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GB111

Mystery! a tale of two Tamron 90mm Macros

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Folks - I own a 25+ year old Tamron MF 90mm f2.8 macro. It works great, but not having AF was limiting when shooting moving objects. 


Since the new Tamron 90mm AF 90mm f2.8 (F017) got pretty good reviews, I purchased it about 2 months ago. I've found that its bokeh is different, so decided to check it against my MF version (which I still have).

 

Now this is strange - the focal lengths are supposed to be the same, but they're not. The following were shot at f 8.0 using a tripod. The newer version appears to be several degrees (at least) longer than the older version.  Comments or explanation?

 

Two images here. The first image is the MF older lens, and the second the newer AF version.

 

 

DSC_6715_Edit1_2000.jpg

DSC_6717_Edit1_2000.jpg

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3 hours ago, GB111 said:

Folks - I own a 25+ year old Tamron MF 90mm f2.8 macro. It works great, but not having AF was limiting when shooting moving objects. 


Since the new Tamron 90mm AF 90mm f2.8 (F017) got pretty good reviews, I purchased it about 2 months ago. I've found that its bokeh is different, so decided to check it against my MF version (which I still have).

 

Now this is strange - the focal lengths are supposed to be the same, but they're not. The following were shot at f 8.0 using a tripod. The newer version appears to be several degrees (at least) longer than the older version.  Comments or explanation?

 

Two images here. The first image is the MF older lens, and the second the newer AF version.

 

 

 

I don't know if it could be the effect of the old Adaptall system that Tamron use to adapt the lens. Just a funny thought ...?


A trace of light that survive a little further than the actual moment of flash.

photodanielm.blogspot.com

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Posted (edited)

In general, the designated focal length of a lens only represents the focal length when it is focused at infinity.  The lenses of modern optical designs (floting elements, rear focus, internal focus, etc.) will change their focal lengths as they are focused closer.

 

Thus there is no wonder if the focal length and the resulted angle-of-view (magnification factor) of two different versions of Tamron 90 macros when focused at the same close distances would be different.

Edited by Akira
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"The eye is blind if the mind is absent." - Confucius

http://www.flickr.com/photos/akiraphoto/

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I have the same thoughts as Akira.

 

Focus "breathing" is a common phenomenon with modern lenses.

 

 

6 hours ago, Akira said:

In general, the designated focal length of a lens only represents the focal length when it is focused at infinity.  The lenses of modern optical designs (floting elements, rear focus, internal focus, etc.) will change their focal lengths as they are focused closer.

 

Thus there is no wonder if the focal length and the resulted angle-of-view (magnification factor) of two different versions of Tamron 90 macros when focused at the same close distances would be different.

 

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Those are not good subjects to illustrate the point! Too dark!


Mike Gorman

 

Lumix G9 , GX8 - Leica 12, 15, 20, 25, 42.5 - 8-18, 12-60, 35-100, 45-175

 

 

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8 hours ago, Mike G said:

Those are not good subjects to illustrate the point! Too dark!

 

Mike, the images are good enough to show the difference of the size of the bottles!


"The eye is blind if the mind is absent." - Confucius

http://www.flickr.com/photos/akiraphoto/

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I've got one in between your two, an older AF version.  I must have had it over 20 years now and still use it quite a bit.  Currently looking into adaptors to use it on Fuji, so it may still have some more life in it yet.    I even think I know where the receipt for it is too - something to add to Mike's old receipt thread?

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Thks fellows. The theory that the different internal elements affect the focal length may be the answer. Note that the two images were shot using the same tripod, same distance to bottles. I will do another test where they are both at infinity and see what happens!


G

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Posted (edited)

Chris, Yeah, I know about that version. It was out there for a good 10-20 years. They only released the F017 about maybe 5 years ago.

 

Footnote: in several ways, the older version one I have is better designed. The actual glass is receded, hence protected from the sun and from anything touching it.  As a consequence, I don't believe I've ever had to clean the lens!  Also, you can have the hood stored on the lens and still use the manual focus, whereas you cannot with the F017 one (that seems like a big time design flaw, as macro photographers do go manual sometimes).  Here is a picture of the old one, you can see how the lens is receded (not sure this is the right version, but you get the idea). s-l1600.jpg

Edited by GB111

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The old AF model is also heavily recessed at the front too.  The focus ring is hard to reach with the hood reversed, you can just manage to get a finger to the edge as it is quite thick.

 

I  think that picture is a newer version than mine given the D designation visible on the side and the focus ring is a bit flatter.

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I just checked both lens at infinity: same thing. The newer F017 has a higher/farther focal length than the older lens. Strange. I wonder which is 'right?'  I will compare to my other zooms that cross 90mm and see.

 

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You’ll have to start photographing tape measures to calculate the actual focal length.  Labelled focal lengths are nominal only and actual lengths can vary as you have demonstrated.  I wonder if there is a website somewhere that lists actual focal lengths for various lenses?

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Posted (edited)

If I remember correctly, some (+/- 5%, I guess?) tolerance is allowed for the published specification of the focal length and the speed.  So, the actual focal length of a lens designated as 90mm can be between 85.5-94.5mm.

 

As for the macro lens, you may want to compare at the same "magnification" based on the scale on the lens barrel (or, more precisely, shoot a scale) and then compare the distances between the target and the sensor plane.

Edited by Akira

"The eye is blind if the mind is absent." - Confucius

http://www.flickr.com/photos/akiraphoto/

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