« on: August 26, 2014, 11:35:09 PM »
Even though the FOV and DOF may be the same, the images will never be "equal". Why is that? For the same reason that a 4X5 image will look "better" than 35 mm--field compression. Let me explain.
Let's take two cameras a 35 mm and 4 x 5. A 50 mm lens on a 35 mm camera and a 210 mm lens on a 4 x 5 camera give the same field of view. However, the images do not look the same because of the apparent difference in distance between the foreground and background. Even through the field of view is the same, the background will appear much closer to the foreground with the longer lens--this is called field compression. These images "look better" and have a more 3D feel. This is why the old master's like Ansel Adams, Ed Weston used large format cameras. Ansel Adams once quipped when asked what kind of camera he used his response was "The heaviest one I can carry".
The same this is going on with an APC sized sensor compared to FF. The equivalent field of view for a 50 mm lens on a full frame sensor is about 35 mm on an APC sensor. The apparent distance between background and foreground for given a field of view is greater in an APC sensor than in a full frame sensor. Hence, the images do not look as good and lack the 3D feel.
Your instructor should know this stuff. Maybe he/she should read Ansel Adam's excellent book "The Camera". In fact, all of us should read the entire Adam's series: "The Camera", "The Negative", and "The Print". There is still much to learn from the old masters even in the digital age.
With the greatest respect, something I am often accused of lacking, that is a complete load of rubbish.
Perspective is perspective, "compression" is a completely erroneous concept that photographers that don't know what they are talking about use to describe perspective.
Perspective is derived from your position. That is it, nothing else, focal length is a red herring. Shoot the same scene from the same place with a 17mm lens or a 200mm lens and crop the 17mm image to the same framing as the 200mm image and the perspective ("compression") is identical, and that is what you are doing when you use smaller sensors.
Dgbarar seems to have deleted his post. As has been stated the perspective remains the same because you are at the same distance, but the 210 mm lens does give more magnification which is then accommodated on a much larger format, so the end result is that you have a larger image. The same thing happens when you shoot a panoramic; you have to use a longer lens to get the same framing because you are creating pieces of a larger format. The difference is subtle but if you put two images side by side, one shot as a panoramic and the other as a panoramic cropped single frame, the difference is there.
Yep, you will never catch me saying a smaller sensor will give you better IQ! The perspective is the same, but the inherent additional IQ you get from a larger sensor, especially if you stitch to effectively make it even larger, will be apparent, things like lens aberrations are more easily seen with more magnification (the intrinsic problem with smaller sensors is the need to enlarge the capture more), the CoC is smaller when you go smaller, AA filters will generally have more impact on smaller sensors etc etc.
To be sure the differences are there, especially if you look very close, but they have nothing to do with perspective or focal length, just a myriad of other more mundane technicalities.