Working out back focus with a filter tray and filter?

[bluesilver]

Hi, I am hoping someone might be able to help me out with this question in regards to using filters in the imaging train and working out back focus

I have a field flattener / reducer and the manual tells me that the back focus needs to be 96mm.

Now i am using a ASI2600mc camera and i have a single filter tray just in front of the camera.

I have taken the thickness if this into account ( 21mm )  but do i actually need to add the thickness of the filter itself ( roughly 0.5mm ) even though it sits inside the filter tray?

So basically with the filter tray being 21mm wide,  do i also add 0.5mm to this to make it 21.5mm  or dose it just stay as 21mm

Hope i haven't made that question too confusing.

Any help would be appreciated.

Thanks.

 

[Waldemar]

In spite of the fact that the filter is inside the already counted with tray, you will need to add 1/3 of the filter's  thickness to the path.
So that will be 0,2 mm making 21,2 mm. Don't think those 0,2 mm don't matter because it is so little... it does!
You can accomplish this by adding a 0,2 mm shim to the filter tray. This info tells you which way to go if the image is not flat.FF distance to sensor.docx

[bluesilver]

Thanks for the reply,

I have yet to do the test to see if i am too close or too far away,  but good to know that i do need to take into account the filter thickness.

Will work on getting some spacers to get the  correct distance.

Appreciated.