Slide sharpness

[Henning Serger]

Resolution tests are immensely important for film and lens makers, but in practical shots many effects come into play which limit achievable sharpness.

Yes, and if you know the factors which are relevant than you can avoid or at least minimize sharpness and resolution losses in your daily photography.
If you know the factors and your gear than avoiding is relative easy, it's not rocket science.

If your subject is closer, DOF becomes an issue, and exact focusing won't save you, unless you shoot flat subjects all day.

Well
- for solid and scientific sharpness and resolution tests you need a flat subject, a test chart. Exact focussing is absolutely necessary for correct results. This problem is solved with the method of focus bracketing (which we use). By this way you can also avoid problems with lenses which have a focus shift effect. FB is the best method for flat objects

- lots of photographers who do tests by themselves rely on DOF, and that is indeed as you correctly say, a real problem and very often leads to wrong results with much too low values; DOF only delivers an "acceptabe level of unsharpness"; the circles of DOF in the datasheets of lenses are calculated for relative small enlargements and acceptable results, not for optimal sharpness and resolution

- with subjects in most normal shots, where the subjects themselves have a certain depth, you can take it more relaxed, because of the depth of the subject it is more likely that something in this depth zone is optimal sharp, even if you have some tolerance in your focusing.

Best regards,
Henning

 

[lxdude]

When it worked for you than it is absolutely o.k.. That a photographers likes his results is most important.

There is a good reason why I have differentiated between 'objective' sharpness (analysing the shape of the lines and edges) and 'subjective' sharpness, the 'sharpness impression' you as an individual have looking at an picture enlarged to normal or smaler sizes.

From the technical point of view, if you analyse the objective sharpness of Elitechrome 100, Sensia 100 etc. and K64 at bigger enlargements, in projection or under the microscope, then the modern ISO 100 slide films are indeed sharper.
But from a subjective point of view, lots of photographers say they would give K64 a bit higher rating for sharpness.
Well, I have used K64 for this reason as well, especially during the 80's.

Best regards,
Henning

When you say "sharpness", are you referring to resolution? Because I think of sharpness as meaning acuity- my understanding is the thin emulsion and relief gave Kodachrome greater acuity, and that acuity gave it that "sharpness impression".

 

[Rudeofus]

Yes, and if you know the factors which are relevant than you can avoid or at least minimize sharpness and resolution losses in your daily photography.
If you know the factors and your gear than avoiding is relative easy, it's not rocket science.

I never said/wrote you can't improve sharpness with better technique. I said that the difference between 120 and 130 lp/mm film is visible only in highly controlled test environments and that the resolution of most (good) shots in the APUG gallery is not limited by film resolution.

I have no doubt your resolution test results are valid. I put them in the same category as the light speed limit for motion: it's a real limit but most of us won't notice it in daily life because we operate so far away from it.

 

[Henning Serger]

When you say "sharpness", are you referring to resolution? Because I think of sharpness as meaning acuity- my understanding is the thin emulsion and relief gave Kodachrome greater acuity, and that acuity gave it that "sharpness impression".

No, in the text from me you have quoted I am referring to sharpness, not to resolution.
If you look at high acutance, subjectively very sharp films like Kodachrome (or Velvia 50 for example) at (very) high magnification (100x enlargement with a microscope), and compare it with other modern, sharp high resolution films (Provia 100F, E100G etc.) than the objective sharpness of Kodachrome + Co. is indeed not as good as E100G, Provia 100F + Co.
Because of the significantly coarser grain and more "rough", "ausgefranzt" contours, edges, lines. of Kodachrome.
You see that if you look directly on the film with a microscope (or on the screen in projection, if you go very near to the screen).

This subjective sharpness with high acutance films works very well at lower or medium enlargements. The bigger the enlargement from a certain point onwards, the less this effect is visible, and the more the grain begins to overcompensate it, and you see this "roughness" (it is difficult to describe in words, you understand it at once when you see it with your own eyes; we intend to test direct shots from the microscope for online presentation in the future, we hope that than it can be shown to more people).
Of course the viewing distance is also important and influence the subjective impression of sharpness.

Best regards,
Henning

 

[Henning Serger]

I never said/wrote you can't improve sharpness with better technique. I said that the difference between 120 and 130 lp/mm film is visible only in highly controlled test environments and that the resolution of most (good) shots in the APUG gallery is not limited by film resolution.

Well, yes that is right if you look at films which are nearly on the same level. For example there is no significant difference in detail rendition (resolution, sharpness, grain) between E100G and Provia 100F for example.
And very little difference between Delta 100 and TMX.

But if you compare Provia 400X with Rollei CR 200 for example, or Delta 100 with FP4+, than you will realise significant differences even at lower enlargement factors and in normal daily shooting conditions.
If I compare Provia 400X slides projected on 1m x 1,5m to Rollei CR 200, the Fuji delivers significantly better detail rendition. Very obvious and clearly visible.
And my 30cm x 40cm optical prints from Fp4+ have no chance compared to my Delta 100 prints concerning detail rendition.

And, what most people either don't know or often forget: Lots of the higher resolution films also deliver better resolution at low object contrasts (less than 1:2). And this advantage is visible even at quite low enlargements.
Whether you have 40 lp/mm resolution or 65 lp/mm resolution with details of lower contrasts in your picture is visible at 24cm x 30cm enlargements.
That is for example one reason for the excellent performance of high resolution microfilms, because they are better concerning this parameter than conventional films (and the Velvias are also a bit better in this respect compared to other color films).

I have no doubt your resolution test results are valid. I put them in the same category as the light speed limit for motion: it's a real limit but most of us won't notice it in daily life because we operate so far away from it.

I think it is a little bit problematic to generalize here, because the shooting conditions and purposes differ a lot between photographers.
For example I love bigger prints and impressive, brillant slide projection (with color and BW films) on a big screen (my "home cinema" ).
And because of these bigger enlargements I often see the smaller differences evaluated in our tests in daily shooting, too.

For someone who mostly do smaller prints or using an amateur scanner all this does not matter so much, of course.

Best regards,
Henning

 

[Rudeofus]

Dear Henning,

so what it basically comes down to is we want insanely high resolution for 1:4 or 1:1000 contrast ratios so we get acceptable resolution for 1:1.5 and 1:1.2 contrast ratios. Wouldn't it be more meaningful to measure resolution for 1:1.5 contrast to begin with? This may be the main problem of the term "film resolution", that it strongly depends on subject contrast yet is often named as universal film property ("Tech Pan is 200 lp/mm!").

PS: Does anyone know a formula how to calculate the resolution for different contrast ratios of the resolution is know for one? Or is this behavior different for every film (type)?

 

[Henning Serger]

Dear Henning,

so what it basically comes down to is we want insanely high resolution for 1:4 or 1:1000 contrast ratios so we get acceptable resolution for 1:1.5 and 1:1.2 contrast ratios. Wouldn't it be more meaningful to measure resolution for 1:1.5 contrast to begin with? This may be the main problem of the term "film resolution", that it strongly depends on subject contrast yet is often named as universal film property ("Tech Pan is 200 lp/mm!").

Well, yes and no. It is a bit more complicated.
First of all we have chosen 1:4 object contrast at our last big comparison (so far tested almost 90% of all films on the market) because it is a rather moderate / low contrast.
In almost all scenes you photograph you have details with such a contrast ratio.
Therefore the results are valid for most cases.
We were very happy to find an excellent test chart with this lower object contrast, because almost all other available on the market have higher contrast, most in the 1:6 to 1:16 range.
So far we have not found a quality test chart with an object contrast of 1:1,5. We have some ideas of making one by our own, but that is not trivial. But we will try it in the future.
Of course we did tests with objects with an object contrast of 1:1,5 or 1:1,3. But then you can only compare two films and say, that one is doing better than the other.
But it is impossible to quantify the results.

PS: Does anyone know a formula how to calculate the resolution for different contrast ratios of the resolution is know for one? Or is this behavior different for every film (type)?

There is no such formula, because
- the films behave in a different manner, therefore one formula can not work with all films
- the relationsship between object contrast and resolution is not completely linear: With most films you have a almost linear relationsship from 1:1,3 up to 1:5, 1:6. But then the curve often significantly flattens.

Or simplyfied: If you double your object contrast from 1:1,5 to 1:3, you will get almost double resolution with most films.
But if you increase your contrast from 1:16 to 1:1000 (full six stops) you will increase resolution with most films only by 5 - 10%.

Best regards,
Henning

 

[Photo Engineer]

Well, yes and no. It is a bit more complicated.
,,,,,,,,,,,,,
But it is impossible to quantify the results.
,,,,,,,,,

There is no such formula, because
- the films behave in a different manner, therefore one formula can not work with all films
- the relationsship between object contrast and resolution is not completely linear: With most films you have a almost linear relationsship from 1:1,3 up to 1:5, 1:6. But then the curve often significantly flattens.

And this says a lot!

In this thread and the one on Ektar resolution / sharpness, much ado is made about this type of comparison when it is really virtually impossible to do due to the differences in contrast and other effects (such as the Kodachrome relief image referred to above).

You cannot compare positive with negative films for just the reasons above, and you have great difficulty comparing pos with pos and neg with neg across product lines due to sensitometric differences based on dye types and interimage along with the cited Kodachrome effect.

I myself am wading through "Photografische Informationsaufzeichnung" by Prof. Dr. Hellmut Frieser (Photographic Information Recording), with thanks to Bill Troop who sent me a copy. I may have more to say later on this, but my German is very rusty.

PE

 

[Rudeofus]

There is no such formula, because
- the films behave in a different manner, therefore one formula can not work with all films
- the relationsship between object contrast and resolution is not completely linear: With most films you have a almost linear relationsship from 1:1,3 up to 1:5, 1:6. But then the curve often significantly flattens.

Or simplyfied: If you double your object contrast from 1:1,5 to 1:3, you will get almost double resolution with most films.
But if you increase your contrast from 1:16 to 1:1000 (full six stops) you will increase resolution with most films only by 5 - 10%.

I would expect such behavior for all films: at first you have linear resolution increase because it takes less and less grains to express the contrast, until to some point where single grains (or lack thereof) represent the contrast and further increase in contrast will no longer increase the resolution. I would describe this with the same formula as first order high pass filter responses (in our case resolution over contrast instead of magnitude over frequency). If we could describe film resolution with key parameters max resolution and cut off contrast we should have a much more meaningful description of film resolution.

Needless to say: my approach neglects any effects from different grain sizes over contrast compensation of the orange mask all the way to neighboring effects, but it would still be interesting how well my approach can model measured results.

 

[Zygomorph]

Maybe this is clarified in another 50 posts or so, but why doesn't this graph have a label for the x-axis?! Bad form!