[Gary Bidwell]

Hi all,

To follow up on the HDR shadow issue:

please find attached a thumbnail of the HDR I'm using and a low res render of a couple of primitives on a floor plane:

The original HDR file is made up of:
9 brackets
and resolution 7144 x 3572

On the HDR you can see the shadows on the grass, which are fairly sharp but on the render the shadows on the ground plane aren't quite the same, and feather out within a short area.

The render settings are:
illumination intensity:
200

Does the full resolution of the hdr get used for lighting, or is the file scaled down internally?

And do I have to adjust the HDR image so the sun is a little tighter?

Cheers,

Steve

[bograt]

I make alot of hdr images and I always make a point to try and capture even the brightest but believe me, it is not easy to capture the full intensity of the sun, I have not put this into practice yet as I have not yet had the need but I imagine that the only way to simulate an accurate representation of the suns intensity is to burn it in in post.. you could waste many many photos capturing only a black photo with a white dot to try and truly capture the suns intensity in your camera

[Gary Bidwell]

Hi Bograt,

do you think it might be an intensity thing rather than the size of the sun in the image?

When we used a black image with a small white square as the light source (created a few stops up in photoshop) we get sharp shadows ok.
This white square had less intensity than the sun in the hdr image.

Maybe we need to pull in the area around the sun. At the mo, the bright area around the sun may be contributing to the softer shadows?

[Mihai]

What does the lowest exposure photo look like? The only thing that should be in it is the sun as a tiny bright dot - you'll get proper shadows this way guaranteed. You should use SS 8000, fstop 18-20 or so and ISO 50 if it can go that low. This way you can get a pretty small sun dot even in bright daylight. Even better if you can use an ND filter of several stops in front of the lens but if it's a fisheye lens....only option is a filter for the back of the lens but that gets messy and can alter too much the image quality.

[Gary Bidwell]

Hi Mihai,

I'm using a 8mm fisheye and the shots were take at:
f11
darkerst stop - 1/2000s
ISO 160

I've attached the darkest shot.
There's a fair bit of the sky present, so I guess this is the issue?

For this 9 bracket set, I might try adjusting the darker RAW files to clamp the area around the sun a little.

cheers,

Steve

[Mihai]

It's much too bright. It won't help much from the RAW, you'll gain about 1.5 stops, anymore and the whole image will loose intensity, defeating the purpose. When you shoot, you can go in 1.5 or 1.7 stop increments instead of 1, if you are merging to HDR directly from the RAW files. So you can still have only 9 brackets but much larger range.

[Gary Bidwell]

Cool, cheers for the info.

My camera only goes to ISO 100 and the Sigma fisheyes lens' sweet spot is supposed to be around the F11.

So with my setup at the mo, it means I'm losing 5 stops
ISO 100 instead of 50 = 1 stop
F11 instead of F22 = 2 stops.
Shutter 1/2000 instead of 1/8000 = 2 stops

The cameras shutter max is 1/8000 sec so I can make up 2 stops here but that's still a few stops off the F22, 1/8000 and ISO 50 setup.

I'll have to do some tests with smaller apertures and see how the F22 shots come out from the Sigma lens, to see if I can gain back a few more stops.

Thanks again.

Cheers,

Steve