Effective zoom/magnification
May 20, 2018 14:28:17 #
Hello all! Although I joined this forum a few months ago, this is my first post. I am excited to be here; the knowledge and experience represented here are vast. About me: I made the leap from point-and-shoot (SX50) to DSLR (t6i) about 2 years ago and have taken thousands of photos with the kit lens (Canon EFS 18-55 IS). I also purchased a Canon EFS 55-250 IS, and continued to shoot everything I saw. I learn everyday yet how much I still have to learn and this forum is a great resource for me. Thank you!
My Q: I have read favorable reviews of the Tamron 18-400 Di II VC HLD, so I recently bought a gently used one. I am confused by the effective zoom presented by this lens. Below are hand held shots taken of the same subject at the same distance; one with the Canon 55-250 @ 250mm, and the other with the Tamron 18-400 @ 400mm. Why am I not seeing the proportional zoom increase (400mm/250mm) in the photo taken with the Tamron?
My Q: I have read favorable reviews of the Tamron 18-400 Di II VC HLD, so I recently bought a gently used one. I am confused by the effective zoom presented by this lens. Below are hand held shots taken of the same subject at the same distance; one with the Canon 55-250 @ 250mm, and the other with the Tamron 18-400 @ 400mm. Why am I not seeing the proportional zoom increase (400mm/250mm) in the photo taken with the Tamron?
May 20, 2018 15:06:25 #
That's a helluva good question, and I have no clue so will stay on your thread to find out why from the pros.
May 20, 2018 15:11:00 #
Is there any way that is the same picture twice?
For handheld after changing lenses the framing appears identical.
For handheld after changing lenses the framing appears identical.
May 20, 2018 15:13:13 #
May 20, 2018 15:20:08 #
You shot the 2 shots at very close distance and thus I think the Tamron lens just have a lot of focus breathing.
May 20, 2018 15:42:10 #
twowindsbear wrote:
Please list your exact step by step procedure for making these 2 photos.
I stood next to my couch and took one photo of my keys with one lens. Switched lenses, re-focused on the same focus point (center of the chrome connecting rod) and acquired the second photo. The two shots do look like the same photo, but they are not. That’s why I included cell phone photos of the info for each photo.
May 20, 2018 15:53:39 #
StarGazerBob wrote:
I stood next to my couch and took one photo of my keys with one lens. Switched lenses, re-focused on the same focus point (center of the chrome connecting rod) and acquired the second photo. The two shots do look like the same photo, but they are not. That’s why I included cell phone photos of the info for each photo.
That is what I said. The Tamron just has too much focus breathing so that its focal length when zoomed to 400mm at close distance is less than 250mm. I am sure the Canon lens also has somewhat focus breathing but much less. Many lenses when focused at close distance shorten their focal length by a whole lot. That is call focus breathing. If you do another test with a far away subject (100ft or more) you will see that Tamron has more magnification.
May 20, 2018 15:55:13 #
Yes, it is focus breathing typical of larger zoom range lenses. The 18-400 will ONLY be an effective 400mm's at infinity. At all closer distances it will be something LESS than 400mm. The 55-250 will have it also - maybe just not as bad.
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May 20, 2018 15:55:23 #
May 20, 2018 15:56:39 #
BebuLamar wrote:
You shot the 2 shots at very close distance and thus I think the Tamron lens just have a lot of focus breathing.
You may be onto something, BebuLamar. The shots below were taken at approximately 30 and 70 feet away, respectively, with each lens. It still appears that the proportional magnification is less that I would have expected but it is greater at these longer distances. Thanks for the insight.
May 20, 2018 16:01:59 #
May 20, 2018 16:24:23 #
StarGazerBob wrote:
You may be onto something, BebuLamar. The shots below were taken at approximately 30 and 70 feet away, respectively, with each lens. It still appears that the proportional magnification is less that I would have expected but it is greater at these longer distances. Thanks for the insight.
What magnification were you expecting?
I don't know if your DSLR is a 'crop' or 'full frame,' but with a 35mm format camera, your 250mm lens will have roughly a 5x magnification, compared to a 50mm lens and the 400mm lens will have roughly a 8x magnification.
Try this: set up your camera, on a tripod, at a fairly long distance - maybe 50' - from an object sized to fill the frame of your camera with the 400mm lens & make a few pix. Then, swap the 400 for the 250 & shoot the same image at the same distance & compare the sizes of the object in the different images. Finally, move your camera & 250mm lens toward the object until the object fills the frame, is the same apparent size in the view finder, as the image of the 400mm lens & compare the distances of the 2 camera positions.
Good luck!
May 20, 2018 16:33:53 #
twowindsbear wrote:
What magnification were you expecting? br br I do... (show quote)
I was expecting a 1.6x (400mm/250mm) size differential between the two lenses at their respective fully-extended focal lengths. The lens breathing phenomenon appears to be the answer which best explains (on nearby subjects) why I am not seeing the expected proportional magnification.
May 20, 2018 22:25:33 #
May 21, 2018 05:53:28 #
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