I shoot mostly landscapes and am often annoyed when bright sky bleeds into the leaf silhouettes.
Would a graduated filter help? Any other ideas?
I have had this problem with my D90, Gf1 and now D800e.
Is it just a Dynamic Range issue?
Difficult to say without seeng an example. But taken from the few describing words it sounds very much like a dynamic range issue. If so then a gradual ND filter could help - depending on the concrete composition of the image - or you apply some HDR techique.
HDR, if properly done, does not need to thave this horrible ovedone "HDR style". Those pictues can actually quite nice in a way that only experts can say whether it is based on an HDR or not.
It may be chromatic aberration that you see if there are any purple/green fringing around leaves. That generally occur in high-contrast objects. If it's this one you can fix this by shooting RAW and than selection "Remove chromatic aberration" in Adobe Camera Raw software or DxO Optics Pro 8.
If by blending, you mean it's not balanced to the ground than you can put on a soft graduate 0.6 neutral density filter(I use B+W and it's great) dark side up on your lens. This will balance the darker ground to the brighter sky so you won't have any problems.
Instead of ND lens you can choose to shoot RAW and then with Camera Raw imitate ND filter again. And/or lessen highlights, brighten shadows and you're set again. Not as effective as a ND filter but it'll do.
If you post a sample photo it'll be easier to help.
If I understand what you're indicating then it's the slightly darker blue of the sky seen between the branches and leaves of the trees. This isn't entirely chromatic aberration (although that could exist too in high contrast areas), but from your example it looks like an effect of the color filter array on the sensor, the demosaic/interpolation algorithm, as well as the relative light intensity in those areas.
What a color filter array does is provide multiple colors for light to pass through, usually giving green a greater opportunity. Here is a basic illustration of how it works:
The Red, Green and Blue inputs, with the composite result:
The reason this is done is because a digital image sensor can only be turned on or off by a ray of light - which is effectively black or white. After passing through a color filter array each pixel on an image sensor effectively has a single color value. The image then needs to be demosaiced and/or interpolated, which means to have information constructed from the known information recorded.
In your case, the sensor is generating color values for the ones recorded in and around the leaves and branches. Blue is the color of the sky, but the intensity (brightness) of the blue is diminished from the surrounding leaves and branches (which are comparatively dark and block some of the light). As a result, you get a slightly darker shade of blue in those areas.
Blame the demosaic/interpolation algorithm your camera uses (if you record as JPEG) or your software uses (if you record in RAW format). Maybe taking digital photographs with something like a Foveon sensor (Sigma) camera or some other technology will work better at preventing this from happening as noticeably. You'll still need to contend with relative light intensity and then chromatic aberration if applicable (look at high contrast areas like in the example below taken with a Foveon sensor), but the issue won't be as pronounced:
Your text isn't very clear. Also you didn't put a photo/crop to show the effect.
bright sky "bleeds" into the leaf 'silhouettes'... hmmm...
Perhaps do you want to say blends ??
Perhaps it is a phenomenon like this?
If yes, then it is called Chromatic Aberration.
One of the biggest factors of influence is the quality of the lens. If you can get/afford/if exist, try to get a better lens. Btw, what lens do you have?
Also, yes, an graduated ND filter helps. OTOH, you can try also with a CPL filter (which, for our discussion, acts also like a weak graduated ND filter) but it has also other properties which are useful for landscape photography (your object of interest).
And as a final note, you can try to remove CAs in post-processing.
... weird blue leaves when shot against a bright sky... – Doctor Atomo
I doubt the blue leaves are caused by the Bayer matrix on your sensor because an image produced by a Foveon sensor also has the same effect. I suspect they are chromatic aberration caused by your lens or diffraction of skylight around the leaves. The resolution of the sample images is too low to tell clearly.
... bright sky bleeds into the leaf silhouettes...
Problems that match this description may include:
Chromatic aberration, color fringing, and spherical aberration are often worst when lenses are used wide open.
The safe answer is that it is a combination of over-exposure and chromatic abberation, which is then very visible over the black leaves.
But there may be more to it than that. Camera sensors are not colorimetrically identical to human eyes, they may see a bit into the infrared and/or ultraviolet spectrum too. IR light may add to the red channel, UV light may add to the blue channel. On such a high contrast scene even a little bit may be enough to do harm. And the lens has been corrected for chromatic abberation over the visible spectrum, but outside that corrected range the errors grow quickly. See the last figure in https://en.wikipedia.org/wiki/Achromatic_lens .
So, thinking that a little bit of UV sensitivity may manifest as a significant blue or violet glare, I am experimenting with a UV filter to see if I can get the CA for this sort of situation under control. It has to be a filter with a deliberate cutoff below ~450 nm. This will be on a Tamron 45mm/1.8 SP lens, which is known for having CA issues.
Usually cameras have software to deal with the worst effects of longitudinal aberration (the effect when near-UV visible and near-visible UV light registered by the sensor have a different focus plane than longer wavelengths). However, for this to work, the sky must not be blown out (or the camera has no way to really guess the brightness and hue of the sky). A polariser can help with some parts of the sky (not everything is polarised) by reducing the overall sky brightness. Even then, correct exposure will most likely render the branches underexposed. Like with many high-contrast backlit situations, a fill flash may help defuse the situation. The danger of the flash dominating the scene is basically non-existent but it may still reduce the dynamic range slightly.