Acufine and 120 HP 5+

Film Photography & Darkroom discussion

Moderator: Keith Tapscott.

pirateoversixty
Posts: 195
Joined: Sun Jun 18, 2006 1:21 pm
Location: Peoria, Illinois

Acufine and 120 HP 5+

Postby pirateoversixty » Fri May 15, 2009 8:42 am

Was just checking the MDC for the above combo, and I noticed that the times were twice for 120 vs 35mm exposed at EI 640-650.
Any views on this? Misprint? Got a roll t develop for a small project.
Jim


Digitaltruth
Site Admin
Posts: 264
Joined: Mon Aug 16, 2004 8:24 pm
Contact:

Postby Digitaltruth » Fri May 15, 2009 12:09 pm

Hi Jim,

I've checked the references on this and the data actually comes from the last ever chart produced by Acufine Inc. The actual times shown are:

35mm: 640 ISO, 6.5 mins, 21C/70F
120 roll: 640 ISO, 12 mins, 21C/70F

More recently, Ilford has published these times for all formats (35mm, 120 roll, sheet):

400 ISO, 4.5 mins, 20C/68F
800 ISO, 6.5 mins, 20C/68F
1600 ISO, 9.5 mins, 20C/68F

I really don't know which data you should believe, but personally I would use the 35mm time as this seems consistent in both Acufine and Ilford's publications and the odd one out seems to be the roll film time.

This brings up an interesting discussion which I hope some others will join in and share their knowledge about. My understanding is that the only reason for any significant difference in times for different formats is due to one of two things: either the emulsion is not the same, or the film base is different. In some cases if the film base differs by format, the emulsion may be modified to enable correct coating. More minor differences in time may be related to other factors, but the huge discrepancy in Acufine's data could only be accounted for by some large physical or chemical difference. The Acufine data dates from the 1980s, whereas Ilford's originally appears in the 1990s, so if there were any changes to the emulsion or film base during the intervening years, this might offer an explanation.
--Jon Mided

Digitaltruth Photo
http://www.digitaltruth.com

pirateoversixty
Posts: 195
Joined: Sun Jun 18, 2006 1:21 pm
Location: Peoria, Illinois

Acufine and 120 HP 5+

Postby pirateoversixty » Fri May 15, 2009 11:41 pm

John:
Thanks for the quick reply.
I have heard it bandied about that there are some differences between 120 and 35mm formats for some brands of film, but none referring to Ilford, that I can recall.
Again, thankyou, and I do hope this post prompts some people to chip in some info; there are many knowledgeable people who do do now and then.
Jim


Who is online

Users browsing this forum: No registered users and 1 guest