# Tamron [email protected] distance



## Plainsman (Dec 12, 2014)

Just done an image size check of the moon this morning at 600 and the same at 400 on both Canon 100-400 and the 400/5.6.

Image size for the Canons was the same but the Tamron was almost exactly 1.50 times bigger i.e. with the Tamron at distance (say beyond 100m) you get the full 600mm. Obviously this falls dramatically with multi element zooms as your operating distance gets down towards close focus.

Brian Carnahan quotes a figure of 570mm but does not say what the calibration distance was.


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## wyldeguy (Dec 12, 2014)

I'm not sure I fully understand your question. If both canons were the same and your tamron image was 1.5 times bigger that would make it 600mm (400x1.5=600). Are you asking if you are at the right distance? There isn't really any correct distance for this. It's purely a factor of the FOV/angle of view. Although there are some usually minor differences depending on how much focus breathing there is with a lens. I know some lenses it changes by upto like 10% from near to infinity. The manufacturer determines the tolerances that are acceptable.


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## neuroanatomist (Dec 12, 2014)

wyldeguy said:


> I know some lenses it changes by upto like 10% from near to infinity.



It can change by a lot more than that. The Canon EF-S 18-200mm is ~155mm at the long end near the MFD, a drop of >20%. The Nikon 70-200/2.8 VR II is around 135mm at the long end near the MFD, a drop of >30%. It's not just zooms, the Canon 100L Macro is ~68mm at 1:1, also a drop of >30%.


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## AlanF (Dec 12, 2014)

Bryan Carnathan did his measurement at one rather short distance. Other reviewers, including I think lens rentals gave it the full 600.


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## neuroanatomist (Dec 12, 2014)

AlanF said:


> Bryan Carnathan did his measurement at one rather short distance. Other reviewers, including I think lens rentals gave it the full 600.



If it's a 600mm lens, it's going to be 600mm when focused at infinity, with allowances for rounding. For example, a 600mm f/6.3 lens would have a 95.2 mm front element, so 95mm filters would be too small. Since the Tamron 150-600mm takes 95mm filters, it's either slightly shorter than 600mm (e.g. 595mm), slightly slower (e.g. f/6.42) or more likely both. 

I do find it useful to know what the apparent FoV is at 'normal' distances as opposed to infinity, to get an idea of how much the lens focus breathes. Compared to some other lenses (like the ones I listed above), the focus breathing on the Tamron 150-600 is minor.


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## Plainsman (Dec 12, 2014)

Roger Cicala at Lens Rentals reports that the Tamron 70-200 only gives 183mm at the long end which is pretty bad for a reputable lens maker!!


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## wyldeguy (Dec 15, 2014)

neuroanatomist said:


> Compared to some other lenses (like the ones I listed above), the focus breathing on the Tamron 150-600 is minor.



I have one and to be honest I didn't pay much attention but I'm glad you think it's minor. obviously since I didn't notice I'm of the same opinion.


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