backfocus distance

[drsureshmohan]

Hi ,

 im using a Baby Q and just got my my 0.73 reducer yesterday , The back focus distance to camera chip recommended is 72.2 mm. Ive added a Hutech LPS 2 filter in the imaging train. I also intend to use the Ha and O 3 filters on my Mono DSLR( which i plane to use from time to time,i have a modifed mono 350D). Here s my question ; When i add the lps filter what happens to the back focus distance due to the refractive index of the filter does it increase or decrease and if so by how much.ive already reached a backfocus distance of 72.1 mm(very close)

Thanks 

Suresh

[swag72]

When you add a filter into the mix, your spacing will increase by 1mm. So, if you have a spacing at the moment of 72.1mm and put a filter in the train, that will be equivalent to 73.1mm.