HiTech and Lee ND Filters and Hot Pixels

[nvw]

Hello,

I am testing the long exposures using Hitech Prostop IRND and the Lee Filters. I am working with 13 stop (10 stop + 3 stop) at 20 seconds and 16 stops (10 stop + 6 stop) at 4 minutes. I have noticed two things which I hope someone can explain.

First, aside from Lee's color cast, I have noticed that the histograms with the Lee are pushed to the right consistently. Is there a technical reason why this might be?  I would have thought (hoped?) that 13 stops of light would be consistent regardless of the filter manufacturer.

Second and more troubling has to do with what I presume are a lot hot pixels at 16 stops, red dust like spots across the image. What I do not understand is why the spots with the Hitech filters are so much more noticeable than with the Lee. I was hoping someone could explain what might cause this. I am trying to decide between Hitech and Lee.

Thanks,
Michael

[robdickinson]

Are you doing LENR with these shots? You probably should be.

And 10+ stop filters are not cinsistent in their claims, a Lee big stopper could be 10 stops or could be more like 11 etc

[spidermike]

Regards the histogram, I presume you are taking a reading without the filters on and then calculating the exposure to be used with the filters?
If the filters are not identical (if you think about, one stop difference is a fraction of the density of the fitler) then I can easily see that one make may give a histogram shifted one way or the other.

Regards red dust like spots what you may be seeing is some infra red contamination on the 4-minute exposure. I bought some HiTech high ND filters for use with my MFT camera and got red 'bloom' in the middle of the picture. Although this was a quite definite artefact in the center of the frame and sounds unlike was you describe, I guess it is possible that if you have 'hot pixels' that are exacerbated in some circumstances.

[nvw]

No, I was not using LENR but I definitely should have. Thanks for pointing that out.

[nvw]

Yes, I did calculate my exposure based on settings without the filters. I'll see what Hitech has to say but it sounds like what I am seeing is not unusual.

[wigasper]

I had the same red pixel issue with the Lee 10 stop ND. Turning on LENR completely fixed the issue for me.

[Arlen]

NVW, the hot (red) pixels are not a consequence of the filters per se, but rather the length of the exposure and the temperature. At 16 stops you are using a much longer exposure, 4 minutes vs. 20 sec, and during that time the sensor heats up and causes that effect. It also happens sooner in a warmer environment. Some cameras (sensors) also show it much more than others. If you google "long exposure" and "hot pixels", you should find lots of info about this subject. With some cameras it can relatively easily be fixed in post, with others just about the only way around it is to use the in-camera noise reduction setting (what I believe others referred to as LENR above).

[nvw]

Thanks for everyone's help, I can see some difference using LENR.

[Alan Smallbone]

Hot pixels are a an issue for all sensors. Many manufacturers have bad pixel mapping to get rid of them My Canon 5dII had a lot of red hot pixels even in short exposures, Canon replaced the sensor under warranty. All sensors will produce hot pixels, especially with long exposures. Subtracting dark frames (which is what LENR is doing) will help to some extent. Some LEE filters will allow more IR and that can lead to color shifts, a different issue than hot pixels. The color shifts can be more pronounced in sensors with greater IR sensitivity or with weak cut off filters in front of the sensor. I also find that exposure time that is calculated is only a starting point and often the exposure length will need to be adjusted from the histogram if you want specific results. My ND filters tend to need longer exposures than calculated.

Alan

[nvw]

I was reading this post where the person writing the second to last comment says he was doing a 15 minute exposure. I wonder how that could be possible without a lot of post processing to get rid of the hot pixels.

[spidermike]

For what it is worth I read a review of the new HiTech Firecrest filters and the pro who was testing them was very impressed.

http://www.stuartlowphotography.co.uk/lee-big-stopper-vs-hitech-firecrest-irnd/

[Graham Clark]

Hello,

I am testing the long exposures using Hitech Prostop IRND and the Lee Filters. I am working with 13 stop (10 stop + 3 stop) at 20 seconds and 16 stops (10 stop + 6 stop) at 4 minutes. I have noticed two things which I hope someone can explain.

First, aside from Lee's color cast, I have noticed that the histograms with the Lee are pushed to the right consistently. Is there a technical reason why this might be?  I would have thought (hoped?) that 13 stops of light would be consistent regardless of the filter manufacturer.

Second and more troubling has to do with what I presume are a lot hot pixels at 16 stops, red dust like spots across the image. What I do not understand is why the spots with the Hitech filters are so much more noticeable than with the Lee. I was hoping someone could explain what might cause this. I am trying to decide between Hitech and Lee.

Thanks,
Michael

Hey Michael,

I own the filters you're asking about, and have used them quite a bit!

Take a look at your own comparison images between the two.

You'll notice the corners are about 33% darker on the Lee than the Format-Hitech.

This is why the exposure is different.

This has to do with the ND being achieved through traditional oven baked vs. coatings.

Check out this review: http://www.the-digital-picture.com/Reviews/10-Stop-Neutral-Density-Filter.aspx

Graham

[nvw]

Thanks for passing this on Graham.