Point source enlargers. Refocusing condensers and lamp question.

[cinefane]

I have the urge to convert a long discarded enlarger of mine to a point source condenser. (Once I've cleaned the cat hair and afterbirth from it. ...but that's another story.)

Firstly: How do you refocus the condensers? Are the pair moved back and forth from the film plane or is the distance between the pair adjusted? How fine does the adjustment need to be?

Secondly, what lamps are traditionally used as a light source? Do you think a single white LED would cut it?

[steven_e007]

I've tried this.

Is your existing enlarger a condenser enlarger?

Most so called condenser enlargers are really condenser / diffuser and so have no condenser movement. The best pattern is probably the the old mahogany horizontal enlargers of 100 years ago. These had the condensers separated from the lamp housing often with separate bellows or a sliding metal cylinder.

To make the adjustments you need to move both the condensers and the position of the bulb. I kept the condensers together as a pair.
Moving the condensers (a bit) is to focus the filament image onto the front of the enlarger lens to ensure maximum light is going through the negative. Maybe not so critical if you are using one size of negative and making similar sized enlargements.
Actually, the bulb is the most critical thing - the bulb needs to be at the focal point of the condensers and needs to be moved as the enlarging lens to negative distance is changed when focussing.

I used a halogen lamp of about 50 watts with a mask in front of it with a small hole (about 3mm). Mechanical challenges involve holding the bulb nice and central whilst allowing it to slide up and down this axis.

Interesting, though. The difference in the resulting images I got was striking. Very gritty and contrasty compared to the condenser / diffuser type, which is only a little different to the diffuser type.

Ultimately a pain, though, to set it all up and not to get big kidney shaped 'blobs' due to misalignment. I did experiments, had fun, then went back to my opemus enlargers without finishing anything.

[cinefane]

How much adjustment is a 'bit'. An inch or so? A centimetre? A spider's leg?

[ic-racer]

I have the urge to convert a long discarded enlarger of mine to a point source condenser. (Once I've cleaned the cat hair and afterbirth from it. ...but that's another story.)

Firstly: How do you refocus the condensers? Are the pair moved back and forth from the film plane or is the distance between the pair adjusted? How fine does the adjustment need to be?

Secondly, what lamps are traditionally used as a light source? Do you think a single white LED would cut it?

The following is from the Durst Varipoint (point source) enlarger manual:

3.3 Black-and-white enlarging with the Varipoint 1200
Check for evenness of illumination
*Switch on enlarger lamp

For unit version equipped with OPTO-TIM press "Light" key
*Open LENS diaphragm fully

Lamp centering:
If there are shadows on the baseboard, center the lamp as follows:
*Turn knobs 103 and 105 until projection is free of shadows.
*Turn lamp and adjust horizontally (103 = horizontal adjustment, 105 = vertical adjustment)

NOTE: do not stop down the lens!

Here is a picture of a Durst Varipoint bulb:

[PDH]

I converted an old federal enlarger to point source. In most of the Federals the blub can be move up and down, I use a clear 100 watt hologen bulb. My Federal is not ideal as it has only a single condenser, but I have taken the time to hunt down a double condenser model.

Paul

[steven_e007]

How much adjustment is a 'bit'. An inch or so? A centimetre? A spider's leg?

It depends what you are trying to adjust for.

The early wooden horizontal enlargers with their spirit lamps etc, were designed to accommodate various plate sizes and had the disadvantage of a relatively feeble light source, so some had condensers that could move quite a bit ( a few inches I suppose) to ensure they just covered the required negative and give maximum illumination. I have an early enlarger of this type and it also has the option to change the condensers.

If you are sticking with 35mm (or medium format) and have a reasonably powerful light source then I think the most important thing is a moveable and adjustable light source. If you kept the condensers fixed in position (where they probably are now) then the disadvantage is that as you move the light source nearer or further away then the cone of light going through the negative changes size, too. This means the intensity and hence the exposure is all over the place as you change image size - but if you are using a meter it may not really be much of a problem. I haven't seem any modern point source condenser heads but it wouldn't surprise me if the condensers were fixed - or at least only designed to be tweaked during initial set-up.

[ParkerSmithPhoto]

I have the urge to convert a long discarded enlarger of mine to a point source condenser.

Hans Namuth was big on point source enlargers. If you find the old Darkroom and Darkroom 2 books from Ralph Gibson's Lustrum Press, he talks a lot about how and why he uses them. I got my copies on Amazon used for less than $10. If you can find it, PM me and I'll send you a scan.

[Ian Grant]

Back in the 70's and 80's I had a point source Large format enlarger it ran with a 275w photoflood bulb, each new bulb needed adjustment and they only lasted a few exposures, the lamp housing was quite long (just under a meter) and had a baffle to prevent light bouncing down the side even though they were matt black Should add the enlarger was horizontal and mininum typical enlargement was 24" and maximum about 16ft.

Ian