to blur the background to oblivion (not that you have to do it every time, depending on what the background is, but, outside of a studio, you need the ability to do it). A narrower aperture gives you more face in focus, but also reduced background blur.

Fortunately, background blur depends just as much on focal length as it does on f-stop. A 200/2.8 lens blurs the background far more than a 100/2.8 lens, even with the same distance between the subject and the background. The depth of field remains the same - just that the parts which are out of focus are far more out of focus than with the shorter lens.

Hence, 200/2.8 rather than 85/1.4 or 105/1.4, for head or head-and-shoulders shots. But you still need the wider apertures for longer shots (e.g. whole-body portraits). A 200/2.0 or 135/1.8 can do both jobs in one lens. They'd be ideal STF lenses.
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Slobodan Blagojevic

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #18 on: March 29, 2018, 07:33:13 am »

Except 100mm offers the most natural rendering of portraits. 200mm flattens it too much.

Rob C

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Re: Sony 100mm f/2.8 STF GM - what's its purpose?
« Reply #19 on: March 29, 2018, 09:20:04 am »

Except 100mm offers the most natural rendering of portraits. 200mm flattens it too much.

What is "most natural"?

The fact of the matter is this: viewing distance. You don't even need a camera to suss it out. Stand at different distances from a person you know well (assuming good eyesight), starting perhaps at kissing range. Now, if you are capable of doing that without finding yourself drifting off topic, just try to look at what you are actually seeing. What you are seeing is a massive pair of nostrils and cheekbones, and ears, if visble, are miles away from the business end and relatively undersized. That's why Hollywood, early on, conditioned peoiple who went to the movies to close their eyes at tender moments and enjoy sensation, if not sight.

Try again at about three feet, and still not Miss America. Stay with it, be optimistic, and try yet again at about six feet and there you have it, the best that average person is probably gonna look this side of the lights being out. Go yet further away, and if your vision is up to it, you discover that different effects are coming into play. It then becomes a judgement call on what looks good as a photograph and what just forshortened.

Now, Hans Feurer seldom uses optics shorter than 300mm or so; take a look at his headshots and tell me where the girls look less than amazing.

https://www.google.es/search?q=hans+feurer+imagenes&rlz=1C2PRFE_enES586ES586&dcr=0&tbm=isch&source=iu&ictx=1&fir=z_REk-6Uot_GLM%253A%252CGVylnewT3UOMkM%252C_&usg=__2vX0Zec2mK3FTqWAYd0feNmudHc%3D&sa=X&ved=0ahUKEwjCrPjqzJHaAhUD1xQKHWtZDMUQ9QEILDAA#imgrc=z_REk-6Uot_GLM:

As with so much in photography, it boils down to lighting, model, focal length/format combination and a sound understanding of your own intentions.

That's where these dry discussions can go awry: photographic reality isn't actually that bound by theoretical certainties, but by trial and error.

By the way, throughout this post I am usng "you" in the sense of "one".

Rob
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