Reciprocity failure?

jemdna

jemdna

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Bryan
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Hey everyone

Just ordered some Welding glass to throw in-front of my film cameras so I can try some long exposure stuff during the day.

My question is - I here the term reciprocity failure thrown about a lot and wondered what it actually means - and what I need to do to achieve usable shots.

(Thinking cloud trails - Water streams etc)

Bry
 
Reciprocity failure means that very long ( and very short) exposures do not retain the time/stop relationship.

So very long exposures times may need more exposure than is indicated by an exposure meter or a simple working out of exposure times.

It usually applies to exposures over 5 mins.

I'm afraid all you can really do is bracket the shots if you exceed these times.

.
 
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jemdna said:
Hey everyone

Just ordered some Welding glass to throw in-front of my film cameras so I can try some long exposure stuff during the day.

My question is - I here the term reciprocity failure thrown about a lot and wondered what it actually means - and what I need to do to achieve usable shots.

(Thinking cloud trails - Water streams etc)

Bry
Click to expand...

How will you correct the colour cast with film ?
 
It probably will only work with B&W as Pauls says you can't easily correct the green cast.
 
Options are shoot B+W or when dev' + Scanned - I can PP it out (hopefully) :)
 
petersmart said:
Reciprocity failure means that very long ( and very short) exposures do not retain the time/stop relationship.

So very long exposures times may need more exposure than is indicated by an exposure meter or a simple working out of exposure times.

It usually applies to exposures over 5 mins.

I'm afraid all you can really do is bracket the shots if you exceed these times.

.
Click to expand...

What would you say using a number 9 welding glass in typical sunny England weather is going to produce time wise? (Hard to say I know but an idea is better than nothing)

Bry
 
petersmart said:
I'm afraid all you can really do is bracket the shots if you exceed these times.
Click to expand...

To help reduce the guesswork, you'll often find that the manufacturers include a graph or table for reciprocity failure compensation in the technical info leaflet in the box with a film and/or have it on their web site.

e.g. Ilford FP4+ http://www.ilfordphoto.com/Webfiles/2010712125850702.pdf

see Making Long Exposures on page 2
 
The longer film is exposed to light the less sensitive it becomes, that's called reciprocity failure and it means you have to add extra exposure time to compensate during long exposures. How much you should add depends on the film you are using but I'm sure there are guides available on t'net.
 
Stay away from anything from Ilford for long exposures, Fuji Acros will do you proud.
 
I dunno about the colour cast,:shrug:, film does not act in the same way a sensor does.
Some colour films take on a colour cast because they are exposed over the recommended time limit, some tungsten balanced films like 64T are warm at night (long exposures) but uselessly blue shot in daylight.
I'm just saying its not a shoe-in that a film frame will have the same cast as a digital frame....it would be interesting to see, but there are a lot of colour films to try..:)
This welding glass isn't actually green to look at, I take it ?
 
joxby said:
I dunno about the colour cast,:shrug:, film does not act in the same way a sensor does.
Some colour films take on a colour cast because they are exposed over the recommended time limit, some tungsten balanced films like 64T are warm at night (long exposures) but uselessly blue shot in daylight.
I'm just saying its not a shoe-in that a film frame will have the same cast as a digital frame....it would be interesting to see, but there are a lot of colour films to try..:)
This welding glass isn't actually green to look at, I take it ?
Click to expand...

Welding glass does look very green when you look through it, I have been meaning to have a go at using some b&w film...

Fomapan is ridiculously bad when it comes to reciprocity failure, for a 2 minute exposure it would have to be exposed for 33 minutes to get an image!
 
joxby said:
I dunno about the colour cast,:shrug:, film does not act in the same way a sensor does.
Some colour films take on a colour cast because they are exposed over the recommended time limit, some tungsten balanced films like 64T are warm at night (long exposures) but uselessly blue shot in daylight.
I'm just saying its not a shoe-in that a film frame will have the same cast as a digital frame....it would be interesting to see, but there are a lot of colour films to try..:)
This welding glass isn't actually green to look at, I take it ?
Click to expand...

Yes the glass is green - it may actually act the same as a green filter with B&W film. :thinking:
 
The good thing about long exposures with films with poor reciprocity is that it's harder to go wrong with your guesswork once you get to a point, since the film gets less sensitive to exposure as time progresses. I once went out shooting at night with Ilford PanF (yeah, craziness) armed with two points on the reciprocity curve in my head. Roughly 4 minutes or 5 minutes exposure, hardly a difference made.

Every shot on the roll came out exposed pretty much how I wanted, except the one where I tried to light something up with a few manual flash pops :p
 
jemdna said:
What would you say using a number 9 welding glass in typical sunny England weather is going to produce time wise? (Hard to say I know but an idea is better than nothing)

Bry
Click to expand...

my #9 welding glass is about 13 stops worth of retardation. So - assuming sunny 16 and a sunny day (yeah right!)

without glass 100 iso film, 1/100th second @ f16

with glass,100 iso film @ f16 gives approx 80 seconds.
 
joxby said:
I dunno about the colour cast,:shrug:, film does not act in the same way a sensor does.
Some colour films take on a colour cast because they are exposed over the recommended time limit, some tungsten balanced films like 64T are warm at night (long exposures) but uselessly blue shot in daylight.
I'm just saying its not a shoe-in that a film frame will have the same cast as a digital frame....it would be interesting to see, but there are a lot of colour films to try..:)
This welding glass isn't actually green to look at, I take it ?
Click to expand...

The glass is very, very green indeed :)

Okay - this wasn't done on film, but it does illustrate things a bit...


Comparison Sheet-No. 9 Shade by The Big Yin, on Flickr

(last 3 shots were actually shot with a custom white balance on the EOS-450D which lost the bulk of the colour shift)
 
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Liam said:
Welding glass does look very green when you look through it
Click to expand...

Dogfish_magnet said:
Yes the glass is green - it may actually act the same as a green filter with B&W film. :thinking:
Click to expand...


:gag: ...sounds like a hiding to nothing then, I know you stoodents are poor, but really.
I'd eat beanz for 6 months and buy a ten stop...:cool:

For B/W, as already mentioned, Fuji Neopan Acros 100 is probably the best available @ 2 minutes.
 
TheBigYin said:
The glass is very, very green indeed :)

Okay - this wasn't done on film, but it does illustrate things a bit...
Click to expand...

yeah, the point besides the financial aspect is going over my head, seems like more trouble than its worth...:shrug:
 
well - in my case it was a free way of experimenting with extreme long exposures on the digital camera (as I already had the welding glass in the welding mask and a cokin ring I could blutack it to) :shrug: A lot cheaper than a B&W 10 stopper just to try things out. Plus I was bored one afternoon last year, crocked so I couldn't get out on the bike, and felt like experimenting.
 
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I see..

OT...sorry
 
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