Durst M601 exposure time problems
 

I have relatively recently started printing b&w in medium format and am having to use stupidly short exposure times of 2 -5 secs with the lens stopped down to f16.

My negatives do tend to be on the thin side and but the last roll appeared to be reasonably dense and I'm still having the same problems.

I'm printing on 5x5 paper, from square format negs and the lens is a schneider componar 75mm.

What little 35mm I have printed on the same enlarger with a 50mm lens has turned out fine with exposures times of 10 - 20 secs.

Can anyone give me some pointers on what might be going wrong?

I'm not sure that you are doing anything wrong, you are just making small prints, hence the short time.
Stopping down to f22 will double the exposure time, or fit a neutral density filter, or if you are using a colour head and variable contrast paper, dial in some cyan filtration along with the other too colours.

Thanks Dave, that's reassuring to know. I'm using a colour head so I'll experiment with filtration.

Dave is correct. When the magnification is small your lens is closer to the paper and print times become very short. Too short.
Get yourself a sheet of Lee Neutral Density lighting filter and place above the negative in the light path. You can cut it to size and use as many layers as you like to get to print times that are useable for that size print.
The following is one stop filter (0.3). They do others but you can layer this one and there is plenty in a single sheet for many layers.

http://www.sound-light-company.co.uk...nd.p81127.html

A longer focal length lens would also make print times longer. A 150 lens would be approx 2 stops slower but I think the ND filter will be cheaper and easier.

Thanks, that's really useful.

I must admit I clicked the link with trepidation having recently bought some Lee ND filters for my husband's camera, but these ones won't break the bank.

I might look out for a longer focal length lens on ebay, but the filters will keep me happy.

The lighting filters are cheap because they are not optical quality. That means they must go above the negative.
They are however very heat resistant so you can put them above the mixing box if there is somewhere to fit them on your enlarger otherwise just below the mixing box.

Dialling in about 30 units of Cyan is the cheapest method but I must admit that is an approximate number and maybe someone else can offer something more exact.

I take it you are using the dials on the head to change the grade of paper and have not forgotten to switch from white light to filterd light. just checking:)

Depends on the enlarger make. And contrary to the accumualated wisdom of the web, Cyan does have an effect on contrast albeit small. The wavelength range it transmits and VC paper wavelength sensitivity do seem to overlap a bit. But having said that you can compensate with yellow and/or magenta.

More importantly the filter factor for a 130 units of yellow on an L1200 is a mere X1.2 and for a 130 units of magenta is only X2.15 (these are time factors not densities) so at the most you would get a single stop but I rekon it would be somewhere between those so probably only around a half stop which isn't much at all.