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Tamron zoom not what it says.

  • 17-04-2021 4:36pm
    #1
    cortinaG
    Registered Users Posts: 113 ✭✭


    I recently had the use of a tamron 18-270 mm zoom lens, I was thinking of buying it to replace my 18-135 and 55-250 mm lenses on a canon 7dmkii.
    Figured it would save changing lenses plus the extra 15 mm would be a nice little extra.
    The problem was, taken on a tripod, 270 mm on the tamron was only equivalent to approx 190mm on the canon 55-250.
    It was a little wider at 18mm than 18 mm on the canon 18-135.
    I found it very strange, as I said photo samples were taken on a tripod.
    Why would this be?
    Thanks, G.


Comments

  • #2
    magicbastarder
    Moderators, Category Moderators, Arts Moderators, Sports Moderators Posts: 48,234 CMod ✭✭✭✭magicbastarder


    it's not a DX specific lens issue maybe?
    i.e. one of the lenses might be DX and the camera has auto-cropped, so it appears to be a different effective focal length.


  • #3
    cortinaG
    Registered Users Posts: 113 ✭✭cortinaG


    magicbastarder wrote: »
    it's not a DX specific lens issue maybe?
    i.e. one of the lenses might be DX and the camera has auto-cropped, so it appears to be a different effective focal length.

    I dont think so as we both use Canon crop sensor cameras and both lenses are aps-c/dx.


  • #4
    NEW WAVE
    Registered Users Posts: 770 ✭✭✭NEW WAVE


    Just done a Google and came up with this:
    https://www.youtube.com/watch?v=YZb9Un9f7Qk Its to do with repairing this lens. However the guy on the video seems to know what he's doing and it appears to be a professional service at: service@digi-service.eu why dont you contact him regarding advice for this problem.


  • #5
    DaireQuinlan
    Registered Users Posts: 6,675 ✭✭✭DaireQuinlan


    So you compared two shots taken with the _same camera_ with the canon 55-250 and tamron 18-270 mm ?

    Or did you compare shots from the 18->270 mounted on one camera, compared with the 55->250 mounted on your camera ?

    One thing that springs to mind is that old pro Canons used to have a different crop factor, right ? the 1D had x1.3, whereas the 7D has their (now) standard x1.6. If you took something on the 1D at 270mm it would look wider than the equivalent on the 7D.


  • #6
    cortinaG
    Registered Users Posts: 113 ✭✭cortinaG


    DaireQuinlan wrote: »
    So you compared two shots taken with the _same camera_ with the canon 55-250 and tamron 18-270 mm ?

    Or did you compare shots from the 18->270 mounted on one camera, compared with the 55->250 mounted on your camera ?

    One thing that springs to mind is that old pro Canons used to have a different crop factor, right ? the 1D had x1.3, whereas the 7D has their (now) standard x1.6. If you took something on the 1D at 270mm it would look wider than the equivalent on the 7D.

    Both sets of shots taken on my 7d mkii Daire,
    while tripod mounted, so no movement involved.
    The 55-250 IS a slightly longer lens so unless that 1 or 2 inches made images appear more zoomed in I dont know.
    There are various scientific explanations online which I dont understand, all I do know is I would expect a 270mm lens to get closer to, let's say, a deer in a field, than190 equivalent on my 55-250.


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  • #7
    ED E
    Registered Users Posts: 36,163 ✭✭✭✭ED E


    Can you post the exact lenses? Tamron have two units the B003 and the B008 that could be what you're talking about.


    Also are you using mount adapters?


  • #8
    cortinaG
    Registered Users Posts: 113 ✭✭cortinaG


    ED E wrote: »
    Can you post the exact lenses? Tamron have two units the B003 and the B008 that could be what you're talking about.


    Also are you using mount adapters?

    No mount adaptors and I just had the Tamron for a few days to try out, dont have it anymore.


  • #9
    athlone573
    Registered Users Posts: 726 ✭✭✭athlone573


    Possible explanations:

    It's really an 18-200 and you are mistaken /
    It's faulty and cannot zoom in all the way /
    You are testing it on a full frame body.

    There is often a bit of leeway in descriptions so that a lens described as 400mm might actually be around 10% less, but not to the extent you're describing.

    To diagnose, would be helpful to see two shots of the same distant object (tree, roadsign) with EXIF info embedded.


  • #10
    cortinaG
    Registered Users Posts: 113 ✭✭cortinaG


    NO, I am not mistaken, and the 7D MKii is not a full frame body.

    [IMG][/img]51131744828_6a5e50686f_c.jpgDM7A2697B2 by Gerry O'Donnell, on Flickr

    [IMG]http://[/img]51132309924_ffc4c5273b_c.jpgDM7A2696B by Gerry O'Donnell, on Flickr

    [IMG]http://[/img]51131744803_38b6452405_c.jpgDM7A2697BM by Gerry O'Donnell, on Flickr

    [IMG]http://[/img]51131752308_6451e5ee3d_c.jpgDM7A2682B2 by Gerry O'Donnell, on Flickr

    [IMG]http://[/img]51132316574_9873c02a0f_c.jpgDM7A2682B by Gerry O'Donnell, on Flickr

    [IMG]http://[/img]51132316544_f0e19df115_c.jpgDM7A2692B by Gerry O'Donnell, on Flickr

    [IMG]http://[/img]51131541096_0abb49cd79_c.jpgDM7A2693B2 by Gerry O'Donnell, on Flickr


  • #11
    DaireQuinlan
    Registered Users Posts: 6,675 ✭✭✭DaireQuinlan


    Ah, all your demo shots are focused quite closely. What are they like focused at infinity ?
    Manufacturers generally mark focal distances at infinity focus, so depending on the lens design they could vary quite a lot as you focus closer.

    I think if you focus both to infinity you'll likely see that the Tamron is longer than the Canon.


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  • #12
    cortinaG
    Registered Users Posts: 113 ✭✭cortinaG


    DaireQuinlan wrote: »
    Ah, all your demo shots are focused quite closely. What are they like focused at infinity ?
    Manufacturers generally mark focal distances at infinity focus, so depending on the lens design they could vary quite a lot as you focus closer.

    I think if you focus both to infinity you'll likely see that the Tamron is longer than the Canon.

    Do you mean a full landscape shot at 270mm? I realise the number plate ones were very close but both the plant and the flowers were quite a distance away, seem closer because of full zoom, is that not the whole idea of a zoom lens?? :-)


  • #13
    DaireQuinlan
    Registered Users Posts: 6,675 ✭✭✭DaireQuinlan


    Sure, but you have to bear in mind that what the manufacturer refers to as 'focal length' is only applicable at infinity. Were you to compare both lenses, with both focused to infinity, you'd probably find that the tamron is indeed slightly longer than the Canon. As you focus from infinity, the FOV will change. It happens both with primes, and with zooms, probably more so and more unpredictably with zooms as they're much more complicated designs.

    Look up 'Focus breathing' for some reading. Really high quality cinema lenses, for example, try to minimize focus breathing as much as possible so that the composition of the scene doesn't change as the focus is racked in and out.


  • #14
    DaireQuinlan
    Registered Users Posts: 6,675 ✭✭✭DaireQuinlan


    Actually, just idly googling, is this the same lens https://radojuva.com/en/2017/06/tamron-18-270-vc-pzd-b008/#af ?

    They note in the review that ...
    The lens has a very pronounced 'Focus Breathing' effect (changing the viewing angle during focusing). When focusing on MDF at 270 mm focal length, effective focal length equals approximately 150-200 mm. This can be frustrating when the telephoto starts to 'shrink' when shooting at close focusing distances. Many telephoto lenses that do not use internal focusing work the other way around - they decrease the angle of view (increase the effective focal length) while focusing towards the MDF, which is much more convenient for most situations.


  • #15
    ED E
    Registered Users Posts: 36,163 ✭✭✭✭ED E


    The Tamron broke records on release so it's not shocking that they had to bodge it a bit like that.


  • #16
    cortinaG
    Registered Users Posts: 113 ✭✭cortinaG


    DaireQuinlan wrote: »
    Actually, just idly googling, is this the same lens https://radojuva.com/en/2017/06/tamron-18-270-vc-pzd-b008/#af ?

    They note in the review that ...

    Daire, thanks for all the insight into the workings of the lens, it was disappointing for me, I'll just have to keep changing lenses for another while :-) On another note, the images from it were very soft in comparison to the canon, if you zoom into the yellow plant photos in particular I would say it's not even in focus.
    Cheers, G.


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