Very long enlarging times, 2-3 minutes

kipkeston · Dec 13, 2007

Hi everyone. I've recently started enlarging at home. I bought a Omega Chromega B enlarger with a 3.5 50mm omegar lens. With 60 magenta filter my enlarging times are anywhere from 2 minutes to 3 minutes with various densities at f/8. I know that my times should be much shorter! 10-30 seconds right? My times are much too high. I believe the enlarger has 6x6 mixbox also, not 4x5. My blub seems very bright when I open the head up but all that light must get lost somewhere. Does anyone know what's wrong? I was considering a new blub but it seems so bright right now.

Lopaka · Dec 13, 2007

If you are using a 50mm lens I assume you are working with 35mm negs. Enlargers that use mixing boxes spread the light evenly over the area of the neg size they are designed for. If you are using a 4x5 mixing chamber you are spreading the light too thin - you need a 35mm mixing chamber to concentrate the light to the neg size. And welcome to APUG!

Bob

kipkeston · Dec 13, 2007

I think it's a 6x6 or 2.25 mixing chamber. But I'm really not certain. How do I verify? I use 35mm.

Photo Engineer · Dec 13, 2007

The opening in the mixing chamber is just a tad bigger than the diagonal of the negative it is intended for. Thus, the opening on the 4x5 chamber would be about 6" and for a 6x7cm negative would be about 8cm.

But, I only see about a 1 - 2 stop difference if I use the wrong mixing chamber. So, I doubt if that is your problem.

PE

bdial · Dec 13, 2007

The Chromega B is a medium format enlarger that doesn't go beyond 6x6 in some models, according to Classic Enlargers.com (http://www.classic-enlargers.com/omega_b22_enlarger.htm).
Though a 35mm mixing box would help, it's not the sole reason you're getting such long exposure times. The guy that runs Classic Enlargers has a q and a forum, which would be another good source of help. Harry has been servicing Omega enlargers longer than some folks here have been alive.
Have you done any tests with white light exposures? Is the mixing box in good shape? Do you have more than the magenta filter in place when your are making these exposures? Especially do you have any cyan dialed in along with yellow? Using all three filters gives you neutral density filtration. Finally, are you using a VC paper?
I don't know if the Chromega B has an attenuator, but if it does, that might be blocking the light.

kipkeston · Dec 13, 2007

Thanks for the replies. I only have magenta filter on. I'm using ilford multigrade IV rc de luxe. I will try Harry too. I didn't really do any white light tests. I think the mixing box is fine. I don't think servicing is worth it, I paid 40 dollars for the whole setup. Perhaps if I can't get it brighter I will look for a normal condenser setup. Staccato sentences, hehe.

srs5694 · Dec 13, 2007

In theory, cyan filtration will have no effect on most B&W papers; cyan filtration just removes red light, to which most B&W papers are insensitive anyway. Using both magenta and yellow filtration will increase exposure time, though, so if both are set that could be an issue.

A few ideas of causes come to mind:

Paper -- What paper are you using? Some papers are much faster than others. I tried some Slavich Bromoportrait 80 recently, and it's very slow compared to the Agfa and Foma VC RC papers I normally use.
Dirt/discoloration -- If the mixing box is dirty or discolored, that could greatly reduce the amount of light reaching the paper. My first enlarger (a Durst C35) had a mixing box that was slightly yellowed with age. I don't think this caused me great problems, but more severe discoloration could. Similarly, a lens that's gunked up would cause problems, and perhaps not just long exposure times!
Aperture problems -- Check that the lens's aperture is working correctly. If it's stuck too small, this could be the source of the problem. Remove the lens and look through it to check the aperture operation (and check for dirty lens elements).
Filters -- Check that you don't have filters in the enlarger's filter drawer (if it's got one). A neutral density (ND) or other filter could be reducing the light reaching the paper.
Development -- Try developing your paper for a longer period of time. Chances are this isn't the only problem (you'd probably never get a satisfactory black if you were seriously underdeveloping), but modest underdevelopment could be exacerbating some other problem.

Suggestions by others -- mixing box issues, for instance -- are also worth checking. I don't mean my list to be exhaustive.

thebanana · Dec 13, 2007

Could also be the wrong bulb.

Photo Engineer · Dec 13, 2007

A cyan filter, dialed in with an M and Y will reduce exposure by a factor equal to the density of the neutral density of the filter pack. Mainly, this is due to the impurity of the cyan filter iteself contributing density to the light even though the paper cannot 'see' the filter itself.

PE

Anscojohn · Dec 13, 2007

. I bought a Omega Chromega B enlarger with a 3.5 50mm omegar lens. With 60 magenta filter my enlarging times are anywhere from 2 minutes to 3 minutes with various densities at f/8.
******
Are you sure there is not some other filter in the light path? And, of course, your paper developer is fresh, right? What paper developer are you using? I sure hope you are not using D-76 or some such film developer instead of paper developer. Sounds strange, but many of us have done that by mistake or for experimentation.

kipkeston · Dec 13, 2007

Hi, forgot about the paper developer. It's Ilford PQ. The paper is ilford multigrade IV RC de luxe.

I believe the light is as neutral as possible. I opened up the head and there are no filters in the way. The bulb sure seem like 75w, I can't look near it for more than a split second with the cover off.

I will check the other things you have all mentioned.

Sirius Glass · Dec 14, 2007

How large is the enlargement? If you are making a large print the exposure time is longer that if you are making a smaller print.

Steve

Michal Kolosowski · Dec 14, 2007

HI!

You can open the lens aperture a bit. Most of the enlanrger lenses I've been using achieve best image quality when stopped down by only one or two stops anyway.

removed account4 · Dec 14, 2007

i have very long exposure times once in a while
sometimes, it just happens (even with negatives that look "normal" )

have fun

--john

cowanw · Dec 14, 2007

I use a lot of Kodak C41 black and White films and I find the exposure times to be just under a minute at 5.6 so your times are just one stop off that. Are you using colour masked films
Regards
Bill

Lee Shively · Dec 14, 2007

If I remember correctly, the Omegar 50/3.5 is a kit lens that came with some Omega enlargers. I think I have one that came with one of my old enlargers (I'm not at home to verify, so I'm working from faulty memory). If it is, it's not a very good enlarging lens and may be a partial source of your problem by not transmitting the projected light efficiently. If it's the lens I'm thinking of, you probably do get better performance at f/8 than wider apertures.

eclarke · Dec 14, 2007

Lee Shively said:
If I remember correctly, the Omegar 50/3.5 is a kit lens that came with some Omega enlargers. I think I have one that came with one of my old enlargers (I'm not at home to verify, so I'm working from faulty memory). If it is, it's not a very good enlarging lens and may be a partial source of your problem by not transmitting the projected light efficiently. If it's the lens I'm thinking of, you probably do get better performance at f/8 than wider apertures.

Really good 50mm lenses are cheap and easy to come by. What temp is your developer at?..Evan Clarke

David Brown · Dec 14, 2007

I've got a Chromega B. I have the manual for it, too. If you don't have one, PM me and I'll xerox you the pertinent pages.

There is no interchangeble mixing box. The "B" is a 6x6 enlarger that will, of course, also do 35mm, but there are no changes to the machine other than the lens.

60 magenta is a lot of filtration. For Ilford MG that is the equivelent of over grade 3 1/2 !!. Have you tried making a print, say, 8x10, without filtration? I would bet that your time will be much closer to what you are expecting. If your prints have next to no contrast without filters (should equal grade 2) then something else is wrong besides the enlarger. This could be exposure, development, bad paper, the variables are many.

As for the enlarger, I hope you got the power supply and the voltage regulator with the kit. The voltage regulator is not critical, I suppose, for B&W, and I don't know IF it makes any difference in light output. The bulb is a 75 watt, 27 volt, part # 471-043 (that may be imprinted inside the lamp housing. There are a lot of these haligen bulbs that look alike, so make sure it's the right one. (EDIT: the voltage regulator - I went back and read the manual - is optional, so shouldn't be pertinent to this discussion.)

The lens might have some haze, too. But all in all, I suspect that attempting to print at a grade between 3.5 and 4 is the crux of your problem. If a filterless exposure was 30 seconds, for instance, dialing in 25 magenta will almost double that, and 60 will likely double it again, and you are at 2 minutes.

srs5694 · Dec 14, 2007

Photo Engineer said:
A cyan filter, dialed in with an M and Y will reduce exposure by a factor equal to the density of the neutral density of the filter pack. Mainly, this is due to the impurity of the cyan filter iteself contributing density to the light even though the paper cannot 'see' the filter itself.

Are you saying that the cyan filter (and presumably the magenta and yellow filters) in color enlargers have substantial neutral density components in addition to their "advertised" colors? If so, this seems a bit surprising to me, but as my own enlarger (a Philips PCS130/PCS150) uses an additive color system, I can't do any tests to check this. Certainly with mine, adjusting "cyan filtration" (really red light intensity) has no discernible effect on B&W VC papers.

bdial · Dec 14, 2007

In the subtractive color system, mixing all three will give you neutral density (eventually black), in an additive system mixing all three gives you white.
How much ND you get depends on how much of all three are dialed in.
In B&W or color you only use 2 of the three filters at most, unless you actually need to reduce the light output, which would not be a common situation. For example, you are making a very small print, the lens is stopped all the way down, and the exposure is too short.
For B&W, you can use combinations of yellow and magenta to keep exposures consistant across grades, Ilford and Kentmere document the filter combinations for this.

Photo Engineer · Dec 14, 2007

srs5694 said:
Are you saying that the cyan filter (and presumably the magenta and yellow filters) in color enlargers have substantial neutral density components in addition to their "advertised" colors? If so, this seems a bit surprising to me, but as my own enlarger (a Philips PCS130/PCS150) uses an additive color system, I can't do any tests to check this. Certainly with mine, adjusting "cyan filtration" (really red light intensity) has no discernible effect on B&W VC papers.

If you look in the Kodak filter books you will see that no filter is perfect. A perfect filter is a rectangle in absorbance or transmittance. So, yes, what I said is true.

In particular, a cyan filter has a lot of green and blue absorption, etc.

PE

Very long enlarging times, 2-3 minutes

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