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10-11-2015, 04:18 PM   #1
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Pentax LX long time exposure and Reciprocity failure / Schwarzschild effect

Hello, I was wondering what experience LX users had, with long time exposures and reciprocity failure - the fact that, beyond 1sec exposures, films become 'less sensitive' and need extended exposure times or adjusted aperture. I assume that the auto-exposure on the LX doesn't compensate for this by itself ? (Since this behaviour is different from film to film...)
I mostly use Ilford b/w films, (Pan F or FP4+ for longer exposures), and the exposure time range I'm most interested in, for the things I do, is between 2 sec and 10 min, so not extreme - but I would be keen to hear from any LX users, about how you have been handling exposure compensation for long time exposures. Or have you just left it to the automatic, and still got decent results?

Thanks to anyone, who might take time to share their experience!

Kai

10-11-2015, 05:50 PM - 1 Like   #2
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Pretty much the datasheet doesn't cover very long exposures so you are left to test on your own.


I have conducted extra long exposures but mostly on color negatives which appear to all not require any compensation. I have used aperture priority and taken advantage of film's huge latitude even adding a stop or two of overexposure and so far so good.


This one on Kodak Gold 100 using the LX for about 15 minutes.





I will need to figure a way for the LX to tell me when the exposure is done so I am not always peeking in the viewfinder.
10-11-2015, 06:42 PM   #3
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QuoteOriginally posted by kai_in_paisley Quote
I was wondering what experience LX users had, with long time exposures and reciprocity failure - the fact that, beyond 1sec exposures, films become 'less sensitive' and need extended exposure times or adjusted aperture. I assume that the auto-exposure on the LX doesn't compensate for this by itself ?
Films like the Classic Fujicolour velvia 50 ( Disneychrome) suffer loss of speed at exposures longer than 2 seconds, films like Kodak E100G never lost speed until after the 120second mark. Having a camera that could adjust it's auto exposure depending on the film used is basically impossible due to the varieties of film.

QuoteOriginally posted by LesDMess Quote
Pretty much the datasheet doesn't cover very long exposures so you are left to test on your own.
The information is there, every technical publication on film I have used from major manufacturers has reciprocity failure characteristics for their products.
10-11-2015, 07:03 PM - 1 Like   #4
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QuoteOriginally posted by Digitalis Quote
The information is there, every technical publication on film I have used from major manufacturers has reciprocity failure characteristics for their products.


I do read all the docs but more importantly I try them out myself as Kodak can't possibly test all the permutations of exposure settings everyone would try. For instance, in the Kodak Ektar 100 document it states as follows:
QuoteQuote:
Adjustments for Long and Short Exposures
No filter correction or exposure compensation is required for exposures from 1⁄10,000second to 1 second. For critical applications with longer exposure times, make tests under your conditions.
So I test as in this >40 minute aperture priority autoexpose on Kodak Ektar 100 using the LX's unparalleled meter.




10-11-2015, 07:19 PM   #5
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QuoteOriginally posted by LesDMess Quote
This one on Kodak Gold 100 using the LX for about 15 minutes.
Dude... why ya fillin up 3x my screen size??

---------- Post added 10-11-15 at 07:27 PM ----------

QuoteOriginally posted by kai_in_paisley Quote
Or have you just left it to the automatic, and still got decent results?
I've been meaning to do some additional LX long exps, but usually it's the above. If it's really long I might bump the exp comp a notch or two but with the LX I've yet to do any real calculations for serious shots. That said, this shot was a moonless night (very very dark) except for a couple street lights. LX set to auto exposure. This was with a 20mm on RVP100 for 2 or 3 minutes (I don't know for certain - the LX was timing ) - or enough time for me to walk all around the foreground and stop where I'm standing for a quite a while.


Last edited by chickentender; 10-11-2015 at 08:00 PM.
10-11-2015, 07:27 PM   #6
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I remember about 8 years ago, I saw website about person and his PENTAX GEARS that Film SLR and camera DSLR for long exposure. One u saw he use film SLR too long exposure for 3 hours. Pictures are awesome. I can't find his website so hard. I think Pentax Forums users should know about it. I hope someone quick find it.
10-11-2015, 07:37 PM   #7
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Beautiful pictures LesDMess, thank you for sharing. Wow.
10-11-2015, 09:28 PM   #8
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QuoteOriginally posted by filmamigo Quote
Beautiful pictures LesDMess, thank you for sharing. Wow.


Thanks as I shoot enough film that I do get lucky sometimes!


Anyway, I do test all my films and cameras as I did with Fuji 100 negative color film series below for long exposure. It is boring but it shows how good the LX is and how nonexistent reciprocity effect is on this film as it looks the same at 1second through +2hours.





Patience is key when doing these kinds of testing . . .

10-11-2015, 11:47 PM   #9
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QuoteOriginally posted by LesDMess Quote
It is boring but it shows how good the LX is and how nonexistent reciprocity effect is on this film
The camera doesn't have much to do with it. Negative films have a high tolerance for egregious exposure errors and still come up with something, though from my experience it is better to slightly overexpose negative films, and slightly underexpose transparency films.
10-11-2015, 11:54 PM   #10
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QuoteOriginally posted by Digitalis Quote
The camera doesn't have much to do with it. Negative films have a high tolerance for egregious exposure errors and still come up with something, though from my experience it is better to slightly overexpose negative films, and slightly underexpose transparency films.
Re: transparency films - I agree, but just wish my scanner did as well.
10-12-2015, 12:10 AM   #11
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The funny thing is that I still have clients that request I use transparency 4X5 and even 8X10 film - the reason for this is for colour accuracy, having a transparency on a D65 light table is a more consistent viewing experience than most monitors are able to replicate.
10-12-2015, 12:53 AM   #12
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QuoteOriginally posted by Digitalis Quote
The funny thing is that I still have clients that request I use transparency 4X5 and even 8X10 film - the reason for this is for colour accuracy, having a transparency on a D65 light table is a more consistent viewing experience than most monitors are able to replicate.
Absolutely. I love them and prefer them... but uber dense RVP slides makes my Epson cry. Tears roll down it's side when it sees me loading up slide frames in the holder.

---------- Post added 10-12-15 at 12:53 AM ----------

... and you have some very astute clients.
10-12-2015, 01:25 AM   #13
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QuoteOriginally posted by chickentender Quote
and you have some very astute clients.
you have no idea how grateful I am for that. I hear some real horror stories from colleagues and students.
10-12-2015, 04:42 AM   #14
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QuoteOriginally posted by Digitalis Quote
The camera doesn't have much to do with it. Negative films have a high tolerance for egregious exposure errors and still come up with something, though from my experience it is better to slightly overexpose negative films, and slightly underexpose transparency films.


Do you know of another camera that will dependably aperture priority autoexpose as long as the Pentax LX? From all that I have tried - past and present by any other brand, there are none.


This one is on Kodak Gold 100. I pressed the shutter about 9pm and it stopped sometime after 3am.





BTW, all the color negative film that I have tested can tolerate considerably more than a slight amount of overexposure as evidenced on Kodak Portra 160 below. I like to know just what I can get from film at the system level.


10-12-2015, 05:43 AM   #15
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For the record, Acros really doesn't' have much in the way of reciprocity failure. Their data sheet says to add 1/2 stop of exposure after 120 seconds but you don't have to. And some of the reformulated tabular grain films such as 400TMY only start to show reciprocity failure after about 10 seconds and you probably could be ignored up to 20 seconds.
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