My focal length

[Rodd]

5 hours ago, ollypenrice said:

The term 'crop factor' is an irritating one since it leads precisely to the confusion under discussion! In implying a relationship between the size of the sensor and the focal length it leads people astray. No such relationship exists and, as rockinrome pointed out at the beginning, only the field of view is affected. In a related error, some folks make the mistake of imagining that a small sensor 'zooms in' on an object as compared with a larger sensor. Again this is totally incorrect. Shown on screen at full size (one camera pixel equals one screen pixel) the smaller and larger chip of the same pixel size will give an identical object size. You can obtain finer resolution (more detail) by changing the chip but to do so you must choose a chip with smaller pixels, not a smaller area. (This will only work in practice if the optics, the guiding and the seeing will support this increase in resolution and they may not.)

Calzone's video maker is making both the errors I describe at the beginning. He is plain wrong.

Olly.

Totally agree (can't dispute a fact).  However, I have noticed that the forum--each one is different, will portray cropped images at a larger size--making cropping and posting without a resample dangerous.  This forum posts them larger initilly--but then when you click on them you see them at reduced (cropped) size.  This adds to the confusion.

Rodd

[freiform]

Good morning everyone,

I certainly agree that there often is confusion about physical facts (surely not just for AP!). I often was confused in the beginning, and sometimes I still am. I think that a terminology used lightheartedly without actually taking time to understand what is going on is the reason for the confusion. The underlying principles are not difficult, but one has to think about it!

But I suppose you are right, if this confusion can be avoided by forgoing potentially ambiguous (or straight out unsuitable) terminology, then by all means, let's do that.   

Sven