Kevin_A So if you plan to get 2, get an f2.8 and if things work out on my end I might just take you up on your generous offer.
OK, I will get two f/2.8 ones made then, one for each of us. Will contact you to get the shipping address later.
i wonder if the fixed iris will need to be painted the same non reflecting matte black as the mechanical iris?
For the one that is currently in the Samyang 135, I had asked for it to be anodized black. However, the parts that they machined, like the edges and the beveled face of the hole are not anodized. Those will need to be painted. I simply used black (looks brown in the photo) magic marker. The parts that needs have glue applied is anodized, so we are not applying glue over paint.
If the hole is too large, we can also glue another plate with a smaller hole to the plate with the larger hole later. Not ideal, but I think it willl work. It is like having two baffles :-). But the opposite will not work.
Possibly, you can use some kind of "reusable" cement or double stick tape, where plate can be pulled off easily. At least during testing.
Or small pieces of nano tape.
In my case with the Samyang 135, it is crossing the Rubicon. A lens that has 18 large spikes is of no use to me anyway (I wouldn't use it), so it was not really a difficult decision. Less angst than Caesar :-).
The difference between f/2.8 and f/3.3 is not huge, but not that small, either. 0.7x exposure time.
Yours will be 0.2mm so not too much of a ledge.
Yes. The plate itself is 1.5mm, but the hole is not a straight wall (like what you get with simple drilling), but is beveled. The wall of the hole is slanted at 60º instead of 90º. Easily cut your fingers if you are not careful -).
Now, the iris that I tested on the Samyang 135 had the ZWO fisheye lens' retaining ring as its aperture. So it is even thinner. I was checking for ill effects from the retaining ring in my test images, and did not see any. I was also looking for non-circularity, which like aperture vignetting, would have caused strong notches, but didn't see any. But the retaining ring size if fixed at f/3.3.
So there is still an unknown if the iris that is free of the ZWO retaining ring is also free of bad diffraction effects.
What we can do is after I received the two copies, is one goes into the USPS "priority mail." "Priority" is just a joke when the USPS is concerned. It will take three or four days for it to reach you. In the meantime, I can make some test shots if the clouds cooperate (it is getting better as we approach August, albetit with fewer dark hours; at times, I feel like I live over the Arctic circle -). You can then decide whether to make the change.
Or, use some removable adhesive.
In any case, you can still close the native iris down to smaller than f/2.8, and the native iris then becomes the actual baffle.
The final resort is to remove the iris assembly (loosening those three tiny black screws in white nylon sleeves, and the iris assembly falls out from the front) and then be able to wedge the plate out of the iris assembly. (Putting the iris assembly back is a bear, since you have to align the thing back on the three screws, and I have not found a good way to do it.)
The good thing is that I have not found even JB Weld "metal" crazy glue to be that strong. Now, the JB Weld two-part epoxies are really strong; I wouldn't use that.
Let me get to the f/2.8 plates. It will probably be Monday before they work on it anyway, so there is no need to rush. For something simple like this, they will be sending the finished product back on Monday or Tuesday afternoon, and I will have it back before Wednesday night, and can drop it off at the post office on Thursday AM.
Chen
