PanF 50 at 32

Hey, another newbie question here.. I guess this something I

generally just don't understand in photography. I get the concept

of ISO numbers and films being 'faster' than others, but I don't

understand shooting x film at y speed.

 

How do you just change it over like that?

 

Specifically, my question is directed toward Ilford PanF 50 film. I

shoot this on my TLR a lot, and just lately I have read that a lot

of people choose to shoot this film at 32.

 

Does this mean that I meter the scene as normal, and adjust the film

speed to 32 instead of 50 on the meter? To me, 32 seems like such a

random number and would not fit into the whole halving/doubling

system in calculating exposure values. Like say at f/16 the meter

says I need a 1/15 second exposure at ISO 50. But what would I do

at ISO 32? Wouldn't I have to open the aperture slightly to like

f/14 to compensate? I understand how this could work on my TLR--my

aperture size runs on a slider so I can get f-stops between, say,

f/22 and f/16.

 

But how could you do this on a 35mm camera that doesn't have this

option? My pentax only shoots at 22, 16, 11, 8, etc. Is shooting

this film at ISO 32 just not workable in that sort of situation?

 

Sorry if this is a weird question or has been asked a thousand

times, but I couldn't find a way to search for it.

32 is not a random number. It's 1/2 stop slower than 50. Setting the camera to ISO 32 while shooting Pan F simply means that you overexpose it by 1/2 stop. Your camera seems to have only full stops. Other cameras allow aperture and/or time be set in 1/2 stop or even 1/3 stop increments. Unless your camera has a stepless shutter in A mode (or the shutter works at least with 1/2 stop accuracy), you can't employ this method in a useful way.

"Does this mean that I meter the scene as normal, and adjust the film speed to 32 instead of 50 on the meter? "

 

Just set your meter or your camera to 32 ASA instead of 50 and shoot and meter like normal. 32 is one of the marked film speeds on my K1000, and is the notch between 25 and 40 on my Chinon.

 

Double check your lens on the f/stops. For example, on my 50 f/1.7, only the full stops are marked, but it has clicks in between, which are half-stops. And many, perhaps most cameras, (including Pentax manual focus gear that I have) you can set the aperture in between clicks (can't do this with shutter speed, though).

 

There should be no reason to meter at 50, then work out the setting for 32- just take the reading at 32 in the first place.

<p><i>I get the concept of ISO numbers and films being 'faster' than others, but I don't understand shooting x film at y speed.</i></p>

 

<p>The film speed assigned by the manufacturer is their recommendedation of the emulsion's sensitivity to light. You can run your own tests to determine the actual sensitivity on your equipment (an essential part of using the Zone system to its full potential), or you may rate it to achieve a better negative or chrome: some rate PanF 50 at 32, some rate Fuji Velvia (50) at 40. In each case you are causing some amount (2/3 and 1/3 stop, respectively) of over exposure.</p>

 

<p>The number used, 32, is not arbitrary: it is 2/3 stop slower than 50. The progression of film ASA film speeds is:</p>

 

<p>25, 32, 40, 50, 64, 80, 100, 125, 160, 200, 250, 320, 400</p>

 

<p>The halving/doubling you mention is concerned with full-stop differences, and this holds up here as well. For example, doubling ASA 32 (32 being 1/3 stop faster than ASA 25) yields ASA 64, which is 1/3 stop faster than ASA 50. Perhaps rearranging the progression a bit differently would help see this:</p>

 

<pre>

-----> +1 Stop ------>

25 50 100 200 400

32 64 125 250 500 + 1/3

40 80 160 320 640 + 2/3

</pre>

 

<p>You read this table top-to-bottom, left-to-right.</p>

<p>The old DIN (<i>Deutsche Industrie Norm</i>) system makes this easier to see (at least to me):</p>

 

<pre>

------> +1 Stop ------>

15 18 21 24

16 19 22 25 + 1/3

17 20 23 26 + 2/3

</pre>

 

<p>Notice that the DIN numbers increase by 1 for each 1/3 stop increase in light sensitivity: a full stop difference is indicated by a difference of 3 between two numbers.</p>

 

<p>If you want to know more about how these values are determined, I'd be happy to write more.</p>

 

<p>So, the effect of rating the film at 32 is to give it 2/3 stop more exposure (you're telling the meter that the film is 2/3 stop less sensitive to light so you need to increase exposure by 2/3). The net effect is that the film is over exposed by 2/3 of a stop. If your camera's (or hand-held) meter cannot do this, then you can get the same effect by using other exposure controls on your camera:</p>

 

<ol>

<li>Increase the recommended shutter speed by 2/3 stop.

<li>Open the aperture by 2/3 stop.

<li>Use the exposure compensation dial to overexpose by +2/3.

</ol>

 

<p>Depending on the camera, you may not be able to do any of these. In which case you're pretty much out of luck. However, if you can adjust in 1/2 stop increments then you may be able get 'close enough' for some subjects, especially with a print film where you have the exposure latitude to get away with the slight difference. With slide film I wouldn't risk it.</p>

I hope I am not getting off topic here, but I shot my first roll of PanF and recently received the prints back. Running at the rated ISO of 50, I found them to be very flat, as if the film is slower than ISO 50. I take it ISO 32 or even 25 is a common EI to use? My camera used for the roll of PanF, a Canon EOS 620, is spot on accurate as Plus-X photos shot thru the same camera turned out great.

 

I have a few more contrasty prints and PanF looks to be a very good film with a wide tonal scale. I just cannot believe that it is SO MUCH slower than 50! My film was processed by Images Photo in Tucson, AZ and they use all Ilford chemistry and paper.

 

As a final note, is FP4+ and HP5+ also flat? I have a roll of each to try out.