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Archive 2005 · lenses with > 2.0 aperture: the truth?
  
 
sebhoff
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p.1 #1 · p.1 #1 · lenses with > 2.0 aperture: the truth?


Hi everybody,

There are a couple of postings on dpreview that suggest that lenses with maximum apertures greater than f2.0 cannot make full use of the light. As a result, a 50mm/f1.0 actually is supposed to "be" a 50mm/f1.4 and a 85mm/f1.2 is something like a 85mm/f1.44. Apparently this has to do with the angle of incidence and the limitations of the microlenses on the sensors. Plus, this is supposed to have an effect on the DOF, too.

Here are two posts of the same thread:

http://forums.dpreview.com/forums/read.asp?forum=1029&message=12651373
http://forums.dpreview.com/forums/read.asp?forum=1029&message=12661100

As somebody who is contemplating whether or not to buy the 85/1.2, I feel a bit worried. If the difference between a 85/1.2 and 85/1.8 is in fact not that big, the huge price difference would even be more difficult to justify...

Also, since the impact of the angle of incidence must be different between a full-frame and a x1.6 crop camera, is this - if it is true - relevant to the same extent for a humble 300D user like me?

Can somebody on this forum point me to sources that can confirm these points - or is it a hoax?

I apologize if this has been discussed here before - I didn't find anything conclusive doing a quick search.

Sebastian



Apr 19, 2005 at 08:11 PM
IanBMW
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p.1 #2 · p.1 #2 · lenses with > 2.0 aperture: the truth?


I think that's getting a bit technical. I mean all that matters is the picture right. So run a couple of test shots on both and see what suits you best. Intersting topic though.


Apr 19, 2005 at 08:59 PM
sstone
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p.1 #3 · p.1 #3 · lenses with > 2.0 aperture: the truth?


Sebastian...do yourself a favor and buy the 85/1.8. I have one that I use on my Dig Rebel and it's a great lens. There's been alot of discussion about the 1.8 and 1.2 and I think the consensus is that there's not a whole lot of difference to justify the cost.

Steve



Apr 19, 2005 at 09:02 PM
Benjamin Munn
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p.1 #4 · p.1 #4 · lenses with > 2.0 aperture: the truth?


I wouldn't go so far as to say that there isn't a lot of difference between the 85mm F1.8 and the 85mm F1.2. Whether it's worth the extra cost is subjective. I have owned both and each does have a purpose. I personally prefer the look that the F1.2 gives. It's harder to use but when you get it right, it's amazing. Personal preference though.

The F1.2 apeture is something that can be very needed in concert shooting or other low light type shoots.

Basically you have to qualify what you want out of the lens. For a lot of purposes the 85mm F1.8 is just as good and sometimes better. It's nice to have faster options at most of the major focal lengths. Just don't discount if you personally don't need them.

Good luck and let us know what you decide.



Apr 19, 2005 at 09:23 PM
Natron
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p.1 #5 · p.1 #5 · lenses with > 2.0 aperture: the truth?


I'm not going to read dpreview threads because they're often started by some internet jockey with no clue as to what they're talking about... but I will tell you there may be truth to this.

Because of critical needs for perfect exposures with movie cameras, movie lenses are often rated with both f-stops and t-stops. Though a lens may be rated at f/1.2, it may only let as much light through as a true f/1.3 lens, etc. That means the lens may be an f/1.2 lens with a T-stop of f/1.3. I've seen this discussion with lenses like the Nikkor 50mm f/1.4 and 50mm f/1.2 lenses suggesting the f/1.2 barely lets in any more light than the f/1.4. Of course, since the PHYSICAL aperture is really open to f/1.2, it gives the DOF of an f/1.2 lens... it just may not expose for a perfect f/1.2.

It's not speculation but fact and there are solid reasons why it happens with superspeed lenses. I'll try to find the articles later. You could do some research on T-stops though.



Apr 19, 2005 at 11:00 PM
Bobster2
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p.1 #6 · p.1 #6 · lenses with > 2.0 aperture: the truth?


Natron is absolutely correct!


Apr 19, 2005 at 11:09 PM
nutek
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p.1 #7 · p.1 #7 · lenses with > 2.0 aperture: the truth?


It does happen on most lenses, even non-fast ones as well.


Apr 20, 2005 at 12:58 AM
chris78cpr
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p.1 #8 · p.1 #8 · lenses with > 2.0 aperture: the truth?


As somebody who is contemplating whether or not to buy the 85/1.2, I feel a bit worried. If the difference between a 85/1.2 and 85/1.8 is in fact not that big, the huge price difference would even be more difficult to justify...

But surely this would affect the 85mmF1.8 aswell as it has an aperture greater than F2.....

I think at the end of the day you should try both lenses and think about whether you will actually use the F1.2 option on a regular basis. If the answer is no then buy the F1.8 version and use the other cash to buy a 135F2L or something else!

At the end of the day buy what suits what you shoot!

Chris



Apr 20, 2005 at 01:16 AM
 

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Nate Fabro
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p.1 #9 · p.1 #9 · lenses with > 2.0 aperture: the truth?


All I know is I had an physics book and one of the glaring remarks I remember from the sections on optics is that it was "impossible to build a lens that was greater than F/1.0"
I didn't really care for the optics lab and my professor was into particle physics, not optics (what physicist does specialize in optics in this day?) Needless to say I never got an answer as to what this statement entailed and/or why it would be...wish I could find that book....



Apr 20, 2005 at 01:21 AM
Bobster2
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p.1 #10 · p.1 #10 · lenses with > 2.0 aperture: the truth?


I did a google search for "fastest lens ever made" and I found a Zeiss 50mm f/0.7. I wouldn't be surprised if the military had faster lenses than that, but they may be classified.


Apr 20, 2005 at 01:42 AM
Monito
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p.1 #11 · p.1 #11 · lenses with > 2.0 aperture: the truth?


From http://medfmt.8k.com/mf/fast.html

Kurt Dieter Solf's book ,,Photography'' also mentions the Zeiss Planar 50mm f/0.7 (for some roentgen fluorescent sheet photography) and the Zeiss Plan-Achromat with maximum aperture of 1/0.55 and the resolution of 1/3000mm...

...

The fastest lens I know of is the 50mm f/0.519 designed in 1959 by Yoshido. It uses aspheric elements (5 elements in 3 groups). The rear element is practically in contact with the film. The lens is about 100mm in diameter (of course).

...

I use f/0.7 lenses almost every day of the week. 16mm, 35mm, 50mm even 100mm. The biggest I have used was a 250mm f/0.68, which required two people to lift it! However, these lenses aren't glass, they are silicon and/or germanium. They are used for infra red imaging and need to be that fast because the signals being used are very low. DoF is somewhat "precise". :-)

...

the real formula must be used to compute the f-stop, as follows: FStop = 1/(2*sin(atan(Aperture/2.0/Focal))) where FStop = true f-stop, Aperture = aperture diameter, and Focal = focal length of the lens. You can see from this formula that the f-stop can never be smaller than 0.5.

...

Incidentally, if you include a refractive index of the medium in which the f/# is defined, you get f/# = 1/ (n * sqrt((f/D)^2 + 0.25)) Thus, if you fill your camera with oil which has a refractive index of 1.5, then in theory you can get down to f/0.33 as a minimum, but your camera probably won't work again. For a purely digital camera without any moving parts between the lens and the CCD, this might not be as impractical as it was with film cameras. :-)

...

come across a reference to a Leica 75mm f0.85 lens made in 1934. The lens is a Leica Summar. A version of this lens was used in the projection room of the German postal authorities to project televisin images during the 1936 Berlin Olympics.

...

have a full description of the F 0.95 50mm lens in the Canon Interchangable Lens Guide published in 1969. The mount fit the outside bayonet mount of the Canon 7. I have only handled the actual lens a couple of times but I believe the ones made for camera use had a Leica like RF cam. The top of the rear element is flattened to permit it to clear the camera cam follower.

...

Conventional wisdom is that Canon's 50/.95 for the Canon 7/7s is the fastest lens made for rangefinders. Apparently not. I am looking at a JPG of a 52/.9 made for, of all things, special normal lens mount of the Russian Kiev V. I am waiting to get more info, it was probably a prototype and not limited production.

....

Marc Small's book peripherally mentions a Zeiss 45mm f/0.85 Biotar (although not what mount it was in) and who knows how many other special-order, special-purpose military, scientific, radiographic, oscillographic and prototype ultraspeeds there may have been from other manufacturers.

...

And Bjorn Rorslett @ naturfotograf.com has this neat Rodenstock TV-Heligon 50 mm f/0.75 that he uses with a D1x..



Apr 20, 2005 at 03:42 AM
sebhoff
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p.1 #12 · p.1 #12 · lenses with > 2.0 aperture: the truth?


Thanks for your answers!

I guess I'll have to find a way of laying my hands on the two 85s in order to test the difference myself. Unfortunately, there are no places (I know of) in Switzerland where you can rent lenses...
I'll be in New York for 2 1/2 days next month and I may rent something there.

The combination of 85/1.8 and 135/2.0 is indeed something I've also looked at. I shoot a lot of portraits (non-professional, family and friends, quite a few in low-light situations) and I often feel the need to crop pictures taken with my 50/1.4. Now, either I learn to go closer or I get a longer lens. ;-)

I've also been loking at the 70-200/2.8 IS, which would certainly allow me to take pictures in low-light situations - assuming my subjects don't move quickly, of course - but after holding one in my hands yesterday, I can't imagine carrying this monster around much. And since the DOF will presumably be rather different from what I would get with the primes, this probably should not be my first choice.

Thanks, Monito, for the interesting link!

Sebastian



Apr 20, 2005 at 08:05 AM
bka20d
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p.1 #13 · p.1 #13 · lenses with > 2.0 aperture: the truth?


it's so interesting that the 85's draw all the attention....no one seems to ask the same questions about the 35's....



Apr 20, 2005 at 11:44 AM
BrianP
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p.1 #14 · p.1 #14 · lenses with > 2.0 aperture: the truth?


Sebastian:

I really don't want to start/continue an 85 vs 85 debate. You can read many of them on-line. I own both 85s and the 135. I like to shoot available light, and I like the extreme narrow DOF for many portraits. The 85 f/1.2L is the king in this area. It is the best for this type of task. Is it worth the extra money for you? I can't say. It is for me.

Why do I own both 85s? I like the 85 f/1.8 for gymnastics and dance, and the 85 f/1.2L for portraits. I use both lenses for different tasks, and they both have their own strengths and weaknesses.



Apr 20, 2005 at 01:22 PM
BrianP
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p.1 #15 · p.1 #15 · lenses with > 2.0 aperture: the truth?


bka20d wrote:
it's so interesting that the 85's draw all the attention....no one seems to ask the same questions about the 35's....


This is a question that gets asked in almost every one of these threads. The answer is obvious. The 85s each have their own strengths and weaknesses. The 35 f/1.4L is better at everything that its little brother with the notable exceptions of price and size.



Apr 20, 2005 at 01:23 PM
MikeZ
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p.1 #16 · p.1 #16 · lenses with > 2.0 aperture: the truth?


BrianP wrote:
Sebastian:

I really don't want to start/continue an 85 vs 85 debate. You can read many of them on-line. I own both 85s and the 135. I like to shoot available light, and I like the extreme narrow DOF for many portraits. The 85 f/1.2L is the king in this area. It is the best for this type of task. Is it worth the extra money for you? I can't say. It is for me .



Brian,
Iím about to purchase a new lens for my 20D strictly for people photography in available light outside. I have the 85 1.8 and I wonder how can I top the bokkeh and sharpness.
Should I get the 85 1.2 or 135 2.0? I donít mind or prefer any focal length. Both 135 and 85 is fine. I just wonder which one is the best for portraits and background blur.



Apr 20, 2005 at 01:59 PM







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