Topic: Just curious...

[sapata]

Just processed some very old bulk Ilford cine film with unknown ISO, I'm doing some tests with different cameras trying to figure it out which ISO should I set the camera since I still got quite a few meters to waste.

I guess I can rate the film at 50 ... I might do other tests to be sure but, what I found strange is that I got sharper (not better in this case) results at a faster ISO rating.

Looking at these frames it gets clearer what I'm trying to say, they're slices of a full frames taken with the LC-A at different ISO ratings, the higher the ISO I set the camera the less the light reaches the film... nothing new here but... look closer at how the sharpness increases as the ISO gets higher?

At the beginning I thought it was the aperture but the LC-A doesn't change the aperture on the auto mode. Would that be camera shake?

[Francois]

Could be camera shake. Sometimes it doesn't take much to alter ultimate sharpness.

[astrobeck]

Camera shake could definitely be the issue at the slower ISO.  
Why not try different ISO's and use a tripod for the next batch?
That would give you a better idea of whether or not it's shake.

Becky

[sapata]

Thanks guys... looking closely it's more like the result of different apertures than camera shake, but since the camera won't change the aperture in auto mode,  there is no other explanation apart from camera shake.

I'll try a different camera and tripod next  time for sure

[hookstrapped]

I don't know if the higher ISO is actually sharper.  It appears sharper, but it reminds me of the effect you get in Photoshop from sharpening an image -- the impression of a sharper image always seemed to me to be the result of increased graininess and increased contrast, revealed upon magnification.

[Francois]

That is another factor indeed.
Sharp grain will give a false feeling of sharpness.
Looking through some stuff a while ago, they said to take a picture of an out of focus gray card at the metered setting and five other apertures. By keeping the gray card out of focus, you don't have any other thing to rely on than the scale. The negative that matches the gray card as closely as possible will give you the sensitivity if you convert the aperture/shutter speed combo back into an EI setting.

[sapata]

The last frame is the very underexposed one and I had to adjust the levels quite a lot in order to have something to see, it does give the impression that the image was sharpened.

The building on the top of the frames is the one that really grabbed my attention...

[Francois]

This is to be expected. Underexposed film causes most of the information to be recorded near or on the toe of the contrast curve (just next to the base+fog level). This is a place where the contrast and exposure is not linear.

[Pete_R]

There is a reason why less exposure could lead to increase in sharpness. I've been looking for references but can't find any.

Light is scattered in the emulsion and this reduces sharpness. For the scattered light to have an effect, it has to be sufficient to expose the adjacent grains to above the threshold whereby they will have some density after development. With less exposure, the effect will be less and the image will be sharper.

Hope that makes sense.

[sapata]

Thanks Peter...

I think this film needs another test with a proper camera on a tripod to eliminate the camera shake factor, I'll definitely do it and post the test results again.

[Pete_R]

Still looking for some references to the effect I previously mentioned I came across another effect which occurs in older, thicker, emulsions which might include yours.

The exposure penetrates the emulsion further with increased exposure and there will be an increase in halation as well as scatter.

[LT]

also, don't underestimate the effect of grain on perceived sharpness. The higher contrast in the under-exposed neg (if over developed) will increase the grain, and give over-all apparently sharper edges etc.

the 100 EI shot certainly seems grainer here.

[sapata]

Still looking for some references to the effect I previously mentioned I came across another effect which occurs in older, thicker, emulsions which might include yours.

The exposure penetrates the emulsion further with increased exposure and there will be an increase in halation as well as scatter.

Peter... this particular emulsion is really thick and if I understand what you're saying, the image on ISO 25 which is the one that has the most exposure is less sharp due to the halation?

[Pete_R]

Peter... this particular emulsion is really thick and if I understand what you're saying, the image on ISO 25 which is the one that has the most exposure is less sharp due to the halation?

Yes, that's how I understand it. I found it in the Society of Photographic Scientists and Engineers (SPSE) Handbook of Photographic Science and Engineering. A doorstop of a book which everyone should have a copy of. 

Here's the quote:

"For the thicker emulsion..., the exposure appears to penetrate more deeply into the emulsion with increasing exposure level. As a result, the more heavily exposed image should not only be more degraded but also be more effected by halation. Most modern thin emulsions show little of this effect"

[Francois]

Wow! I'm not the only one to collect obscure books on the subject 

I think they also mention something similar in "Photographic Sensitometry"...

[hookstrapped]

This reminds me of a question I have about wet plate and what exactly is the focal plane since the collodion sits on the plate fairly thick.

[sapata]

That's fascinating Peter, I'll be doing more tests with this flm for sure...