07-22-2010, 04:00 PM
[quote name='wim' date='22 July 2010 - 04:44 PM' timestamp='1279813441' post='1241']
Any lens at 1:1 loses two stops of light, no matter what the FL is. That is a given, BTW. It is exactly that, no more, no less.[/quote]
So why does my test not corroborating this?
[quote name='wim' date='22 July 2010 - 04:44 PM' timestamp='1279813441' post='1241']
First of all, the Canon has IF and shortens the FL at 1:1 to approximately 70 mm, no longer 100 mm IOW, and this is a contimous change from infinity to 1:1. This means it captures a lot more of the environmental light in the background than the Mamiya does, and that light may include a larger chunk of bright(er) areas. Spot metering with the 7D is still 4 percent or thereabouts.[/quote]
1. 7D spot metering is 2.3%.
2. The link mentions nothing about lens design (IF or non-IF) so I conclude it is not a factor.
[quote name='wim' date='22 July 2010 - 04:44 PM' timestamp='1279813441' post='1241']
Secondly, the Mamiya must be closed down manually for metering, while the Canon meters wide open. Here alone you will likely get a difference.
Thirdly metering with a manual lens, especially when stopping down, is not as accurate as with a EF lens. This may not be a large influence, if at all in case of using the lens wide open, however.[/quote]
Exactly. The Mamiya was metered wide open. I did not change the aperure in it.
[quote name='wim' date='22 July 2010 - 04:44 PM' timestamp='1279813441' post='1241']
Then there is the issue of daylight and testign in an essentially non-controlled environemnt. This needs to be tested a bit more rigorously IMO, with a fixed amount of light rather than with day light, IOW, indoors with an evenly illuminated wall either with flash or some fixed lighting.[/quote]
It took me a minute or so to change lenses and meter. Light levels did not change. I was so amazed that I did it again several minutes later. Same results.
Any lens at 1:1 loses two stops of light, no matter what the FL is. That is a given, BTW. It is exactly that, no more, no less.[/quote]
So why does my test not corroborating this?
[quote name='wim' date='22 July 2010 - 04:44 PM' timestamp='1279813441' post='1241']
First of all, the Canon has IF and shortens the FL at 1:1 to approximately 70 mm, no longer 100 mm IOW, and this is a contimous change from infinity to 1:1. This means it captures a lot more of the environmental light in the background than the Mamiya does, and that light may include a larger chunk of bright(er) areas. Spot metering with the 7D is still 4 percent or thereabouts.[/quote]
1. 7D spot metering is 2.3%.
2. The link mentions nothing about lens design (IF or non-IF) so I conclude it is not a factor.
[quote name='wim' date='22 July 2010 - 04:44 PM' timestamp='1279813441' post='1241']
Secondly, the Mamiya must be closed down manually for metering, while the Canon meters wide open. Here alone you will likely get a difference.
Thirdly metering with a manual lens, especially when stopping down, is not as accurate as with a EF lens. This may not be a large influence, if at all in case of using the lens wide open, however.[/quote]
Exactly. The Mamiya was metered wide open. I did not change the aperure in it.
[quote name='wim' date='22 July 2010 - 04:44 PM' timestamp='1279813441' post='1241']
Then there is the issue of daylight and testign in an essentially non-controlled environemnt. This needs to be tested a bit more rigorously IMO, with a fixed amount of light rather than with day light, IOW, indoors with an evenly illuminated wall either with flash or some fixed lighting.[/quote]
It took me a minute or so to change lenses and meter. Light levels did not change. I was so amazed that I did it again several minutes later. Same results.