After some of the recent discussion on the percentage of reflectivity on the mirrors, I did a quick survey of the 2 dozen scanheads we currently use. I did not have the old DT-40 (non pro) model here as one of our guys took it home to play with it, but they were just classic aluminized mirrors. Great reflectivity but no power handling capabilities. Here I am comparing the CT6215 with stock mirrors as shipped ($75 mirrors), CT6800 with expensive aftermarket high power mirrors ($150 mirrors) and the DT-40 Pro with stock mirrors as shipped. All three use dielectric mirrors, in fact I was rather surprised when I had first discovered that the new DT's used dielectric mirrors!
The line up, the each pair is psyching themselves up before the battle!
I'm sure the newcomer DT-40 pro is nervous about competing with such heavyweights.
The contestants greet each other.
(The interesting thing to note here is the mirror thicknesses. The thickness is part of how you get away with >30k scanning. The DT is obviously not suitable for 60k scanning.)
So there I was rigging up a table and playing around with power meters when I found a shocking discovery... so crystal clear that I didn't even need to use a power meter! Pictures will tell the story! No photoshopping tomfoolery is involved, it's actually 10x even more dramatic in real life!
First up is the CT6800HP, a solid galvo which is still the baseline of the industry.
Because we regularly use higher power (>10W) lasers in shows we have upgraded most of ours to high power dielectrics. In terms of specifications these are nominally rated >98% reflectivity, though as with most "visible range" dielectric optics the deep blues and violets are not fully reflected. These are $150 mirrors.
From a distance straight on it's clear that it meets or beats the 98% claim,
There is only the barest light leakage even up close.
At nominal 45 degrees (the angle the coatings are designed to run optimally at) it is as perfect as 99.9% aluminized mirrors.
Next up is the DT-40 Pro, a new entry into the market it certainly claims a list of features that could make it a serious player in the market.
This unit is bone stock, and is completely "as shipped". As you can see above, the mirrors are very thin, this reduces rotational inertia but they're definitely fragile. Jian rates these at >95% reflectivity.
From a distance they definitely let more light leak than the 6800s. It's hard to see in the photo, but in person you can see a hair more purplish from the light than the 6800s.
Even visually you can tell that it's far better than 95% even dead-on
even in the lossiest zone of deep blue and UV.
At the optimal 45 degree angle they are almost perfect, but you can see
slight losses in the deep blue and UV range.
Obviously in terms of reflectivity they are not perfect. I would definitely like to see aftermarket mirrors available for these as I would not put more than 6 or so watts through these.
Last up, the CT6215 with stock mirrors as shipped from cambridge.
This unit is the surprise for the day, with mirrors nominally rated at >95% reflectivity, the CT6215 is quickly pulling the lead as the defacto show scanner. These are the same standard mirrors you order for $75. These can nominally take up to 10W of power, an improvement on the stock 6800's
5W.
Here you can start to see some interesting behaviour. This effect is even more dramatic in person!
The mirrors are translucent! The camera can't even see itself in the reflection!
At the optimal 45 degrees, you can guess how CT computed >95%...
You can also guess why they can take 10W of power!
Synopsis: I don't want to hear about "cheap chinese mirrors, buy Cambridge instead"...
It was so hard to believe I put an LED flashlight up behind the CT6215!
Thoughts? different testing mechanisms? problems with my droid?
You can get the highres versions of these photos from their gallery.
http://photonlexicon.com/gallery/album64?page=1