Pearl lamps in enlargers

[swmcl]

Hi,

A reply in particular in my other thread concerning enlarger electronics has me asking about frosted or pearl lamps (thanks Jim Jones).

In some of the Durst literature I have read, in particular a document titled "Collimated light vs diffused light.pdf" there are a number of diagrams and discussion about effectively projecting the filament onto the paper via various lenses in a condenser enlarger.

If there are a number of particular condenser lenses made to suit certain bulb sizes for an enlarger (and enlarging lenses) and also when there is a table in the enlarger documentation which speaks of a 'point light' condenser elements, how much does lamp diffuseness play into things? You are trying to focus a filament onto the paper - not a whole bulb ... (in a condenser enlarger anyway) according to the documentation.

The Durst L184 10x10 enlarger does not have point light lenses. The L138 enlarger does have point light lenses.

As the bulbs are not available, I am looking to make up something. I have bought two different sized lamps (quartz halogen 240Vac). Both are not frosted.

I am off to a local manufacturer within the hour to get them mounted in the housings and will discuss perhaps making a polished stainless reflector - hopefully in an elliptical shape to aid in shoving light into the system. I have nothing to get ideas from so I'm sucking and seeing.

The other thing I'm thinking of trying is sanding the heat shield - effectively making it a ground glass heat shield! I'll buy another piece of glass for that purpose of course. This will diffuse the source somewhat yes?

At the end of the day I'd like to get as collimated and as sharp as possible. Diffusion can be had with a big piece of frosted glass or two in the filter drawer!

Cheers,

Steve

[BetterSense]

Can you attach the document about enlarger optics? I've alwats found the designs of enlarger optics odd and would enjoy some explanation.

[swmcl]

Sure I'll give it a go ...

Nope. Its 2M4 (2.4 meg) so it is probably too big.

The website address is:

http://www.durst-pro-usa.com/resources.php

Look in the Appendix section for a Collimated vs Diffused Light article.

[wombat2go]

In case it is relevant,
I have a 1950's Federal enlarger here
It is a condensor type with a big glass lens.
The lamp is a GE Photo enlarger type 211 75 watt which I see is still available.
That lamp has a heavy white coating inside the bulb, and the label is on the neck of the bulb.

Between the lamp and the condensor is a cylindrical sheet of glass that has been sand blasted with a bias to the centre, while the outer is lightly sand blasted and more transparent.
Something like a centre filter.

At one time I checked an 8 by 10 inch sheet of white paper with a dslr in spot metering.
There was some fall off (I recall about 0.5 of a stop) at the corners.
It has not affected the prints, as far as I can see.

[ic-racer]

I'm not sure I follow, but it seems as if you have a 138 condenser head and don't have the appropriate bulb? There is a related thread here: http://www.largeformatphotography.in...l=1#post816464

[swmcl]

Hi,

That centre filter arrangement sounds interesting. I think the equivalent would be in sandblasting the heat proof glass at the centre more than at the edges...

ic-racer I have an L138 and an L184 to get running.

Rgds,

[Doremus Scudder]

Hi,

A reply in particular in my other thread concerning enlarger electronics has me asking about frosted or pearl lamps (thanks Jim Jones).

In some of the Durst literature I have read, in particular a document titled "Collimated light vs diffused light.pdf" there are a number of diagrams and discussion about effectively projecting the filament onto the paper via various lenses in a condenser enlarger.

If there are a number of particular condenser lenses made to suit certain bulb sizes for an enlarger (and enlarging lenses) and also when there is a table in the enlarger documentation which speaks of a 'point light' condenser elements, how much does lamp diffuseness play into things? You are trying to focus a filament onto the paper - not a whole bulb ... (in a condenser enlarger anyway) according to the documentation.

The Durst L184 10x10 enlarger does not have point light lenses. The L138 enlarger does have point light lenses.

As the bulbs are not available, I am looking to make up something. I have bought two different sized lamps (quartz halogen 240Vac). Both are not frosted.

I am off to a local manufacturer within the hour to get them mounted in the housings and will discuss perhaps making a polished stainless reflector - hopefully in an elliptical shape to aid in shoving light into the system. I have nothing to get ideas from so I'm sucking and seeing.

The other thing I'm thinking of trying is sanding the heat shield - effectively making it a ground glass heat shield! I'll buy another piece of glass for that purpose of course. This will diffuse the source somewhat yes?

At the end of the day I'd like to get as collimated and as sharp as possible. Diffusion can be had with a big piece of frosted glass or two in the filter drawer!

Cheers,

Steve

I have to respond here to a couple of things.

First, I went to the Durst site and read the paper you refer to about condenser vs diffuser heads. All I have to say is that the paper is riddled with errors, misconceptions, faulty logic and unsupported (and erroneous) conclusions. The idea that somehow you cannot make a sharp image with diffused light is completely wrong. People make photographs of things in diffuse light all the time, and they are not less sharp than those made in direct sunlight. And, enlarging a negative is really nothing more that "photographing" it onto printing paper. The quality of the light source makes absolutely no difference in the sharpness of your prints. Contrast from diffuse and collimated sources can be different, but that is simply something to adjust to.

A point source vs a frosted bulb or other semi-diffuse source gives you more and less collimated light, respectively. The difference showing in the final print as a small change in contrast. I don't think that it would make any difference using a point source or a frosted bulb with any particular set of condensers. The object is complete and even coverage of the negative format and nothing else. Maybe someone with more knowledge of optics can chime in here and let us know conclusively if there really are, or should be, a different set of condensers for point-source or more diffuse frosted bulbs.

Keep in mind that the main reason for a condenser source in the first place was to get as much light as possible for enlarging. With today's faster enlarging papers, many often have the opposite problem: too much light, and have to find ways to attenuate it. You may want to take that into consideration when choosing your light source.

I like to use condenser sources for getting a little extra contrast from time to time. I see absolutely no other change in quality using a condenser over a diffuse source.

Light fall off is, indeed, a problem, with almost all enlargers. I'd be interested if you can somehow get a frosted glass made that really works like a center filter as in the old Federal enlarger. Seems like a good idea.

Best,

Doremus

[Jim Jones]

Hi,

That centre filter arrangement sounds interesting. I think the equivalent would be in sandblasting the heat proof glass at the centre more than at the edges...

ic-racer I have an L138 and an L184 to get running.

Rgds,

Rather than alter the valuable heat blocking glass, I'd cut a piece of ordinary glass to fit over the heat blocking glass and do any alternation to it. Grinding that glass with valve grinding compound and a small glass tool might give you more control over the process than sandblasting.

[ic-racer]

Hi,

That centre filter arrangement sounds interesting. I think the equivalent would be in sandblasting the heat proof glass at the centre more than at the edges...

ic-racer I have an L138 and an L184 to get running.

Rgds,

There are four Durst 5x7 heads on ebay as of today. Do you need the whole head or just a lamp?

[BetterSense]

The difference showing in the final print as a small change in contrast.

The paper goes on to explain that since diffusion heads produce less contrast, there are a couple things that must be done to correct for that. Typically that includes developing the negatives more, which will increase grain and decrease fine detail retention. That, I agree with, even if I don't think it's that big of a deal. The author also claims that using diffusion heads requires not just developing negatives more, but exposing the negatives more, since, I gather, the diffuse light typical of diffusion enlargers can drop shadow detail. I'm not too sure about that, but it makes me want to test some very underexposed negatives in my D2 with condensers vs. cold light head, to see if the condenser can really dig more detail out of the shadows.