Posted by William Vrolyk on November 28, 2006 at 11:10 AM
Does, for example, a 50mm really become an 80mm on a DSLR with an aps-c sensor? Or is it an illusion because the field of view is narrowed? That in reality it is still a 50mm but cropped to an 80mm field of view equivalent?
If lenses are designed specifically for DSLRs with aps-c sensors then they cannot be totally compatible with a DSLR with a full frame sensor. Or are lenses always designed for full frame sensors or 35mm film?
I am curious about this.
Thank you for your replies.
Will
Edmonton, Alberta
Canada
Posted by Ed Dubois on November 28, 2006 at 11:32 AM
Hi Will,
It's an illusion. As you said the field of view is narrowed but the lens is still a 50 mm with all the benefits and/or drawbacks of that focal length. It's much the same as adding a doubler to a 300. What you see is the same area as a 600 would cover but with the perspective of a 300.
Some lenses are designed for smaller sensors which means that the lens itself can be smaller and lighter (and presumably cheaper) than one designed for a full 35 mm. The smaller the format the smaller the lenses: look at some old 16mm film cameras and compare the size of a 300mm for 16mm, 35mm and medium format. The larger the image the lens has to throw on the film plane or sensor the larger the optics have to be.
Posted by Guy Tal on November 28, 2006 at 12:05 PM
Actually there's no illusion. A 50mm is a 50mm is a 50mm. The only difference is how much of the image circle you're capturing.
In effect you're seeing the same field of view as an 80mm on a full-frame but in reality you still have all the characteristics of a 50mm lens (i.e. magnification, DOF etc.).
Lenses designed for smaller sensors simply don't project a large enough image circle to be used on larger areas.
Guy
Posted by Paul Skoczylas on November 28, 2006 at 12:55 PM
Lenses designed for smaller sensors will seriously vignette if used on cameras with larger sensors. An example is the Sigma DC series. They will mount on cameras with larger sensors, but the corners will be blacked out. (The DG series, on the other hand, won't vignette--any more than the older designs, anyway--but have coatings on them which are optimized for digital (and won't have any effect on film).
As others have stated, a 50mm lens is a 50mm lens, all you're doing is cropping.
This has no effect on DOF at the sensor, but it DOES affect DOF in the image. Let's look at an example: On a full frame sensor, assume you want a circle of confusion (CoC) of 0.03mm to get acceptable sharpness on an 8x10 print. Shooting an object at 3 m at f/8 with your 50mm lens, this gives you a DOF of 1847mm. Switch to your 1.6 crop factor camera now. You have to blow it up more to get 8x10 because the sensor is smaller, so you need to start with a smaller CoC: 0.01875mm to be comparable (0.03/1.6). Now your DOF is reduced to 1096mm. This makes sense, since you've just cropped and reenlarged the centre portion of your previous shot, making any softness more apparent. But say you don't want an enlargement of the centre of the image, but the same full subject. Now you need to move back to 4.8m (3x1.6). This will change the perspective a bit, of course. But now your DOF is 2978 mm--the increase in distance has outweighed the increase in magnification.
-Paul
Posted by William Vrolyk on November 29, 2006 at 6:11 PM
Not exactly and illusion (only a seeming illusion ) but my thoughts on this was right.
The clerk at the camera store said to be that a common complaint about the Canon 5D was vignetting. I suspect it was the lenses used that was to blame. He said it would only accept the "L" series lenses. I understand "L" stands for "Luxury" so in other words only the most expensive and likely designed for full frame sensors would do for the 5D.
I visualized my money taking wing and fluttering away from my wallet.
Thank you Paul for that further insight and to all for your replies.
Will
Edmonton, Alberta
Canada
Posted by Les Barstow on November 29, 2006 at 11:13 PM
Vignetting occurs when lens tolerances are tight - usually more often on cheaper lenses. Digital full-frames suffer doubly over 35mm SLRs because digital sensors aren't very tolerant of off-angle light, whereas film doesn't much care.
However, a 5D or other full-frame DSLR doesn't make your cheaper lenses useless; at worst, you'll have to stop down a bit from wide open to remove the vignetting. I used to have to do this with my Nikkor 28-105mm lens when it had a filter on it and I wanted to shoot at 28mm - it's not a big deal if you're used to it. As an aside, most lenses are better stopped down a bit anyway...
Posted by Paul Skoczylas on November 30, 2006 at 12:26 PM
The 5D has a reputation for vignetting on very wide angle lenses. The 1Ds2 does not, even though the sensor size is virtually the same. Conclusion: It's not just the lens. The sensor has something called "microlenses" over each pixel site. The microlens design in the 1Ds2 is better than in the 5D. You do get something for all that extra money.
BTW, the 5D can definitely accept all EF lenses, not just L-series. If the clerk told you it could only take L lenses, he was full of it! (It will not accept the EF-S lenses, though, which are for the newer 1.6x cameras only.)
Discussion
6 repliesIf lenses are designed specifically for DSLRs with aps-c sensors then they cannot be totally compatible with a DSLR with a full frame sensor. Or are lenses always designed for full frame sensors or 35mm film?
I am curious about this.
Thank you for your replies.
Will
Edmonton, Alberta
Canada
It's an illusion. As you said the field of view is narrowed but the lens is still a 50 mm with all the benefits and/or drawbacks of that focal length. It's much the same as adding a doubler to a 300. What you see is the same area as a 600 would cover but with the perspective of a 300.
Some lenses are designed for smaller sensors which means that the lens itself can be smaller and lighter (and presumably cheaper) than one designed for a full 35 mm. The smaller the format the smaller the lenses: look at some old 16mm film cameras and compare the size of a 300mm for 16mm, 35mm and medium format. The larger the image the lens has to throw on the film plane or sensor the larger the optics have to be.
In effect you're seeing the same field of view as an 80mm on a full-frame but in reality you still have all the characteristics of a 50mm lens (i.e. magnification, DOF etc.).
Lenses designed for smaller sensors simply don't project a large enough image circle to be used on larger areas.
Guy
As others have stated, a 50mm lens is a 50mm lens, all you're doing is cropping.
This has no effect on DOF at the sensor, but it DOES affect DOF in the image. Let's look at an example: On a full frame sensor, assume you want a circle of confusion (CoC) of 0.03mm to get acceptable sharpness on an 8x10 print. Shooting an object at 3 m at f/8 with your 50mm lens, this gives you a DOF of 1847mm. Switch to your 1.6 crop factor camera now. You have to blow it up more to get 8x10 because the sensor is smaller, so you need to start with a smaller CoC: 0.01875mm to be comparable (0.03/1.6). Now your DOF is reduced to 1096mm. This makes sense, since you've just cropped and reenlarged the centre portion of your previous shot, making any softness more apparent. But say you don't want an enlargement of the centre of the image, but the same full subject. Now you need to move back to 4.8m (3x1.6). This will change the perspective a bit, of course. But now your DOF is 2978 mm--the increase in distance has outweighed the increase in magnification.
-Paul
The clerk at the camera store said to be that a common complaint about the Canon 5D was vignetting. I suspect it was the lenses used that was to blame. He said it would only accept the "L" series lenses. I understand "L" stands for "Luxury" so in other words only the most expensive and likely designed for full frame sensors would do for the 5D.
I visualized my money taking wing and fluttering away from my wallet.
Thank you Paul for that further insight and to all for your replies.
Will
Edmonton, Alberta
Canada
However, a 5D or other full-frame DSLR doesn't make your cheaper lenses useless; at worst, you'll have to stop down a bit from wide open to remove the vignetting. I used to have to do this with my Nikkor 28-105mm lens when it had a filter on it and I wanted to shoot at 28mm - it's not a big deal if you're used to it. As an aside, most lenses are better stopped down a bit anyway...
BTW, the 5D can definitely accept all EF lenses, not just L-series. If the clerk told you it could only take L lenses, he was full of it! (It will not accept the EF-S lenses, though, which are for the newer 1.6x cameras only.)
-Paul