Hotspot with Photolux bulbs?

[batwister]

I've just bought my second Photolux bulb after thinking the first was defective. Both have given me a prawn shaped hotspot which is completely unworkable. It's visible with and without the condensers - tried with both 35mm and 6x6. With another bulb however, which has a thicker coating, the light is completely uniform but the exposure times are running into a minute or more.

The enlarger is a Krokus 3.

 

[MartinP]

Aren't Photolux bulbs for illumination, not for in enlargers? I've not had any problems with Photocrescenta bulbs anyway. Those are the usual white enlarger bulbs - if you have something which is a translucent grey (similar to a standard opal household bulb) then it was intended for use in some sort of tungsten lighting fixture, not an enlarger.

 

[Worker 11811]

I don't know your enlarger but I am wondering whether the lamp house is focused correctly.

Does your enlarger have a prefocused lamp? If so, that's probably not the problem. Otherwise, check the lamp socket to be sure it is aligned correctly so that it produces even light.

Secondarily, check to be sure the lamp is inserted into the socket correctly. If it doesn't fit right, it won't position the filiament in the focal point of the reflector.

After that, as others say, the lamp you have chosen might not be up to spec.