Topic: Condenser lenses - what and why?

[jojonas~]

I recently got a Durst M 670 (yay!) and it came with one condenser lens for 6x7 and one for 35mm (I think)

it's my first time getting a machine with several of these so I dunno what the benefits are.
- does the one for 35mm compress the light to give shorter exposure times?
- would the one for 6x7 still be okay for 35mm? would the results suffer in any way?

[Francois]

Condensers are actually a pretty technical thing.
They're not as much linked to a specific format as much as a specific lens focal length.
What condensers do is focus the beam in a spot that is lower than the negative. So the light that goes through the neg is severely out of focus.
This is all great but it has some problems when the lens focuses too close to the negative and both focal points mix-up. You end up with severely uneven exposure towards the edges which is just no good.
You can expose a 35mm using the lens and condenser set for medium format. Only thing is you're going to have to crank-up the head to the top to get a decent sized print. Exposure times will also become quite long (inverse square law). But it will work.

Exposing medium format using the 35mm condensers and the 50mm lens will not work unless you want a big partial enlargement.

[KevinAllan]

I was given an M670 a few years ago and used it for a while but had to scrap it after the plastic cog that drives the column up and down broke. However I was able to sell some parts including the condensors - so hang on to both even if you don't use them as they have value

[Francois]

Plastic parts can now be printed so it's really not much of a problem for anyone with Sketchup and Nettfab experience.

[jojonas~]

Francois: okaay, I think I get it. probably easiest to test it out once I set it up if the change is so clear like you say with distances and that.

Kevin: yeah, I saw a few pieces on ebay so I'm glad I got it with extras and all in good nick

Plastic parts can now be printed so it's really not much of a problem for anyone with Sketchup and Nettfab experience.

that's a comfort to hear!

[Francois]

For the condensers, you'll definitely see a difference in the light fall-off.

As for printing, companies like ponoko and shapeways can print in strong plastic and charge by the volume of the piece.
And if the part can be built from a flat material, Ponoko can laser cut it from just about anything. Delrin is a good choice for things that need to be tough. They can also cut from stainless.

[Dave Elden]

I recently got a Durst M 670 (yay!) and it came with one condenser lens for 6x7 and one for 35mm (I think)

it's my first time getting a machine with several of these so I dunno what the benefits are.
- does the one for 35mm compress the light to give shorter exposure times?
- would the one for 6x7 still be okay for 35mm? would the results suffer in any way?

-Benefits are you can print more than one size/format negative.
-The condensers are designed to provide even illumination of the negative size they are specified for. Printing times are controlled by other factors.
-The 6x7 would obviously evenly illuminate the 35mm negative area. Suggest that you use the lens/condenser combo that matches the negative format though. If you use the 6x7 combo for 35mm you will unnecessarily limit your enlargement ratio and you may find a small loss in image sharpness since your enlarger lenses may be optimised for typical enlargement ratios for the format; once you go outside this you are straying away from the optimum. You have a good quality enlarger design there, with good lenses (e.g. 6 element Nikors etc.) you will get good results when you print.

Have fun,

Dave.

PS, Francois re "Condensers are actually a pretty technical thing.
They're not as much linked to a specific format as much as a specific lens focal length."
FTR  the focal length and diameter of the condenser lens is dependent on the negative size (format)and nothing else really. The enlarging lens focal length also depends on the negative size - amongst other things.

[jojonas~]

thanks, dave I'll keep that in mind when I start using it.