Lens coverter vs focal reducer

lotech · 09-26-2016, 09:30 PM

Hi there,

Please excuse my ignorance I am just a noob !
I got a cheapo add on lens to convert my standard lens into a wide angle for casual shooting, it is one of those attach to the front of the standard lens, it reduces the focal length to 0.75, so I can shoot like with a 37mm lens, of course the image quality is much worst than a real wide angle lens, but does the converter produce more light like a focal reducer, theoretically ? if it does it would be a cheaper alternative to a real focal reducer and can be used on any camera for casual shooting in low light situation, far more cheaper than a fast wide angle lens.

surfar · 09-26-2016, 10:56 PM

Those things work, to an extent....they do widen the lens but they are not

FR/speedboosters....dont expect great results.For simple jpegs they are ok.

**THoog** · 09-27-2016, 06:46 AM

Originally posted by lotech

does the converter produce more light like a focal reducer, theoretically ?

No. While the lens with wide-angle converter might collect more light, it is from a wider scene. Assuming the scene is evenly lit, the average would be the same and the result would be no brighter. Also, because of light losses due to the conversion lens, you would probably come out worse overall.

A focal reducer does not produce more light; instead, it works by refocusing the image circle projected by the lens to a smaller circle. The "extra" light is light the lens collects normally; it's just the part that usually falls outside the sensor area. The lens MUST be for a format that has a larger image circle than the sensor, such as a 35mm FF lens and a APS-C sensor. Also, because the focal reducer moves the lens closer to the sensor than its designed flange distance, the lens must be designed for a mount with a longer flange distance than the camera (you can't make a focal reducer for full-frame K-mount lenses on APS-C K-mount cameras, because the flange distance is the same).

lotech · 09-27-2016, 07:07 AM

You said right !

"because the focal reducer moves the lens closer to the sensor than its designed flange distance....." matters, there is no free lunch !

Originally posted by THoog

No. While the lens with wide-angle converter might collect more light, it is from a wider scene. Assuming the scene is evenly lit, the average would be the same and the result would be no brighter. Also, because of light losses due to the conversion lens, you would probably come out worse overall.

A focal reducer does not produce more light; instead, it works by refocusing the image circle projected by the lens to a smaller circle. The "extra" light is light the lens collects normally; it's just the part that usually falls outside the sensor area. The lens MUST be for a format that has a larger image circle than the sensor, such as a 35mm FF lens and a APS-C sensor. Also, because the focal reducer moves the lens closer to the sensor than its designed flange distance, the lens must be designed for a mount with a longer flange distance than the camera (you can't make a focal reducer for full-frame K-mount lenses on APS-C K-mount cameras, because the flange distance is the same).

09-26-2016, 09:30 PM	#1
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312	Lens coverter vs focal reducer Hi there, Please excuse my ignorance I am just a noob ! I got a cheapo add on lens to convert my standard lens into a wide angle for casual shooting, it is one of those attach to the front of the standard lens, it reduces the focal length to 0.75, so I can shoot like with a 37mm lens, of course the image quality is much worst than a real wide angle lens, but does the converter produce more light like a focal reducer, theoretically ? if it does it would be a cheaper alternative to a real focal reducer and can be used on any camera for casual shooting in low light situation, far more cheaper than a fast wide angle lens.

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09-26-2016, 10:56 PM	#2
surfar Pentaxian Join Date: Jan 2015 Location: mid nth coast,nsw Photos: Gallery Posts: 6,141	Those things work, to an extent....they do widen the lens but they are not FR/speedboosters....dont expect great results.For simple jpegs they are ok.

09-27-2016, 06:46 AM	#3
THoog Loyal Site Supporter Join Date: Aug 2012 Location: North Carolina Photos: Gallery \| Albums Posts: 3,685	Originally posted by lotech does the converter produce more light like a focal reducer, theoretically ? No. While the lens with wide-angle converter might collect more light, it is from a wider scene. Assuming the scene is evenly lit, the average would be the same and the result would be no brighter. Also, because of light losses due to the conversion lens, you would probably come out worse overall. A focal reducer does not produce more light; instead, it works by refocusing the image circle projected by the lens to a smaller circle. The "extra" light is light the lens collects normally; it's just the part that usually falls outside the sensor area. The lens MUST be for a format that has a larger image circle than the sensor, such as a 35mm FF lens and a APS-C sensor. Also, because the focal reducer moves the lens closer to the sensor than its designed flange distance, the lens must be designed for a mount with a longer flange distance than the camera (you can't make a focal reducer for full-frame K-mount lenses on APS-C K-mount cameras, because the flange distance is the same).

09-27-2016, 07:07 AM	#4
lotech Pentaxian Join Date: Apr 2012 Posts: 1,312 Original Poster	You said right ! "because the focal reducer moves the lens closer to the sensor than its designed flange distance....." matters, there is no free lunch ! Originally posted by THoog No. While the lens with wide-angle converter might collect more light, it is from a wider scene. Assuming the scene is evenly lit, the average would be the same and the result would be no brighter. Also, because of light losses due to the conversion lens, you would probably come out worse overall. A focal reducer does not produce more light; instead, it works by refocusing the image circle projected by the lens to a smaller circle. The "extra" light is light the lens collects normally; it's just the part that usually falls outside the sensor area. The lens MUST be for a format that has a larger image circle than the sensor, such as a 35mm FF lens and a APS-C sensor. Also, because the focal reducer moves the lens closer to the sensor than its designed flange distance, the lens must be designed for a mount with a longer flange distance than the camera (you can't make a focal reducer for full-frame K-mount lenses on APS-C K-mount cameras, because the flange distance is the same).