Evenness of light source

I’m new to the world of camera scanning but not photography. I just built my copy stand, bought a lens and bought the Negative Supply 4x5 Light Source MK2. The first copy of the light source I received had a lot of fall off towards the edges (almost a full stop on one side), I returned it and they sent a replacement, this one is much better but it still falls off by about a third of a stop at one edge/corner and about a quarter of a stop on the other. My question is, is this normal? I realize it’s very hard to get perfectly even light but that’s what I expected. Wouldn’t be an issue but I was hoping to scan 4x5 film on this. Thanks for any replies!

Disappointing that you had to send the first one back but good that they didn’'t quibble about sending a replacement. Is it possible that the light fall off you are seeing is coming from your lens? Are you using a particular branded film holder for your copying so that you need a panel of a certain size to fit underneath it? Just asking because I think a lot of panels aren’t quite as good at the edges so a larger panel might be better if 5x4 is a priority. Otherwise Flatfield Correction in Lightroom should deal with it.

Thanks for your reply Harry. The fall off is actually visible with the naked eye so I’m quite sure it’s not my lens (Sigma Art 105mm Macro at f8). On the first box I received the fall off was glaringly obvious as you can imagine. I suspect you are right that a larger panel is the answer for 4x5 but this model is advertised as, and I quote ‘boasts perfect light uniformity for up to 4x5 sheet film’. The way I tested was I have a blank sheet of processed 4x5 film, I photographed it two ways, first laid flat on the panel and then raised a quarter inch and held in a 4x5 negative carrier. Both times the results were the same.I left a message with Negative Supply and I’m waiting for a call back (they are slow to respond to emails so I’m trying this way). If it’s normal then I’ll just accept that 4x5 scanning is slightly compromised with this light panel and work around it. BTW I have never used it but I read that Flat Field Correction only deals with colorcast and not light falloff. Thanks again.

Thanks for all those details I think you’ve covered all the bases in fact! I imagine this doesn’t apply to your experience either but I’ve also read a theory that with LED panels it is possible that there is some fall-off towards the edges simply because the lens is ‘looking’ obliquely at the LEDs towards the edge. However it does sound as if your panel isn’t even I admit.

There is another option open to you with 5x4 and that is to turn your film so that the long edge of your sensor aligns with the short edge of 5x4 and then take 3 shots, moving the film around 45mm each time and photomerge. You would get significantly higher resolution that way and you would only be using a100mm x 70 mm area from the centre of your panel but there would be a bit of DIY involved to create a ‘rig’ that would allow this.

Flat-Field Correction does deal with both colour and evenness, or rather unevenness, at the same time so it would certainly work for this.

Thank you for the information, suggestion and interesting links Harry, I appreciate you taking the time to send those! All the best.