Long exposure colour cast

Thanks for publishing your controlled tests. The results are quite interesting.

I've never used my filters with any lens shorter than 24mm, and there I use the wide angle adapter ring. I've never experienced the level of vignetting you do at the 20mm setting, in 1.3. The flare that you show seems to be an issue with the square filters. I've gone to the Lee wide angle hood, rather than the foundation kit holder and it seems to help; BUT there is a greater risk of introducing vignetting if I am not extremely careful in setting up the hood (it uses the classic accordion approach to telescope).

Quote:

---

Originally Posted by Manfred M

Thanks for publishing your controlled tests. The results are quite interesting.

I've never used my filters with any lens shorter than 24mm, and there I use the wide angle adapter ring.

---

I use the LEE 77mm Wide Angle adapter ring with this 16 to 35 mm Nikon lens and am able to use it at 16mm perfectly ok. With a protection filter fitted there is a minute darkening in the corners which can be addressed or cropped. Without the protection filter nothing is evident.

Quote:

---

Originally Posted by Manfred M

I've never experienced the level of vignetting you do at the 20mm setting, in 1.3. The flare that you show seems to be an issue with the square filters.

---

The vignetting, flare and spots in 1.3 are the results of shining the bright torch into the gap where the closest filter (10 stop) had been reversed (no seal to holder). So far I have not come across anything that suggests flare when used correctly but have not taken enough shots at different light angles to eliminate the possibility.

Quote:

---

Originally Posted by Manfred M

I've gone to the Lee wide angle hood, rather than the foundation kit holder and it seems to help; BUT there is a greater risk of introducing vignetting if I am not extremely careful in setting up the hood (it uses the classic accordion approach to telescope).

---

Once we get another break in the weather I'll get out and give them a good trial in blazing sunshine at different angles to see if I put the hood on my shopping list:)

Quote:

---

Originally Posted by xpatUSA

A bit of GIMP analysis:

Hue-map:

http://kronometric.org/phot/post/CiC...x1llcz-hue.jpg

There's some kind of split down the middle (arrowed). With this hue-map opened in RawTherapee, the affected area has virtual no green, a good bit of red, 100% blue and an HSV saturation of 100% . . not good but I have no idea why. :(

Blue channel center-area histogram:

http://kronometric.org/phot/post/CiC...e/blue-ctr.jpg

Pretty skinny compared with -

Blue channel lower left histogram:

http://kronometric.org/phot/post/CiC...e/blue-hor.jpg

Food for thought . . .

---

Thanks for sharing. Useful fact