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Calculating Blur For Mft Portrait Lenses


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#1 Tony Northrup

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Posted 14 September 2013 - 07:39 AM

As I'm updating the Buying Guide and expanding the information on MFT, one of the most frustrating aspects is the lack of great portrait lenses for the system. It's keeping me from recommending micro four-thirds for portrait work, but it's not a problem inherent with the system--it's just that manufacturers haven't bothered to make a real portrait lens. I actually feel like the problem is caused because many camera buyer's don't understand how sensor size and crop factor affect background blur.

 

Anyway, I'd love to get your thoughts (and some double-checking on my math) on this new section of the Buying Guide, which I'm writing because I've heard from so many people frustrated by their inability to get the same background blur that they see from the full frame cameras.

 

Depth of field factor

Different sensor sizes change the field of view provided by a focal length. We refer to this as the “crop factor”, and it allows us to quickly determine that a 45mm micro four-thirds lens is equivalent to a 90mm full frame lens.

While the crop factor works for determining the field of view, it does not work for determining the depth of field and background blur that you’ll get from any given lens. While camera manufacturers often provide a “35mm equivalent” when describing a lens, they don’t tell you that you won’t get the same background blur when using smaller lenses, and this has led to many frustrated portrait photographers.

 

For example, consider two portrait lenses that seem very similar:

·         The full frame Canon 85mm f/1.8 ($400)

·         The micro four-thirds Olympus 45mm f/1.8 ($400)

 

Knowing that you double the focal length of micro four-thirds lenses to determine the 35mm equivalent, the Olympus seems to compare favorably to the Canon. You might see portraits taken with the Canon 85mm f/1.8 (such as the following), and assume that you’d be able to achieve similar background blur.

f18.jpg

 

The Olympus can’t achieve the same background blur, however, because you must apply the crop factor to the aperture to calculate depth-of-field (and thus background blur). In this example, the Olympus 45mm f/1.8 lens is equivalent to a full-frame 90mm, f/3.6 lens when considering both field of view and background blur.

 

You can also multiply the depth-of-field by the crop factor. Therefore, a micro four-thirds camera with a crop factor of 2x, has about twice the depth-of-field (and thus half the background blur) of a full frame camera, even after you multiply the focal length by the crop factor. An APS-C sized DSLR has 1.5X to 1.6X more depth of field, or 50-60% less background blur than a full frame camera.

 

For calculating the shutter speed you’d need in any given lighting scenario, you wouldn’t need to multiply the aperture—the Olympus would still have the same shutter speed as a full frame 90mm f/1.8 lens, or any f/1.8 lens, for that matter. However, for portrait work, lenses for smaller sensors have far less background blur. To achieve similar background blur to the Canon 85mm f/1.8, you would need a 45mm, f/0.9 lens, and nothing like that is currently available.

 

Currently, the best micro four-thirds lens for achieving a nice background blur is the Olympus M Zuiko ED 75mm f/1.8 ($830). For calculating background blur, this lens is equivalent to a full-frame 150mm f/3.6 lens. Unfortunately, that doesn’t compare favorably to traditional 35mm portrait lenses. My budget full frame portrait recommendation, the Tamron 70-200 f/2.8 ($750), is just as sharp, less expensive, offers much better background blur, and provides a very useful zoom range.

 

Let’s consider that lens on crop and full-frame DSLRs. On a Nikon DSLR with a compact sensor, it becomes equivalent to a 105-300 f/4.2. On a Canon DSLR with a compact sensor, it becomes equivalent to a 112-320 f/4.5. Only on a full-frame body will you be able to achieve the full potential of the lens’ ability to blur the background.

 

I don’t want you to feel bad about purchasing a micro four-thirds or APS-C camera; they’re very capable cameras, and background blur is only one aspect of photography. Smaller sensors, and their large depth of field, actually show you much more of a scene, making them ideal for landscapes. There are also other ways to control background blur, including moving your subject further from the background. For detailed information, refer to Chapters 4 and 6 of Stunning Digital Photography.

 

I hope that highlighting this weakness of smaller sensor designs for portrait work will help push lens manufacturers to offer faster lenses for the smaller sensors. The first manufacturer to give fair treatment to APS-C sized sensors is Sigma, with the Sigma 18-35mm f1.8 lens. When calculating background blur, this lens is roughly equivalent to a 27-52mm f/2.8 lens. It’s still too wide angle to make a viable portrait lens, but it’s an amazing lens for general photography with compact sensors, and I'm glad to see Sigma manufacturing faster lenses for smaller sensors.


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#2 Herr Dice

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Posted 15 September 2013 - 03:17 AM

Hey Tony,

I don't know if I'm misunderstanding you, but look at the picture/portrait I posted in the following thread. It was taken with the 45mm f1.8. and that looks quite blurry for me: http://sdpcommunity....t-your-opinion/


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#3 Billy

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Posted 15 September 2013 - 01:09 PM

Great post and very informative!  Can't disagree with any of it, except that Voigtlander has released some F0.95 lenses (17.5, 25, and 50).  Unfortunately, they're not particularly affordable (>$1k) and are manual focus.

 

http://www.amazon.co...nder hyperprime

 

M43 is certainly a niche and I guess it's not really conceived for professional portraiture, but fits in well for "rising amateurs" and I think travel photography.  My entire system fits in a 10" x 6" x 4" top loading bag and I don't hesitate to leave it in the car, take it on every business trip, etc.

 

I'm actually afraid to play with an APS-C or FF camera and a fast lens, could be an expensive indulgence!  I do hope you get to try one of the new flagship M43's.  I'd love to hear your thoughts on the experience, not just usability and image quality, but some of the use cases where M43 makes a lot of sense.



#4 Jasón Nargiz

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Posted 15 September 2013 - 10:13 PM

Tony, I'm glad to hear you're giving us m4/3 users some attention!

 

The Voigtländer f/0.95 lenses actually are actually available in 17.4mm, 25mm, and 42.5mm focal lengths. You can see a list of almost all of the lenses available for m4/3 here: http://www.four-thir...roft/lense.html

 

I own the Olympus 45mm f/1.8 and I'm satisfied with the bokeh for portraits. I think for portraits you generally have a lot more control over where you place the model, how cluttered the background is, and the distance of the person from the background. I don't think it's that big of a deal except for "bokeh peepers". Besides, there are ways to blur the background in post-processing software! It's a large improvement over point-and-shoot cameras and not that much different than 1.5x crop cameras to be worth complaining about. Maybe a professional portrait photographer wouldn't care for it.

 

Your math seems to be correct, Tony. I just want to point out that the properties of the lens doesn't change by cropping it. The Olympus 45mm f/1.8 is a 45mm lens and not a 90mm lens. It will act just like a 45mm f/1.8 lens on a full-frame camera, it will just have a wider field of view than on a m4/3 camera. It will have the same depth of field as a 45mm lens on a full-frame camera set to the same aperture. Wider angle lenses have a greater depth of field at equivalent apertures. For example, a 300mm lens will have a shallower depth of field at f/4 than a 24mm lens at f/4.

 

There is also the advantage that Tony alluded to with larger depth of field. For example, with a m4/3 wide-angle lens such as a 12mm lens set at f/4, you can get the same field of view and depth of field as a full-frame 24mm at f/8, thus giving the m4/3 lens a 2 stop advantage. You can leverage that advantage by either using faster shutter speeds or lower ISOs. This is an especially nice advantage to have when you're doing street or macro photography.


Edited by Jasón Nargiz, 16 September 2013 - 04:32 PM.

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#5 Tony Northrup

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Posted 17 September 2013 - 07:23 AM

Hey Tony,

I don't know if I'm misunderstanding you, but look at the picture/portrait I posted in the following thread. It was taken with the 45mm f1.8. and that looks quite blurry for me: http://sdpcommunity....t-your-opinion/

 

I don't mean to say background blur is impossible with micro four-thirds; just that it's twice as hard. You'll need to substitute the nice background blur by finding a location with a bigger background, further away from your subject, or by adding some blur in post-processing. 

 

Great post and very informative!  Can't disagree with any of it, except that Voigtlander has released some F0.95 lenses (17.5, 25, and 50).  Unfortunately, they're not particularly affordable (>$1k) and are manual focus.

 

http://www.amazon.co...nder hyperprime

 

M43 is certainly a niche and I guess it's not really conceived for professional portraiture, but fits in well for "rising amateurs" and I think travel photography.  My entire system fits in a 10" x 6" x 4" top loading bag and I don't hesitate to leave it in the car, take it on every business trip, etc.

 

I'm actually afraid to play with an APS-C or FF camera and a fast lens, could be an expensive indulgence!  I do hope you get to try one of the new flagship M43's.  I'd love to hear your thoughts on the experience, not just usability and image quality, but some of the use cases where M43 makes a lot of sense.

 

Ah, thanks for showing me that lens, I'll definitely mention it in the buying guide. Why couldn't they add some AF?! That's the lens Micro Four-Thirds needs!

 

Thanks for your feedback, everyone!


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#6 Miguel Arbusto Solito

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Posted 27 September 2013 - 12:28 AM

I know this is late, but as Jasón mentioned, 75mm is 75mm. I have the 45mm and the 75mm, and I have to say, the 75mm is just an incredible lens. Micro 4/3 is a great compromise system. Good enough to do 85% of what most people need. I never leave home without a camera now. I can pop it in any bag and take off.
 
08.18.2013 12.48.06
Album: 75mm
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#7 Earl

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Posted 09 February 2014 - 06:23 PM

I have a need for bokeh!  I have a couple of lenses in mind, but not the budget for them yet.  After reading Tony's advice on portraits and the his previous statement that bokeh is much harder to get on the M43 cameras. I decided to use my old Canon 5d for portraits  I still did not have a real portrait lens.  I looked around for something that might work on my budget.  I found an Opteka 85mm 1.8 on Amazon for a little over 100 dollars for the Canon.  It was a manual lens.  The sight did mention that being manual it could be also adapted to the M43 format with an EOS adapter.  I decided to try it.  

 

The bottom line is it worked great on the 5d, but I had a lot of self inflicted misses because of the manual focus on the 5D.  It did have great separation and was easy to blur the background.  I then tried it on my GX7, and was really surprised.  Because the GX7 has focus peaking and also some in body stabilization, my  shots with it are much sharper, especially around the eyes.  I think this will work for me at least until I can afford a better auto focus portrait lens.

 

I would for sure say for the 100 dollars, I am very happy with the Opteka on both the Canon and my Panasonic.



#8 Miguel Arbusto Solito

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Posted 10 February 2014 - 08:56 PM

I have a need for bokeh!  I have a couple of lenses in mind, but not the budget for them yet.  After reading Tony's advice on portraits and the his previous statement that bokeh is much harder to get on the M43 cameras. I decided to use my old Canon 5d for portraits  I still did not have a real portrait lens.  I looked around for something that might work on my budget.  I found an Opteka 85mm 1.8 on Amazon for a little over 100 dollars for the Canon.  It was a manual lens.  The sight did mention that being manual it could be also adapted to the M43 format with an EOS adapter.  I decided to try it.  

 

The bottom line is it worked great on the 5d, but I had a lot of self inflicted misses because of the manual focus on the 5D.  It did have great separation and was easy to blur the background.  I then tried it on my GX7, and was really surprised.  Because the GX7 has focus peaking and also some in body stabilization, my  shots with it are much sharper, especially around the eyes.  I think this will work for me at least until I can afford a better auto focus portrait lens.

 

I would for sure say for the 100 dollars, I am very happy with the Opteka on both the Canon and my Panasonic.

If you want to go cheap, you can use a legacy 50mm 1.4 lens like the SuperTakumar or Olympus 50mm 1.8. I also have used a Canon FD mount 1.8 85mm, but I have ditched all of those now that I have an Olympus 75mm 1.8.

 

85mm Canon 1.8 FD 

85mm Canon FD 1.8

 

50mm 1.4 SuperTakumar

50mm SuperTakumar 1.4

https://www.flickr.c...ith/8739952558/


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#9 Earl

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Posted 18 February 2014 - 08:33 PM

The 75, 1.8 is one of the two I mentioned that are on my list.  The other is the Pano 35-100 2.8.  I saw a good buy on the Pano and just ordered it.  Now I am down to one (until something else comes out I can't resist  :D .


Very nice pics, by the way.  Thanks.



#10 Earl

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Posted 04 November 2014 - 10:11 PM

Miguel, I have used the legacy lenses, and they worked pretty well.  I  now have the lenses I was wanting and my favorite is the Olympus 75mm 1.8.  Any of these will provide bokeh.   I have also heard that the 45mm OLymus does a good job, and is much cheaper.  I don't have it (yet) :D .



#11 Guest_Jose_*

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Posted 02 July 2017 - 02:12 AM

1,8 multiplyed by 2 is not 3,8 in photo terms it is 2,5 ...sorry



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