Point source enlarger

[cliveh]

Can someone enlighten me here? Is there a difference between a point source enlarger and a condenser enlarger? Or is the term point source enlarger another name for a condenser?

 

[MattKing]

A point source enlarger is a relatively rare beast. I have never actually used one.

Most enlargers that we see described as condenser enlargers are actually a compromise. They combine condensers to focus and collimate the light with a semi-diffused light source, such as a frosted bulb.

A point source enlarger replaces the frosted bulb with a point light source. The condensers need to be carefully matched to the source, and everything needs to be accurately positioned.

The result: excellent accutance, and maximized dust in your prints!

 

[ic-racer]

In technical terms it can be reduced to the presence or absence of a frosted globe between the filament and condenser. Back in the heyday the point source was excellent for enlarging electron micrographs. Today some have posted on these forums they use point source enlargers for their expressive printing.

 

[miha]

http://www.durst-pro-usa.com/world_images/theofcon.htm

"Most condenser systems are designed to work at a certain given f-stop when using a point light lamp. Most often this f-stop will be f11. When using an opal lamp you are free to use any f-stop on the lens:"

http://www.durst-pro-usa.com/world_images/theofcon_files/image005.jpg

 

[cliveh]

A point source enlarger is a relatively rare beast. I have never actually used one.

Do any APUG members use one? If so what do you think about this method?

 

[KenS]

Point-source enlargers exposures are used by controlling the timing of the exposure while adjusting voltage to the lamp... with the lens ALWAYS used wide open. They also require special 'coatings' on the condensers. Their use is usually the most common for either 'extreme' enlargement of transmission electron micrographs.... scanning electron micrograph negatives are were usually printed using the 'standard' opal lamp.
A secondary benefit can be obtained by the point-source enlarger is (was?) for making LOW magnification B/W negatives from stained and sectioned tissue slides in order to get the fine detail often difficult to 'acquire' at lower magnification... with even the best of 'standard' microscopes. I have to imagine that 'digital' sensors have now 'replaced' the silver-gelatin negative in electron microscopy.

In my last job position, I spent many a happy (or frustrating) hour standing in front of a Durst 138S... over some 20 years) .

Ken

 

[David A. Goldfarb]

There was a fair amount of discussion of this topic around 2005-7 on APUG, so try the search engine to find lots of information in the archive. Here's one of the more detailed threads:

(there was a url link here which no longer exists)

 

[RalphLambrecht]

A point source enlarger is a relatively rare beast. I have never actually used one.

Most enlargers that we see described as condenser enlargers are actually a compromise. They combine condensers to focus and collimate the light with a semi-diffused light source, such as a frosted bulb.

A point source enlarger replaces the frosted bulb with a point light source. The condensers need to be carefully matched to the source, and everything needs to be accurately positioned.

The result: excellent accutance, and maximized dust in your prints!

ExactlyIf I were you I'd stay away from themunless you have a specialized need.I recommend an enlarger were the light source can be changedsuch as the Durst L1200.point source enlagers need experience to be tamedand even then print very harsh.so,be prepared to develop very soft negatives.

 

[Mike Crawford]

I used to have a point source head to fit on a DeVere 504 condenser head by replacing the top of the head. I didn't use it too much, (before giving it away) as found it quite difficult to work with. As I remember, the condenser lenses have to be aligned exactly and the lamp must be in exactly the right position. I think the enlarger lens could only be used at a certain f stop as otherwise would vignette. It certainly gave more contrast and the sharpest grain ever, but the amount of dust and scratches it found made spotting more of a chore. And normally I enjoy spotting! Couldn't even use anti newton glass in the carrier as the texture would show. Was used now and again 20 years ago for lith printing with even more crunch, but would image we would have then sent the prints out for retouching! Personally, I wouldn't be rushing to use one again!

 

[Ian Grant]

I made a point source head back in the mid 1970's for a De Vere 54a which I used horizontally, the head was quite long. Like Mike says it was very finicky I had to check the alignment of the light source and adjust depending on the degree of enlargement.

I used it to get maximum contrast and also get the best light output for large prints to keep exposure times under a couple of minutes with the lens stooped down to f11/f16. When I close the company I scrapped the head and enlarger.

Ian

 

[miha]

The author of the following paper advocates the use of a point light source system: http://www.durst-pro-usa.com/pdf/COLIMATED LIGHT VS DIFFUSED LIGHT.pdf

His argument is that a minimally exposed and developed film is to be preferred for maximum resolution and best tonality. (start with page 36)

 

[DREW WILEY]

Point light sources are pretty arcane, and I don't see why anyone would even need one. But if you love spotting prints... Otherwise, the best
way to get great tonality along with great resolution is to shoot a larger sized film to begin with, and otherwise have all you darkroom gear
precisely aligned. The link provided above probably wants to sell you something for tens of thousands of dollars with a mandatory service contract. Don't ask me how I happen to know that.

 

[cliveh]

Am I correct in assuming that a point source enlarger would be more suited to a smaller format size?

 

[richard ide]

Point source enlargers were ideal for document reproduction (maps, engineering drawings etc). I have the head of a camera enlarger for 8 x 10 negatives. You could make a print from a negative with a Dmax of .30 and the print would be black lines on a white background. The largest condenser enlarger I came in contact with could enlarge a 21" x 27" image. Distance from lamp to condenser is very critical but easy to set up. Image sharpness is not a problem. As said before, every bit of dust shows.

 

[ic-racer]

Am I correct in assuming that a point source enlarger would be more suited to a smaller format size?

Back in the day electron micrographs were frequently made on sheet film a little smaller than contemporary 4x5" film. That film size is small to some, and large to others

 

[KenS]

I was just re-reading these posts and just realised that some time ago I had written in an MS Word' to allow me to edit/correct before posting and was interrupted... I 'put it away' and somehow for got to finish what I had 'started'.

One of the 'other' advantages of the point source enlarger was making 'low' ie 4 to ~20x magnification negatives directly from sectioned and stained tissue samples rather than making the required negatives under the microscope lenses... especially if the sections in question were cut with an ultra-microtome.
The glass microscope slide is 'inverted' (ie. coverslip 'down') when placed in the negative carrier and 'projected' onto sheet film in a film holder that is 'adjusted' such that the plane of the film is parallel to the plane of the microscope slide.

This technique was the subject of a paper published in the Journal of Biological Photography some years ago and having used the technique myself, I can confirm the advantages. if anyone is interested, I'll see if I can find my copy and forward or post the issue/date/author.

Ken

Ken