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I'm not sure why, but I'm getting, at times, images like the one below, while doing long exposure with the 15 big stopper.

Sample image

I had this problem today for the first time, and not with all pictures. What could it be?

Note: I'm using a full-frame mirrorless camera.

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  • \$\begingroup\$ Looks like the front of your lens reflecting off the back of your filter. Is this one of the thread-on style filters, or one that sits in a filter holder in front of the lens via a bracket? If the latter, you're probably not getting the filter flush with the front of the lens... \$\endgroup\$
    – twalberg
    Commented May 24, 2018 at 1:33
  • \$\begingroup\$ I'm using the Lee 100mm holder. But I've been using it for ages and only a few times today happened. I'm not sure why. \$\endgroup\$
    – zzzbbx
    Commented May 24, 2018 at 1:42
  • \$\begingroup\$ I was not using the lens hood, just the holder. The vignetting is due to the 16mm focal length, my mistake \$\endgroup\$
    – zzzbbx
    Commented May 24, 2018 at 1:43
  • \$\begingroup\$ I know - I've got a similar system. I'm saying, because you can't use the hood, you need to find another way to shade the filter. \$\endgroup\$
    – OnBreak.
    Commented May 24, 2018 at 1:44
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    \$\begingroup\$ Sure - a rain cover would work. I use my reflector and either hold it in place (yea, crappy for long exposure) or try to rig it to a tree or something nearby. Point is, you need to create a shadow that falls onto the lens and position your light blocker in a place where it doesn't get into your frame. \$\endgroup\$
    – OnBreak.
    Commented May 24, 2018 at 1:46

2 Answers 2

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Light is reflecting off the back of the filter. You can plainly see the reflection of the front of the lens bouncing off the back of the filter.

Some type of makeshift hood may solve the issue if the light is entering in front of and passing through the filter. But I suspect the offending light is not coming through the filter.

With 100mm square filter holders, sometimes light can leak in at the sides of the holder through the small gaps between the filter and the lens in the areas where the "springs" that hold the filters in place are cut out. If the hood alone does not solve the problem, try covering the side holes with some tape that leaves no residue such as gaffer tape. If the top and bottom of your particular holder leaves gaps between the filter and the 'back wall' of the filter holder, cover those as well.

This review of the Sensei 100mm filter holder discusses what causes light leaks and ways different manufacturers and users deal with them. This review of the Haida 150mm system has some closeups that show the foam gaskets some makers put on either the edges of the filter or the edges of the holder to help prevent light leaks.

You can even buy self adhesive 100mm foam gaskets to apply to bare filters yourself. Be warned, though, they may cause (additional) vignetting with very wide angle lenses as they do slightly crop the edges of the filter to which they are attached.

Although it is not the cause of your reflection, Lee also recommends the viewfinder be covered when using their filters for long exposures. Light can leak around the raised mirror and get into the light box of many cameras, particularly if the camera is well used and the seals around the mirror assembly are worn.

This article by Paul Reiffer delves into the issue of light leaks with filter holders and shows example photos. It also include a comparison of three 150mm systems for his wide angle lens with built-in hood. The winner may surprise you.

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  • \$\begingroup\$ Thanks, I'll try that, especially because the hood for the filter holder is very expensive. \$\endgroup\$
    – zzzbbx
    Commented May 24, 2018 at 2:05
  • \$\begingroup\$ My eos1v has a switch that causes a "blast door" lookin' cover to come down on the eye piece. I wonder why canon didn't see fit to continue this feature onto digital models? \$\endgroup\$
    – OnBreak.
    Commented May 24, 2018 at 16:56
  • \$\begingroup\$ @Corey I'm pretty sure the Digital 1-Series models still include this feature. To the best of my knowledge, the 1-series are the only EOS film cameras that had it. \$\endgroup\$
    – Michael C
    Commented May 25, 2018 at 17:47
  • \$\begingroup\$ I guess I'll have to get my hands on the digital 1 series to see. My pockets aren't quite deep enough. I guess I was just surprised to not see the feature migrate down to the 5 series. But, I'm consistently surprised by a lot of their product decisions. I sure would love to interview a PM over there... \$\endgroup\$
    – OnBreak.
    Commented May 25, 2018 at 18:34
  • \$\begingroup\$ You gotta' save something to give to those 1-series owners to make them feel superior to the rest of us. \$\endgroup\$
    – Michael C
    Commented May 25, 2018 at 18:35
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In addition to my comment for using something to cast a shadow on the lens...

Here is my rig, a 16-35 f/4 with Formatt-Hitech's 100mm square filter holder attached. Both are shaded under a Canon soft lens bag with the bottom cut out. I don't know if the bag is 100% lightproof, but it's been good enough so far.

enter image description here

Good luck!

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