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09-12-2013, 10:10 AM   #31
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QuoteOriginally posted by ripit Quote
I'm pretty sure the promaster is a tamron as stated in my other post I just made. It is probably the same tamron xr (if) that I have two of. The 72mm version I had almost seems to have a better image in some ways, but not in others (more contrast but maybe a bit less sharp, but I only briefly used it). How would you compare the 72mm version that you had to your daughters 62mm version?
I would have to go do a side-by-side comparison (which is possible, since the pics are in Lightroom), but IIRC, the 62mm is sharper but the 72mm produced nicer colors. That's my memory of it.

09-12-2013, 01:19 PM   #32
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QuoteOriginally posted by thornburg Quote
I would have to go do a side-by-side comparison (which is possible, since the pics are in Lightroom), but IIRC, the 62mm is sharper but the 72mm produced nicer colors. That's my memory of it.
That sound about like what I remember. The newer version was sharper but the older one seemed like the contrast or color or something was a little better. It was a while ago so I do not recall for sure.
09-12-2013, 01:26 PM   #33
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One other question that hopefully someone can answer ... is the field of view the same at 200mm for both the 18-200mm and the 28-200mm?? Or, does the crop factor (x1.5) of the 28-200mm actually make it a 300mm view?
09-12-2013, 02:30 PM   #34
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QuoteOriginally posted by tomwil Quote
One other question that hopefully someone can answer ... is the field of view the same at 200mm for both the 18-200mm and the 28-200mm?? Or, does the crop factor (x1.5) of the 28-200mm actually make it a 300mm view?
I feel like we should put a banner at the top of forum or something, because this comes up *all the time*.

No, 200mm is 200mm, no matter what lens you're talking about.

It's the camera sensor that determines the crop factor.

If you use a 28-200 on film, it's "35mm equivalent" of 28-200mm.

If you use that same 28-200mm on APS-C, it's "35mm equivalent" of 42-300mm.

When you use the 18-200mm on APS-C, it's "35mm equivalent" of 27-300mm.

So the APS-C "28-200" equivalent is actually the 18-135mm.

09-13-2013, 12:59 AM   #35
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QuoteOriginally posted by tomwil Quote
One other question that hopefully someone can answer ... is the field of view the same at 200mm for both the 18-200mm and the 28-200mm?? Or, does the crop factor (x1.5) of the 28-200mm actually make it a 300mm view?
Think of it this way. You have your lens at 28mm and point it at a car. The whole car fills the frame. You zoom to 200mm and only get the wheel. you are getting a smaller image and the longer focal length.

Ok so you have a full frame lens and a full frame camera. At 28mm, the car fills the frame. The lens is putting through the image of the whole car. The full frame sensor captures the image of the whole car. You use that full frame lens on a apsc sensor that is smaller. The sensor only captures a smaller image out of the center of the full frame image that the lens is putting through. It doesn't capture the whole car. Its a smaller image compared to what the full frame sensor captured. The smaller sensor is only capturing what the full frame sensor would at 133mm. The only time there is a difference is when you are comparing what a full frame sensor camera will capture compared to a smaller sensor camera.

Ok so you have the full frame lens on an apsc camera, and it is only taking part of the image out of the center. The extra image the lens sends through around the edge is unused/wasted. You are getting part of the car. With a lens designed for apsc like the 18-200mm, you are removing that unused glass making the glass smaller, basically removing the glass that was unused anyway so it has no effect. 200mm is 200mm.

Here is another way of looking at it. You have a 60x magnification telescope. Lets say the glass on the eye piece is 1/2". You see a particular size image. You then take a piece of paper that has a 1/3 inch hole in it and place it over the eye piece. You are seeing a smaller image as if you had more magnification, but you don't have more magnification. The telescope is still 60x, you are just looking at a smaller portion of what the telescope is putting through so you see a smaller image. That extra image the telescope is putting through, that is being blocked by the 1/3" hole in the paper is being wasted/blocked. The 1/2" eye piece telescope is like a full frame lens, and putting the 1/3" hole paper over it is like using a crop sensor camera. You then take a telescope that is 60x but has smaller diameter glass. The eye piece is only 1/3" to start with. It is still 60x so you get the same magnification. If the telescope is 60x, it is 60 x. If the lens is 200mm (the magnification), it is 200mm. You see the same image on the larger telescope with the 1/3" hole paper, as you see with the smaller telescope with a native 1/3" hole. They are both 60x magnification.

Does that make any sense?
09-13-2013, 01:11 AM   #36
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Something else to be aware of with these lenses that came as a shock to me. They are internally focusing. I was checking out my pentax f 100-300mm and compared it at 200mm to the tamron in a bedroom so distances were under maybe 12 feet. The pentax lens had a lot more magnification. This is apparently normal for internally focusing lenses. At closer ranges, you loose a lot of magnification. The longer distance you are shooting, the more magnification you get till you reach the actual 200mm. I'm not really sure at what distance you get the actual 200mm but close up the lens is not actually 200mm when set to 200mm. I'm thinking at very close ranges it was more like 140mm but can not recall for sure.
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