joerngreuling
Hi,
Since it’s been rumoured here and there that the Adox CHS 50 (=Efke KB 17) is remarkably similar to the Maco PO 100c, I decided to have it reverse-processed using the Scala process. This works quite well with the Maco, but not quite as well with the Adox. Specifically:
Base: Contrary to what the friendly FOTOIMPEX sales assistant said, the ADOX does not have a clear base, but a grey-tinted one, which is quite similar to that of the Agfa APX 100, perhaps even a shade darker. This doesn’t exactly make the ADOX the first choice for reversal processing. The Maco, on the other hand, is crystal clear.
Emulsion: The ADOX emulsion reacts somewhat sensitively to the chemical ordeal of the Scala process, run at nearly 40°C in a continuous-process machine. In two images, tiny, isolated instances of emulsion peeling were observed, though these only became visible upon projection or when viewed under a magnifying glass. This does, however, happen from time to time with the Maco as well.
Achievable speed: The Scala process is actually known for extracting more than the films’ nominal speed from them. Thus, the Maco PO 100c yields 125 ASA, the Agfa APX 100 200 ASA, and so on. I had expected something similar from the ADOX, especially as FOTOIMPEX emphasises that its nominal speed is its true speed, whereas modern films generally have a lower actual speed than the nominal speed stated for them. However, the ADOX only produced reasonably exposed images at 50–64 ASA. Even at 85 ASA, the shadows visibly close in, and skin tones look as though the person photographed has been out in the hot sun for too long. At 40 ASA, the rendering of highlights is still unsatisfactory.
Conclusion: Adox CHS 50 and Maco PO 100c may well come from the same stable, but they are nowhere near as similar as is claimed here and elsewhere. Due to its sensitive emulsion, the ADOX is only of limited suitability for reversal processing using the Scala process. Its grey-tinted base also means it is not the ideal film for reversal processing using alternative, gentler methods (Fomakit etc.).
Greetings from Hamburg
Jö
MirkoBoeddecker
Jün,
The CHS 50 is not identical to the PO 100c.
I’ve read that too, but I never got the impression that the films were being marketed as identical; rather, the CHS 50 roll film was suggested as a replacement.
The PO 100c derives its high resolution from its orthopanchromatic sensitisation, whereas the CHS 50 is a panchromatic film.
The CHS 100 would be the closest comparison, but that too is a panchromatic film with entirely different properties and a completely different sensitisation/resolution.
The speed achieved is also comparable (as you yourself noted, the PO 100c yields 125 ASA and the CHS 50 around 65 ASA). This is exactly in line with what was to be expected.
Under no circumstances can 100 be achieved from the 50 in slide processing – to do so, the process would have to be modified.
I believe what has led those who think the 50 is similar to the PO100c to make this comparison is the fact that the PO100c has a very high resolution for a 100 film. This naturally leads one to suspect that it is a 50 film with 100 ASA printed on the packaging, but that is not the case. It is a 100 film with a Rectepan emulsion (orthopanchromatic), similar to Neopan Acros.
Only the roll films are cast onto a clear base, NOT the 35mm films (see my thread on the problems of sourcing clear
roll film bases).
We never carried out tests with the film using the Scala process, as Agfa had, until recently, gagged the labs and they were not permitted to develop other films using the Scala process. There were always two labs that didn’t strictly adhere to this, but we couldn’t shout it from the rooftops so that Agfa wouldn’t come down on them.
I’m interested in the skin tones. Theoretically, that should be achievable by adjusting the development parameters.
Could you have a go at scanning that?
It is, however, conceivable that the 50 film cannot be developed using the Scala process at all.
40 degrees is definitely too high for the delicate emulsion.
Best regards,
Mirko
joerngreuling
Mirko,
I was actually surprised myself that the emulsion of the Adox CHS 50 survived the rigours of the Scala process at all. After all, you specifically point out that the film should ideally be developed in a canister or a hanging tank rather than in a continuous-action processor, that a stop bath that is too acidic should not be used, and that a fixer should be used where possible. The ADOX actually came through the process very well. Only two out of 36 frames had tiny, isolated instances of emulsion damage; otherwise, the emulsion held up. I’ve experienced quite different results with the Scala process in the past.
You write that the Adox CHS 50 is a panchromatic film and not an orthopanchromatic one. However, your Adox website states otherwise. There, it refers to an ‘orthopanchromatic sensitisation’ of the CHS 50. Perhaps this is the source of the rumoured assumption that Adox CHS 50 and Maco PO 100c might, figuratively speaking, be fraternal twins. The statements regarding the actual speed of the supposedly underrated Adox CHS 50 then further support this false conclusion.
As for skin tones during underexposure: I don’t have a scanner. If it’s important to you, I’d be happy to look around for a way to get it scanned. But as I said: at 50–64 ASA, the CHS 50 produces normal skin tones; at 40 ASA, they’re a bit chalky and pale; and from 85 ASA upwards, they look like they’ve been burnt in a solarium.
Regards
Jü
MirkoBoeddecker
Hello Jörn,
You’re right, it is confusing and, unfortunately, rather complicated because words don’t describe it precisely enough.
So, the CHS 50 is, of course, a true panchromatic film—for a 50-speed film—but compared to modern 100-speed films, it appears orthopanchromatic. It sits, so to speak, in the panchromatic corner at the very bottom, just slightly behind ortho.
The PO100c, on the other hand, is an orthochromatic film that extends slightly into the panchromatic range. In terms of emulsion technology, it therefore still falls within the orthochromatic category, but it is not completely insensitive to red. However, one would expect significantly greater red sensitivity from a 100-speed film if it is sold as a panchromatic film.
This becomes much clearer when comparing the CHS 100 with the PO100c, as the CHS 100 is significantly more panchromatic.
A 50-speed panchromatic film is always less sensitive to red than a 100-speed panchromatic film, and so the difference compared to the PO100c is really much smaller.
Best regards,
Mirko
Gast
Hello everyone,
I find it interesting that it’s said the CHS 50 is less suitable for reversal processing because of its grey-tinted base. I too had toyed with the idea of reversing this film as a trial and had always assumed that the film was cast onto a clear base. At least, that is the case with the films I have used so far, which still bear the EFKE label and which I bought at the end of 2004.
Hence the question: has a different base been used for the 35mm material recently? Doesn’t the grey-tinted base also mean that the way the antihalation coating works has changed?
Regards
Thomas G.
joerngreuling
Mirko,
Following on from Thomas’s post, I’d be interested to know whether your Adox CHS 50 will be available again as a 35mm film with a clear base in the near future, as was the case when you were still marketing it as Efke KB 17. Because, conversely, it actually works very well as a black-and-white slide film: it has a fine grain and delivers a very wide range of grey tones. However, it would be even better with a clear base.
My second question concerns the can-based development of Adox CHS 50 using Fomakit. Are there any empirical findings regarding the actual speed achievable with this method (50 ASA?)? And: What development times do you recommend at what temperature and with what agitation frequency – as mentioned, for can-based development, not in a Jobo processor with a continuously rotating drum.
Regards
Jü
RomanJRohleder
Joern,
> Since it’s been rumoured here and there that the Adox CHS 50 (=Efke KB 17) is remarkably similar to the Maco PO 100c, I decided to have it reverse-processed using the Scala method.
> Base: Contrary to what the friendly FOTOIMPEX sales assistant said, the ADOX does not have a clear base, but a grey-tinted one,
At the time, I was referring to the roll film version of the Efke R50 and an emulsion that was about 2 to 3 years old. Back then, it came on a crystal-clear base – with a slight longitudinal twist – and worked with EI50, 12 mins, 20°C in the Foma self-developing process.
What I didn’t know at the time, though I did have a similarly exposed and simultaneously developed CHS100/120 to hand – is that batch variation is enormous; current AdOX and Efke films require development times roughly 15 to 30% longer than the older stock from 2004. More on this soon; I haven’t yet completed and measured my series of tests. Mirko’s lab technician confirmed this via official channels 10 days ago.
With scalaisation, you unfortunately have little influence over the initial development time (does any lab still offer push/pull?), so your only option is to compensate via exposure.
> Conclusion: Adox CHS 50 and Maco PO 100c may come from the same stable, but they are nowhere near as similar as is claimed here and elsewhere.
You are comparing materials that were produced two to three years apart.
> Its grey-tinted base also means it is not the most suitable film for reversal processing using alternative, gentler methods (Fomakit etc.).
And that applies only to the 35mm version. The current 120 films (up to 04-2008 and 05-2008) are on a different base, which is still suitable for reversal processing and shows only a slight ‘grey cast’. I haven’t yet processed a reversal with these, but this can be overcome in Fomakit by extending the initial development time.
Roman
