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Why 300mm ain't the same on different lenses?
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Feb 20, 2017 06:57:01   #
waegwan Loc: Mae Won Li
 
Yea I know the door handle ain't interesting and the focus could be better but that ain't the point. Point is I took both photos from the same point on a tripod approximately 2.3 meters from the subject (door handle) with the same camera with different lenses one a Tamron 28-300 and the other an old Canon 100-300 both set at 300mm. I had to move the camera nearly 50% closer with the Tamron lens to get the same frame fill as with the Canon. Yea I know I could look on the Internet and find out why they aren't the same but I thought maybe some folks here would like to see the difference. Why does this happen?

Canon 100-300 at 300
Canon 100-300 at 300...
(Download)

Tamron 28-300 at 300
Tamron 28-300 at 300...
(Download)

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Feb 20, 2017 07:02:52   #
Erv Loc: Medina Ohio
 
Wow I didn't think I would see that much difference!! This will be very interesting to see if some of the folks know. And now I have to try this with my lenses.:)

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Feb 20, 2017 07:03:45   #
Ctrclckws
 
Short answer, design compromises.

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Feb 20, 2017 07:06:53   #
Tom DePuy Loc: Waxhaw, N.C.
 
My guess would be focal length...

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Feb 20, 2017 07:06:57   #
Ol' Frank Loc: Orlando,
 
This will be interesting to hear if others are finding the same. My friend Gregoryd45 gets more and better images with his 400 prime than most anyone else with longer focal length. Gotta be some4thing else.

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Feb 20, 2017 07:14:07   #
jerryc41 Loc: Catskill Mts of NY
 
waegwan wrote:
Yea I know the door handle ain't interesting and the focus could be better but that ain't the point. Point is I took both photos from the same point on a tripod approximately 2.3 meters from the subject (door handle) with the same camera with different lenses one a Tamron 28-300 and the other an old Canon 100-300 both set at 300mm. I had to move the camera nearly 50% closer with the Tamron lens to get the same frame fill as with the Canon. Yea I know I could look on the Internet and find out why they aren't the same but I thought maybe some folks here would like to see the difference. Why does this happen?
Yea I know the door handle ain't interesting and t... (show quote)


Interesting comparison. This has come up here before. If you compared a Canon 28-300 to the Tamron, I bet there wouldn't have been as much of a difference.

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Feb 20, 2017 07:19:01   #
rdubreuil Loc: Dummer, NH USA
 
The term generally used to describe this is known as "focus breathing" or "lens breathing". It's a variation in angle of view between the two lenses when zooming/focusing. Higher quality lenses tend to control this effect much better than lower quality lenses, hence why your Canon looks much better than your Tamron. There are many articles on the web about this, just do a general search for focus breathing, I hope this helped you out.

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Feb 20, 2017 07:28:58   #
Picdude Loc: Ohio
 
It might help to know specific models of lenses to answer your question, but I do have one question for you. When you say 'old Canon 100-300' are you talking as in old 35mm lens or old DSLR lens?

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Feb 20, 2017 07:31:16   #
travisdeland Loc: deland, FL
 
waegwan wrote:
Yea I know the door handle ain't interesting and the focus could be better but that ain't the point. Point is I took both photos from the same point on a tripod approximately 2.3 meters from the subject (door handle) with the same camera with different lenses one a Tamron 28-300 and the other an old Canon 100-300 both set at 300mm. I had to move the camera nearly 50% closer with the Tamron lens to get the same frame fill as with the Canon. Yea I know I could look on the Internet and find out why they aren't the same but I thought maybe some folks here would like to see the difference. Why does this happen?
Yea I know the door handle ain't interesting and t... (show quote)


Is one lens designed for crop sensor, and the other for full frame?-THAT would make a considerable difference.

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Feb 20, 2017 07:33:30   #
waegwan Loc: Mae Won Li
 
Erv wrote:
Wow I didn't think I would see that much difference!! This will be very interesting to see if some of the folks know. And now I have to try this with my lenses.:)


The Canon is about 2 inches longer than the Tamron when both are extended to 300mm so initially I thought it was the 2 inch difference so I started moving the tripod closer to the door and found out I had to get it more than one meter closer.

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Feb 20, 2017 07:34:18   #
waegwan Loc: Mae Won Li
 
Tom DePuy wrote:
My guess would be focal length...


Both were set to 300mm, check the EXIF

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Feb 20, 2017 07:35:39   #
Apaflo Loc: Anchorage, Alaska
 
waegwan wrote:
Yea I know the door handle ain't interesting and the focus could be better but that ain't the point. Point is I took both photos from the same point on a tripod approximately 2.3 meters from the subject (door handle) with the same camera with different lenses one a Tamron 28-300 and the other an old Canon 100-300 both set at 300mm. I had to move the camera nearly 50% closer with the Tamron lens to get the same frame fill as with the Canon. Yea I know I could look on the Internet and find out why they aren't the same but I thought maybe some folks here would like to see the difference. Why does this happen?
Yea I know the door handle ain't interesting and t... (show quote)

Not at all surprising!

The marked focal length of a lens is defined when it is focused at infinity. So you can expect that those two lenses would produce a nearly identical field of view of an object significantly distant. A boat out in a harbor, a mountain, and the moon are objects that should be the same sizes.

However, there are two significantly different ways to design the focus mechanism for a lens (one that is relatively new and now almost universal, but was not used on older lenses), and one characteristic of what is called "Internal Focus" is called focus breathing where the focal length decreases at relatively short focusing distances.

The older focus method simply moved the entire lens farther from the sensor to focus closer. With Internal Focus (IF) the entire lens stays in one place and one or more groups of elements move in relation to the other elements. This has many advantages, primarily being that of sharper images at close focusing distance.

It may be that the older Canon lens does not use IF. It may be that it does but its design results in much less focus breathing. An example is that of the many current 70-200mm f/2.8 lenses the actual maximum focal length when focused at less than 10 feet varies by brand from perhaps 125mm to 165mm. We might well expect a great deal more focus breathing in a consumer grade 10x zoom than a professional 3x zoom!

Regardless, it is useful to be aware of, but for most general photography is not a problem. And image quality is better due to the IF design.

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Feb 20, 2017 07:36:17   #
waegwan Loc: Mae Won Li
 
jerryc41 wrote:
Interesting comparison. This has come up here before. If you compared a Canon 28-300 to the Tamron, I bet there wouldn't have been as much of a difference.


Gee thanks, now I fee a GAS attack coming on :b

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Feb 20, 2017 07:42:06   #
waegwan Loc: Mae Won Li
 
Picdude wrote:
It might help to know specific models of lenses to answer your question, but I do have one question for you. When you say 'old Canon 100-300' are you talking as in old 35mm lens or old DSLR lens?


The Canon 100-300 is a discontinued EF model and one of the earliest EF lenses, that is why I say old. Condition wise it works great and I really like it, it is Canon 100-300 f/5.6L. the other lens is Tamron 28-300 Di VC PZD also in excellent condition.

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Feb 20, 2017 07:47:48   #
waegwan Loc: Mae Won Li
 
Apaflo wrote:
Not at all surprising!

The marked focal length of a lens is defined when it is focused at infinity. So you can expect that those two lenses would produce a nearly identical field of view of an object significantly distant. A boat out in a harbor, a mountain, and the moon are objects that should be the same sizes.

However, there are two significantly different ways to design the focus mechanism for a lens (one that is relatively new and now almost universal, but was not used on older lenses), and one characteristic of what is called "Internal Focus" is called focus breathing where the focal length decreases at relatively short focusing distances.

The older focus method simply moved the entire lens farther from the sensor to focus closer. With Internal Focus (IF) the entire lens stays in one place and one or more groups of elements move in relation to the other elements. This has many advantages, primarily being that of sharper images at close focusing distance.

It may be that the older Canon lens does not use IF. It may be that it does but its design results in much less focus breathing. An example is that of the many current 70-200mm f/2.8 lenses the actual maximum focal length when focused at less than 10 feet varies by brand from perhaps 125mm to 165mm. We might well expect a great deal more focus breathing in a consumer grade 10x zoom than a professional 3x zoom!

Regardless, it is useful to be aware of, but for most general photography is not a problem. And image quality is better due to the IF design.
Not at all surprising! br br The marked focal len... (show quote)


That makes sense, thanks :) I'll do some infinity shots tomorrow or the next day when I get a chance and post them.

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