opal lamp for durst 4x5

hi together,
recently my last 300w opal bulb gave w.o.
i wanted to purchase a new one, just to learn that they are not produced anymore- in my area (austria) they just sell the smaller 150 or 250 W bulbs- they are approx. 5cm in diameter, while the old bulb was maybe twice as big.
now my problem is that with the smaller bulb i get vignetting when enlarging 4x5inch... is there a way around this? does anybody know where to get the big bulbs?

Is there a way to adjust te bulb / mirror distance?
For my Durst 1200 I have to adjust the distance of the lamp to get an even image.

yes, there is, i have a durst 138 and one can adjust the distance and the position of the lamp, but still there is vignetting at 4x5 inch. do you use the small bulbs on your 1200 without any vignetting?

I have also small vignetting with my laborator 1000 on 4x5 enlargment. I have onlu a 150w bulb. Is there any internetshop who can provid 250w or more?

jhochstoeger said:

yes, there is, i have a durst 138 and one can adjust the distance and the position of the lamp, but still there is vignetting at 4x5 inch. do you use the small bulbs on your 1200 without any vignetting?

Click to expand...

I use 150watt opal lamps from grobet (belgium)
http://www.grobet.be/index.php?page...d=531&option=com_virtuemart&Itemid=35&lang=nl

The also have 250 watt.

jhochstoeger said:

yes, there is, i have a durst 138 and one can adjust the distance and the position of the lamp, but still there is vignetting at 4x5 inch. do you use the small bulbs on your 1200 without any vignetting?

Click to expand...

I don't have any vignetting using the smaller 2 1/2" opal bulbs on my Durst S-45 (similar to the 138) when the bulb position is adjusted properly. I've even used a clear 12w bulb with a tiny filament successfully for formats from 35mm to 4x5in (but sometimes this doesn't work for smaller enlargements).

This requires centering the bulb both horizontally and vertically and then adjusting the front-to-back bulb position to focus it through the condensers on the lens opening. Note that when the lens focus changes, you may also have to adjust the bulb position to keep it from vignetting. Generally, there are a wide range of bulb positions that give even illumination when using 2 1/2" opal bulbs -- the range narrows considerably for clear bulbs, but it's usually possible to find a position that works.

It's also possible that the lens design has some effect on the illumination. I haven't had any trouble with el-Nikkors and older Schneider Componons, but maybe other lenses are more sensitive to bulb size.

BTW, did you adjust the vertical position of the bulb socket when you went from the 3 1/2" bulb to the 2 1/2" bulb?

Cheers,

-andrew