why shoot at a different ASA than the film is rated for?

[nightsky]

Hi,

I am trying to get my head around why one would shoot at a different ASA then a film is rated for? What technique or thought process do I need to use?

I see examples of photos shot at ASA 200 using HP5+ (rated ASA 400) but why would one do that? Is it okay to change the ASA setting for the film mid-film?

 

[Ranchu]

You can do it without changing the development, because you like the way your pictures look with your specific meter(ing) set at a different ASA.

With black and white people also change the development to change the contrast.

Pushing means develop for more contrast so the midtone is brighter, giving the impression of a faster film. Pulling gives less contrast.

Gernerally, it is not OK to change the ASA mid film.

 

[Charlie Lemay]

You can't change ISO midroll, but you can open up two additional stops in shade or cloudy coditions, if your highlights and light greys can stand the two stop development push aesthetically. You. can read all about it on my website (www.charlielemay.net) in the ZoneSimple section. You don't even need a meter outdoors in daytime. There are free data downloads too.

 

[fdarnell]

It has to do with how ISO is really measured. The true test used to be you would expose test shots at standard ASA (which became ISO) and go over and under a couple of stops on the test scene. Then process your normal method. Make a contact print of the negatives with just enough exposure so you can't see the sprocket holes and base anymore, then see how much you had to over expose to get a good image with a true base black. This puts the first true black on the print at just over "base+fog" which does not contain any imaging area.

That's for traditional printing. I found that in almost all cases, to get this "true black" I had to cut the ISO by one-half for my normal d76 1:1 processing.

This was for the case of black and white film. For color film, we always shot it at the specified ISO since the C-41 process was machine driven and more controlled. Never really tried the black test, but usually the orange mask gave some issues.

Now in the area of scanning, I've never really done this test, but I would suppose that you'd scan a blank frame and adjust scanner exposure to give you an RGB value of either 255,255,255 or 0,0,0 depending on how your working. then use that for the balance.

Truth is, seems I always adjust the exposure and levels for each image scanning to taste anyway, so I just make sure there is enough shadow detail.

With modern films like XP2, none of the above seems to apply - grain can change but you don't seem to get so much.

Just the old school talking here. The days of contact sheets!

 

[mpaniagua]

umm for different reasons. One would be to use the same film on different light conditions. Another would be because you like how the film at differents ASA looks like. For example, I always use HP5+ at ASA 800, on Caffenol. Get very nice result on that ASA, without changing the developing times. It also depends on the film, because not every film suit itself for changing ASA. I think Ilford Delta 100 or 400 dont really suit themself for using them on a different ASA. Of cours, thats my own opinion so everyone else probably have different tastes and results.

Regards.

Marcelo

 

[fdarnell]

One caveat on my comment, I never did this with a system/lens combo that had really good micro contrast like a Zeiss Contax G or Leica lens. This additional level of micro contrast might pull out shadow detail and give you a different result when you look at contact sheets and try to judge the effective exposure index (E. I. we used to call it) since there's more contrast in the shadow's "highlights" and this can be perceived as more film speed. We always had to report or "E. I." on shots - if we said ASA we'd get laughed at (circa 1980).

 

[johannielscom]

Hi,

I am trying to get my head around why one would shoot at a different ASA then a film is rated for? What technique or thought process do I need to use?

I see examples of photos shot at ASA 200 using HP5+ (rated ASA 400) but why would one do that? Is it okay to change the ASA setting for the film mid-film?

Because film manufacturers tend to exaggerate the light sensitivity of their films...

Many 400 ASA films for example do much better in terms of saturation and color brightness when exposed at 250 or 200. In B&W you get deeper blacks with less grain. 200 ASA I usually rate @ 100, and get good results.

Plus, modern film is much better in handling overexposure than it is handling underexposure. One stop underexposed can cause drab colours, while three stops overexposure can easily be corrected in scanning or printing. So overexposing one stop reduces the risk of underexposure.

Finally, when shooting expired film: that loses some of its sensitivity but can still be very good when you rate it at half of box speed to compensate. Divide by two for every decade past expiry date I've read but I've never shot film that old...🙂

Changing sensitivity mid-roll isn't a particularly good idea but if I have to, I change one single stop. Most modern films can handle that in development, but don't do it with slide films or Kodak Ektar or you'll be in trouble.

YMMV, happy shooting!

 

[Roger Hicks]

Because film manufacturers tend to exaggerate the light sensitivity of their films...

No. ISO speeds are normally very accurate. That's what "standard" means. A very few (e.g. Fuji Acros, Foma 200) do not reach their box ISO speeds in anything other than speed-increasing developers, but a manufacturer can choose ANY developer for ISO determination, provided they say what it is.

The main reasons to use other EIs (Exposure Indices) are:

1: Pushing, i.e, under-exposing and over-developing.

2: Using a developer that delivers a lower true ISO.

3: Using a developer that delivers a higher true ISO, e.g. Ilford DD-X.

4: You prefer the tonality with "overexposure".

5: Variations in metering technique, whether resulting from incompetence or defective equipment.

6: Variations in development technique, whether resulting from incompetence, defective equipment or personal preference.

The theory that wicked manufacturers are lying is for the most part nonsense. And ALL film handles overexposure better than underexposure, not just modern films. Consider, after all, how ISO speeds are determined for negatives: the least exposure required to give a good negative...

Cheers,

R.

 

[Solinar]

Excellent post Roger - #2 seem to be the case with Rodinal.

The prevailing popularity of stand development of pushed film in Rodinal comes with a big hit to #4 tonality.

 

[gavinlg]

I personally love pushing black and white film a stop or so for the increased contrast and grain.

Conversely, shooting color negative at 2-4 stops over but developing normally will yeild really creamy muted colors and tones if the scanner knows what they are doing. As an example, I don't like fuji pro400h shot at 400 where I find it to be a bit brown and muddy. I much prefer it overexposed at 200 and than metered for deep shadows (4-5 stops over generally). At this rating, the colors go super creamy and pastel.

 

[charjohncarter]

For B&W film, it is to achieve more shadow detail (or less if you are raising the EI).

 

[John Bragg]

ISO (ASA) or Box Speed is a good place to start your journey from as it is a scientifically measured definition of film speed. Not all of us choose the same route to the final destination though and that is where Ei (Exposure Index) may differ from box speed. Think of ISO as a "serving suggestion" and Ei as your "personal recipe" derived either from personal testing or pure preference or habit.

 

[Roger Hicks]

ISO (ASA) or Box Speed is a good place to start your journey from as it is a scientifically measured definition of film speed. Not all of us choose the same route to the final destination though and that is where Ei (Exposure Index) may differ from box speed. Think of ISO as a "serving suggestion" and Ei as your "personal recipe" derived either from personal testing or pure preference or habit.

Dear John,

A perfect analogy!

Cheers,

R.

 

[john_s]

.................
4: You prefer the tonality with "overexposure".

5: Variations in metering technique, whether resulting from incompetence or defective equipment.
...................

Cheers,

R.

To that I would add, in addition to "incompetence or defective equipment" the design of meters. When the only camera I had was a Nikkormat (1970s) with centre-weighted metering, I set the box speed and it seems that I must have instinctively pointed the camera downwards to reduce the influence of the sky (which would have led to underexposure). When I got a much later (better?) matrix metering model I at first relied on the meter working out what the sky was and I expected it to give correct auto exposure but it didn't. I reverted to centre-weighted metering and have been happy ever since (metering then reframing, not AutoExposure and focus all in one). Of course this could be explained as "personal preference" and, for black and white, my development technique, but the same applied to colour negative prints which were done by the standard commercial process.

I tend to give a bit extra exposure for portraits to avoid the shadowy eye socket look.

 

[leicapixie]

Contrary to Mythology, photography is not an exact science.
Shutter speeds never really exact on mechanical cameras.
F-stops are theoretical! If they were exact, it would be "T-stops".
Film speed/sensitivity varies! Reason for bracketing.
Pro-Films had other exposure guides in box!
Personal method of getting exposure or guessing..
Finally after shooting many rolls, developing(keep good records), one gets the "feel" of the reqd. negative(or slide) that one is happy with.
Your ISO may vary from the box.
All is not again so "exact"!
I shot Tri-X many eons ago at ASA(ISO) from 10ASA to 1600.
I made contact and found a few almost perfect exposures!
I then made prints of each! Quite easy to get projection times!
I realized at end of tests, that any exposure from 100 to 800 yielded almost perfect prints. The best exposures and print was 200 ASA.

 

[Dale D]

Sometimes shooting at a higher EI is a necessity due to low available light conditions. Last month, my daughter performed a violin solo at an old concert hall. I took photos of her as she was waiting in her dressing room beforehand, and in the concert hall after her performance. I rated my Tri-X at 1600. If I had shot it at it's 400 box speed, my shutter speeds would have been too slow, even with lens wide open. Sometimes, it's just what we have to do to get the photo.

Dale

 

[Contarama]

It is possible to shoot half a roll at one ASA and then the other half at another ASA. In the darkroom you snip the roll in half (losing one frame) and develop each half accordingly.

 

[Sarcophilus Harrisii]

Hi,

I am trying to get my head around why one would shoot at a different ASA then a film is rated for? What technique or thought process do I need to use?

I see examples of photos shot at ASA 200 using HP5+ (rated ASA 400) but why would one do that? Is it okay to change the ASA setting for the film mid-film?

Since you have mentioned HP5 Plus, take a look at this page by Ilford about push processing, and also their page on pull processing. There are documents with more detail linked on the relevant pages and they're a trustworthy source of solid information on the subject to help get you started. If you have any queries about it many of us will be happy to help.
Cheers
Brett

 

[John Bragg]

Dear John,

A perfect analogy!

Cheers,

R.

Many thanks Roger.

I Do my best thinking in the middle of the night.

Regards,

John.

 

[Ko.Fe.]

Maybe OP or else still might need some help? 🙂

Push. It is having bw 400 film in the camera, measuring exposure for ISO1600 and developing longer.
Q: Why?
A: Because with ISO1600 you could take images in darker areas, but maintain higher shutter speed and (or) aperture.

Example:

ISO400 flm @1600. Why? Because lens was slow f2.8 and it was dark.


Pull. Is taking pictures with bw or color ISO100 flm, but rating it as ISO 50.

Q: Why? A1: Because if color film is old and expired it is better to lower ISO for exposure measurement. Emulsion is not as sensitive as it used to be.

Example 1:

It is very old Kodak Vision 50D cinefilm. Original ISO 50, but because it is so old I rated it as ISO 25.

A2. Because some film manufacturers are rating their film too optimistically. They sell it as ISO 400, while its best quality (sensitivity) is only at ISO 200. For example, Kentmere 400 and Foma 400 are more like ISO 200 film, not 400.

A3: Because if you pull any bw film it might gives you less grain.

Example:

Very fine grain Kodak 100 TMAX pulled at ISO50. Result is grain-less a.k.a. digital 🙂

A4: Because if you will put not coded film cassette of ISO400 film into $5 P&S, it will not find the ISO code and shot will it at default rating, which is ISO100 🙂