Dichroic vs. Diffusion Enlarger

[DanielJohannes]

Hi all,

I've been doing some research into enlarger types, and am slightly confused regarding the practical difference between dichroic and multi-filter diffusion enlargers. I understand the concept of thin film interference, and see the distinction between this and the use of normal colour filters. I would however appreciate it if someone could clarify:

A. How exactly dichroic filters are used in enlargers. (I've read that dichroic heads are essentially a variation of diffusion ones - if so, what is the nature of the inner workings, and how do they differ?)

B. What the benefits of each are.

I've looked for answers online, but haven't had any luck since dichroic heads seem to be mostly grouped with multi-filter diffusion ones, even though there is obviously a distinction.

 

[aizan]

1) dichroic filters are used for variable contrast and color papers. they have cyan, magenta, and yellow filters built in, while solely diffusion heads don’t. there are books and articles on the web that explain how to use them.

2) it’s a matter of convenience since diffusion heads always(?) have a filter drawer for sticking in color filters.

afaik, the two terms (dichroic and multi-filter) are synonymous, unless you’re talking about vc heads with green and blue filters.

 

[x-ray]

A diffusion head whether cold light or halogen produces the same end result no matter whether it has dichroic filters or dye based filters. Dichroic heads generally have halogen hight sources and non dichroic can have halogen, regular incandescent or cold light sources. Non dichroic use dye based filters either in a filter drawer in the head or in the light path under the lens. Dichroic heads use metallic vapor coated filters in the light path above the negative.Advantages of a dichroic are the filters do not fade with light exposure and time and do not degrade the image due to imperfections in the filter. Dye based plastic filters in the head do not degrade the image but are subject to fading over time. Filters under the lens have the potential to degrade the image if they're fingerprinted, dusty or scratched and can fade with time although I've never seen any fade.

Dichroic heads work by using a halogen light source, a dichroic set of cyan, magenta and yellow filters (for color) between the light source and a diffusion chamber or mixing box diffuses and evens out the light before passing the light through the negative. The filters work by moving in and out of the light path. The amount they intrude into the light path determines the strength of the effect of the filter. For example an .05c will just barely extend into the light path here as a 100c will be about 50% in the light path and a 180c will be roughly 100% in the light path. The same is true with each filter.

I use an Alford MG head for my B&W work, It's a bit of a different halogen diffusion head. In this case there are two halogen bulbs that shine 100% through a dichroic magenta and and another yellow filter. The intensity of the lamp determines the amount of yellow and magenta light which determines the contrast. this light enters a mixing chamber and passes through a diffusion material then the negative.

All of the above are diffusion heads and therefore the end result is the same.

In the 70's I owned a Chromega 4x5 with a set of dye based filters in the head. They were dialed in and out in a similar manner as a dichroic but the filters faded with time and use. When the Chromega II with dichroic filters came out I purchased one of them. Dichroic filters do not face therefore the results are more consistent over time. With the old Chromega I you might need a filter pack of 65m and 30y for a particular neg but that might change (using the same emulsion batch of paper) over a few months and be 85m and 60y the next time you print. Given yours the same emulsion batch of paper with a dichroic system it theoretically should remain the same as the first time you printed the neg.

 

[Dwig]

Hi all,

I've been doing some research into enlarger types, and am slightly confused regarding the practical difference between dichroic and multi-filter diffusion enlargers. I understand the concept of thin film interference, and see the distinction between this and the use of normal colour filters. I would however appreciate it if someone could clarify:

A. How exactly dichroic filters are used in enlargers. (I've read that dichroic heads are essentially a variation of diffusion ones - if so, what is the nature of the inner workings, and how do they differ?)

B. What the benefits of each are.
...

A: While most dichroic color heads are also diffusion heads, this is not universally the case. Notably, Beseler offered dichroic heads for the 23c II series that could be used with a diffusion chamber or with the enlarger's condensers.

B: Dichroic "filters" are VASTLY superior to conventional filters (read: true filiters). Actually, dichroic "filters" are not truly "filters" as they do not absorb parts of the spectrum. Instead, they function by passing some portions and reflecting the rest. This produces the same color effect. By not absorbing light energy, they are not subject to the fading to which conventional true filters are prone.

 

[Ko.Fe.]

These days I would choose not by something which was more less relevant to the final print thirty years ago, but by available light source. The bulb, is it still possible to buy replacement or it is obsolete? Or replacement is made by one person and it costs same price as enlarger. Or conversion is available. Or you still could buy replacement lamp and it is not arm and leg.

 

[Dante_Stella]

These days I would choose not by something which was more less relevant to the final print thirty years ago, but by available light source. The bulb, is it still possible to buy replacement or it is obsolete? Or replacement is made by one person and it costs same price as enlarger. Or conversion is available. Or you still could buy replacement lamp and it is not arm and leg.

Dursts dichro heads run on 24V/250W halogen ELCs, as I recall, which are neither illegal nor out of print. They are essentially track light bulbs. I have a box of them in the basement. They're $3-6 apiece online. There are only two issues buying generic: (1) they may unbalance the color slightly (for b/w it doesn't matter), and (2) they may have a shorter life due to the shock of having the head moved up and down when they are hot. But when I say short, it's still like 2 years of weekend sessions.

Even so, there are LED replacements for a lot of old enlarger bulbs. It's not really hard to re-rig lighting with diffusion enlargers; it's a little harder with condensers, since you need the bulb to be in exactly the right place.

I think the bigger issue with enlargers is stability and ability to keep alignment. On that basis, Durst is way better than Beseler. Maybe not so much from a cost-of-accessories standpoint. Or the ability to find parts etc. So buy complete!

Dante

 

[x-ray]

One of my enlargers is a Durst 138 5x7. The Osram bulb has been discontinued for years and if you can find one you'll pay $400 if you want it. A lot of us though have converted our enlargers to LED and the work great.

I think one of the versions of the Focomat V35 uses a bulb that's not made any longer. It's my understanding there's a replacement but it's lower wattage and quite dim.

Other than those two I'm not aware of any other mainstream enlargers that you can't get bulbs for at a reasonable price.

 

[Ronald M]

Dichroics are a type of filter on glass substrate used to color the bulb light either for color or VC monochrome printing.

Diffusion is non condenser enlarger where light is diffused before reaching the negative.

The only condenser enlarger that uses dichroics is Phillips. They are usually reserved for diffusion as built in filters and and they work the same in either case.

 

[Graybeard]

One of my enlargers is a Durst 138 5x7. The Osram bulb has been discontinued for years and if you can find one you'll pay $400 if you want it. A lot of us though have converted our enlargers to LED and the work great.

I think one of the versions of the Focomat V35 uses a bulb that's not made any longer. It's my understanding there's a replacement but it's lower wattage and quite dim.

Other than those two I'm not aware of any other mainstream enlargers that you can't get bulbs for at a reasonable price.

I've been using a PH213 incandescent bulb in my Durst138 for some time now with satisfactory results on 5x7, 4x5, and 6x9cm on B&E. I'm aware that some users may not agree, just take a bit of time to align the bulb.

 

[Deleted member 65559]

Xray, I have a Durst 138 with a color head & it uses the same bulbs as slide projectors & when the light burnt out I bought 5 or 6 of ebay for under $2 @ I'm still on the first one. Work like a charm.