Quote:
Originally Posted by Dilsh
Thanks Adam,
So to get that right, 55mm back focus means that you have to be within 55mm. Right now all I have is a T2 ring between the back of my ED80 and my DSLR and I can achieve focus and the T2 ring is no 55mm?
Sorry about this very simple question.
Thanks,
Dilshan
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Let me see if I can explain it in another way as I too had issues understanding such a simple thing.
Let say you DONT have no flattener or flattener/Corrector.
The ED80 straight out backfocus is maybe around 100mm. Your camera & T-Ring will aready be 55mm, so to gain focus you will need to rack the ED80 focuser out to about 45mm to gain perfect focus.
Now if you introduce a flattener or flattener/Corrector. Most have a back focus of around 55mm.
So, you connect the flattener or flattener/Corrector to the ED80, now you only have 55mm to play with from the back of the flattener or flattener/Corrector. And the ED80 focuser will be almost racked in with a fine adjustment to gain perfect focus.
The above are not hard fix numbers, but more round-about to give you an understanding of the back-focus concept.
Cheers
Wayne