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Old Apr 23, 2006, 6:28 AM   #1
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Can someone please help me understand the difference between these two lenses? I own the first one and use if with my Canon Digital Rebel XT. Most of my photos are taken on our wooded lot, so they are in the shade, and most are taken of moving or perching birds. They don't come out as clear as I would like them. I have to take photos at ISO 400 or 800 many times and even at that speed, I can only get maybe 1/200 of a second at 7.1 or 8.

I'm a relative newbie and I was all ready to buy the more expensive lens because I thought it would provide clearer photos. Now several people have told me that it will cut down my DOP.

Can someone PLEASE explain this to me in real simple terms.

Thanks. Here is a sample shot: It was taken at ISO 800, 1/400 at 7.1


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Old Apr 23, 2006, 6:33 AM   #2
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IMO You don't need another lens...

(and you seem to have ample of light from the EV value)

-> Try sharpening in Photoshop :idea:

BTW - Did you take this picture through a window - or have a filter up front?


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Old Apr 23, 2006, 7:29 AM   #3
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I do take some through a window and do not know whether that particular one was taken through a window. However, most of the shots look the same.

BUT can you still explain to me the difference between the two lenses so that I can understand it?

thanks
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Old Apr 23, 2006, 7:33 AM   #4
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Two differents values:

1. The main difference is f/2.8 vs f/5.6 aperture

-> An f2.8 lens is two stop faster which is four time brighter than f/5.6 lens meaning you can quadruple your shutter speed for the sameamount of light- At the same time you are decreasing the DOF (Depht Of field) when the aperture becomes larger (the largest opening in the lens) ,i.e. more defocus in front and behind the main subject



2. The 2nd difference is the 200mm vs 300mm reach

-> A 300mm has a longer reach than a 200mm so you have to get closer to the subject more which might not be possible with the shorter (200mm) lens...

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Old Apr 23, 2006, 7:37 AM   #5
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I understand that. But can you explain how it will effect my shots. If that lens is f2.8, does that mean that my depth of field will be less on all of my shots.

If my current lens automatically shoots at 7.1 when it is at 1/200, will the new lens also shoot at 7.1 when it is at 1/200, or will it allow me to shoot faster at 7.1?


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Old Apr 23, 2006, 7:45 AM   #6
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Are you in Av or Tv - which mode?

Exposure is exposure (EV)it remains the same @ 7.1 at 1/200s and do not change with a lens :idea:

(provided the lighting change or how you force the camera to 1 way or another - like opening up theaperture which will then increase your shutter speed)
-> Inone case you can only open up to f/5.6 with your current lens whereas witha faster lens you can open 2-stop more to f/2.8... gaining two more stops in shutter speed!
However from the posted picture I don't see the need since I don't see any motion blurs, but a slight contrast reduction either from a window or filter up front due to the strong backlit situation- plus you can still lower the aperture on your current lens to get aslightly higher shutter speed than 1/200s

A 300 f/2.8 prime is mighty expensive - I shoot regularly with a Sigma 120-300 f/2.8 EXwhich actually costs more than the 70-200 f/2.8 ISif you need the reach...


-> f/2.8 @ 300mm 1/180s handheld fromthe aboveEX:






A shorter 200mm may force you into a 'digital' crop or the use of a TC which againwill affect the image quality (and lens speed)which is what you try to improve in the 1st place! :evil:
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Old Apr 23, 2006, 8:31 AM   #7
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Okay. I think that helps me understand things a little. I usually shoot in AV mode but I THOUGHT that I needed at least 7.1 to 8 aperature to get any sort of depth of field. But by setting it at that setting, I guess that only allows in a certain amount of light, no matter what lens I am using. If I change my aperature to 5.6, which is the largest setting this lens will go to at 300mm, then I will be letting more light in so I can increase the speed of the shot which might make PART of the photo clearer. At that point I need to get my birds to pose perfectly parallel to the lens (which that one was) and try to get the focus point on the eye. Correct?

I don't know why all of this is so difficult for me to understand. :?
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Old Apr 23, 2006, 8:32 AM   #8
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You got it!

-> Try USM (Photoshop) and a slight contrast increase - The image is OK
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Old Apr 23, 2006, 8:55 AM   #9
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Thanks a bunch. You saved me $1600 on the new lens!
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Old Apr 23, 2006, 6:40 PM   #10
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Backyarder.....
Try a few shots using the "action" setting on your camera...I use the 75-300mm with a 1.4x tele converter to shoot surfing shots...The action setting has a different in camera default setting than "program" or "AV" or even "auto"...I get better pictures using the action or sports setting instead of the av or program mode...At least I dont have as much photoshoping to do to them...
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