Correlation between enlarger lens focal length and condenser

[seadd]

I have recently bought a Durst M605 enlarger, with a 50mm condenser (Siriocon 50) and 50mm lens (Rodenstock Rogonar). Lens is mounted on Siriotub mount, so it is closer to the negative holder. When I want to enlarge up to 18x24cm format, everything is OK, but for anything beyond that, I cannot place the lens close enough to the negative.
What's even funnier is that on my old Meopta, I could easily enlarge on wall 2m away (so I'm used to having enlargers which can do that. The only thing that seems different is that Meopta has large dual condenser.
I guess now I have two options - I can either find a big condenser for Durst (Siriocon 80), or try to place a lens with shorter focal length (or scavenge Meopta for condenser.
Still, I have seen many instructions that shorter focal length lenses are for smaller film formats, etc. In theory, what can I expect with e.g. 30mm lens? Spherical abberations?
In general, what is normally done in such situations?

 

[Nick Zentena]

Okay if I understand you can't make a big print?

The problem isn't likely the condensor setup. You might need a recessed lensboard. You might need a flat one. Basically you need the lens closer.

If you have an 80mm it'll work with in reason. Really big prints will mean you'll have the head higher up and the enlarger might shake.

A shorter lens will only give you the same problem you get from the 50mm but earlier.

 

[Shangheye]

You need a recessed board to get the biggest enlargements possible with the 50mm lens. I use both 80mm and 50mm lenses and have the commensurate condensers, and the right boards (non-recessed rfor the 80mm). If you have the wrong condenser (e.g. 50mm condenser in with the 80mm lens) then you get light fall off. You can print 35mm with the 80mm set up (all be it smaller enlargements), but you can't print 6x6 with the 50mm set up. I also thought the 605 can project on the wall....? The condensers are hard to get hoild of on their own.K

 

[BillMar]

I have recently bought a Durst M605 enlarger, with a 50mm condenser (Siriocon 50) and 50mm lens (Rodenstock Rogonar). Lens is mounted on Siriotub mount, so it is closer to the negative holder. When I want to enlarge up to 18x24cm format, everything is OK, but for anything beyond that, I cannot place the lens close enough to the negative.

I have a Durst M605 but with the colour head. I use a Nikon 50 mm lens on a Siriotub and have no problem getting large images. You say you cannot get the lens close enough to the negative holder. I may be wrong but I thought that as the image got bigger you move the lens away from the negative to achieve focus. Have you tried racking the lens down?:confused:

BTW you can project onto the wall with the M605 by loosening the knob on the LHS and rotating the head around the supporting spigot. There is also an extension column available to extend the column height.

Hope this helps

Bill

 

[Bob-D659]

You probably need a deeper lens mount tub. There is a difference between lens flange to focal plane distances. I have a couple of Schneider Componons in Durst mounts and they have rear lens cell recessed enough that it is well below the lens registration flange on a durst mounting plate.

 

[fschifano]

Not possible for the condenser to be the problem. It sits ABOVE the negative carrier, and cannot interfere with focusing. Whether or not you'll get even light output from center to edge is a different question, and I can't answer that without having seen the setup. Sometimes condenser sets designed to work well with a lens of a given focal length will be okay with a lens of a shorter focal length - sometimes not. It doesn't work the other way around. Chances are good that you need the recessed tub that has been mentioned here already.

 

[seadd]

Thanks for the replies - I didn't get a chance to check all your advices until today, as my "darkroom" is available on weekends only, and even that only when there's not much light outside
Anyway, I do have a lens panel which brings the lens closer to the negative (Siriotub), and lens indeed has to be closer to the negative the larger the image gets. It turns out that I am just barely able to enlarge to some A4 paper size, which is about the declared value for the lens-condenser combination that I have.
Right now, I can remove the cloth thing on the lens holder, which will give me some extra 1-2cm of space. But I didn't expect Durst meant to work this way?

 

[Bob-D659]

Durst made several different depths of lens mounting plates. With the short lens travel on some units, you just need a deeper tub to account for a lens with a short flange to image plane. Durst also made two adjustable extension tubes as well, they won't accept some of the recessed lens mounting plates.

 

[seadd]

Managed to find one 75mm lens and put it on M605. WoW! I can make huge enlargements now. True, to get the same size as 50mm, I have to lift the head a bit higher, but I can get huge enlargements now and bellows still have 2-3 cm of space.
I guess I'll have to get some book and reiterate the whole geometrical optics course from college