Canon 28-300mm L vs. 75-300mm IS USM

[clos]

Okay so there really is no comparison. The 28-300mm is awesome! My first L series lens by the way, I digress...

I took some test shots comparing the two at 300mm. I found that the cheaper 75-300 zoomed or it's magnification was greater than the 28-300mm lens. I had to zoom out to 220mm on the 75-300mm to cover the same frame as the 28-300mm at the full 300mm.

Not complaining, just wondering why that is. Shouldn't both lenses cover the same frame at 300mm?

I checked the magnification specs, the 28-300mm is x .3 (at 300mm) and the 75-300mm is x .26 (at 300mm). Not that I know what that means but the numbers don't add up.

What gives?

-Clos

[roanjohn]

...........I'm stumped too.

Ro1

[John57]

I've had this as well - a few years ago I checked a Tamron 28-300 against my 75-300IS and found roughly the same thing.

I contacted Tamron and they said both lenses would be correct and cited something about the method of construction and way they focused which was different and would account for the fact the Tamron was at 300mm when the Canon was only at about 220mm.....

I sort of understood what they were getting at but never did understand exactly why...... All I needed to know was that the Tamron was in my view - as a result - a 28-220 and that particular copy a poor one at that - so I kept the 75-300IS !

[Jon]

How far away was your target? If the lenses' front nodal points aren't at the exact same distance from the subject, they'll exhibit slightly different magnifications. At anything less than approaching infinity, this may be apparent; at close range (within 5 ft.) it will.

[clos]

Jon,

My target was about ten feet away. I will try again tomorrow morning at a further distance.

Anybody else have any ideas?

Thanks!

-carlos

[Skip Souza]

I found the same to be true when comparing my Tamron 28-300 to the wife's Canon 70-300 IS. The Tamron seamed to be about 20mm 'short'. It may have something to do with the wider range of the 28-300 over the 70-300. I just wrote it off to the Tamron being somewhat 'optimistic' and put the Canon 70-300 DO at the top of my wish list.

[ron chappel]

Hyperzooms,like many cheap lenses all tend to be not as long or not as short as they claim.I'm abit surprised that the canon L is like that tho (to that extent!)
One thing i can say is that the 75-300 models do tend to be right at or near 300mm-one of the few genuine ones around.

The other aspect is that any internal focus lens changes focal length as you focus closer.(the 28-300is is a IF lens isn't it?I know the 75-300 isn't)
This means that the situation won't be as bad when both lenses are focused on a distant object...but they will differ more as you focus closer.

...and it doesn't surprise me that the 28-300isL is sharper at 300mm.A lovely lens :) I want one:(