I’ve been using NLP and film scanning for a few months now, 35mm but likely will start shooting medium format soon. I have a Fuji XT-5 (APS-C). Getting started, I read up on the best macro lenses and picked up the Lawoa 65mm f/2.8. Started with the Valoi Easy35 for scanning, but experienced orange haze on thinner negatives due to vignetting / uneven light source.
I thought upgrading to a full sized setup might be an improvement, as others had reported issues with the Easy35. Went with Negative Supply’s gear, but still experiencing vignetting on dark / underexposed / night photography negatives.
So I figured it’s the lens after all. Okay, well others seem to use Lightroom’s flat field correction to fix the problem, using a blank shot to compensate for vignetting. The problem is, flat field correction in Lightroom only works half the time, it’s absolute garbage in terms of reliability. It often doesn’t recognize which frame is the calibration frame, or creates ghost images on your shots using the wrong frame for calibration. It’s also awful in terms of workflow as you need to do each image one at a time to make sure it doesn’t screw something up (if it works at all). I tried to appeal to Adobe techs to fix it, provided them examples of it malfunctioning and everything. They initially responded but have since gone silent.
So, here’s what I’m thinking - others seems to use Lightroom’s lens profile corrections to fix vignetting automatically when film scanning. Unfortunately, there is no lens profile for the Laowa 65mm (confirmed by Laowa).
Does it make sense for me to change macro lenses to one that has a lens profile in Lightroom such that I can use that feature to correct vignetting, as opposed to being forced to use flat field correction? Want to seek input before I waste money trying something else that might not work. If I could pick up a lens that Lightroom could correct that would cover both 35mm and medium format for APS-C, that might be the ticket.
Hi there, welcome to the forum. If it is true radial vignetting from the lens then you should be able to correct it with a radial filter, if you take your time you should be able to neutralise it very accurately and then save that as a setup. If it is in any way caused by an interaction between your panel and your negative holder and you’re getting an ‘edge’ effect then that isn’t going to work but it seems that this isn’t the case. Copying a blank unexposed frame of colour negative film to give a mid-tone, centred histogram, should tell you a lot. A radial filter is a lot easier to use than Flat Field Correction in my opinion.
I’m pretty sure that there are some users of that lens on here who can advise more specifically.
I explained this on a couple of instances around the NLP forum, but folks seem to have a hard time accepting it.
In short: It’s not (only) lens vignetting but due to your light source not being infinitely large compared to your negative, but it’s indeed easiest to fix with a luminosity mask, with an aspect ratio that is the same as the aspect ratio of your light source (if the light source is square, you use a radial luminosity mask, if it’s rectangular, you use an elliptical luminosity mask). Take a shot of a blank negative and tune the mask so that the histogram shows the sharpest peak, which means the most homogeneous brightness distribution. Apply the mask on import and done. A hardware correction would be better but is not trivial.
Hi Harry - thanks for the insight, I hadn’t considered using a radial filter, I will look into that.
ArnoG - thanks for the link and your analysis, that makes perfect sense. Creating a luminosity mask in Lightroom seems like a great alternative to FFC. I’ll investigate and try your method using a blank frame and the histogram. If you have any links to practical guides on creating this filter, let me know, otherwise will experiment on my own, thanks again.
It’s funny, digital film scanning is discussed in several places beyond this forum and you would never know that this is an issue, you never hear about light falloff or vignetting being an issue that needs to be addressed when film scanning. The practical experience is very different.
If I get this luminosity filter working as intended and it solves my issue, will shout this method from the mountaintops as I have not come across it elsewhere.
I don’t know if you’ve seen this post, here @Graham has uploaded some blank frames using 3 different lenses:
I’m not sure that there is a reliable way of quantifying vignetting, as a guide with my setup using a masked CS-Lite and a home brew film holder about 3cms above I photographed the afore-mentioned blank frame of colour negative at my chosen aperture of f5.6/8 on APS-C with a 75mm Apo-Rodagon 2x. I then converted it to B&W and adjusted the exposure slightly to get the centre at 50% in Lightroom. The corners were then around 48.5%, no less than that, barely noticeable to the naked eye and easily corrected. I find that the shape of the vignetting shows up much more clearly on the thumbnails.
You can if you like just have an empty frame and expose accordingly, I like to use a piece of blank colour negative film in case there are any unexpected effects pertaining to the presence of the film itself. If I was photographing transparencies I wouldn’t bother about the radial filter but colour negative conversion boosts the contrast greatly and vignetting shows up as pale corners.
After work today I had some time to experiment with your suggestion. I created an elliptical gradient mask such that the extreme corners would have an exposure increase of 0.1 stops, tapering to the center by the gradient. I did this with a blank image of my light source (I will fine tune with a blank image including a blank negative, just didn’t have one on hand). I got to 0.1 stops adjustment by getting the narrowest peak in the histogram. I will say, it’s unfortunate Lightroom doesn’t allow you to enlarge the histogram to fine tune, but did my best by eye.
I think the improvement in vignetting / orange haze is pretty significant, and I will be able to simply apply as a preset. Thanks for the suggestion, a much better solution than FFC, just need to fine tune.
Once I feel it is optimized, I think I will make some sort of guide for others as I don’t think this method is very well known in the general film community online, at least not from my reading.
Glad that’s working out for you. The vignette from a lens is essentially circular so extends beyond the rectangular frame of your sensor, you may find that a circular mask will prove more accurate at balancing the light fall off than the elliptical one. Checking by increasing the contrast may also help in refining your mask and will help simulate the effect of the colour negative conversion process.
Glad it worked for you. I’ve been communicating this on quite some places in the forums here but indeed folks seem to prefer to do flat field correction, which I didn’t want to do because it needs to create additional files. Also, folks don’t seem to accept that a finite light source will always give light fall-off towards the edges (this comes on top of any lens vignetting). My partner is a physics professor in optics and in that field it’s a standard issue. I’m a physicist myself and we discussed in length how to solve it mathematically since the integrals are not at all trivial, but the effect of a finite light source is indeed real. Any lens vignetting comes in addition.
Edit: And indeed looking at the histogram is a very good method: If the light is homogeneous in intensity, the histogram should be a spike. The wider the spike, the less homogeneous the light is.
If you have a square light source, you can get away with a circular mask for both the light fall-off due to the finite source as well as due to lens vignetting. If you have a rectangular light source, you would need an elliptical mask for the light source being finite and a second circular mask for the light fall-off due to lens vignetting.
Thanks. Yes, using flat field correction is quite tedious, it rarely works well, and creates additional files, the increased storage size is quite large. My light source is rectangular, the Negative Supply Light source mini.
There is a physical mask in the Negative Supply carrier for 35mm, which is obviously rectangular. The mask I created in Lightroom won’t be perfect. I first checked luminosity across the frame, which can be seen by using a luminosity range mask with overlay, and it isn’t evenly distributed at the corners, it seems the light falloff is higher on the right corners than the left. Regardless, I think in practice the improvement with a mask that equally affects all four corners is quite noticeable. But again, I need to optimize it, and perhaps the results will be different using a blank negative. Flat field correction is the most accurate way I’m sure, but it has so many downsides and Adobe doesn’t seem to be interested in improving it.
The forum software limits what a new user can do. This includes attachments and unmonitored posting. The limitations will go away when you e.g. read posts.
You can always add a link to a share (Google Drive, Dropbox etc.) or use a free sharing service like wetransfer.com.
Display a reduced view of a blank capture of the backlight (Kaiser Plano in my case)
Draw a radial mask, circular in my case, that extends from corner to corner
Reduce exposure until the center and corner brightnesses are about the same
and let the histogram guide you: the narrower, the better
Adjust mask feathering until brightness is about the same from center to corner
and let the histogram guide you: the narrower, the better
Adjust overall mask size if that further improves evenness
Close the mask tool and adjust global exposure to compensate the darkening you got from the local adjustment (the gradient mask) you just made
Save as a new preset (only check exposure and mask items)
Notes:
The Plano extended well over the field of view of the lens which was set to capture 1:1.
For perfect masking, you’d probably run through steps 3 to 6 more than once.
For perfect masking, you’d have to create a filter for each imaging ratio (1:1, 2:1,…) and f-stop.
For higher f-stop numbers, I had to adjust feathering mostly and correct exposures slightly.
Use Virtual copies for experiments.
Make the Lr background about the same tone as the image.
