Long Exposure Problem - severe red tint

[TCampbell]

The ND filter (ND = "Neutral" density... emphases on "Neutral" because it's not supposed to favor any part of the visible light spectrum more than any other) are sometimes not so neutral after all. Even the Lee "big stopper", while designed to be "neutral" suggests that each filter is unique and some may not be so neutral and may require a white balance correction. Lee suggests owners test their Big Stopper filters.

So I'm wondering... if your filter isn't actually "neutral".

I am skeptical that it's light leaking through the back. Once the reflex mirror swings up it usually blocks any light from the viewfinder from reaching the sensor (usually it's more of a problem with 'metering' accuracy than exposure.)

I read an article where the author was skeptical about the need to cover the viewfinder. So they did an experiment where they left the lens cap on, wrapped the entire body EXCEPT for the viewfinder (so the only way for light to enter the camera was in the viewfinder) and then took a very long exposure with a bright light shining into the viewfinder's eyecup. They inspected the images for signs that light had leaked in and saw... nothing. No signs of light leakage whatsoever even after going out of their way to create a problem. The conclusion is that modern DSLRs may do a much better job of sealing out light leaks from the viewfinder than older cameras.

 

[Derrel]

It's worth it to actually watch this video, just to see the way Lee actually dyes its filters...with women hand-dunking filter blanks in open-topped tubs of chemical solutions, doing everything mostly "by feel", basically. This explains the reason Lee filters are so often out of stock. Lee Filters is run like a cottage business.

In the comments section on YouTube, one photographer wrote, "I just obtained a Big Stopper(my goodness finally after all the wait!!) and I love it!! Contrary to what people say about the blue cast, I actually like the effect of the blue cast on my images; in my opinion it gives it a slight boost to the blue sky in a daylight and make it look deeper."

 

[ontarioguy]

The ND filter (ND = "Neutral" density... emphases on "Neutral" because it's not supposed to favor any part of the visible light spectrum more than any other) are sometimes not so neutral after all. Even the Lee "big stopper", while designed to be "neutral" suggests that each filter is unique and some may not be so neutral and may require a white balance correction. Lee suggests owners test their Big Stopper filters.

So I'm wondering... if your filter isn't actually "neutral".

I am skeptical that it's light leaking through the back. Once the reflex mirror swings up it usually blocks any light from the viewfinder from reaching the sensor (usually it's more of a problem with 'metering' accuracy than exposure.)

I read an article where the author was skeptical about the need to cover the viewfinder. So they did an experiment where they left the lens cap on, wrapped the entire body EXCEPT for the viewfinder (so the only way for light to enter the camera was in the viewfinder) and then took a very long exposure with a bright light shining into the viewfinder's eyecup. They inspected the images for signs that light had leaked in and saw... nothing. No signs of light leakage whatsoever even after going out of their way to create a problem. The conclusion is that modern DSLRs may do a much better job of sealing out light leaks from the viewfinder than older cameras.

It's worth it to actually watch this video, just to see the way Lee actually dyes its filters...with women hand-dunking filter blanks in open-topped tubs of chemical solutions, doing everything mostly "by feel", basically. This explains the reason Lee filters are so often out of stock. Lee Filters is run like a cottage business.

In the comments section on YouTube, one photographer wrote, "I just obtained a Big Stopper(my goodness finally after all the wait!!) and I love it!! Contrary to what people say about the blue cast, I actually like the effect of the blue cast on my images; in my opinion it gives it a slight boost to the blue sky in a daylight and make it look deeper."

So if this is a case and my ND filter isnt so neutral, how do you explain the difference between these two photos that I took, both using the same filter, both in daylight with similar settings.

OK, i understand now that the problem must be that light from the IR spectrum must be getting in causing the red tint problem (it's apparently quite common with ND filters). Apparently I need something to block this IR light as well, what can I use?

 

[Derrel]

I am more concerned about white balance and tint settings than anything. The regular color image is shot with AUTO1 white balance setting. I think the filter's presence might have affected the white balance applied to the reddish images. Can you look at the EXIF information in the long exposure shots, and see in your software what the exact white balance and color tint settings were?

 

[Buckster]

My Cokin NDs have a very strong magenta cast, and it seems to be stronger the longer the exposure is. I started using B&W NDs a few years ago, and they are working much better for me in terms of keeping things neutral.

On the issue of light leak through the viewfinder, I recall having that problem once while shooting the San Francisco Bay Bridge one night from Treasure Island using a Canon 20D. As I reviewed the shots I saw a very noticeable "ghost" of light in the images. As I worked through isolating the problem, it turned out to be the uncovered viewfinder letting light in from the parking lot street lights that were all around behind me. Once I covered that up, I was good to go again.

 

[TCampbell]

So if this is a case and my ND filter isnt so neutral, how do you explain the difference between these two photos that I took, both using the same filter, both in daylight with similar settings.

View attachment 110323

OK, i understand now that the problem must be that light from the IR spectrum must be getting in causing the red tint problem (it's apparently quite common with ND filters). Apparently I need something to block this IR light as well, what can I use?

When I inspect the tree line at the falls, it does indeed appear "red".

The red won't be IR light -- your camera filters that out (internally).

You could certainly test the filter by taking a photo of a plain white sheet of paper in bright sunlight to see if the "white" paper comes out with a red cast.

Are you shooting RAW or JPEG? If JPEG, the camera white balance might be over-warming the image.

 

[KmH]

With DSLR many cameras Auto White Balance is a pox that needs to be eradicated.

I too am thinking it's mainly a white balance setting issue, even if AWB wasn't used.

 

[Malavok]

It's hard to know whether or not it's a white balance issue without being able to fiddle with the RAW file.

My Cokin NDs have a very strong magenta cast, and it seems to be stronger the longer the exposure is. I started using B&W NDs a few years ago, and they are working much better for me in terms of keeping things neutral.

On the issue of light leak through the viewfinder, I recall having that problem once while shooting the San Francisco Bay Bridge one night from Treasure Island using a Canon 20D. As I reviewed the shots I saw a very noticeable "ghost" of light in the images. As I worked through isolating the problem, it turned out to be the uncovered viewfinder letting light in from the parking lot street lights that were all around behind me. Once I covered that up, I was good to go again.

I had the same problem with Cokin filters, which is why I'll never buy them again. I've used Tiffen, Hoya, B&W with no issues. Even my dirt cheap Altura ND filters don't cause the awful purple cast that Cokin did.

 

[ontarioguy]

Thank you for everyone who replied to this thread.
This last few days I played around with my camera, and alas my issue was indeed white balance.
I assumed it was my Tiffen Filter to blame (but I love it now that I know how to manually adjust my white balance).
The red colour-cast / tint is gone!