In the ongoing debate of filtered versus naked lenses, Roger Cicala makes a compelling argument over on his Lensrentals blog as to why, when it comes to filters, you either go big or you don’t go at all.In his post he talks about a customer who complained about a “soft” lens – and it turns out that it was the customer’s protective filter that was the cause of the issue. He figured it out because the customer returned the lens with the filter attached.
Cicala shows before and after tests done that show the difference between a filterless lens, and then talks about the differences between filters that use optical glass and cheaper sheet glass. He tested multiple copies of the lenses in question with the same filter, and the results were the same the cheap filter hurt the image quality out of the lens. This isn’t a surprise – Cicala is known for his meticulous tests and lens teardowns, so it’s a safe to say he knows what he’s talking about here. He talks about certain cases where you'd want to use quality filters, and others where you'd want none at all.
In a completely informal test using a B+W MRC filter on a Canon EF 85mm f/1.8 USM lens, I shot these photos below directly into a light source to see what the differences would be – take a look for yourself:
There seemed to be some flaring (the blue circle in his head) and some slight color differences. He (and I) moved slightly in each shot, but you can see how the filter affected the shots. Sharpness seems about the same. Is it enough to make it worth the case to not use filters? Your call – how often are you shooting into the light like this?
I’m firmly in the UV filter camp for two reasons – I always use to leave lens caps on, and then missed moments after raising the camera to my eye like that. Now, I stick a good UV filter (B+W MRC, generally) and I just keep things in my bag lens-cap free, ready to shoot. A small trade-off in my mind for extra flaring.
But the bigger reason is that I’ve actually seen these “protection” filters offer protection. I can’t count the number of times (OK, I can, it was three) students have come to me thinking their lens was destroyed only to find out that they merely broke the filter and the lens underneath was unscathed. I don’t want to think about what they were doing to cause this situation, but in each case the actual glass on the lens remained intact. Admittedly, it was sometimes a source of amusement to perpetuate the myth of the broken lens for a short time.
The protection aspect extends to weather sealing – you’ll often see in lens manuals (y’all read those, right?) that you need a protection filter to complete the weather sealing on a lens. Take this line, from Canon’s EF 16-35mm f/2.8L II USM lens instruction manual - it’s bold, and so it must be serious: “Since the front element of this lens moves when zooming, you need to attach a Canon PROTECT filter sold separately for adequate dust-and-water-resistant performance. Without a filter, the lens is not dust or water resistant.” I can attest to the fact that this is true – though I haven’t tempted fate by venturing out in the rain without a filter.
So, back to the title of this post – to filter, or not to filter? That is the question – what’s your answer? Leave your thoughts in the comments below.