Extenders question for BM

Gaviscon might help.

Take a look on u-tube again, they might be a bit clearer  I think Steve Parry has done something on this topic.

GL

Having re-read my earlier post, perhaps a clearer way to explain would be as follows

If you changed to a full frame camera and kept your 100-400mm F4.5-F5.6, you lens would give exactly that magnification.

Your 70D with the 1.6 crop and 100-400 lens, this combination would give you an effective 160-640mm F4.5-F5.6 lens. This is in effect the same magnification as using a 1.6 converter on a full frame without loosing a stop and a half. 

As we tend to rarely fill the frame, the crop factor works in our favour when photographing small objects.

Hope this is a clearer example.

BM....it is now crystal clear...thank you very much.

Gaviscon...just got it!

Grey and blowing outside...Tesco it is then!

Glad to help GL

Please also consider that the other consideration, and that is beyond my expertise, is pixel count/size

With the full frame sensor in general there are more pixels and the size and quality of those pixels make a difference.

The more pixel cameras these days are between 40mp and 60 odd with the latest range of sony sensors.

So there is a trade off at some point in the quality of the post camera processing cropping the small image in the original image taken by the camera.

So using an image taken from the same distance of your Owl sat on the post for 2 hours, using your 100/400 lens set at 400mm 

Without post camera processing, a full frame sensor camera will give you a smaller image of the Owl than a cropped sensor camera.

When we come to post camera processing the full frame with say 40megapixels will allow greater cropping than the lower pixel count cropped sensor of 20mp without loosing quality. But as the original image of the Owl on the sensor in the cropped sensor camera is larger, it requires less post camera cropping than the full frame image.

Where the quality crossover point of these two examples are is not possible for me to advise.

All I can say is that reverting to the images posted on Flickr. there are exceptional shots taken with crop sensored  cameras such as Canon 7D 20pixel cameras Nikon D500 20 pixel cameras that I know were large crops from original as many were taken stood next to me. They are as good a final image as those taken with Canon 5D 47mp  or Nikon D850 42mp that required a larger crop for the same image given the same length lens. ( pixel counts are from memory, so approximate)

For the pics we take, probably the most important camera requirement is fast and accurate focussing, frames /second to my mind is less important and just creates so much more time spent sorting the good/average/rubbish.

Spent many hours listening to togs taking 10 or more frame a second in bursts of 20 or 30 of the same bird sat on a branch and often wondered how many go straight in the bin and the extended time to process rubbish. 

Again, if this is a bit garbles, ask again for clearer waffle.