Using Poser 11. I've noticed some glittery/sparkly shaders don't work correctly. They were intended for Firefly and that's the render I'm using. For example, this shader:

When rendered in draft mode, it looks correct (left). But when I crank up the quality, the sparkles disappear (right).

Trial and error shows the problem is the shading rate.  I can fix it by changing the shading rate in the object properties, but I'm curious about why this happens. Can I change the shader so it looks better at a lower shading rate?

Min shade rate determines the detail in a render for shaders. It's the sampling frequency. Values of 0.2 and below are good for detailed renders. The lower the value the more detail will be rendered from textures and shaders. I usually use a value of 0.10 for detailed stuff. MSR also has a big part in how each poly is subdivided into micro polygons during render, so its critical for things like displacement effects. Note that if you want to render at a lower value than default 0.2 you'll need to have the target value match in the actor properties AND render settings. So if I wanted to render out V4 at a MSR of 0.1 I would need to set the MSR value at 0.1 in render settings and corresponding value in each actor desired. If I were to switch V4's actors to 0.10 and leave the render setting at default 0.2 it would render out at 0.2 and ignore the set value in the actors, it's a global value in render settings. There's scripts to change all of the figure's actors simultaneously to a target value rather than having to go through each and do it manually.

Turn off reflection multiply on the Firefly root.

Change the actor and render settings MSR to 0.2 or lower

Try using  Type Sinc/Size 2 in your post filter Firefly setting, that's a sharp post filter.

...looking at the 2 results side by side it looks like your shader is dependant on a low quality MSR to make the sparkles more pronounced. The higher quality setting is more detailed in number of sparkles but the sparkles are more subdued. If the shader is intentionally constructed in such a way that the effect is dependant on a particular render setting to work properly there's really not much to be done in the material room. Perhaps increasing the Specular value and tweaking the roughness in combination with a less dense noise pattern, or a different type such as Spots would work. Hard to say...

A speckled ambient mask would definitely create more pronounced sparkles. Maybe you could experiment with rewiring your noise patterns to function as a mask to the ambient channel and rely on ambient rather than specular to create the effect of the sparkles. That would be what I would attempt, it would take a bit of fiddling though and not a guaranteed outcome. An image map mask could definitely do it more predictably, but it would be at the mercy of the UVs about the seams.

Or someone like Bagginsbill could do it in 5 minutes procedurally lol.

Thanks. I assume people like BB are now all about Superfly.

I usually have my shading rate set to .01 for a final render, knowing each part in the scene has its own shading rate that will override it. I got into the habit of setting a very low shading rate back when Firefly first came out, and you'd end up with problems like visible seams if the shading rate wasn't low enough.

I'll have to look for that script. It would be very useful for figures with a lot of parts.

"I usually have my shading rate set to .01 for a final render"

That's an incredibly low MSR ( lower value being higher quality)

I've never gone below 0.1, which some would say is too low (high quality), Bagginsbill feels that 0.2 is sufficient for the most detailed displacement and shader effect details. You may be unnecessarily taxing your render times by using such a low value as 0.01. Just giving a heads up on that.

Also if you're rendering at that MSR value for the sparkle shader try setting it actor/render value 0.2 and see if it renders out properly.

I think the problem was with texttures created for the Poser 4 renderer. Some would have visible seams rendered in Firefly, unless you set the shading rate very low. Or turned texture filtering on, but that made things look blurry. Probably not an issue these days, when nobody's making textures for the P4 rendererer any more.

I might have to give up on this shader. Raising the shading rate looks fine at a distance, but for a closeup, you lose the glittery look, unless you set the shading rate to 10 or something. Maybe I'll just Photoshop it.

Here's an Internet Archive link to a snapshot of Bagginsbill's Sequin Shaders for Firefly. At the bottom of the page is a little blue download arrow. There will be a momentary redirect and then the zip will DL. It's not the Sparkly Shader you show but it's similar, or at least it's sparkly. It's probably very complicated node arrangements...

BB Sequins Shader page snapshot

I get the feeling that it's not really the Sequins look you are going for though. More of a 1960s 1970s Glittery fabric you might see on a dress in a sci fi ensemble...

I have those shaders! But your're right, I'm looking for more a vintage sci-fi dress texture.