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Old Apr 16, 2004, 2:05 PM   #1
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Default 70-200 f4L with convertor. How to figure magnification on DR

Is this how it works? On my 300D with a 1.6 crop factor I times that by 200 which makes this lens a 320mm then ad a 1.4 convertor and times it by the 320mm for a 448mm lens? If not how do you figure it?

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Old Apr 16, 2004, 3:05 PM   #2
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320 x 1.4 = 448

You got it!!!
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Old Apr 16, 2004, 3:10 PM   #3
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Well......I predict an arguement in the making. A 200 mm lens with a 1.4 TC attached effectively becomes a 280mm lens and will display the parameters of a like 280mm lens. There is no further magnification or benifet to be had using a DSLR. There is however a 1.6 crop factor due to the smaller sensor. The result would appear to have been a 448mm lens but in reality it is the same size image meerly taking up more of the smaller sensor there by appearing to be larger. They are in fact the same size, light through a lens, can't change that or alter it without additional glass as in the case of the TC.
Go ahead Eric, I'm ready for the rebuttal!
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Old Apr 16, 2004, 3:18 PM   #4
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I don't get it! What would be the point of this ? The same amount of light will hit a smaller area - and so what. That's just an advantage for tele lenses as the aperture is the same.
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Old Apr 16, 2004, 3:29 PM   #5
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You are correct it is the same light and infact the same image that will hit the film or sensor, that is the physics of the focal length. The only difference is that the sensor is smaller than the film by the 1.6 crop factor so as it takes up more of the sensor people think that this is a magnification of the image but it is not as the focal length is the same in both. Both images are the same size.
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Old Apr 16, 2004, 10:17 PM   #6
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HMMMM... Now im really confused. I was hoping that that it was the way I explained because i need the reach.

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Old Apr 16, 2004, 10:37 PM   #7
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Hmmmm........Everyone here is involved in the quest for more reach. The problem is that there is no magic elixur to make a lens longer. The only remedy is longer glass and that takes money.
As I stated when you view your images in the computer it will appear as though they had been taken with a 448mm lens but the reality of it is that the image will be that which was taken with a 280mm lens and displayed on a smaller canvas. So if this suits your needs then that is wonderful. It may give you the appearance you wish to see but at least you'll know the truth.
Hey...maybe its magic just like the right side rearview mirror on your car! Objects may appear closer!
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Old Apr 17, 2004, 12:31 AM   #8
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Tom I have not bought the lens yet. I was trying to determine if this lens would have the reach i need with the convertor. I figured a 200mm then a convertor might be a very nice combination. But if it comes up short on the long end I might be better off with the sigma 50-500mm. The 200 f4l I think would have been a nice versatile pkg. I see you have the bigma do you think I might be better off with that lens even tho its slower. Also thx for all your imput.

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Old Apr 17, 2004, 12:38 AM   #9
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I do agree with you, but It really doesn't matter, does it ? The result will be the same - or very near! Especially to telelenses. Wide-angles will cause some optical visible problem. That's another story.

The megapixels are going up and up. It will not stop, as it has become buyers parameter for quality (unfortunately). And I think that most digital photos still stay on the PC and not in a photoalbum. With plasmascreens and such we will be back to viewing on screens (remember dia-positives...) and therefore the in-camera-cropping will not be that important. The MP will make you zoom and crop, and the quality of your glass is what's really matters. As it is today!


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Hey...maybe its magic just like the right side rearview mirror on your car! Objects may appear closer!
:lol: :lol: :lol:
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Old Apr 17, 2004, 1:20 AM   #10
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We should get on the same page here.
Is the Sigma 50-500 a slow lens?....YES, however is it slower than a 70-200 f4 with a TC attached?....NO, and it has a longer focal length. Even if you put a 2X TC on the 70-200 f4 it falls short in focal length and will not auto focus. Now is the 50-500 slow? I guess it depends on how you look at it. Will it work in a dark Gym or at a predawn shoot?....No, best tool for that job is a 70-200 f2.8. This is the point we were trying to make in the other thread. I'm a user of both of these lenses because they are very different tools but the combination of them allows me to shoot the varied objects that I enjoy. I could not choose just one and I don't regret the purchase of either.
I hope that I may have given you some items to consider before you make a choice but no one can help you much beyond that. Each of us must weigh our needs and try to get a good balance in the camera bag. Just don't skimp, those choices always come back to haunt you time and again. Good luck & good shooting.
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