Posted by Greg Maklae on December 8, 2009 at 8:45 AM
What are the advantages of a 77 mm dia lens vs a 52 mm? My only thought is more light is focused on the detector, thus lessening exposure time for a given f/stop. Are there any real advantages?
Posted by Alan Olander on December 8, 2009 at 9:05 AM
An f/stop transmits the same amount of light no matter what the lens diameter is. Lens diameter depends on the lens design and maximum aperture. F/4 on a 300mm lens with a 72mm lens diameter is the same as f/4 on a 50mm lens with a 52mm diameter.
Posted by Luke Ormand on December 8, 2009 at 9:08 AM
I could be way off base... but I think the larger diameter of the lens, the more light can get in, which means the faster the autofocus, also it's associated with aperture. If you look at the diameter for a 70-300mm zoom, the aperture at 300 is f/5.6 and the diameter is 52. But on a 300 f/4, the aperture is, well, f/4 with a diameter of 72.
- Luke
Posted by Kent Staubus on December 8, 2009 at 9:20 AM
Advantages in general for 77mm: Fast maximum aperture, generally pro level construction.
Disadvantages: More expensive, heavier/bulkier, polarizer is more expensive.
All of my main lenses are 77mm. I like the f2.8 speed they give me.
Kent in SD
Posted by Keith Bauer on December 8, 2009 at 9:22 AM
f/stop is calculated as the focal length of the lens divided by the size of the "hole" or "aperture" created by the aperture blades. As Alan noted above, an f/4 lens is an f/4 lens no matter the filter size. clearly a 500mm f/4 has a larger diameter than a 17mm f/4. The 500mm needs an aperture opening of 125mm to achieve f/4, while the 17mm needs an aperture opening of 4.25 mm. The math is clear. Your question seems to be about the filter size, but the real issue is the largest aperture the lens is capable of creating.
Posted by Mel Ladewig on December 8, 2009 at 1:59 PM
A 77mm front filter ring has nothing to do with the light that can enter the lens and proceed through to the sensor.
I have a Fuji 125-NW/f5.6 large format lens in a 46mm front threaded configuration. To the best of my knowledge, this lens is also available in 52, 55 and 67mm filter configurations. In all of these cases, the glass design is identical, but the shrouding for the front element changes. They all can produce exactly the same image, just take different filter sizes. They all require exactly the same exposure time for a given meter reading shot at f5.6. They all give exactly the same field of view.
Do not put weight solely on the front filter diameter.
The important factor is the maximum aperture, but even this may not be critical. For instance, an f4 lens may be just as sharp as an f2.8 lens when both are using an aperture of f8. In some cases, the f4 may be sharper or may have other properties making it superior for your application.
The advantage to 77mm filter threaded lenses is that the filter size accommodates a wide variety of lenses allowing the photographer to reduce the quantity of filters he carries. In Canon's lineup in 77mm threads you can find lenses from the EF-S 10-22 and 17-55f2.8IS to the 17-40 f4L, 16-35 f2.8mkI (and its predecessors), 24-70 f2.8l, 28-70 f2.8-4L, 24-105 f4L, 28-300L, 70-200f4L, 70-200 f2.8L, 100-400L, 400 f5.6L + a number of other lenses I did not mention. This is the key reason why 77mm filter threaded lenses are so popular, but you'll also see standardization at other thread diameters. In Canon, there is a large variety of lenses with 58mm threads from the 28-105/f3.5-4.5 and 70-300IS models and all the 75-300 variants to the primes 28/1.8, 50/1.4, 85/1.8. 100/2, 135/2.8SF, etc...
Posted by Austin Booth on December 8, 2009 at 2:23 PM
While the advantage is not the lens diameter itself, lenses with wider diameters usually let more light in and have a better maximum f-stop than lenses with smaller diameters. The advantage is you can usually shoot in lower light, stop the action of fast moving subjects and with longer lenses you can blur the background better if you want to add importance to your subject. For example the Canon 50mm f/1.8 lens has a 52mm filter size, the 50mm f/1.4 has a 58mm filter size and the 50mm f/1.2 has a 72mm filter size because it requires an opening with a wider diameter to allow more light in. That is the only real difference in the lens diameters.
However, most of the time those lenses with better f-stops are also better quality lenses. It isn't because they have a wider diameter and better f-stop but because people usually pay more for those lenses the manufacturers usually build the lenses to higher standards so they are usually sharper and have better contrast and have less imperfections such as flaring, vignetting, chromatic aberrations and distortion. The more expensive lenses with better f-stops usually have a better build quality as well with a metal body and in some cases even weather sealing where as the cheaper lenses with smaller lens diameters are often have a cheap plastic body.
Posted by David Bostedo on December 8, 2009 at 5:01 PM
While the advantage is not the lens diameter itself, lenses with wider diameters usually let more light in and have a better maximum f-stop than lenses with smaller diameters.
Completely true, but to me that's the backwards way to think about it. As others have noted, the lens diameter is based on the focal length and max. aperture. Otherwise, lenses would be narrower and lighter. A lens designer wouldn't set out to make a wide lens - they'd choose max. aperture and focal length and the width would come from that.
Posted by Buck Ward on December 8, 2009 at 6:41 PM
Clearly, there is a relationship between the diameter of the aperture and the diameter of the lens. That's why a 300 f2.8 lens is larger than a 300mm f4 lens. Obviously there's more to it than that though. Canon 17-40 f4 and 70-200 f2.8, for example, both take 77mm filters. That's a convenience, since you don't have to carry a bunch of different sized filters.
Posted by Kent Staubus on December 8, 2009 at 6:52 PM
Buck--
It gets more complicated with wide/ultra wide angle lenses. With a 35mm lens, the lens is actually 35mm from front element to sensor plane. Or something like that. Ultrawwides are a different beast. They are what's called "retro focus." In effect the light beam travels a longer distance. For example, a 20mm lens is actually longer than 20mm. It's a sort of optical trick that's made so the lens doesn't end up getting whacked by the shutter.
Discussion
9 replies- Luke
Disadvantages: More expensive, heavier/bulkier, polarizer is more expensive.
All of my main lenses are 77mm. I like the f2.8 speed they give me.
Kent in SD
I have a Fuji 125-NW/f5.6 large format lens in a 46mm front threaded configuration. To the best of my knowledge, this lens is also available in 52, 55 and 67mm filter configurations. In all of these cases, the glass design is identical, but the shrouding for the front element changes. They all can produce exactly the same image, just take different filter sizes. They all require exactly the same exposure time for a given meter reading shot at f5.6. They all give exactly the same field of view.
Do not put weight solely on the front filter diameter.
The important factor is the maximum aperture, but even this may not be critical. For instance, an f4 lens may be just as sharp as an f2.8 lens when both are using an aperture of f8. In some cases, the f4 may be sharper or may have other properties making it superior for your application.
The advantage to 77mm filter threaded lenses is that the filter size accommodates a wide variety of lenses allowing the photographer to reduce the quantity of filters he carries. In Canon's lineup in 77mm threads you can find lenses from the EF-S 10-22 and 17-55f2.8IS to the 17-40 f4L, 16-35 f2.8mkI (and its predecessors), 24-70 f2.8l, 28-70 f2.8-4L, 24-105 f4L, 28-300L, 70-200f4L, 70-200 f2.8L, 100-400L, 400 f5.6L + a number of other lenses I did not mention. This is the key reason why 77mm filter threaded lenses are so popular, but you'll also see standardization at other thread diameters. In Canon, there is a large variety of lenses with 58mm threads from the 28-105/f3.5-4.5 and 70-300IS models and all the 75-300 variants to the primes 28/1.8, 50/1.4, 85/1.8. 100/2, 135/2.8SF, etc...
However, most of the time those lenses with better f-stops are also better quality lenses. It isn't because they have a wider diameter and better f-stop but because people usually pay more for those lenses the manufacturers usually build the lenses to higher standards so they are usually sharper and have better contrast and have less imperfections such as flaring, vignetting, chromatic aberrations and distortion. The more expensive lenses with better f-stops usually have a better build quality as well with a metal body and in some cases even weather sealing where as the cheaper lenses with smaller lens diameters are often have a cheap plastic body.
Completely true, but to me that's the backwards way to think about it. As others have noted, the lens diameter is based on the focal length and max. aperture. Otherwise, lenses would be narrower and lighter. A lens designer wouldn't set out to make a wide lens - they'd choose max. aperture and focal length and the width would come from that.
It gets more complicated with wide/ultra wide angle lenses. With a 35mm lens, the lens is actually 35mm from front element to sensor plane. Or something like that. Ultrawwides are a different beast. They are what's called "retro focus." In effect the light beam travels a longer distance. For example, a 20mm lens is actually longer than 20mm. It's a sort of optical trick that's made so the lens doesn't end up getting whacked by the shutter.
Kent in SD