Today’s Question: I use Hoya Fusion Antistatic UV filters [https://timgrey.me/hoyauv] on my lenses. Should I remove them and screw in my variable neutral density filter when the need arises? Or can I screw the neutral density filter onto the protector filters?
Tim’s Quick Answer: I recommend removing the UV filter from the lens before attaching the neutral density filter, simply to reduce the risk of lens flare caused by having multiple filters stacked together.
More Detail: You can most certainly stack more than one filter together if you have a reason to do so. For example, if an exposure would benefit from using both a graduated neutral density filter along with a solid neutral density filter, you can absolutely stack those two filters together on the lens.
However, there are a couple of reasons to avoid using more than one filter if you can. First of all, whenever you add a filter, you are reducing overall sharpness and detail in the images you capture at least a small amount. This isn’t generally a significant concern with high-quality filters, but it is worth keeping in mind that if a filter isn’t really providing a benefit, it is probably better to not use it.
When stacking more than one filter you are also increasing the risk of lens flare caused by light reflecting back and forth between those filters. This can result in bright spots in the image, just as you might see with lens flare caused by the internal lens elements, when the sun or other bright light source is in front of the lens.
If there isn’t a strong light source in front of the lens this lens flare with the filters won’t be a concern. But I recommend avoiding the stacking of filters in general to avoid this risk, so that you’re in the habit and don’t forget to remove an unnecessary filter when there is a risk of flare.