Using coloured filters in b&w photography

[Keith (M)]

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Old hat to many forum users but perhaps useful to those new(ish) to b&w film.

Using coloured filters in b&w photography

 

 

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[Michael Hiles]

Excellent! Many thanks.

[mikemgb]

Old hat or not, it's always good to read through these things to see if there are things you've forgotten you can do. For instance, this reminded me I need a couple of different sized orange filters. Thank you.

[Keith (M)]

When I took delivery of my 'new' Hasselblad 500C + Planar 80mm recently, it came with a yellow/green filter (filter factor 2).  I'm used to using a medium yellow for all of my b&w film usage, so yellow/green seems to be somewhat contradictory in its effects.

[pico]

Also consider that a filter for B&W can cut through haze or fog, and it usually increases image contrast. My favorite is an orange 1 or 2. Try it.

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[jaapv]

But do note that red, and to a lesser extent orange, filters will produce focus shift.

[Michael Hiles]

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But do note that red, and to a lesser extent orange, filters will produce focus shift.

 

Interesting point. Enough to matter? I am thinking about landscapes focused most often at infinity.

[chris_livsey]

But do note that red, and to a lesser extent orange, filters will produce focus shift.

 

I beg to differ, only in your use of the term "focus shift" as I feel the usual use these days will lead readers astray as to what is happening and the filters don't produce it they expose (sorry) it.

 

The plane of focus is not changed at all, shifted, by the presence of the filter it is focussed exactly where it would be without the filter. (Excluding a tiny effect as the filter has a refractive index which will change the focus minutely, any filter will do that, even plain optical glass). All the filter does is selectively reduce the transmission of some wavelengths of the light passing though it.

What happens is that in a lens system that is not truly apochromatic the various wavelengths of light are brought to focus at slightly different planes the image is normally seen as in focus within acceptable limits (depending how poor the lens is  ) with no filter.

Adding the filter changes the proportion of the wavelengths passing through the lens to include more of those that are not as well focussed so the overall image appears out of acceptable focus. The IR mark is the extreme example of this effect. The lens focus is changed so that the image is formed at the sensor where those wavelengths are brought to focus. That point was always there it hasn't shifted at all with the filter it is just that now we wish to make those wavelengths the majority making up the image so must focus them correctly at the expense of those wavelengths that we have removed and will not make up our image.

 

In real life the effect will depend on the lens used, some are better corrected, the sensor, digital is flatter and thinner so will show the critical plane of focus more clearly, and the f stop where depth of field comes into play but brings us back to acceptable focus arguments.

It will be necessary to test your system as a whole to see if the effect is sufficient to change focus, certainly in astrophotography it is.

[jaapv]

Yes, that is the definition of focus shift. As you are aware the "traditional-aperture" focus shift follows a similar pattern. Anyway semantics will not change that we are in complete agreement on the facts

Thanks for the clarification.

[jaapv]

Interesting point. Enough to matter? I am thinking about landscapes focused most often at infinity.

Yes, it does matter, depending on the chromatic correction of your lens. You only need to look back in Digiloyd's blog to find that he was totally surprised by this effect (known for at least the last hundred years) when the Monochrom came out.

[semi-ambivalent]

Yellow, that old standby, can not only make a woman's skin look better but improves the shade of the teeth of both genders (assuming they are not already being painted titanium dioxide white).

 

s-a

[Soden]

But do note that red, and to a lesser extent orange, filters will produce focus shift.

But on a APO lens, this would not occur, because all colors are corrected to focus on the same spot?

[chris_livsey]

But on a APO lens, this would not occur, because all colors are corrected to focus on the same spot?

Which is what I said in my admittedly rather long reply above 

BUT that depends on how the maker interprets APO, there is no standard set so you can call it APO but not correct "all colours" as that depends on your definition of colours and of correction which is why I refer to wavelengths. 

For example the Coastal optics 60mm is a corrected apochromatic lens in the range 310-110 nm so you would expect no focus shift in UV, visible and IR region which exceeds "colours". 

[Soden]

Which is what I said in my admittedly rather long reply above

BUT that depends on how the maker interprets APO, there is no standard set so you can call it APO but not correct "all colours" as that depends on your definition of colours and of correction which is why I refer to wavelengths.

For example the Coastal optics 60mm is a corrected apochromatic lens in the range 310-110 nm so you would expect no focus shift in UV, visible and IR region which exceeds "colours".

I was thinking in particular of the Leica APO-Summicron lenses. 50-90mm. With use of dark red/orange filters. Not quite in the IR or UV range.

 

I've seen quite dramatic focal shift from my f/1 Noctilux @ f/1 so I know the effect.

[jaapv]

But on a APO lens, this would not occur, because all colors are corrected to focus on the same spot?

Not quite. For most manufacturers APO means correced for two wavelengths, like red and green, Anything outside those points is anybody's guess.  Leica uses three wavelngths, but still makes no claims for the wavelengths in-between and outside the calibration values.

However mostly a red filter on a Leica APO lens will be approximately within DOF, and IR a lot better than with a non-APO lens.

[chris_livsey]

I was thinking in particular of the Leica APO-Summicron lenses. 50-90mm. With use of dark red/orange filters. Not quite in the IR or UV range.

 

Without personal experience I can only quote:

 

 

 Leica has always claimed that making a good lens is not a problem nowadays, but making a good small lens is. Indeed, it has to be noted again and again: the superior performance of the Leica M lenses in combination with the s all size is the true accomplishment. The graphs show how well they have succeeded.A very important characteristic of a new lens is its correction of the secondary spectrum. Normally lenses are best corrected for the green and red part of the spectrum, but the blue and purple part is neglected. Below is a table of the wavelengths:380 - 440: purple440 - 483: ultramarine483 - 492: iceblue492 - 542: sea green542 - 571:  foliage green571 - 586: yellow586- 610: orange610- 780: red780- … : IR-A Because of the relative insensitivity of silver-halide emulsions for the blue region, most designers in the past assumed that one did have to pay attention to this part. This attitude has been referred to as the 'cursed 435 wavelength'. Even a talented designer as Dr. Mandler evaded this wavelength.The modern approach is to pay much attention to this wavelength as it is responsible for the blue color fringing, so visible in digital photography. The Apo-Summicron-M shows the much improved correction of the blue region. The correction is four times better than what one should expect normally.

 

http://www.imx.nl/photo/leica/lenses/styled-4/