Quote:
Originally Posted by Merlin66
Rodney,
You’re over thinking things.
Possibly, but I would still like to explore the issue.
The back focus of the Canon lenses is 44mm.
According to my analysis above, only when mounted on the DSLR body
Nothing to do with the secondary filters etc inside the Canon body.
See previous answer
With the removal of filters the focus is still 44mm.
see previous answer
(I have to add internal filters - in my case clear, to allow the camera lenses to give infinity focus on a fully moded camera.)
This sounds like you are confirming that the filter is changing the length of the light path  |
Ken,
My starting positing in this thread was to present my analysis which concluded that moving a lens from a Canon DSLR body to a CCD or CMOS camera will mean that the stated 44mm set back distance does not apply. I have provided details of my analysis above. The reason for starting this thread was to test my analysis and subject it to peer review. I'm more than happy to be proved wrong but so far though, nothing has been presented that conflicts with my conclusions.
I have attached a diagram which provides a pictorial representation of my theory. Placing a filter in the light path must alter the point at which the light comes to focus because glass has a different refractive index to air and, therefore, the optical length of the light path will change. The response from JA above is consistent with this position. If there is something wrong with this analysis Ken please point out where it is.
Your post #6 above states:
The sensor position is therefore set to match the optical length including the built-in filters.
Exactly, on that we agree. So if you take the filter out (or remove the lens from the DSLR body, which does the same thing) the optical length will change.
When the Canon is modified ie removal of filters (either one or both) requires the position of the sensor to be changed or additional filters re-installed.
This is confirming that the filters in the DSLR body are changing the length of the optical path which is exactly my conclusion.
This seems to be inconsistent with stating that the
"backfocus of the Canon lens is 44mm" and has nothing to do with the
"filters etc inside the Canon body.".
If the filters inside the Canon body are not affecting the 44mm set back distance then why is it necessary to change the position of the sensor when they are removed
We maybe (hopefully) are getting crossed wires on semantics here Ken. I'm keen to continue to explore this to make sure I haven't got my own wires crossed
