Spectral sensitivity om BW films and perceived sharpness

pkr1979 · Jul 13, 2024

Hi all,

Ive been shooting Ilford Ortho and Tmax 400 interchangibly for a while. And often when shooting landscapes Ive found Tmax 400 to be sharper then Ortho, especially on subjects in the distance. However... I did a massive film test for grade 2 and 3 to try and figure out what kind of films I actually like (using a Pentax 67ii), and again ended up with these two films. And again when I compared distant subjects Tmax 400 would appear sharper (aperture would be the same, but not shutter speed - also shot on tripod). Based om this I assumed that films seeing more blue would appear less sharp on distant subjects then films not seeing as much blue. However, I then shot two 35mm rolls (one of each film) using two cameras and one lens. Same aperture, different shutter speeds, and hand held. Now however, they seemed equally as sharp. This puzzles me.

And I guess my question is if the spectral sensitivity actually would affect perceived sharpness, particularly for distant subjects?

Cheers
Peter

pentaxuser · Jul 13, 2024

Have a look at a video on Ilford Ortho by someone called Steve O'Nions. In this one he is comparing Ilford Ortho and Ilford D100 for what seems to me to be landscapes. So OK not TMax 400 but it may be that the conclusions he draws might be applicable I found it worthwhile

pentaxuser

reddesert · Jul 13, 2024

For distant subjects in particular, haze and water vapor in the atmosphere scatter blue light more strongly than they do red. This is likely to cause a decrease in contrast, not actually visibly blur the objects; so not technically resolution, but the decrease in contrast for bluer-sensitive film could be perceived as distant objects are less clear.

This is a reason that landscape photographers were known to use yellow filters (it's not only to darken the sky), and why IR landscape photography sometimes has an appearance of extreme depth, because it shows the horizon more clearly than your eye sees it. A "haze" filter instead of a UV filter also cuts a little more blue light and might be useful with the ortho film.

These effects will depend on local atmospheric conditions of course.

You may not have seen a difference in handheld shots for a variety of reasons, including slight motion blur, different subjects/atmosphere, etc.

pentaxuser · Jul 13, 2024

So, reddeser, does your #3 accord with what Steve O' Nions' comparison seems to show, namely , that Ilford Ortho appears sharper than D100 which is a panchro film as is TMax or is there no link or reason why Ilford Ortho should be any sharper?

To my eye the scene improved in terms of sharpness as follow from poorest to best: D100 no filter, D100 with yellow filter and then Ilford Ortho without any filter

The OP seems to have felt that TMax was sharper initially but on, shall we call it, the second test things were equally sharp for both films

Thanks

pentaxuser

Lachlan Young · Jul 13, 2024

pkr1979 said:
is if the spectral sensitivity actually would affect perceived sharpness

Acutance/ trimmer dyes play a part, as do fundamental aspects of emulsion structure design and various addenda specifically intended to boost sharpness relative to granularity, much more so than spectral sensitisation. TMY-II is intentionally engineered to be ultra sharp.

That said, all spectral sensitisation seems to apparently have an across-the-board impact on developer characteristics, specifically superadditivity.

Todd Niccole · Jul 13, 2024

I would assume acutance plays into this. Faster and grainier films can look sharper than these ultrafine grained films like Ilford Ortho, Tmax 100, Fuji Acros. They are so fine grained that objects lack that distinct perceived sharpness in transitions between tones, depending on development of course. Often objects look almost like they are "melting" into the background especially if they are metal and lack a certain realism, IMO. The other issue of matching qualities in the 35mm format I would assume has to do with smaller format and image scale and the fact Tmax 400 is extraordinarily fine grain for its class as we all know.

MattKing · Jul 13, 2024

As acutance is the most important component in the predominantly subjective phenomena that we refer to as "sharpness", finer grain frequently results in lower perceived sharpness, even if the resolution is higher with the finer grain films.

bluechromis · Jul 13, 2024

MattKing said:
As acutance is the most important component in the predominantly subjective phenomena that we refer to as "sharpness", finer grain frequently results in lower perceived sharpness, even if the resolution is higher with the finer grain films.

Overall contrast is also a significant sharpness cue for the brain. If one image is more contrasty, it may be perceived as sharper.

pkr1979 · Jul 14, 2024

Thanks guys for the feedback. Its interesting. I tested with yellow filter in addition to no filter at all as well. And I have to admit that for both films I prefer without (at least as default). I found it to mainly reduce overall contrast. Especially for Ortho. It does improve separation between sky and clouds though. Some of the portraits with Tmax 400 looked good with the yellow filter though (not necassarily better, but different and nice). For landscapes I find that a polarization filter is nice with Tmax 400 to get separations in the sky.

Mark J · Jul 14, 2024

Acutance increases the MTF ( modulation Transfer Function ) of the film at frequencies typically in the range up to 20 to 50 cy/mm.
In this area, the film can deliver more than 100% MTF.
Unfortunately only Kodak publish MTF curves of their films.
For example of you look at TMax-100 and T-Max 400, the 400 has a higher MTF at 20cy/mm than the 100.
TMax 100 shows very little enhanced MTF , and I think ( from use ) that Delta 100 is rather similar.

Is it known what film stock Ortho 80 is based on ?
I mean - for instance - is it FP4+ without one of the dyes ?

snusmumriken · Jul 14, 2024

pkr1979 said:
Hi all,

Ive been shooting Ilford Ortho and Tmax 400 interchangibly for a while. And often when shooting landscapes Ive found Tmax 400 to be sharper then Ortho, especially on subjects in the distance. However... I did a massive film test for grade 2 and 3 to try and figure out what kind of films I actually like (using a Pentax 67ii), and again ended up with these two films. And again when I compared distant subjects Tmax 400 would appear sharper (aperture would be the same, but not shutter speed - also shot on tripod). Based om this I assumed that films seeing more blue would appear less sharp on distant subjects then films not seeing as much blue. However, I then shot two 35mm rolls (one of each film) using two cameras and one lens. Same aperture, different shutter speeds, and hand held. Now however, they seemed equally as sharp. This puzzles me.

And I guess my question is if the spectral sensitivity actually would affect perceived sharpness, particularly for distant subjects?

Cheers
Peter

I know you used a tripod for the initial test, but did you consider the effect of mirror slap? I don't know the Pentax 67ii, but is there a mirror lock or a self-timer, so that the mirror can be long out of the way by the time the shutter fires?

Then in the 35mm hand-held test, I can easily imagine that the two films were equally unsharp. I'm not being sarcastic, just that distant landscape details are extremely small objects from the camera's POV. A fair comparison would again use a tripod and eliminate the mirror - unless there is some kind of image stabiliser in the system.

pkr1979 · Jul 14, 2024

I used Mirror-Lock-Up. And I had the same experience when using sheet film... so mirror/shutter shake should not be part of it.

And I agree, for the 35mm hand held test they may be equally unsharp.

DREW WILEY · Jul 15, 2024

A film engineered for improved sharpness via spectral sensitivity tweaking would be Fuji Acros, which is Orthopanchromatic rather than either regular Pan or true Ortho. But the greater red sensitivity of TMax films can dramatically cut through atmospheric haze using a deep red 29 filter. (With some P67 lenses there might be a little bit of focus shift using red filtration; so you want to fine tune the focus with filter in place plus a magnifying eyepiece).

The problem with TMX 100, however, is not its very high detail capacity, but its relatively poor edge acutance unless specially developed to improve that (I use Perceptol at 1:3, which allows just enough grain growth to do that). TMY 400 does not have that problem, so I typically develop it in PMK pyro instead. So there are different potential strategies to attain perceived sharpness in an enlargement.

Another trick is to do unsharp masking, and then print at higher contrast - both the edge acutance and overall micro-tonality will be visually improved; but it's easy to overdo it if you're not careful.

I've shot these particular films, plus many others, in formats all the way from 35mm to 8x10. Acros is no longer available in sheets. Delta 100 is somewhere in between TMX100 and TMY400 grain structure in my opinion, but with less deep shadow gradation than either; for that reason, I rate it at 50, in order to boost shadow values further up the curve.

Lachlan Young · Jul 17, 2024

Mark J said:
For example of you look at TMax-100 and T-Max 400, the 400 has a higher MTF at 20cy/mm than the 100.
TMax 100 shows very little enhanced MTF , and I think ( from use ) that Delta 100 is rather similar.

Overlay them and you'll see that the peak difference is quite a bit smaller (maybe 10% or less - visible, for sure, but less dramatic than the difference between Tmax and a conventional 3D crystal emulsion like 400TX) - while Tmax 400 is a bit more boosted than 100 (it should be, it's a newer emulsion design, with layered dyes etc), but the important other aspect is that Tmax 100 retains 100+% response out to 50 cyc/mm - this performance is a trade-off, as a significant MTF improvement can come at a significant noise/ granularity increase - what Tmax did was very drastically improve on what had gone before - in comparison to Tri-X, current Tmax 400 offers several significant areas of significant MTF improvement - especially in the 10-30cyc/mm range and above 40-50 cyc/mm.

The other complicating factor is what exposure seems to do to sharpness improving addenda within the higher tech emulsions - I've experienced this with Delta 100 and 400, where giving just a bit too much exposure will seemingly enable the developer to access those features more strongly, boosting sharpness and visual granularity quite rapidly - i.e. visible granularity isn't necessarily bigger from more exposure, but more visible because it's much sharper edged (in fact, some of these components are precisely intended to keep apparent grain size under control). In some cases this can also depend on the developer having enough solvency to access the emulsion components effectively, although some emulsions are now seemingly designed to be less sensitive to those characteristics.

Mark J said:
Is it known what film stock Ortho 80 is based on ?
I mean - for instance - is it FP4+ without one of the dyes ?

It's very very close to FP4+ with a different sensitising dye (there could be some J-aggregate stuff going on, but I suspect Tmax of more likely using that). Overall, the Delta emulsions also tend to be a bit shorter in red sensitivity (seemingly closer in rendering to how the eye perceives scenes - Acros is doing similar things, they're all essentially variants on Type B panchro, nowhere near short enough a cut-off to be Type A, but with modified sensitivity in the 570nm range) and Tmax 400 has relatively stronger green sensitivity (like a less extreme Agfapan APX 100).

DREW WILEY · Jul 17, 2024

Acros conspicuously has the highest green sensitivity and least red sensitivity of the aforementioned varieties (exclusive of real Ortho). It's officially orthopanchromatic.

Lachlan Young · Jul 18, 2024

DREW WILEY said:
Acros conspicuously has the highest green sensitivity and least red sensitivity of the aforementioned varieties (exclusive of real Ortho). It's officially orthopanchromatic.

Only under certain conditions. Compared to Tmax 400, it actually has relatively lower green and higher red sensitivity, but a much deeper trough at 500nm. However, this is exposure dependent (e.g. Tmax 400's sensitivity evens out with more exposure), and will obviously make certain filters have far more dramatic impacts on relative speed, thus making most statements about what EI you claim certain films should be exposed at rather more a description of how their relative colour sensitivity relates to your average/ test exposure light conditions/ filter choice than ISO test conditions. As a further illustration of this, APX 100 sensitisation could deliver quite ortho-ish rendering - or the equivalent of a fairly strong green filter effect (more so than even underexposed Acros) at ISO rating - it had a similar proportional trough as Acros, but a dramatic fall off in sensitivity from 565-585nm before the final cut-off started around 635nm (like Acros and TMY-II). So it's a bit more complex than simple didactic statements.

albireo · Jul 19, 2024

Lachlan Young said:
Only under certain conditions. Compared to Tmax 400, it actually has relatively lower green and higher red sensitivity, but a much deeper trough at 500nm. However, this is exposure dependent (e.g. Tmax 400's sensitivity evens out with more exposure), and will obviously make certain filters have far more dramatic impacts on relative speed, thus making most statements about what EI you claim certain films should be exposed at rather more a description of how their relative colour sensitivity relates to your average/ test exposure light conditions/ filter choice than ISO test conditions. As a further illustration of this, APX 100 sensitisation could deliver quite ortho-ish rendering - or the equivalent of a fairly strong green filter effect (more so than even underexposed Acros) at ISO rating - it had a similar proportional trough as Acros, but a dramatic fall off in sensitivity from 565-585nm before the final cut-off started around 635nm (like Acros and TMY-II). So it's a bit more complex than simple didactic statements.

Thank you Lachlan. Could you expand on the link between exposure and spectral response variation.

How much delta in exposure wrt ISO rating would be needed to appreciate significant differences in spectrum using common development density ranges (eg .58-.65)?

Are there films/brands/products more susceptible or more resilient towards this?

Mark J · Jul 19, 2024

Thanks for the info Lachlan.

DREW WILEY · Jul 19, 2024

Lachlan - In the world of common sense, simply put a very light yellow-green filter in place (Wratten 11 or Hoya XO) when shooting Acros, and the effect will be similar to a relatively deep green filter in conjunction with typical pan films. Or conversely, Try a hard cutoff 29 red filter, and it simply truncates, and can't be improved with any amount of filter factor. The furthest red you can realistically go with Acros is a 25 med red, whereas TMax 100, for example, respond nicely to a deeper 29 as well.

Now if you want to talk about long exposure characteristics in relation to specific pan film filter responses, that is a much more involved question - the kind of issue which has to be ironed out in order to make successful color separation negatives, which indeed takes quite a bit of testing and densitometer plotting to tame. Been there, done that. Responses do shift. The most consistent, across the board behavior occurs with TMax100; but it is coated in a manner that poses problems for UV printers.

TMax 400 loses some green sensitivity at long exposures, whereas many pan film, including FP4, lose some blue sensitivity instead. I haven't tested the new Acros II in relation to this kind of issue, and don't really have any reason to, since it's not available in sheets like the previous version.

Lachlan Young · Jul 20, 2024

albireo said:
How much delta in exposure wrt ISO rating would be needed to appreciate significant differences in spectrum using common development density ranges (eg .58-.65)?

The most easily accessed data is the spectral sensitivity information within the various current Kodak B&W product data sheets - they give information for 0.3 above Dmin, and 1.0 above Dmin. It's quite likely that their competition are working to similar methodology, but are publishing only one line of data (almost certainly the 0.3, at least for equal energy/ daylight balanced sources). It's not about the CI/ gamma/ G-bar you develop to, but a function of exposure.

The main aim with shorter red sensitivity seems to be to try and more closely match how the eye perceives colour rendering from shadow to highlight, as opposed to a more absolute rendering of spectral makeup of those values.

Andrew O'Neill · Jul 20, 2024

I was under the impression that Acros II has slightly more red sensitivity, and slightly less blue sensitivity. Sensitivity to green remains the same. I still consider it a panchromatic film. I regularly expose Acros I with a #29 filter.

Lachlan Young · Jul 20, 2024

Andrew O'Neill said:
I regularly expose Acros I with a #29 filter.

Under normal daylight balanced conditions, the 600nm and shorter cut-off of a #29 shouldn't cause major problems with any of the shorter red films if correctly compensated - on the other hand, a #70 (cut off below 650nm) is a different matter.

reddesert · Jul 20, 2024

pentaxuser said:
So, reddeser, does your #3 accord with what Steve O' Nions' comparison seems to show, namely , that Ilford Ortho appears sharper than D100 which is a panchro film as is TMax or is there no link or reason why Ilford Ortho should be any sharper?

To my eye the scene improved in terms of sharpness as follow from poorest to best: D100 no filter, D100 with yellow filter and then Ilford Ortho without any filter

The OP seems to have felt that TMax was sharper initially but on, shall we call it, the second test things were equally sharp for both films

I can only address the original question of whether spectral sensitivity can affect the perception of sharpness (or contrast) on distant subjects. There are pictorial or atmospheric effects that can play a role independent of the film's grain properties or whatever, whether that matters for the OP, I don't know.

I've never used Ilford Ortho and cannot offer guesses as to its grain vs TMax or Delta. I watched a little of the Steve O'Nions video, and first, I don't think I can judge film sharpness from photos shown in Youtube clips (even if zoomed in), second, the choice of an ortho versus a pan film may have pictorial reasons beyond just the quest for the sharpest. IOW, I don't think there's any need to demand that the OP, Steve O'Nions, and everybody else need to agree on the film.

pentaxuser · Jul 21, 2024

pentaxuser said:
So, reddeser, does your #3 accord with what Steve O' Nions' comparison seems to show, namely , that Ilford Ortho appears sharper than D100 which is a panchro film as is TMax or is there no link or reason why Ilford Ortho should be any sharper?

To my eye the scene improved in terms of sharpness as follow from poorest to best: D100 no filter, D100 with yellow filter and then Ilford Ortho without any filter

The OP seems to have felt that TMax was sharper initially but on, shall we call it, the second test things were equally sharp for both films

Thanks

pentaxuser

reddesert said:
. IOW, I don't think there's any need to demand that the OP, Steve O'Nions, and everybody else need to agree on the film.

I said what I thought based on what I have seen in his video. I also if your experiences accorded with the Steve O'Nions video and finally tried to sum up what the OP had found in his two "trials"

I didn't think that I demanded anyone agree. I simply linked to the video to present what I thought was a useful video that had some relevance and to hopefully add to his and to anyone else's knowledge of Ilford Ortho's behaviour in a comparison with a panchromatic Delta film of a similar speed

I have just noticed that I had missed the "t" at the end of your name so apologies for that

pentaxuser

DREW WILEY · Jul 21, 2024

Lachlan - just try it. I often carry both a 25 and 29, and know through considerable real-world experience which films simply can't handle deeper cutoff, regardless of extra exposure compensation. You won't get any usable gradation past a certain point. But there is some variation between 29's, with the B&W version being particularly sharp cutoff.

Spectral sensitivity om BW films and perceived sharpness

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Spectral sensitivity om BW films and perceived sharpness

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