Native Magnification?

collinj · 04-18-2017, 11:15 PM

Just purchased a 25mm extension tube to use with my K5 and SMC A 28mm f2.8 lens. Can anyone confirm that the 28mm lens has a native magnification of 0.13x and if so would therefore result in an approx. magnification of:

0.13x + (25mm/28mm) = 1.02x

in addition, does this magnification result in a 1:1 image ratio?

Thanks in advance.
Jeff

**seventhdr** · 04-19-2017, 04:10 AM - **1 Like**

According to the Asahi Pentax Auto Extension Tube Set instruction manual (06821) a 28mm lens has a magnification of 0.13. When combined with the following extensions tubes the magnifications are: Tube 1 (12mm) 0.56x; Tube 2 (19mm) 0.80x; Tube 3 (26mm) 1.05x.

So a 25mm extension tube would correctly give you 1.02x magnification. This is approximately a 1:1 image. The image captured on the sensor plane is 1.02 times the size of the object being photographed.

Regards

Chris

04-18-2017, 11:15 PM	#1
collinj New Member Join Date: Apr 2017 Posts: 3	Native Magnification? Just purchased a 25mm extension tube to use with my K5 and SMC A 28mm f2.8 lens. Can anyone confirm that the 28mm lens has a native magnification of 0.13x and if so would therefore result in an approx. magnification of: 0.13x + (25mm/28mm) = 1.02x in addition, does this magnification result in a 1:1 image ratio? Thanks in advance. Jeff

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04-19-2017, 04:10 AM - 1 Like	#2
seventhdr Site Supporter Join Date: Mar 2007 Location: Christchurch, New Zealand Photos: Gallery Posts: 1,439	According to the Asahi Pentax Auto Extension Tube Set instruction manual (06821) a 28mm lens has a magnification of 0.13. When combined with the following extensions tubes the magnifications are: Tube 1 (12mm) 0.56x; Tube 2 (19mm) 0.80x; Tube 3 (26mm) 1.05x. So a 25mm extension tube would correctly give you 1.02x magnification. This is approximately a 1:1 image. The image captured on the sensor plane is 1.02 times the size of the object being photographed. Regards Chris

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