[Lowell Goudge]

Is it a negative?

In a word. NO

At least in my opinion. I have over 30 lenses both MF , and AF and in all of this only 2 are ASP-C specific. These are the samyang 8mm fisheye and the sigma 10-20

I don't see any issue because of all the "extra" light bouncing around. In fact when you consider it fully since aperture is focal length divided by diameter any lens will have the same amount of light entering regardless of the unrestricted image circle is

[stevebrot]

I shoot almost exclusively with FF glass on my K10D and can't say that it has been a negative experience in any way. The main concern, as noted above, is that the light from the larger image circle might result in the equivalent of veiling flare by reflecting off the sides, top, and bottom of the mirror box onto the sensor as unfocused "extra" light.

As for the "sweet spot" argument...yes, the center tends to be sharper than the corners, but that extra corner sharpness on a cropped image is offset somewhat by the extra enlargement to the final image imposed by the smaller sensor. Translation...you can accomplish the same thing by cropping a FF image, but who would want to?

The main advantages of lenses designed for the APS-C format can be summarized in a few bullet points:

• Less extraneous light in the mirror box
• Lighter and more compact than FF lenses
• Rear element coatings and design optimized to minimize sensor artifact and surface reflection (!?!?)

That last point has is the most difficult to demonstrate and is probably the most disputed. Low angle light such as that originating from the margins of a lens with a large exit pupil (more typical of FF lenses) has potential to cause problems for the detectors on the sensor and has been blamed for a number of ills including purple fringing and degraded resolution. Digitally optimized designs claim to minimize that low angle light resulting in a cleaner image. The theory makes sense, but I don't know that it is born out in practice.


Steve


(P.S. The photozone.de comparison of the Canon 50/1.2 is interesting, but MTF comparison is not appropriate since the numbers are not normalized for format size or the difference in sensor resolution between the 5D Mk II and 350D. FF always cleans house compared to APS-C.)

[Laurentiu Cristofor]

(P.S. The photozone.de comparison of the Canon 50/1.2 is interesting, but MTF comparison is not appropriate since the numbers are not normalized for format size or the difference in sensor resolution between the 5D Mk II and 350D. FF always cleans house compared to APS-C.)

MTF numbers shouldn't be compared directly, but one can compare the relative performance of center and corners - there's a much larger gap on FF where the border performance can only be rated as poor.

[rhodopsin]

... In fact when you consider it fully since aperture is focal length divided by diameter any lens will have the same amount of light entering regardless of the unrestricted image circle is

Huh? Yes light entering is the same, but for FF lens image circle covering 24x36mm to be as bright (same light intensity per unit area) as APC-C lens image circle, the FF lens lets in more light.

[stevebrot]

MTF numbers shouldn't be compared directly, but one can compare the relative performance of center and corners - there's a much larger gap on FF where the border performance can only be rated as poor.

...so true for the Canon 50/1.2. Did you catch the vignette numbers? 3 stops on FF! Tunnel Vision!

I don't want to minimize the happy nature of the APS-C "sweet" spot. It allows soft-corner/sharp center lenses such as my Helios 44M to really shine on APS-C where the same lens on 35mm film is obviously less-than-sharp in the corners. (The cool thing about the Helios is that it is sharp in the center at ALL apertures!)


Steve

[Lowell Goudge]

Huh? Yes light entering is the same, but for FF lens image circle covering 24x36mm to be as bright (same light intensity per unit area) as APC-C lens image circle, the FF lens lets in more light.

No it does not. The rest us restricted internally in the lens In fact most ASP-C lenses cover full frame. Take my sigma 10-20. Above 13mm it covers a full frame. I've tested it on my PZ-1. Remember exposure is light per unit area. F2.8 means a ratio of lens length to diameter. And at any magnification with a lens the intensity on the sensor regardless of format is the same. I think it is immaterial as to whether all or some of the light is trapped in I ternal baffles in the lens or bounces off the black inside of the mirror box.

If ASP-C lenses truly did not need to let in the same amount of total piggy in then why is the DA300/4 heavier and bigger than the K300/4?

[Jewelltrail]

...so true for the Canon 50/1.2. Did you catch the vignette numbers? 3 stops on FF! Tunnel Vision!

I don't want to minimize the happy nature of the APS-C "sweet" spot. It allows soft-corner/sharp center lenses such as my Helios 44M to really shine on APS-C where the same lens on 35mm film is obviously less-than-sharp in the corners. (The cool thing about the Helios is that it is sharp in the center at ALL apertures!)


Steve

The Canon 1.2 L is great example of how a FF lens, which struggles with corners, can be redeemed by the APS-C sensor gods. As for the Helios, the only MTF scores I've seen are for the 40-2 85mm 1.5. For this lens, even APS-C can not redeem its borders: they are still way behind until 5.6. Here, the poor borders @ large A's make sense in portraits, adding to the dreamy, surreal quality--nobody really wants a perfectly accurate shot of themself anyway. So the sharp center of the Helios, coupled with the poor borders @ large A's, only increases the dramatic effect of in to out of focus, giving the lens the "magical" quality which attracts so many. Ironic, in that the Helios' short-comings actually work to its benefit, so long as one uses it for portraits, or subjects which can be kept entirely in the center. It is no accident, within this scope, the good people @ PHotozone give the 40-2 5 stars. Here is what they measured the Helios 40-2 @ on K10d.

[rhodopsin]

No it does not. The rest us restricted internally in the lens In fact most ASP-C lenses cover full frame. Take my sigma 10-20. Above 13mm it covers a full frame. I've tested it on my PZ-1. Remember exposure is light per unit area. F2.8 means a ratio of lens length to diameter. And at any magnification with a lens the intensity on the sensor regardless of format is the same. I think it is immaterial as to whether all or some of the light is trapped in I ternal baffles in the lens or bounces off the black inside of the mirror box.

If ASP-C lenses truly did not need to let in the same amount of total piggy in then why is the DA300/4 heavier and bigger than the K300/4?

FF sensor is approximately 1.5 times larger than APS-C sensor. To cover a larger area with the same light intensity, i.e. the same light intensity per unit area, the lens covering FF must let in more light than the lens covering only APS-C.

I wonder does Sigma 10-20mm covers FF above 13mm with the same light intensity across the entire frame? I think there is light intensity drop-off beginning outside the APC-C frame.

My Sigma 1.4/30 (APS-C lens) did not cover FF, not even close, was heavily vignetted.

[Lowell Goudge]

FF sensor is approximately 1.5 times larger than APS-C sensor. To cover a larger area with the same light intensity, i.e. the same light intensity per unit area, the lens covering FF must let in more light than the lens covering only APS-C.

I wonder does Sigma 10-20mm covers FF above 13mm with the same light intensity across the entire frame? I think there is light intensity drop-off beginning outside the APC-C frame.

My Sigma 1.4/30 (APS-C lens) did not cover FF, not even close, was heavily vignetted.

I think you are missing something here, F stop is the ratio of diameter to focal length and is independent of projection circle.

The image magnification, is a function of focal length and subject distance only,

Considering these two points, and ONLY these two points, assuming there is no difference in transmission through any two lenses at one specific focal length, the average illumination is the same regardless of the image circle they are designed to project onto.

Now, when you consider a lens designed for a cropped sensor, there are several areas where the light outside of the projection circle goes, compared to a full frame lens. First and foremost is the lens hood, which for ASP-C sensors will lead to vignetting. It is designed for ht efield of view of the ASP-C sensor not full frame, remove this.

Second, the internal design of the lens may have things that restrict the light that is outside the image circle, and lastly, the lens may actually, as with my sigma 10-20, cover the full frame under most circulstances., in which case the light is absorbed by the black surfaces of the mirror box.

the simple fact that a lens projects an image onto a smaller sensor does not alter at any aperture how bright the image is. Brightness is determined by magnification ratio and aperture only. Magnification ration because the bigger an image is (i.e.the more spread out it is) the lower the light per square area, and aperture because the smaller the diameter the less light entering the lens. That is all.

The bigger issue with full frame lenses, especially related to pentax lenses or older film lenses is the lack of rear element coatings that can assist in reducing reflection off the sensor, but that is another issue all together.

The bottom line here is that prividing the lens and camera body are properly designed and manufactured, and there are no shiny reflective parts in the mirror box or on the rear of the lens to reflect any stray light, it does not matter.

As I pointed out above, just look at any telephoto lens, the diameter of the front element in a digital lens is the same diameter as a film lens, it has to be, that is what deternines maximum aperture.

[rhodopsin]

I think you are missing something here, F stop is the ratio of diameter to focal length and is independent of projection circle.

The image magnification, is a function of focal length and subject distance only,

Considering these two points, and ONLY these two points, assuming there is no difference in transmission through any two lenses at one specific focal length, the average illumination is the same regardless of the image circle they are designed to project onto.

Now, when you consider a lens designed for a cropped sensor, there are several areas where the light outside of the projection circle goes, compared to a full frame lens. First and foremost is the lens hood, which for ASP-C sensors will lead to vignetting. It is designed for ht efield of view of the ASP-C sensor not full frame, remove this.

Second, the internal design of the lens may have things that restrict the light that is outside the image circle, and lastly, the lens may actually, as with my sigma 10-20, cover the full frame under most circulstances., in which case the light is absorbed by the black surfaces of the mirror box.

the simple fact that a lens projects an image onto a smaller sensor does not alter at any aperture how bright the image is. Brightness is determined by magnification ratio and aperture only. Magnification ration because the bigger an image is (i.e.the more spread out it is) the lower the light per square area, and aperture because the smaller the diameter the less light entering the lens. That is all.

The bigger issue with full frame lenses, especially related to pentax lenses or older film lenses is the lack of rear element coatings that can assist in reducing reflection off the sensor, but that is another issue all together.

The bottom line here is that prividing the lens and camera body are properly designed and manufactured, and there are no shiny reflective parts in the mirror box or on the rear of the lens to reflect any stray light, it does not matter.

As I pointed out above, just look at any telephoto lens, the diameter of the front element in a digital lens is the same diameter as a film lens, it has to be, that is what deternines maximum aperture.

Well, now it gets complicated, not too bad

F = f/D, yes, but D is the diameter of the entrance pupil, which is not necessarily the physical diameter of the front element.

The lens rear element exit pupil projects the image circle. Lens designed for APS-C coverage has smaller exit pupil than lens designed for FF coverage. Sure, the light intensity per unit area is the same for both lenses, but the FF lens projects a 1.5x larger circle -- the FF lens must let in 1.5x more light to project the larger image circle with same intensity per unit area -- increasing the area illuminated requires more light...

[Lowell Goudge]

Well, now it gets complicated, not too bad

F = f/D, yes, but D is the diameter of the entrance pupil, which is not necessarily the physical diameter of the front element.

The lens rear element exit pupil projects the image circle. Lens designed for APS-C coverage has smaller exit pupil than lens designed for FF coverage. Sure, the light intensity per unit area is the same for both lenses, but the FF lens projects a 1.5x larger circle -- the FF lens must let in 1.5x more light to project the larger image circle with same intensity per unit area -- increasing the area illuminated requires more light...

this is where you are wrong. Look at virtually any prime. I say prime here because zooms have some special design criteria that makes the front element oversized, for example a 300F4 needs a front element at least 75mm in diameter to be F4. My old SMC uses a 77mm filter, the same holds true for almost every prime I own. The real front element diameter is exactly the size needed to permit the maximum aperture. While there may be some correlation between image circle and rear element diameter it is not a 1:1 correlation some film lenses have smaller rear elements than digital ones because film can accept light on more accute angles than digital sensors. The only way to have light more perpendicular to the sensor is to have larger rear elements not smaller

[rhodopsin]

this is where you are wrong. Look at virtually any prime. I say prime here because zooms have some special design criteria that makes the front element oversized, for example a 300F4 needs a front element at least 75mm in diameter to be F4. My old SMC uses a 77mm filter, the same holds true for almost every prime I own. The real front element diameter is exactly the size needed to permit the maximum aperture. While there may be some correlation between image circle and rear element diameter it is not a 1:1 correlation some film lenses have smaller rear elements than digital ones because film can accept light on more accute angles than digital sensors. The only way to have light more perpendicular to the sensor is to have larger rear elements not smaller

comparison:

SMC Takumar/6x7 55mm f/3.5 takes 100mm filters

S-M-C Takumar 55mm f/1.8 takes 49mm filters

The 1.8/55 lens here is multiple times faster (in f/#) than 6x7 3.5/55 lens, yet the front element is only half as large.

[Lowell Goudge]

comparison:

SMC Takumar/6x7 55mm f/3.5 takes 100mm filters

S-M-C Takumar 55mm f/1.8 takes 49mm filters

The 1.8/55 lens here is multiple times faster (in f/#) than 6x7 3.5/55 lens, yet the front element is only half as large.

go back and measure the front element diameter not the filter ring

The filter diameter is based upon the angle of view for the format and the need to have the filter out of the angle of view. What is the element diameter itself? Note I also said wide angle lenses specifically zooms but the same also applies towide angle primes have design criteria usually associated with FOV that make the element large

[DogLover]

I would consider the 150 macro, the 70 macro, and the 100-300 f/4 HSM to be great lenses.

The 50-150 2.8 and 70-200 2.8 are very good lenses.


.

I only have experience with one of these, the 100-300/4, but I also consider it to be a great lens. From the looks of things, the 85/1.4 may also fall into this group, as may the new 150 macro, and I'll probably end up with both of these someday.

[rhodopsin]

go back and measure the front element diameter not the filter ring

The filter diameter is based upon the angle of view for the format and the need to have the filter out of the angle of view. What is the element diameter itself?

2nd version of 6x7 3.5/55 has 60mm front element, the first version I don't have to measure, but from photos and diagrams its front element appears to be near 80mm.

Note I also said wide angle lenses specifically zooms but the same also applies towide angle primes have design criteria usually associated with FOV that make the element large

Sorry I don't see where you also said wide angle lenses. 1.8/55 is a 'normal' lens.