Lens flare as "contrast contol" ?

[Mark Sawyer]

Here are some numbers I am pulling out of my hat. Are these right ?

Let a subject start out at 100% contrast. A lens with low flare delivers 85%. A lens with a lot of flare delivers... 75% ?

In other words, how much are we talking about anyway ?

Exact numbers are pretty loose, but here goes... Each uncoated air-glass surface scatters 4 to 8% of the light passing through. The front element reflects it back out into the world, and the rear surface only reflects what's bouncing back from the film plane, so I discount those two surfaces. So an old uncoated Dagor with two inner air-glass surfaces is losing 8-16% of the light, about half to flare and the other half absorbed by the barrel walls. So you're talking 4 to 8% flare vs. clean image making light. (BTW, two inner air-glass surfaces is the minimum with compound lens designs, so the Dagor was very popular because of its high contrast.)

Split the Dagor into an "air-spaced Dagor" (aka Plasmat), and there are now 6 inner surfaces, so 24 to 48% of light is lost, with 12 to 24% being flare. That's why the Plasmat was never popular until coatings came in.

Early coatings reduced flare to 1 to 2% per air-glass surface. Modern multi-coatings are claimed to get it down to 0.1%.

The flare acts like pre-flashing the film. It affects the shadows most because the flare is evenly distributed, while little image-making light is hitting the shadow areas, so the flare can overwhelm it. If you adjust your processing for uncoated lenses, coated lenses will seem harsh, and if you adjust your processing for modern lenses, uncoated lenses will seem flat or mushy.

[Taija71A]

Since, there seems to be quite a bit of confusion about this topic.
Perhaps, the following may be of interest to some.

Pre-Exposure of course... Doesn't have to be placed as high as Zone II.
(This of course is just an example).

Ansel Adams -- The Negative (Pre-Exposure) pp. 119 - 124.

https://manualesdecine.files.wordpre...eries-no-2.pdf

Regards, -Tim.

[sanking]

....
In BTZS testing, a correction is made for flare. In the end it affects what we consider our effective film speed, developing time etc.

Perhaps a BTZS adept could explain what happens when we allow "a much greater" correction for flare. I presume we lose more film speed and develop longer. Sounds like contrast control to me.

My presumption is same as yours. We adjust for increasing flare by increasing time of development, which results in higher average gradient. This procedure does control overall contrast, i.e. macro contrast. However, the adjustment in macro contrast does not entirely restore the acutance (micro contrast) that is lost by lens flare. You may recover some of the loss with a digital work flow with sharpening, but lens flare results in some loss of image quality that is impossible to recover.

Sandy

[Doremus Scudder]

Lens flare, since it is non-image light and evenly-distributed, is exactly the same as an intentional overall flashing, or pre-exposure of the film. There's really no way it can be different. These both affect the low values for the most part, flattening out the toe portion of the curve and reducing separation in the area most affected while at the same time allowing more detail to be recorded.

The end result is not much different than using a film with a long toe vs one with a steep one (e.g., TXP vs TMY). Getting more separation in the shadow with either flare or a long-toed film is often just a matter of exposing more to get the desired shadow values up onto the straighter portion of the curve. I suspect this is why a lot of photographers in the past rated their film a bit slower. On the other hand, as proponents of long-toed films, uncoated lenses and flashing realize, the trading of separation in the lowest values for more detail and softer shadows can be quite gratifying.

I routinely manipulate TXP this way, choosing a full exposure in cases where I want more separation in the shadows and less when I want the look the long toe of this film delivers.

Pre-flashing can be done rather easily if one has accurate shutters, and delivers the same effect as lens flare. An evenly illuminated grey card held close to the lens (so it's out-of-focus) and an exposure anywhere from Zone II down to Zone 1/2 or so will often do wonders for pulling substance from deep shadows. For most subjects, there are better ways of dealing with the shadows. However, as one tool in the toolkit, flashing has its place.

Best,

Doremus

[Hans Berkhout]

I "encourage" some lens flare by omitting the use of lens hood/shade quite often. The result still leaves me with better separation at the lower end than I would get with a single coated older lens and I still have the advantages of modern lens design. Choice of developer helps to avoid the steel wool look that some modern lenses tend to produce.

[Taija71A]

In my "simulation" of lens flare, I applied the following curve:

Image: http://www.kenleegallery.com/images/forum/flare.jpg

Should it have been this one instead ? In other words, not just the shadows, but the whole scale simply lifted up ?

Image: http://www.kenleegallery.com/images/forum/flare2.jpg

No.
Of the two curves that you have shown Ken... The first curve is better.

But...

As you can see by the histogram for the first curve, you are still lifting not only just the shadows -- But also the rest of your Zones to a lesser but still, too significant degree.
This is not necessarily what you want to do (*If you are trying to 'simulate' Lens Flare)

Ken, can you apply a partial custom curve that only lifts the Lower Zones (perhaps not at all above Zone V)? This would even be... Much better still!

Best regards, -Tim.

[Mark Sawyer]

Just a couple of practical notes...

Pre-flashing film is actually kind of dumb. If it needs a thresh-hold fog, make a note on the holder and do it right before development. That way you can decide if and how much is needed.

Most uncoated lens flare is randomly scattered, but if you need a lens hood and you're leaving off to encourage flare, you may get defined reflections of the aperture shape.

[Bill Burk]

__

Yes!

What you have tried to 'simulate' Ken, would be exactly the same...
As adding the proper amount of 'Pre-Exposure' of your Film (*for 'Contrast Control').
--
In an 'Analog Only' workflow... This is most certainly a very, valid option.
One of the best 'treatises' on this subject... Was discussed in the Book:

"Way Beyond Monochrome" by Ralph Lambrecht.

http://www.waybeyondmonochrome.com/W...xposureEd2.pdf

--
Best regards,

-Tim.
_________

Tim, You struck gold here!

Ralph Lambrecht's curves and examples prove the point.

Flashing / flare / long toe. They all sensitometrically look exactly the same to me. Doremus Scudder already explained. But I see it too.

Maybe not exactly the same, as the toe shape may differ from the flare curve. But they ARE very similar. Again if they are not exactly the same (flare versus pre-exposure) the differences are very minor and can be named. For example some trivial differences due to reciprocity / intermittence effect. Maybe a pictorially significant difference if flare includes aperture image shapes.

But by gum, I see the same thing, an upswing in the curve in the shadows... While midtones are trivially affected and highlights are barely measurably affected.

In other words, if you WANT a long-toe and the film you are shooting has a sharp toe... Pre-exposure will give it to you.

Yes. You must calculate exposure precisely... Because if you want the benefit of the curve you changed with pre-exposure... You sure do not want to put your shadows on the straight line. That would defeat the purpose!

[Bill Burk]

Drew Wiley, You were right all along!

[Jac@stafford.net]

Just a couple of practical notes...

Pre-flashing film is actually kind of dumb. If it needs a thresh-hold fog, make a note on the holder and do it right before development. That way you can decide if and how much is needed.

Indeed! There is the fact. No need to pre-flash on site.
.