wide angle converter

[qqqavi]

Hi everyone, 

Can anyone recommend me a wide angle converter with decent quality of x0.43 or x0.5x for a canon lens with 52 or 58 filter diameter? I know a lot of them are very soft .

Thank you. 

[ebiggs1]

" An f/1.8 50 mm lens with a subject at 3 m has a DOF of 2.8 - 3.2 m

 An f/1.8 21 mm lens with a subject at 3 m has a DOF of 2.3 to 4.3 m"

                                                                                           = 1.6 meter

"I used a depth of field calculator."

Not correctly it seems!  Because the DOF is increased with the shorter FL. A 20mm lens at f1.8 and a subject 3 meters away has a DOF of 1.6 meters.  A 50mm lens at f1.8 and a subject 3 meters away has a DOF of only .7 meter. 

[kvbarkley]

I just checked with another DOF calculator:

http://www.dofmaster.com/dofjs.html

For an APS-C at f/1.8 and a subject distance of 3m:

50 mm DOF is .24 (I had .32)

21mm DOF is 1.45 (I had 2.01)

I certainly had the increased DOF at shorter focal lengths* in there, so I am not sure what your beef is.

*Though I misstated it in the text.

[ebiggs1]

"I certainly had the increased DOF at shorter focal lengths* in there, so I am not sure what your beef is."

There is no "beef" !  I simply reacted to this statement.  

"You can't get a wide DOF with a wide angle lens."

Obviously you can.  I certainly had no intention to offend you.

[TCampbell]

The whole point of an interchangeable lens camera is that you can change the whole lens... and there are many benefits from doing so.

When you put a focal length multiplier/reducer on a lens, you can create a lot of problems.  Not least... is that the camera doesn’t know you put this on the front of the lens.  It alters the focal ratio of the lens so there’s no free lunch (you no longer get the DoF of a 50mm lens when you put a reducer on it).  But since the lens is going to report what it is (and doesn’t know about the focal length reducer/multiplier) it can screw up it’s notion of metering and focus.  And of course the optics aren’t optimized for it.

MUCH better idea to get a lens with the focal length and focal ratios you need for the type of photography you want to do.  That’s why the lenses are removeable.

[RobertTheFat]

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@TCampbell wrote:

The whole point of an interchangeable lens camera is that you can change the whole lens... and there are many benefits from doing so.

When you put a focal length multiplier/reducer on a lens, you can create a lot of problems.  Not least... is that the camera doesn’t know you put this on the front of the lens.  It alters the focal ratio of the lens so there’s no free lunch (you no longer get the DoF of a 50mm lens when you put a reducer on it).  But since the lens is going to report what it is (and doesn’t know about the focal length reducer/multiplier) it can screw up it’s notion of metering and focus.  And of course the optics aren’t optimized for it.

MUCH better idea to get a lens with the focal length and focal ratios you need for the type of photography you want to do.  That’s why the lenses are removeable.

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Those adapters are relics of a time when zoom lenses were mediocre and relatively expensive. The adapter was a cheaper alternative that didn't cost you all that much in image quality.

Zoom lenses are still relatively expensive, but now range from good to excellent in quality. Adapters are still a cheaper alternative, but usually cost you dearly in image quality. And as Tim pointed out, the modern symbiotic interactions between camera and lens are not supported by the adapters. (Note that their purveyors are fond of calling the adapters "lenses", but that's really inconsistent with the current meaning of the term.) Tim, Ernie, and others have advised against their use, and that advice is best heeded.