Durst 138 - condensors & lenses

[andreios]

Hi all,
I need a small help - when using the Durst 138 to enlarge from smaller negatives, the manual gives appropriate condensors combinantions and focal lengths - e.g. for enlarging 6x9cm neg one should use the 240 and 130 condensors and 105mm lens.
Now, my question is, if for some reasons I'd like to use a 150mm lens for enlarging the 6x9 neg (I am making fairly small enlargements and like to keep the head higher from the baseboard), do I keep the condensor combination the same or use larger lower condesor? Should the two LATICOs match the neg size or the focal length of the enlarging lens?

Thanks!

 

[MartinP]

The condenser lenses gather the light through the negative while the lens projects the result of that light -- two separate functions. In other words, keep the condensers appropriate for the neg format and use whatever lens you want (assuming that it can cover the size of the neg of course).

If you find that the exposure time is too short with a small degree of enlargement then you could also try the condensers for the next size up (probably 4x5, so two Latico 180s, writing from memory) as that will spread the light over a larger area than you are using, "wasting" some of it, but still be even within the 6x9 neg. Whether that is useful depends on the power of the light source you have installed, as the original bulb hasn't been made for years this could be a big variable.

 

[AgX]

The condenser lenses gather the light through the negative while the lens projects the result of that light -- two separate functions. In other words, keep the condensers appropriate for the neg format and use whatever lens you want (assuming that it can cover the size of the neg of course).

To the contrary: the condensor has to project light in a certain way into the image-forming lens. Condenser and lens thus need to be couple, adjusted for any extention. Nonwithstanding which negative-format is actually used.

At least this is the case for a point-lightsource.
With large lamps or with a diffusor there does not need to be that precision.

 

[John Koehrer]

The condenser lenses gather the light through the negative while the lens projects the result of that light -- two separate functions. In other words, keep the condensers appropriate for the neg format and use whatever lens you want (assuming that it can cover the size of the neg of course).

If you find that the exposure time is too short with a small degree of enlargement then you could also try the condensers for the next size up (probably 4x5, so two Latico 180s, writing from memory) as that will spread the light over a larger area than you are using, "wasting" some of it, but still be even within the 6x9 neg. Whether that is useful depends on the power of the light source you have installed, as the original bulb hasn't been made for years this could be a big variable.

I'd go along with this. You use the central portion of the condensers and "waste" a tiny bit of light.
There are theoretical limits and practical usage. They aren't always the same.

 

[ic-racer]

Hi all,
I need a small help - when using the Durst 138 to enlarge from smaller negatives, the manual gives appropriate condensors combinantions and focal lengths - e.g. for enlarging 6x9cm neg one should use the 240 and 130 condensors and 105mm lens.
Now, my question is, if for some reasons I'd like to use a 150mm lens for enlarging the 6x9 neg (I am making fairly small enlargements and like to keep the head higher from the baseboard), do I keep the condensor combination the same or use larger lower condesor? Should the two LATICOs match the neg size or the focal length of the enlarging lens?

Thanks!

Use the condenser combination to match the lens and magnification in use. On way to remember it is to think of the condensers focusing light to the center of the lens. If the lens is way up close (big enlargement or small focal length) or if the lens is racked out (long lens or small enlargement) the condensers need to be appropriately chosen. That is why in the Durst condenser chart it mentions lens focal length and magnification.

 

[bernard_L]

+1 siding with AgX and ic-racer. The purpose of the condenser is to pass the light from the source through the lens.

 

[Kimberly Anderson]

Please don't forget that the condensers need to be inverted relative to each other. IOW...the curved sections of the condensers need to be pointing towards each other and the flat sections away from each other.

Like THIS CHART on pp. 9-10 shows.

 

[andreios]

Thank you all for your suggestions, I will keep the condensers and lens matched. Makes sense.

Michael, thanks, I am aware of this, it is not my first enlarger with condensers - and I have that manual as well.

 

[Marco Buonocore]

What condensors would one use with an Apo Rodagon 90mm lens? I'll be making small (3x) enlargements of 6x6 negatives.

What about a Nikkor 68mm lens? I use it for enlarging 35mm, as I get vignetting with my Nikkor 50mm and the recessed lens board.

For the record, the condensors I have are: 85T, 110T, 130T (x2), 200T, 240T and 240R

Any advice welcome!

 

[ic-racer]

What condensors would one use with an Apo Rodagon 90mm lens? I'll be making small (3x) enlargements of 6x6 negatives.

What about a Nikkor 68mm lens? I use it for enlarging 35mm, as I get vignetting with my Nikkor 50mm and the recessed lens board.

For the record, the condensors I have are: 85T, 110T, 130T (x2), 200T, 240T and 240R

Any advice welcome!

Condenser chart is in the manual here: https://www.trippingthroughthedark.com/files/durst138/Durst Laborator 138 Instructions.pdf

 

[Marco Buonocore]

Hi ic-racer,

The problem is, neither lens is listed on that chart. They're both sort off oddballs, although very sharp lenses.

I've been using the 240/130 for the Apo 90, and the 200/130 for the Nikkor 68mm.

 

[ic-racer]

Hi ic-racer,

The problem is, neither lens is listed on that chart. They're both sort off oddballs, although very sharp lenses.

I've been using the 240/130 for the Apo 90, and the 200/130 for the Nikkor 68mm.

Try the two closest combinations. After focusing, stop down about 3 stops and take the negative out and make a gray print on the highest contrast paper you have. See which combination of condensers and light position gives the most even illumination.

 

[Marco Buonocore]

That's sound advice, I appreciate it. Thanks!