Lens focal length comparison

[teddest]

I have stupid question... But first, let me give an introduction to my question.

I have 2 lens. One is a EF 28-135mm kit lens, the other is EF 70-200mm f/4L USM. Prior to me purchasing a brand new 70-200mm for myself, I borrowed one from a friend and immediately fell in love with it. So when mine arrived, I jumped in the car and went looking for shots… When I came home and brought the images up, I was extremely disappointed. They weren’t the tack sharp images I was expecting.

My stupid question is. Is 135mm, 135mm? The image below was taken using a tripod. All I did was switch the lenses and set the focal length to 135mm. Notice the one on the right looks like I zoomed in father than the one on the left… One of the reasons I did this is because I feel that I received a lemon… I have included some samples also to show the comparison between my friends 70-200 f/4L and my 70-200 f/4L, as well as my 50mm f/1.8 II for the sake of showing how sharp my 70-200 f/4L ISN'T.

Any assistance would be greatly appreciated.


both.jpg
Left image:
1/250 sec at f / 8.0,
ISO 200,
135 mm (EF28-135mm f/3.5-5.6 IS USM) IS was turned off
Flash Did fire

Right image:
1/250 sec at f / 8.0,
ISO 200,
135 mm (EF70-200mm f/4L USM)
Flash Did fire


FredzGlass.jpg
My Friends 70-200mm f/4L:
1/1250 sec at f / 4.0,
ISO 100, 131 mm (EF70-200mm f/4L USM)
Flash Did not fire

my70-200.jpg
My 70-200mm f/4L:
1/250 sec at f / 8.0,
ISO 100,
200 mm (EF70-200mm f/4L USM)
Flash Did not fire

pie.jpg
Finally, my 50mm:
1/500 sec at f / 2.8, ISO 100, 50 mm (EF50mm f/1.8 II)
Flash Did not fire

[OsmosisStudios]

First two images: there is such a thing as focal length breathing, but not that bad. There's no way both images were shot from the same position at 135mm. Millimeters are millimeters: 135 is 135.

Next two images: these are VASTLY different images that could cause vastly different results. In the first case, the vehicles are A) big, B) motionless. The second is of an object that is A) small and B) likely moving. Apples and Oranges.

[Aegea]

If those two images really were taken at the same distance, something is very wrong with one of the lenses - one image is almost 2x the other. Manufacturers are sometimes optimistic in specifying the focal length of their lenses but not to that extent.

You can make a rough determination of the actual focal length by photographing an object of known size (e.g., a meterstick) at a known distance from the lens, and determining the size of the image on the sensor. Then simple ratios give you the focal length:

Focal_length = (Image_size/object_size)*distance

Might be worth doing for these two lenses.

[kuvahmagh]

Can I just ask, these are done with the same body right, you aren't using a Full Frame (or APS-H) for one and a Crop Body (APS-C) for the other, I know it shouldn't make that much difference but it wouldn't help.

[teddest]

Thanks everyone!!! To answer a few questions. Yes all images were taken with a 50d. I also forgot to mention that i took the first photo from 54 inches away from the object to the front of the lens, and then ~54 inches from the sensor. Still, the difference was blatantly obvious. Also; as for the sample from my lens, yes the butterfly was moving, but nothing else in the frame was, it was calm and no breeze. The reason why I used that images is because I think the bokeh is a little much for f/8. All the other images are between are f/2.8 and f/4. I’m going to send it in to the Canon service facility. Just wanted to make sure I wasn’t crazy. Again, thank you everyone!!!