filter naming

[Josh Mitchell Frey]

I'm new to shooting on film, and hence new to using filters, so forgive me if my question seems basic.

 

I'm wondering what the reasoning is behind assigning filters a specific number. eg what does the "85" in "85B filter" connote? I can't make sense of the fact that an 80 raises colour temperature, an 81 lowers it, and an 82 raises it again.. are the numbers completely arbitrary or what?

[Dominic Case]

are the numbers completely arbitrary or what?

It does seem that way, but there are fragments of logic if you look at the entire catalogue of filters - from Kodak.

 

There is a range of filters numbered from 1 to 99, with some additional but related filters having an A or B etc. Most of them are colour filters, some designed for use with black and white film for a range of purposes from sky darkening to colour separations. 8 is a weak yellow, 12 stronger, 15 more orange, up to reds in the 20s, then through magentas, blues and on to greens and so on around the colour wheel.

 

Colour temperature filters are all in the 80s. The 80s (A,B,C & D) and 85s (-, B & D) are officially Conversion filters, to correct daylight to tungsten and vice versa. 80D is the weakest of the artificial to daylight filters and 80A is over twice as strong (i.e. 130 Mireds).

 

The 81 series (-, A,B,C,D & EF) and 82 series (-, A,B & C) are officially Light Balancing filters, with each in the series very roughly 10 Mireds stronger than the previous one. They are grouped separately as they are seen as having a different purpose - i.e. to fine tune light sources, rather than to convert one type of light for a different film stock. But you are right, it might have made better sense to have the 81 and 82 ranges reversed to fit in with the 80 and 85 range.

 

I guess if they started again from scratch, there could be a much more rational system applied.

 

Somebody from Kodak or another filter supplier might know more.

[Chris Keth]

I thought the B in an 85 B refers to the type of film it is meant to convert daylight to. Film balanced for 3200K used to be referred to as type B. Type A was balanced to 3400K, type D was daylight. I don't if there was ever a type C or not.

[Dominic Case]

I have a table published by Kodak some time ago:

 

The 80 series convert to 5500K

80A from 3200K (-131M)

80B from 3400K (-112M)

80C from 3800K (-81M)

80D from 4200K (-56M)

 

The 85 series convert from 5500K

85 to 3400K (+112M)

85B to 3200K (+131M)

85D to 3800K (+81M)

 

It also shows which 81 or 82 filter (A,B, etc) is required to correct any given colour temperature either to 3200K or 3400K. Basically, the 81 will reduce colour temperature by 100K, the 81A by 200, 81B by 300, etc. The 82 series will increase colour temperature in steps of 100K.

 

I do recall that 3200K and 3400K were called tungsten type A or B, but that isn't the same as the filter name.

[Leo Anthony Vale]

I thought the B in an 85 B refers to the type of film it is meant to convert daylight to. Film balanced for 3200K used to be referred to as type B. Type A was balanced to 3400K, type D was daylight. I don't if there was ever a type C or not.

 

Yes there is an 85C. It's listed as converting daylight to 3800K.

But I think it was originally used for converting a no longer manufactured flash bulb which was around 4000k to tunsten.

[Phil Jackson]

It's called the Wratten Scale and it's used and its used generally ubiquitously for optical filters regardless of use. Photographers generally stay in the 80s, but these filters can be used for a DSLR or for the Hubble.

 

Wratten Scale