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Why 50mm so inexpensive AND sharp

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jlam

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I'm trying to understand what is so "special" about the 50mm focal length. You can buy a 50mm F/1.8 for ~ $100, yet primes at nearby focal lengths (85mm, 35mm) command significantly higher prices.

Not being an optics guy, I would presume it has to do with the number and quality of lens elements / that are required to focus the light onto the image sensor.

Does anyone have any rationale / pointers to resources to help me better understand this aspect of the technology?

Thanks!
-John
 
The engineering for the 50mm f1.8 has long been paid back and Nikon with the Chinese have developed a very inexpensive way to make the lens and maintain the high quality.

Chris
 
Hi:

My guess: A 50mm is often considered the closest to a natural field of view(at least with film) and, therefore, was the basic "kit" lense for most cameras. For that reason they have made XXXmillion of them. Economy of scale factors. At least that is my take on it. Also the extremes (12mm or 500mm) are hardest to design and 50mm is nicely in the middle.

Cheers
Craig Ryder
 
  • They can sell many of them, which helps economies of scale.
  • They are small and use only a few elements compared to zooms. Very simple, easy to get right optical design. No need for ED glass. No big geometry issues. No extra barrels for zooming.
  • Optically they don't need the length and number of glass pieces that tele zooms need.
  • Small elements mean easy focus efforts for the AF motor the 1.8 and 1.4 use the camera's AF motor hence have no internal motor to add cost. AF-S lenses have internal motors. The kit lens has a fancy SWM internal AF motor to increase speed (large lens elements) and remain quiet. Larger elements for the same speed.
  • Wide angle glass needs lots of extra effort...aspherical glass...geoemtric distortion correction. Vigentting. Larger elements for the same speed.
  • I'm sure there are other factors.
AX
 
Thanks for the replies!

I'm trying to isolate the different effects, and this is what I think:

Regarding prices:

1) The difference in price between 50mm primes and other similar primes (35mm, 85mm) that don't require radical changes in the optics can be explained by economies of scale.

2) The difference in price between 50mm primes and more extreme primes (20mm, 300mm) can be explained by the complexity / quality of the optics.

3) The difference in price between various zoom lenses are combinations of economies of scale + optics.

Regarding sharpness:

This is where I'm still stuck. I'm blown away by the sharpness of my 50mm/f1.8. Since I don't own any other primes, I don't know how it compares with other primes at different focal lengths. Comments?

Thanks
-John
 
The reason the 50s (and 45s) are so good is the film to flange distance is right about that same distance as the focal length which allows the use of a simple symmetric gaussian design.

Jason
jlam said:
I'm trying to understand what is so "special" about the 50mm focal
length. You can buy a 50mm F/1.8 for ~ $100, yet primes at nearby
focal lengths (85mm, 35mm) command significantly higher prices.

Not being an optics guy, I would presume it has to do with the
number and quality of lens elements / that are required to focus
the light onto the image sensor.

Does anyone have any rationale / pointers to resources to help me
better understand this aspect of the technology?

Thanks!
-John
Click to expand...
 
Most people like them and want them but most give up a noticeable amount to a manual transmission vehicle.

Zooms require the designer to compromise and balance out priorities. Even the lens hood cannot work properly past the lowest focal lenghts. Since if it was large enough for the long end, it would vignett (dark corners) at the wider settings.

Almost any primes is faster and sharper than almost any zoom in the same range.

AX
 
jlam said:
I'm trying to understand what is so "special" about the 50mm focal
length. You can buy a 50mm F/1.8 for ~ $100, yet primes at nearby
focal lengths (85mm, 35mm) command significantly higher prices.

Not being an optics guy, I would presume it has to do with the
number and quality of lens elements / that are required to focus
the light onto the image sensor.

Does anyone have any rationale / pointers to resources to help me
better understand this aspect of the technology?

Thanks!
-John
Click to expand...
The 50mm is easy and cheap to make.

--
Greg Gebhardt in
Jacksonville, Florida
http://www.pbase.com/greggebhardt
 
Ryder said:
Hi:

My guess: A 50mm is often considered the closest to a natural field
of view(at least with film) and, therefore, was the basic "kit"
lense for most cameras. For that reason they have made XXXmillion
of them. Economy of scale factors. At least that is my take on it.
Also the extremes (12mm or 500mm) are hardest to design and 50mm is
nicely in the middle.
Click to expand...
If this were the case, then I'd expect to see 50mm lenses that perform far better than the ones we have (from Nikon) at the present time. Both the 50mm f/1.4 and f/1.8 lenses are poor performers wide open, yet the 85mm f/1.4 and 105mm f/2 are excellent wide open, as are some of the Nikkor WA's. Even going back into the earlier AI lenses, they weren't any good wide open either, at least none of the ones I've tested, inlculding the 55 f/1.2, 50 f/1.2, 50 f/1.4 and 50 f/2.

So from my perspective, I'd have to say that 50mm F.L. lenses must be posing a problem for Nikon to design. I will say that these problems are not evident for 50mm Summicrons, although these are of course rangefinder lenses.
 
jlam said:
Thanks for the replies!

I'm trying to isolate the different effects, and this is what I think:
Click to expand...
jlam said:
2) The difference in price between 50mm primes and more extreme
primes (20mm, 300mm) can be explained by the complexity / quality
of the optics.
Click to expand...
The quality of the optics in the 50mm f/1.8 are first rate, so optical quality is not one of the differences from other lenses at other focal lengths. It is just that the lens elements needed to make this focal length are easy to make and a normal lens doesn't need many elements, so the lens costs less.
jlam said:
Regarding sharpness:

This is where I'm still stuck. I'm blown away by the sharpness of
my 50mm/f1.8. Since I don't own any other primes, I don't know how
it compares with other primes at different focal lengths. Comments?
Click to expand...
It is on par with the best of them. Hopefully you aren't stuck on this point anymore. It is duck soup to make a high quality, tack sharp lens of this focal length. Notice also that the build quality, while adequate to hold the elements aligned properly, is not exactly lavish.

--
FJP
 
It's hard for me to like the 50mm for digital with the 1.5x crop factor. With Nikon cameras, it becomes an approximate 75mm. For me it becomes to short to be a useful tele and to long for a decent standard lens. Closest thing to a true 50mm is the 35mm (which becomes about a 52mm), but is significantly more expensive.
jlam said:
I'm trying to understand what is so "special" about the 50mm focal
length. You can buy a 50mm F/1.8 for ~ $100, yet primes at nearby
focal lengths (85mm, 35mm) command significantly higher prices.

Not being an optics guy, I would presume it has to do with the
number and quality of lens elements / that are required to focus
the light onto the image sensor.

Does anyone have any rationale / pointers to resources to help me
better understand this aspect of the technology?

Thanks!
-John
Click to expand...
--
----

My D100 was stolen. I will beat the cr@p out of all thieves.



inhousephoto inc. digital / photography / media
http://www.inhousephoto.com
 
Wouldn't a 75mm length (digital) be about perfect for portraits?
Jonathan F. said:
jlam said:
I'm trying to understand what is so "special" about the 50mm focal
length. You can buy a 50mm F/1.8 for ~ $100, yet primes at nearby
focal lengths (85mm, 35mm) command significantly higher prices.

Not being an optics guy, I would presume it has to do with the
number and quality of lens elements / that are required to focus
the light onto the image sensor.

Does anyone have any rationale / pointers to resources to help me
better understand this aspect of the technology?

Thanks!
-John
Click to expand...
--
----

My D100 was stolen. I will beat the cr@p out of all thieves.



inhousephoto inc. digital / photography / media
http://www.inhousephoto.com
Click to expand...
 
I've done many portraits with my 50 1.8 (mainly indoor, low light, high ISO shots), and, although it's a good lens for such work, you must get really close to your subject if you want a close-up portrait (just the head). I find this very disturbing for your subject, unless he/she is a friend/relative or so. AA 75 mm FOV becomes strange for me, not a "normal" lens nor a real telephoto one. Anyway, if you or your subject don't mind to shoot/be shot so close, you can get outstanding portraits with it (the bokeh is not the best out there, but I find it very decent most times).
Here you have a portrait of my daughter at f2.4 or so.


danfriz said:
Jonathan F. said:
jlam said:
I'm trying to understand what is so "special" about the 50mm focal
length. You can buy a 50mm F/1.8 for ~ $100, yet primes at nearby
focal lengths (85mm, 35mm) command significantly higher prices.

Not being an optics guy, I would presume it has to do with the
number and quality of lens elements / that are required to focus
the light onto the image sensor.

Does anyone have any rationale / pointers to resources to help me
better understand this aspect of the technology?

Thanks!
-John
Click to expand...
--
----

My D100 was stolen. I will beat the cr@p out of all thieves.



inhousephoto inc. digital / photography / media
http://www.inhousephoto.com
Click to expand...
Click to expand...
--
http://www.beatusille.net
'Who are you going to believe, me or your own eyes?'
Groucho Marx

(Gear list in profile)
 
Cute kid! Love her eyes.

Thanks for the insight. How far away were you when you took that shot?

Dan
Felipe Rodríguez said:

danfriz said:
Jonathan F. said:
jlam said:
I'm trying to understand what is so "special" about the 50mm focal
length. You can buy a 50mm F/1.8 for ~ $100, yet primes at nearby
focal lengths (85mm, 35mm) command significantly higher prices.

Not being an optics guy, I would presume it has to do with the
number and quality of lens elements / that are required to focus
the light onto the image sensor.

Does anyone have any rationale / pointers to resources to help me
better understand this aspect of the technology?

Thanks!
-John
Click to expand...
--
----

My D100 was stolen. I will beat the cr@p out of all thieves.



inhousephoto inc. digital / photography / media
http://www.inhousephoto.com
Click to expand...
Click to expand...
--
http://www.beatusille.net
'Who are you going to believe, me or your own eyes?'
Groucho Marx

(Gear list in profile)
Click to expand...
 
Jason Hutchinson said:
The reason the 50s (and 45s) are so good is the film to flange
distance is right about that same distance as the focal length
which allows the use of a simple symmetric gaussian design.
Click to expand...
That is exactly right. I was beginning to give up hope for this thread.

It's easy to correct a lot of aberrations in a symmetric lens. Much of the damage that is done by the front elements gets "undone" by the "mirror image" rear elements.

Although with film-flange distances in the 45mm range for most SLRS, it's hard to make a symmetric 45mm. 50 is easier, 55mm is easiest.

50mm lenses are slightly asymetrical, just enough to keep them from running into the mirror.

--
A cyberstalker told me not to post anymore...
So I'm posting even more!

Ciao!

Joe

http://www.swissarmyfork.com
 
jlam said:
Thanks! I now have some keywords to Google for :)
Click to expand...
Here's a few more for you.

Registration distance - the "film to flange" distance that Jason referred to.
Retrofocus - the type of asymetric design used for wide angle lenses.
Telephoto - the kind of asymetric design used for long lenses.
Double Gauss - the typical f1.4, f1.8, or 2.0 normal
Tessar - the typical f2.8 normal

--
A cyberstalker told me not to post anymore...
So I'm posting even more!

Ciao!

Joe

http://www.swissarmyfork.com
 
Shooting children I don't think is a problem with the 50mm, but I think the 85mm 1.8 would do a better job at portraits. You would be further away and you wouldn't get so much distortion, especially around the nose.

I think for me though, the 50mm on film was perfect for a walk around lens, you just don't get that same feeling with the 50mm on digital.
Felipe Rodríguez said:
danfriz said:
Wouldn't a 75mm length (digital) be about perfect for portraits?
Click to expand...
Click to expand...
----

My D100 was stolen. I will beat the cr@p out of all thieves.



inhousephoto inc. digital / photography / media
http://www.inhousephoto.com
 
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