Manual use of Durst AC 650

[Fafi]

hello, I really need your help !!!

I work since month in my darkroom with a Dust AC 650. This enlarger is fully automatic. It uses a Cosixel system which measures the exposure time. The light is turned on when pushing a button on the transformer.

Otherwise, the light can be turned on to focus by pushing a button on the head.

After few month of fun I would like to "cross et new step" : i.e. I would like to expose more the sky...

But I don't know how to deactivate the automatic exposure and install a timer like a Stopclock.

Is there any "tips" like taking off the Cosixel or anything else.

I've asked an electrician who asked me to provide him the motherboard diagram...but I can't get it also from Durst directly.

As I don't want to buy another enlarger just for doing manual exposure, I would really appreciate if someone could help me.

In advance great tanks !

 

[niels]

Hi,

I also own an AC650. Hope this helps...

But I don't know how to deactivate the automatic exposure and install a timer like a Stopclock.

I assume from your story that you wish to "burn" i.e. overexpose particular areas in your print?

To my knowledge, you cannot deactivate the automatic exposure on the AC650.
But I don't think you need too! By using the "dials" on the enlarger head you can correct the automatic exposure to -4 and +4 stops (so when the automatic exposure exposes the paper for say 8 seconds, you can correct it to do anything between like 0.5 and over a 100 seconds).

So, if you want to push "the sky" in a picture:
1) make a normal automatic exposure like you are used to
2) Determine how much extra you would like to have the sky exposed (let's assume a 50% of the original exposure time for this example)
3) Turn the left dial on the enlarger head to -3 (which is one stop below the original automatic exposure, so 50% of the time)
4) Get ready with your piece of carton or whatever you use to block the part of the picture you are not pushing and push the enlarger button again.
5) Voila!



Let me know if I am being too vague...

cheers,
./Niels

 

[Fafi]

I'm really Happy to find an AC650 user !!!

Your explanation seems to be clear...but I'm not sure with the term "stop" : If you can tell me more about the "Stop".

Let me know if I've understood correctly :

if I have the dial setup to 140 and I want to add 50 % from the basis to burn the sky, I would have to setup the dial to 136 and expose a second time.

If I want to "reduce" the light, I would have to setup to dial to 136 and start the first exposition on the "white" parts of my neg and then setup the dial back to 140 to have a normal exposure for the other areas of my neg.

Cheers,
Fafi

 

[niels]

Well, from your reaction regarding the values on the dials (140) I can deduce that you seem to have another type of dials on your AC650!
That may make things more complicated...
With a "stop" I mean double or half the amount of light, like in using a camera:
Say I have an exposure of 1/60 sec with aperture 5.6, 1 stop more means doubling the exposure to 1/30,5.6 (or 1/60,4.0). One stop less means 1/125,5.6.

With the enlarger you mostly stick to a fixed aperture, so in this case a stop means doubling or halving the exposure time.

I have enclosed a picture of the dials on my AC650. Maybe we can see if the scales/dials are similar enough to figure out what you would need to do.

cheers,
./Niels

 

[bvikesa]

Hi
I have another problem using the AC 650 (and I have spoken to other experiencing similar difficulties with the M-670 color).
How on earth do I use the color head to print with different grades?
I think I have tried most possible settings with slope 20-100%, density 0-6 and a variety of combinations using the three other control knobs.
???
bv

 

[niels]

Hi,

Well, supposing your AC650 color head does the same as mine in color mode; i.e. three consecutive exposures in blue, green and red, the answer is you cannot use the AC650 color head instead of a filter set for use with multigrade paper!

I myself was pretty disappointed when I found out...

The point is that the multigrade paper expects a "mixed" single light source varying between yellow and purple which cannot be provided by the AC650 as it only gives three blue/green/red exposures (and you know BW paper is not sensitive to red anyway)

I believe, but correct me if I'm wrong, that the official terms are that the AC650 uses the "additive" system, while you need a "subtractive" one for multigrade BW paper.

Sorry for the bad news...

./Niels

 

[Bob F.]

Hi,

Well, supposing your AC650 color head does the same as mine in color mode; i.e. three consecutive exposures in blue, green and red, the answer is you cannot use the AC650 color head instead of a filter set for use with multigrade paper!

I myself was pretty disappointed when I found out...

The point is that the multigrade paper expects a "mixed" single light source varying between yellow and purple which cannot be provided by the AC650 as it only gives three blue/green/red exposures (and you know BW paper is not sensitive to red anyway)

I believe, but correct me if I'm wrong, that the official terms are that the AC650 uses the "additive" system, while you need a "subtractive" one for multigrade BW paper.

Sorry for the bad news...

./Niels

Multigrade emulsions are sensitive to green (soft) and blue (hard) light. If you can control the blue and green then you are away - but I have no idea how you do that on an AC650. On my AC1200 I just switch it to B&W mode and then use the head filters (subtractive) manually with the built-in timer but the AC1200 is very different from what I have seen of the AC650 so that's probably not much help ...

Good luck, Bob.

 

[bvikesa]

hmmm...
If I had known this before I used a box of VC paper to conduct tests...
Well, this sucks.

 

[Fafi]

Well, from your reaction regarding the values on the dials (140) I can deduce that you seem to have another type of dials on your AC650!
That may make things more complicated...
With a "stop" I mean double or half the amount of light, like in using a camera:
Say I have an exposure of 1/60 sec with aperture 5.6, 1 stop more means doubling the exposure to 1/30,5.6 (or 1/60,4.0). One stop less means 1/125,5.6.

Niels, I spoke about the "F.Counter" (140) but I have similar dials as yours. Now I see what you mean with "1 stop".

I use mine in B&W with a Ilford Multigrade filter holder, so I don't use the colour dials.

Do you play with colour dials or with the density, or when you mention changing the stops you work with the objective aperture ?

 

[niels]

Hi Fafi,

I happen to have the user manual for the AC650. Unfortunately it is in Dutch, you most probably are not :-(

So according to the manual, and that works just fine for me, for B&W you:
1) push the BW knob (obviously...)
2) Set the "slope" adjuster (top right next to the buttons) to 20%
3) Set all other dials to 0
4) Set the F.counter to the value indicated at the enlarger column (it depends on how much you are enlarging), this also influences the photo-electric measurement circuits

This is the basic setup for making a print.
If you want to adjust the exposure, use the Density dial (the one on the left) to control the print to -2 stops (-6 on the dial) and +2 stops. If you need even more range than that you can use the R-C dial on the right in addtion to the density dial for a total range of -4 to +4 stops.

Hope this helps!

As a sidenote: Of course you can still use the aperture on the objective as well. In my situation I need only *very* short exposure times when I use aperture f5.6. I ended up using -1 stop or more all the time, which leaves almost no room for adjustments. So I actually always set the aperture to f8. This may also have to do with the fact that modern paper is more sensitive than when this enlarger was made, I don't know...

cheers,
./Niels

 

[Fafi]

I happen to have the user manual for the AC650. Unfortunately it is in Dutch, you most probably are not :-(

You're right, I speak french!

So according to the manual, and that works just fine for me, for B&W you:
1) push the BW knob (obviously...)
2) Set the "slope" adjuster (top right next to the buttons) to 20%
3) Set all other dials to 0
4) Set the F.counter to the value indicated at the enlarger column (it depends on how much you are enlarging), this also influences the photo-electric measurement circuits

Until now, it's ok, that's what I do.

This is the basic setup for making a print.
If you want to adjust the exposure, use the Density dial (the one on the left) to control the print to -2 stops (-6 on the dial) and +2 stops. If you need even more range than that you can use the R-C dial on the right in addtion to the density dial for a total range of -4 to +4 stops.

Now I understand what happens when I change the Density dial !

Hope this helps!

Yes, Of Course !

As a sidenote: Of course you can still use the aperture on the objective as well. In my situation I need only *very* short exposure times when I use aperture f5.6. I ended up using -1 stop or more all the time, which leaves almost no room for adjustments. So I actually always set the aperture to f8. This may also have to do with the fact that modern paper is more sensitive than when this enlarger was made, I don't know...

I also had too few times when exposing with the default f5.6 aperture...and even when playing with my Multigrade filters it does not change enough; the white is just a hell grey !

I did also some tests with other apertures but I was sure it was the wrong direction it because I've read the the F.counter value is setup for a f5.6.

Cheers,
Fafi