Resolution Chart/Targets

Photo Engineer · Sep 29, 2010

QG;

Bloom and fill are chemical effects in film and are related to the type of image, the chemistry involved and the emulsion being used. Both a negative and positive resolution chart are used to check out these effects. Fundamentally, one is related to macro contrast and the other is related to micro contrast.

Turbidity of the emulsion governs internal reflections and therefore affects the sharpness of the exposure.

Bloom makes a 1 micron line appear wider but often have less density than it should. It is a dark line on a white background on the negative. Fill makes a 1 micron line appear narrower and have less density than it should. It is a light line on a dark background. If you reason this through, you will understand the effects gong on.

PE

Q.G. · Sep 29, 2010

Bloom and fill are not just chemical effects, PE.

Photo Engineer · Sep 29, 2010

Bloom and fill are not just optical effects. They must be tested properly for all varieties of effects. Generally, you will find that the chemical effects tend to overwhelm any optical consideration when using high quality professional equipment.

PE

Q.G. · Sep 29, 2010

PE,

You're right about the 'chemicals' being more of a limiting factor than the optics are in an reasonably ideal scenario. (More often it's the optics though.)

Anyway, the OP asked about testing a lens.
An often used measure for lens' performance is the MTF graph. Which is about nothing but bloom and fill - the optical effect. Spread.

Grif · Sep 29, 2010

Ok, getting closer. My example of "printing" or "exposing" were more examples of two different types of flare, whither induced on purpose or by accident, right?

Bloom and fill are effects that occure within the emulsion, both chemical and optical?

Grif · Sep 29, 2010

Dark doesn't Spread/Fill/Flair

Grif said:
If I understand correctly,,, fill/spread are the terms for diffusion on the lens, and diffusion at the enlarger? Light spreads into the shadows,,, or shadow fills into the hilights?

I think that's when I first got the difference, but I sure don't remember them being referred to as fill and spread back before grey hair. I just remember going, wow, that didn't turn out like I thought in the dark room one day.

I was thinking about an enlarger, with a negative image, allowing the shadow (bright projected part) of the image to bleed into the hilights (less projected light) of the print.

Q.G. · Sep 29, 2010

Grif said:
Ok, getting closer. My example of "printing" or "exposing" were more examples of two different types of flare, whither induced on purpose or by accident, right?

Bloom and fill are effects that occure within the emulsion, both chemical and optical?

They do inside the emulsion, yes.

But (and PE keeps obscuring the fact) they also happen to the light that passes through a lens, before it even reaches an emulsion, and before chemical effects do their part to make matters worse.

It's not flare, by the way. That's another thing. It is called spread.

Grif · Sep 29, 2010

Q.G. said:
They do inside the emulsion, yes.

But (and PE keeps obscuring the fact) .

Semantics,,, gotta love it. But having the civil disagreement and conversations between you two is really helping me understand some of the issues.

How about we throw in some anti-halation layer conversation? So that's designed to cut the "reflection" from the film base/air boundry? (the black stuff on the old school microfilm).

Photo Engineer · Sep 29, 2010

My point is that to test a lens, you must know the response of the entire system and then "subtract" the chemistry and film. What remains is the optics. I have done is to describe a method of doing this!

PE

Jim Noel · Sep 29, 2010

I don't believe that any target you print on an ink jet printer will serve your purpose because they do not make smooth lines. Best to print them on a laser printer which does produce very sharp edges on the lines.

craigclu · Sep 29, 2010

I think I posted this once before but.... Here's the old Modern Photography lens testing guide that used to be sold with some USAF targets. It's an interesting read and gives their grading criteria (the old Exc+, Medium, etc). It's also got a simple astigmatism test and how to plot your lens' field curvature.

Sorry, the file is just a bit big and the site won't accept it. If you have an interest, drop me PM and I'll send it off to you.

Q.G. · Sep 29, 2010

Photo Engineer said:
My point is that to test a lens, you must know the response of the entire system and then "subtract" the chemistry and film. What remains is the optics.

Were it not that there are methods of testing the lens itself directly.

Given that, we not only do not "must" test the entire system, and then try to separate the individual component's effect, but we must not do that, because it's hard to separate the individual component's effect, unless you test each one separately.

Which we can.
So why make life impossibly complicated?

Which, by the way Grif, isn't semantics (as little as "flare" is just another word for "spread"): If you want to test a lens, all you need to do is test that lens.

Grif · Sep 30, 2010

Q.G. said:
Were it not that there are methods of testing the lens itself directly.
.

So, how do you test a lens directly, with no subjective interpretation possible and nothing else that could affect the outcome?

Photo Engineer · Sep 30, 2010

Grif;

Generally, direct lens testing requires specialized equipment and recording devices (if one is to have a permanent record). Otherwise, one must resort to indirect means such as I have described. Once you do that, you involve film and must subtract out its effects as stated above.

Optics benches and associated lab equipment are staples in the optics industry but not with us, so we must do it indirectly or spend a lot on the equipment. I suggest that you read up on this subject a bit.

Personally, I have only used the indirect methods to get at what we would call Lens Flare. We used the terms Fill and Bloom for chemical effects. The optics engineers did the direct measurements on our own lenses and made some comparisons, but we film builders often filled in with the indirect tests to compare lenses and systems from other companies.

PE

Grif · Sep 30, 2010

Photo Engineer said:
Grif;

Generally, direct lens testing requires specialized equipment and recording devices PE

Actually was my point, just better stated. Testing a lens always includes other items that have the chance to introduce their own issues into the process.

Q.G. · Sep 30, 2010

Grif said:
Actually was my point, just better stated. Testing a lens always includes other items that have the chance to introduce their own issues into the process.

That's correct.
But unless you design bad test set ups, the errors introduced by your test equipment are smaller by a, or several different orders of magnitude.

As mentioned in post #9, testing a lens requires a bit more than a test chart.

What we can do however, the next best thing, is record images on film, and examine those.
That introduces lots of different, extra ways to change the result, besides lens performance itself. And unless you can subtract those from the result...

... you're left doing relative testing. You can test a lens against another one.
You could declare one lens to be your bench mark, and see how others do compared to it.
Or you could test one lens at different apertures, with and without filters, etc.

Even then, you will have to make sure that, for instance, errors in focussing, variance in developing the film, etc. do not mask the thing you want to test.

The more we stray from direct testing, the lower the probability that what we measure actually is what we wanted to measure.

Q.G. · Sep 30, 2010

Photo Engineer said:
Personally, I have only used the indirect methods to get at what we would call Lens Flare.

In optics, flare is non image forming light bouncing around eventually ending up 'on' the image, creating a general lowering of contrast.

The thing that reduces resolution, the thing you test with charts, is spread. The phenomenon that an image of a point (or line) source never is a point, but that instead the light that should all have ended up in a single spot in the image is spread around the place it should have been in.
The result of that is that an abrupt transition from light to dark in the subject space is rendered as a more or less gradual transition from light to dark in image space. If the detail is smal enough, the light to dark gradients of adjacent detail mixes (what you call fill/bloom, PE), and detail gets lost in a gray blur. The end of resolution.
Diffraction is what is responsible for that.

Two quite different thingies. Despite chemists calling (according to you, PE) the second "Lens Flare".

Photo Engineer · Sep 30, 2010

Well, flare lowers contrast but it also causes spread and fill if you look at it objectively. The light is spread and unwanted areas in. It therefore lowers contrast.

PE

Q.G. · Sep 30, 2010

Flare does not cause spread.
Flare is a different phenomenon entirely. Flare doesn't blur the edge of light-dark transitions. Flare doesn't change a 'block wave' into a 'sine wave'. Just lifts the amplitude of both trough and peak equally.
Flare doesn't make fine detail disappear (except in areas close to overexposure, due to the additional exposure). Flare does not reduce resolution.
Flare is not what you test using test charts like the USAF thingy.

Photo Engineer · Sep 30, 2010

Flare is defined very well here: http://en.wikipedia.org/wiki/Lens_flare

Basically, it places light where you do not want it. You are right. It reduces contrast. I should clarify then that flare "can" produce the effect of spread and fill if it is distributed properly by using the chemical definition. I am crossing terms that I should not cross.

Spread and fill in optical terms are different.

PE

craigclu · Oct 6, 2010

I had quite a few requests for the manual that outlines the old Modern Photography lens testing procedures. The size was too big to upload to APUG so I separated the portion that deals with the descriptions of procedures, plotting field curvature and the simple astigmatism test from the ratings' charts. The charts are the old magazine ranges of ratings for different formats/focal lengths that range from acceptable to excellent. I'll upload them separately for those interested... If I already sent the original to you, these are a bit easier to read because I bumped the resolution a slight amount and you might find these more pleasant to view.

I had a lot of fun with this test kit when I first got it many years ago (25?). I had kind of forgotten about having it but pulled it out when I happened into a number of duplicate optics when buying some Pentax 67 and 645 systems a few years back. I used it to cull the lesser examples and was surprised at the variation in the samples that I had. I've also used it to confirm a suspicion of a lens that's not as snappy as expected. My Konica optics (slr and rf) have been quite consistent and a number of medium format RF optics from Mamiya and Bronica have all tested at the high end of expectations, too.

One odd thing that I've noticed is that some of my favorite optics don't necessarily test out at the very top of the charts. They're quite good and fit into the high "good" and low "excellent" charts but deliver a look and snap that are very pleasing.

Resolution Chart/Targets

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