Underexposure strip across prints

[Sorrycharlie]

Hi there. I’ve been enjoying my time in the darkroom lately and have noticed that some, not all, of my prints have a strip across the bottom that seems to be underexposed and gives a kind of reverse vignette across the bottom. I’ll include some examples below.

I can’t really work it out on my own, and was wondering if anyone had ideas about what may be causing it. Cheers

 

[koraks]

Please share some information on your enlarger setup, lens used, negative carrier etc.
Your images suggest light falloff of some kind towards the affected edge(s), either due to, for example:
* Misalignment of the negative and the lens
* Obstruction of the light path by a protrusion of e.g. a negative carrier, part of the enlarger bellows, etc.
* Insufficient coverage of the lens used (although this would typically result in the problem being worse towards the corners and not just along one or more edges, although your 3rd picture does not exclude this possibility)

 

[MattKing]

Nice picture of your foot .
I'll add to koraks' excellent suggestions by mentioning the light path in your enlarger. If the condenser and/or diffusers are set for a smaller format, you could end up with this.

 

[koraks]

@MattKing yes that's a very good addition as this may indeed be due to an incorrect condenser setup!

 

[Sorrycharlie]

Thanks for the replies guys. So my enlarger is an Agfa c66 (durst m-605). I’m using two pieces of glass in the negative carrier and I’m printing 6x7 negs. I’ve got a feeling that the enlarger my not be intended to run 6x7, only 6x6, but when using 6x7 I see the whole neg clearly on the easel and as I said, this doesn’t happen to all my prints. Some have printed perfectly to all corners of the paper without this line. I thought it might be an issue with the easel I’m using or perhaps the paper was warped when in the easel or something.

Anyway, now I’m assuming it must be that I’m using 6x7 negs when it’s designed to take 6x6 and it’s a thing where the condenser isn’t covering the image fully and that’s fine as I’m happy they’re working at all. I’m just trying to get away with using it with 6x7’s as that’s what I mostly shoot.

 

[Bill Burk]

I think you’re right. Probably pushing the limits. Maybe you will be OK if you’re real careful about positioning the negative or cropping just a bit.

 

[koraks]

The m605 is indeed only fit to go up to 6x6.

 

[MattKing]

Which edges are lighter - the edges on the short dimension of the negative, or the edges on the long dimension of the negative?
The edges on the long dimension should work fine, save and except the corners.
The edges on the short dimension may be both outside the best light path.
Centering the negative will be critical. You may also get better results at some lens apertures than others, but that shouldn't matter a lot.
Of course, if you are willing to crop your negatives, the centre 6x6 portion should be fine.

 

[kevs]

Using a longer enlarger lens may give better coverage. 'Standard' lenses for medium format are in the range 70 mm to 90 mm. If that's not the problem, increasing the neg-to-lens distance might help. You'll get a smaller baseboard image but wider coverage of the neg.

 

[Bill Burk]

The m605 is indeed only fit to go up to 6x6.

But the light edges are not on the “7” side which makes me suspect alignment... Or pushing limits. My Omega D-II “Omegalite” was engineered for a cropped 4x5 which showed up similarly when I sawed my negative carrier for full frame black borders. Took some careful alignment to get even exposure.

One thing I noticed though, after looking through several prints online (you can see my prints in the media here on Photrio)... I noticed the overall light distribution was unpleasant with that enlarger head, so I got an Aristo grid.

 

[andrew walmsley]

hey mate, i've just got this enlarger too. do you use the original timer? love some advice of you if you are.