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Peter Manojlovic May 28th, 2011 10:24 PM

Noise in the picture
1 Attachment(s)
I had some location shots done for the very first time with a Brevis..
The lens was a zoom (i believe it was 70-120mm). Fstop goes down to 2.8..

It was a very sunny day, and there was unfortunately, NO ND filter on the lens.
The video camera was an XHA1...

Is this the result of diffraction, of is this a combination of camera/adapter?
Please look closely, the mosquito noise, although more prominent in the blue, is actually showing throughout the frame...
I suspect that an ND filter would be the main fix, but if anybody has any other suggestions, i'm all ears.


Bob Hart May 29th, 2011 10:51 AM

Re: Noise in the picture

What f-stop did you have your Nikon lens set to? The artifacts in the image are consistent with a lens aperture set to about f8 -f11.

What shutter speed do you have your camera set to? This may also provoke a similar artifact.

It is generally accepted that apertures of no higher a number than f5.6 are selected. Also, shutter speeds in ballpark of 1/50th sec are recommended. You can get away with 1/100th sec in certain conditions.

It may be that you either had a smaller aperture selected on your Nikon lens or the light levels forced your camera to autoselect a faster shutter.

Your zoom maybe should be operated in the zone, f3.5 - f4, which will be as close to its sweet spot as you are going to get whilst staying below f5.6, which you can use but perhaps should be wary of.

Your camcorder aperture should be in the zone f4 - f6.3, likely to be its own sweet spot.

Shutter should be at 1/50th sec or 1/60th sec.

To achieve those settings in the lighting conditions of your example, my imagining is you should probably look to a ND3 filter or ND6 filter in front of your Nikon lens. It is desirable to have ND in front of the lens attached to a 35mm groundglass based adaptor in order to minimise flare in the groundglass. With most 35mm stills lenses, it is desirable not to operate them wide-open as they may tend towards flare and soft image in the last half to full f-stop to wide open.

Depending on how susceptable your camera is to IR contamination, you might need to investigate a truecut IR filter if you are using NDs.

Does your camera not have an inbuilt switchable ND filter? If it does not, at a pinch you could cut one or more round pieces of clean and scratch-free new ND lighting gel and shove it in the space between the back of the Nikon lens and the front glass in the 35mm adaptor. I would make a spacer ring of plastic or thin cardboard to keep the gel from floating about and maybe scratching the rear element of your Nikon lens or the front glass of your Brevis adaptor. You may lose some sharpness and maybe get some reflections with a piece of lighting gel in there as it will not be dead flat.

Smarter people than I know about these things so heed the opinions of others.

Peter Manojlovic May 29th, 2011 08:37 PM

Re: Noise in the picture
Thank you Bob...

This is the only info. that i can supply at the moment. I will try and find out the shooters' settings....

Shot on XHA1 at 30P with 1/30th shutter speed.
Sweet spot set to F5.6 on the video camera, but the shooter rides the aperture manually to control exposure.

The camera definately has built in ND filters, but i have a feeling all the ND filters in the world won't help the image, if the lens in front is experiencing diffraction...

The only reason i bring up diffraction, is because of the softness of the image..

So to understand better.
In a highly lit situation like this, don't be wide open, and don't be stopped all the way down?
Try and keep to the sweep spots in both zoom and aperture?

Bob Hart May 29th, 2011 11:50 PM

Re: Noise in the picture

With your Nikon, diffraction from this lens will not be an issue in the aperture range a 35mm adaptor forces you to work within.

In the conditions you were shooting in, my guess as to best settings :-

Nikon iris, f3.5 or f4.
Camcorder ND1 selected. - Camcorder iris f6 or thereabouts.
Camcorder ND2 selected. - Camcorder iris f2.8 or thereabouts.
Shutter 1/60th sec if you are in 30P or 60i country.

Diffraction from the camcorder's own lens may become an issue if you do not use in-camera ND and close the camcorder iris to f16-f22.

It is perfectly acceptable to use in-camera ND to control light in order to keep both Nikon and camcorder's own lens in their respective sweet spots. In fact it is essential if you are to achieve the best possible image. ND in front of the Nikon lens is a sweetener but you can do adequately without it.

If the camera offers no control over the shutter speed, you may need to force the camera to select a slower shutter speed by using ND2. If the camera chooses to gain up rather than lower the shutter speed, then you may end up with a noisy image from gain noise.

I will look up the camcorder type when I have some time and comment furthur. IN meantime, I would change the camcorder shutter speed to 1/60th sec. If the shutter setting is referred to by frame rate, then it should be set to 30FPS or 30P for the US or any countires where the AC power is 60Hz.

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