Long exposures and negative contrast

alexmuir

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I have it in my mind that longer exposures, 10-20 seconds in this case, cause a noticeable increase in contrast when the film is developed normally. I can't recall where I saw this, but wondered if it is correct?
I am interested because I have exposed a few sheets of Delta 100 in a still life situation with natural light, and the meter readings suggested the scene was of lower than normal contrast. I had planned on extending development to boost the contrast, and place the main subject tones where I had visualised them. It then occurred to me that this may not be necessary if the longer exposure would already create more contrast with normal development. I used the recently published data from Ilford to arrive at the corrected exposure times. Any advice would be appreciated before I develop the sheets.
Alex


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David M

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Yes.
Reciprocity failure can affect the shadows, before the highlights are affected. I suspect that a bit of testing might be needed, but others on the forum may have a more specific answer.
 

alexmuir

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Thanks David and Keith. I had used the calculation to adjust the exposure time from the measured reading. The final times were between 10 and 20 seconds. I might develop one sheet at the normal time to see how it looks.
Alex


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Ian Grant

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Often when we shoot longer exposures the scene has less contrast anyway, I had no issues with a long exposure earlier this year with HP5, and haven't with other films in the past.

These two image which I posted here recently were shot the same day and processed together, two extremes of lighting:






The first is a long exposure 2 mins @ f22, lowish contrast from fluorescent lighting, the second the 1/100 top shutter speed @ f22 with the Compound #3 shutter on my 360mm Tele-Xenar. I did double the exposure to allow for reciprocity failure.

The two negatives print using the same filtration (grade) in the darkroom and that's matched by scans as well.

You shouldn't have problems with Delta 100 at 10-20 second exposure times. I've shot a lot at around those times, just remember that tungsten lighting needs extra exposure if that's how you're lighting.

Ian
 
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Ian Grant

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Just tried on a different PC and no problems, I thought the images were hot-linked from my own website but it appears the Forum software converts images to PNG files, images don't sow on my phone.





This may be why there's a slight quality drop here, happens with other Forums using the same software. These are Code inserts
so should work.

Ian
 

David M

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Ian (G),
On my screen (2017 27" iMac) the interesting detail of the locomotive's linkages in picture 2 seems to vanish into blackness. Is this the kind of loss of quality you're talking about?
This has made me wonder if we should apply any compensating adjustments before posting.
Perhaps a new thread to deal with preparation of images?
 

Keith Haithwaite

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Black against black in shadow in a 750px wide image at 72dpi screen resolution is always going to leave a lot to be desired David and no amount of faffing is going to improve on that imho. With apologies IanG I dropped a screen dump into PS, changes the resolution to 300dpi and cranked up the images size and I could see lots of lovely detail in the running gear even with this bodge up. I'm not sure adulterating an image just to try and get it looking perfect on a web screen is a good idea - but that's just me.
 

David M

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I realise that it was a lot to ask, but then, I believe Ian has a lot to give. This was my curiosity speaking. I do like to know.
If it had been a forest picture, and the same shadow detail occured in some dark tree roots, my eye might not have scrutinised the area so closely. The locomotive attracted my attention much more, hence my question.
[A pause]
I've just done the much the same thing. Dragged a copy off, increased to 2000px wide and applied 70% Shadow/Highlight to the shadows. You're right, there is a good deal more of the interesting detail. There is much more detail in the dark opening one-third in from the left, too. The image as a whole stands up quite well to this butchery.
 

Ian-Barber

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Preparing images for the web for ultimate clarity can be challenging at the best of times.

If scanning negatives, make sure you stay in 16bit right up to the point of resizing for the web
If downsampling and using Photoshop, try to use one of the Bicubic algorithms.
For this forum, the max size is 1400px (wide) and 1200px (tall) and a max file size of 3mb.
If you go any higher than this then the forum software will downsample again which will reduce quality.
 

Ian Grant

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David, Kieth, looking at the HiRes cscan and the Intermediate file I corrected slightly to match the print before saving there's far more detail in those shadow areas. I then resized it for the web, there were no changes made to contrast, shadow detail etc.

What's happening is there's a lot of fine detail lost in those shadow areas during resizing,

upload_2018-8-10_19-49-35.png

left is the large file at 120%, compared to the file posted here (above) at 300% but at 100% it looks quite a lot darker

upload_2018-8-10_19-56-9.png and shadow detail disappears

Ian
 

David M

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Ian G,
Interesting. It's worth knowing this. My butchery showed that there might be even more detail, but masked by the reduction.

Ian B,
Could we publish these details somewhere for future reference, please? Is there a level of JPEG we should use? I've been saving at 10 and 800px longest side. I didn't know about the benefits of keeping 16-bit as long as possible and there are almost certainly other things that I don't know. Should we perhaps alter the Levels histogram in some simple way?
 

Ian-Barber

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Could we publish these details somewhere for future reference, please? Is there a level of JPEG we should use? I've been saving at 10 and 800px longest side. I didn't know about the benefits of keeping 16-bit as long as possible and there are almost certainly other things that I don't know. Should we perhaps alter the Levels histogram in some simple way?
Over the weekend I will post a sticky thread
 

David M

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Afon Gamlan from Early Landscapes. I have several others, mainly bought on workshops.
 
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