Doesnt blow the highlights

[swmcl]

OK here's another of my little queries ...

What does it mean when a developer 'doesn't blow the highlights' ?

Specifically, Pyrocat-HD but any others too.

Picture the film response curve that starts out flat then proceeds past a 'toe' to a hopefully linear gradient upwards. If a developer didn't blow the highlights, the curve would again have a shoulder at the higher densities and would stop proceeding upward to level out again. To not 'blow the highlights' that shoulder would be at a density of around 1.35 to say 1.5 ?

So perhaps the tanning and staining does something the densitometer cant see and does it in a controllable and highly non-linear way just chopping the top densities off ?

I have numerous film tests that show the developer being as linear as you like all the way past a density of 2.2. Perhaps other developers see an increase in the gradient of the curve as the densities rise ! To infinity ! This would make it look as though Pyrocat-HD didn't blow the highlights - because it remains linear ...

I fear that what the phrase might mean is, "My developing solution is so weak and my developing times are so short that there is a shoulder to my response curve that I am not aware of and as a result, my highlights never go the chance to blow. My negatives are as thin as ..." !

:-)

Corrections to my reasoning are welcome.

[ic-racer]

In general one would not want any image on the shoulder. The highlights will then print a gray, or if they are forced to white the mid-tones in the image will be way too bright.

After the toe, the curve can go upward, almost exponentially or it can taper off. When it continues upward, looking like an exponential equation, the highlights can get very dense and hard to print without the middle values going too dark. I'd call that blown highlights.

Here is a curve I made in the 1980s before I had a computer (yes!). When T-max film first came out. T-max is different and may not be as prone to this as I have not had issues with it since.

When looking at this remember there won't be any image on that shoulder (it is twelve stops out), the evil highlights are on that steep portion just before the shoulder.

[LabRat]

The simple answer is the highlights don't block up to Dmax... So you can still print through them...

I find the easy way to avoid them is don't over develop the film... If you slightly overexpose and underdevelop the film, you also gain other benefits, and plenty of detail to print in the highlights, without having to burn them in too often (or at all)...

Steve K

[Drew Wiley]

Hard to make one shoe fit every foot correctly, theory-wise. The shape of the toe and shoulder has a bit impact on how things will print, and a staining developer distinctly modifies this in ways a typical densitometer can't see. Yeah, you can follow the advice to read through a deep blue filter like a 47B, but it won't take long to figure out that that amounts to way more overall density than most such devices can handle, unless you happen to have a color transmission densitometer with
a dedicated blue channel. If you do slightly overdevelop the negative, a fair amount of correction can be made during printing using either an unsharp contrast mask or a premium VC paper. But too much overexposure, where the shoulder has essentially leveled off, and you've lost your high values.

[Drew Wiley]

Ice-racer: old and new TMax differ in this respect. But it's still a film I shoot at box speed because the toe is steep enough to separate shadows way down there,
while it is still relatively easy to blow out the highlights with overexposure. TMY400 is analogous. Two films where one never wants to assume "latitude" will obtain a decent neg unless the scene contrast is rather mild. But correctly metered, I have no problem getting sparkly highlights in fresh sunlit snow along with full detail in adjacent black volcanic rocks, without resorting to minus development. I gave up on TMX in the mountains, however, due to that other subject we have been discussing - lack of sufficient edge effect. But TMY400 is fine in that respect, and of course, the extra speed is advantageous for 8x10 photography.

[swmcl]

Good discussion. Thanks Drew again for your input.

Is 'blown highlights' a flattening of the curve or is it a curve to infinity ? Perhaps other developers other than Pyrocat cause more of a shoulder ? Then when Pyrocat does its linear thing people say, "Oh it doesn't blow the highlights ..."

Maybe I've got my understanding of 'blown' upside down.

[Michael R]

The problem is that the term "blown highlights" means different things to different people depending on their perspectives (and skill levels).

Strictly speaking, from a sensitometric perspective a blown/blocked highlight should mean no detail (ie no contrast) exists in the negative. This means the highlight fell beyond the exposure scale of the film. This can happen for different reasons, and it can depend on the developer since developers can alter the length of the film's exposure scale and shape of the curve. Some developers/processes tend to lengthen the shoulder, which means highlight contrast decreases progressively. However this type of negative can sometimes be as hard or harder to print than one with a straighter curve in the highlights. All this to say, you can have blown highlights even if the densities on the negative are not very high.

On the other hand, many people simply define a blown highlight as one that is too dense to print straight, or print easily. There may very well be excellent detail in the negative, but it requires work to bring it in on the print. Certain films such as TMY-2 and Acros will be more prone to this than other films since they exhibit comparatively high highlight contrast and will develop to higher densities than say TMX, which has much lower contrast at extreme exposure levels.

So it really depends on your perspective.

[ic-racer]

My definition of a blown highlight is a printing problem. The low values and mid values look good and are in good proportion but the highlights are off the paper's scale. Printing with more exposure spoils the low tones. Printing with less contrast makes mud. Burning makes a dark outline around the highlights.

[Bill Burk]

I have numerous film tests that show the developer being as linear as you like all the way past a density of 2.2.

I see the same and so I've come to the conclusion that the shoulder... of the film... never enters into the problem.

It's the shoulder... of the paper.

Now you will certainly reach the paper shoulder (blow out your highlight) in the parts of your picture where you hit the film with several (maybe four) stops over your "important" highlight. Hopefully this would be a few places in the picture that make it look good.

[stawastawa]

well said.

My definition of a blown highlight is a printing problem. The low values and mid values look good and are in good proportion but the highlights are off the paper's scale. Printing with more exposure spoils the low tones. Printing with less contrast makes mud. Burning makes a dark outline around the highlights.