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08-10-2011, 02:47 PM   #46
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My test results: I took pictures with my Nikon AF-S 18-200VR and Pentax DA 18-135WR set at 70mm focussed at infinity. The subject measured almost the same in size in both the photographs. I repeated the test with both lenses set at 135mm and noticed the same difference, that is - almost none, with respect to size of the subject recorded in the photographs. I conclude that this proves the magnification of both lenses remain equal at the same focal lengths, when focussed at infinity.

08-10-2011, 03:26 PM   #47
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QuoteOriginally posted by debmalya Quote
My test results: I took pictures with my Nikon AF-S 18-200VR and Pentax DA 18-135WR set at 70mm focussed at infinity. The subject measured almost the same in size in both the photographs. I repeated the test with both lenses set at 135mm and noticed the same difference, that is - almost none, with respect to size of the subject recorded in the photographs. I conclude that this proves the magnification of both lenses remain equal at the same focal lengths, when focussed at infinity.
If you can find the time it would be helpful if you would check them at the same focal length, closest focusing distance for which you can have the same distance for both lenses..

Thanks
Dave
08-10-2011, 05:07 PM   #48
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QuoteOriginally posted by newarts Quote
If you can find the time it would be helpful if you would check them at the same focal length, closest focusing distance for which you can have the same distance for both lenses..

Thanks
Dave
Sure. I will post the results of my observation after I try that out. If I understand you correctly, you want me to set both my lenses at same focal length (say 70mm - since this # is marked on both my lenses), focus on a subject placed as close as possible to the lens with the greatest minimum focus distance (say 12"). Then try the same shot with the other lens with the subject at the same distance from that lens (eventhough it is capable of a lesser focussing distance). Measure the size of the subject on the recorded picture and report the results. Correct me if I misunderstood any step.
08-10-2011, 05:41 PM   #49
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QuoteOriginally posted by debmalya Quote
Sure. I will post the results of my observation after I try that out. If I understand you correctly, you want me to set both my lenses at same focal length (say 70mm - since this # is marked on both my lenses), focus on a subject placed as close as possible to the lens with the greatest minimum focus distance (say 12"). Then try the same shot with the other lens with the subject at the same distance from that lens (eventhough it is capable of a lesser focussing distance). Measure the size of the subject on the recorded picture and report the results. Correct me if I misunderstood any step.
That's right. If the two lenses are at the same distance from the subject (actually the camera's tripod hole should probably be the same distance from the subject.) Then there will be little to argue about in comparing results to predictions; besides the info might be useful to you, especially if you also take a photo at the shortest possible distance with the shorter distance lens.

A collection of raw data about distance and apparent ruler size (like take a photo of a yardstick) would also be very useful.

Whatever you have time for will help.

Thanks for responding!

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