Optical Density and Diabatic Graphs and Transmission %

[Cadmium]

Someone asked about the MIDOPT BP365 filter, and if it would work instead of S8612 for UV suppression, stacked with a U filter (UG1, UG11, U-360, U-340...B+W 403=UG1).

You can see the BP365 here:

https://midopt.com/filters/bp365/

 

First notice the graph shows the filter doesn't suppress above 800nm, that is the obvious part, but because this the graph is linear, and doesn't show optical density (OD),

where the graph goes down to "0", we assume this suppresses everything. We can't really tell, we don't know, not with a linear graph.

That is why the diabatic graph style (such as in the Schott filter program) is so handy for calculating and visualizing suppression and OD.

Scroll down on the MIDOPT BP365 page and you see actual transmission data showing % of transmission per each 10nm.

 

Here is a quick handy reference for converting % ot transmission to optical density:

100% = OD 0

50% = OD 0.3

10% = OD 1

1% = OD 2

0.1% = OD 3 (1E-03 Schott diabatic graph)

0.01% = OD 4 (1E-04 Schott diabatic graph)

0.001% = OD 5 (1E-05 Schott diabatic graph)

0.000001% = OD 8 (1E-08 Schott diabatic graph)

 

Here is a graph expressing the above numbers (I have posted this graph before):

 

When stacking for UV only, you should have OD 4 or stronger in most situations.

OD 3 is an absolute, you WILL see IR pollution.

OD 4 is advised, (although you can sometimes use OD between 4 and 3, but not advised)

OD 5 is preferred if you don't care about exposure time.

Anything stronger than OD 5 is not needed and will only reduce UV content (amplitude and band width) and increase exposure time.

OD from 4 to 5 is the range to try for.

 

Also: Schott graph use "1.00" to represent 100%, and "0.50" to represent 50% (for example).

That can be confusing when it comes to Schott diabatic graphs, because at 1E-03 and below Schott diabatic graphs % is what I have listed above in the post (not converted from 100 to 1).

 

S8612 is the best Red/IR suppression for UV only stacking (get 2mm thick when in doubt):

 

Some U glass examples:

[Andrea B.]

A very nice overview! Thank you, Cadmium.