Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-09-2011, 06:47 AM   #1
New Member




Join Date: May 2011
Location: West Coast
Posts: 6
Underexposure

I recently purchased a well used 6x7 with a 105mm f2.4 lens. Shooting only B&W presently. Negative appear a bit underexposed. This is a work in progress...

Cheers!

05-14-2011, 01:56 AM   #2
Site Supporter
Rense's Avatar

Join Date: Dec 2008
Location: Zetten - The Netherlands
Photos: Gallery | Albums
Posts: 8,822
Good luck with it! I love my 6x7.....
05-14-2011, 12:00 PM   #3
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
Who is developing the negatives?
05-14-2011, 01:31 PM   #4
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
Then turn the ISO down a bit. While I haven't shot film for almost a decade now, I do recall that I found the manufacturer's speed rating rarely corresponded to what I felt gave me correct exposure.
Ilford FP4, for example was a wonderful ISO 40 film.
I think T-Max came the closest to speed rating for me, but even it liked being overexposed by a little bit compared to what Kodak said.

05-14-2011, 11:41 PM   #5
New Member




Join Date: May 2011
Location: West Coast
Posts: 6
Original Poster
Q. Who is developing the negatives?
A. A professional lab.
05-15-2011, 02:18 AM   #6
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
QuoteOriginally posted by rmarkus Quote
Q. Who is developing the negatives?
A. A professional lab.
That means you have to adjust your EI to their process. Best to do BW yourself and conduct a speed test if you can. You can beat a lab these days at BW processing because you can select the developer and control the process.
05-15-2011, 07:43 AM   #7
Veteran Member




Join Date: Feb 2011
Photos: Gallery
Posts: 573
The film speed is most likely accurate. The problem exists with your equipment--inaccurate shutter speed, meter, lens transmission, etc. The good news is that the compensation should be constant. You can even adjust the ISO on your meter to make the change.

BTW, how do you know the negs are underexposed?
05-15-2011, 02:08 PM   #8
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
There are very few BW developers that will yield box speed when you conduct a speed test by measuring density above base + fog.


Last edited by tuco; 05-15-2011 at 04:33 PM.
05-15-2011, 05:07 PM   #9
Veteran Member




Join Date: Feb 2011
Photos: Gallery
Posts: 573
But there are developers that will achieve the box speed. If the film is going out for development, then the chances are it will be one of those. Most labs are not going to play with specialized developers. One of my many jobs in this life was working in a professional photofinishing lab. We assume the client shot at box speed unless informed otherwise.

If it is underexposure, the first place to look is other places in the system. The film manufacturers know how to determine ISO and produce consistent emulsion batches.
05-15-2011, 06:32 PM   #10
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
QuoteOriginally posted by tuco Quote
There are very few BW developers that will yield box speed when you conduct a speed test by measuring density above base + fog.
QuoteOriginally posted by Yamanobori Quote
But there are developers that will achieve the box speed. If the film is going out for development, then the chances are it will be one of those. Most labs are not going to play with specialized developers. One of my many jobs in this life was working in a professional photofinishing lab. We assume the client shot at box speed unless informed otherwise.

If it is underexposure, the first place to look is other places in the system. The film manufacturers know how to determine ISO and produce consistent emulsion batches.
My experience echoes tuco. When I ran speed measurements on various B&W films as part of teaching myself the Zone System, I found that most films were off by a stop or more.
Kodak T-Max in T-Max developer was the closest, and it almost within the resolution of my densitometer (X-Rite 810).
I ran my own B&W pro developing service for a decade or more, and found that most photographers under exposed their film, though still printable on a grade 1-2 paper.
05-15-2011, 06:49 PM   #11
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
QuoteOriginally posted by Yamanobori Quote
But there are developers that will achieve the box speed. If the film is going out for development, then the chances are it will be one of those. Most labs are not going to play with specialized developers. One of my many jobs in this life was working in a professional photofinishing lab. We assume the client shot at box speed unless informed otherwise.

If it is underexposure, the first place to look is other places in the system. The film manufacturers know how to determine ISO and produce consistent emulsion batches.
And which developers would that be? Replenishment developers are popular with labs. I can't think of any of those that give box speed off hand but I haven't used them all. They don't use anything exotic as far as developers go. Most likely something from Ilford or Kodak. Especially today with so few being processed, I suspect. Note a speed test also takes into account variations of your light meter and camera shutter. Especially in the case of leaf shutters that tend to slow down with time.

It is easy to verify. Just perform a series of exposures tests needed for a speed test ( can be done with one, 120 roll of film) and ask the lab to measure and record the density difference above film base + fog for each frame in the test and send it to you or just density as long as they include a single reading from the base + fog only (which should be one of those frames in your test). You'll now know what EI to use with that film and for their process. You need to do that with each film you shoot. As far as finding what the "normal" development time should be, that is out of reach when you send it out. That's why doing it yourself is much better. You can establish a "normal" developing time too and you'll be able to place tones more accurately with your work.

Note Many years ago I purchased a Kodak photographic step table. I thought I'd save a some money and get the uncalibrated one and have a "pro lab" measure the densities off it for me. With these "uncalibrated" versions, Kodak did not record the density but guaranteed that each step difference would be within 0.15 of density. Well, the numbers back from the lab showed their densitometer was not very accurately calibrated either because I was getting greater and smaller than 0.15 difference between steps. At that point I wish I would have bucked up for the calibrated version and I have since then.

Last edited by tuco; 05-15-2011 at 07:44 PM.
05-16-2011, 11:36 AM   #12
Veteran Member




Join Date: Feb 2011
Photos: Gallery
Posts: 573
Are you testing for just the film speed or your systemic/person ISO? I would say the film speed is good and the error is systemic.

But we still don't know if the OP is underexposing his negs. Or even how he has determined that.
05-16-2011, 12:56 PM   #13
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
QuoteOriginally posted by Yamanobori Quote
Are you testing for just the film speed or your systemic/person ISO? I would say the film speed is good and the error is systemic.

But we still don't know if the OP is underexposing his negs. Or even how he has determined that.
The test is for the chain of shutter/meter/developer system. When Ilford or Kodak establish their box speeds, do they include tests with staining/tanning developers such as PMK Pyro that is a bit notorious for being on the slow side? I doubt it.
05-16-2011, 04:56 PM   #14
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,157
My understanding of the ISO speed test is that it uses a very specific developer formulation, and a very specific film density to determine the speed point (IIRC, .15 over BD+F), and unless you have that particular developer, you are not going to get that exact speed out of the film.
Also, many photographers, myself included, preferred a somewhat denser negative with a shorter tonal range than what the manufacturer's rating would give (IE: compared to the manufacturer, the convention was to over expose and under develop).

The tests I ran were separate from any light meter reading, and were based Fred Picker's method for determining film speed.
Sorry, it is too long ago now for me to remember details beyond that.
What matters to the OP is that if he is going to continue having his film developed by the particular lab he is using, then he will need to determine that the lab is consistent in it's processing, and will then need to adjust his ISO until he gets a negative density he is happy with.
Since he appears to not be happy with the box speed, all that matters is determining what the film speed actually is with his equipment and developing routine.
A more useful method of determining useful film speed (as opposed to hidebinding oneself to the official ISO) is to close the loop entirely and include the range of the photographic paper in the equation, and work backwards from the enlarger to the film tank to the exposure.

Last edited by Wheatfield; 05-17-2011 at 04:45 PM.
05-16-2011, 07:44 PM   #15
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,103
Wikipedia has an explanation of ISO 6;1993 method of determining BW film speed. The test I used also used 0.1 above film base + fog except you wrap your metering system into that and place 0.1 above fb+f as zone 1 density.

So you meter an out of focus, evenly light white board to place that value 4 stop below middle gray at box speed, shoot, adjust subsequent exposures 1/2 (or 1/3 stops if you have lenses capable of that) above and below the initial metering. Measure the density of each frame and the closest one to 0.1 above fb+f will be your film speed which you determine by the number of stops or fractions thereof from the metered shot.

Ansel Adam's book The Negative has a test procedure like that.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, medium format
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
K-r underexposure vs. k-7/k-5 jackero27 Pentax K-r 17 05-17-2011 05:13 PM
Underexposure? spidey Pentax K-r 8 03-27-2011 01:10 PM
Another Underexposure...please help PentaxKX-2011 Troubleshooting and Beginner Help 16 01-19-2011 12:27 PM
Pentax K7 and underexposure ulrich Pentax DSLR Discussion 13 05-13-2010 03:15 PM
MZ-7 and underexposure photolady95 Pentax Film SLR Discussion 89 07-09-2009 09:44 AM



All times are GMT -7. The time now is 08:29 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top