I am currently looking for a replacemant for my ageing 300D as it has now suffered the AF Sub Mirror failure. My prefered subject matter is aviation and a bit of adventure sport (My son is training to be an adventure sports instructor). I have been shooting aviation since by early teens (late 70's) starting with my farthers old Pracktica Nova B with a 135mm Carl Zeiss Jena lens with 2× converter. I then moved on to a Pentax ME Super eventually shooting with a 80-200mm again with 2× converter. Back then I shot with BW and E6 Slide (did all my own D&P as well, happy days in the dark!).
Fast forward to now, and I have been using my 300D with Sigma 28-300, and have fallen into what I think is a bit of a trap. My 300mm lens now it is on my APS-C sensor has the FoV of a 480mm on the old FF. So although I only have 300mm it is still better than when I shot 400mm on FF.
I think that actually this is not true, If I am shooting a fixed sized object, i.e the aircraft, at a fixed distance. Most airshows have the flight line at about the same distance from the crowd line so the distances stay reasonably close from show to show. Now the realisation that I had was that a 300mm lens will reproduce the fixed size × distance image at the same size on the sensor irrespective of the actual sensor size, be it APS-C or a 10"×8" plate. Until the image formed on the sensor actually fills that sensor then the format "FoV" in relation to the focal length of the lens actually makes no difference to the actual size of the image recorded. So if I am still having to crop on any format then I have gained nothing in "Effective focal lenth". In the old days when shooting on film then the size of the finnished image that could be produced was dependant on the quality of the film that you were using (slow speed fine grain / high speed lots of grain) and of course the quality of your enlarger lens! Assuming that one was using the best (or at least equivalent quality) camera lenses avilable. I know that pixels don't really have a "size" but again we all accept that there are normally accepted pixel resolutions for printing, so for example if we are printing for an image that is likely to be held in the hand (or viewd form an equivalent distance) then 300 ppi is accepted as being an optimum resolution for example. Now unfortunatly even with unlimited money for some of the new super Tele's or Tele zooms such as Sigmas 300-800mm (which would be my focal range of choice now) are so big and heavy that they are only useable from a tripod, which is something I have never been able to use for aviation. Looking back at my images 600mm seems to offer a reasonable reach, well at least being almost able to almost fill the APS-C frame when the ship is level with you along the flight line, although I find that my current 500mm is a bit short a lot of the time especially when the ship is pulling up at the ends of runs.
So even with a lens in the 500-600mm range needing croping on both the APS-C and FF sensors (I know that the FF crop is going to be 60% more). So the total number of pixels is not really of much interest, but the pixel density is, as what we are limited by is the essentially fixed size of the image on the actual sensor.
Now I hope that at least some of you are still with me. Am I correct in the statements that I have made above, and that what I need is a good pixel density within the limits of IQ? This is different from what the majority of users are looking for when they are in a position to fill what ever size frame they have with the image that they want.
Comments on my thoughts are very welcome.