Andy Perrin Posted April 15, 2016 Share Posted April 15, 2016 Got a new-to-me filter, a 24.5mm Omega 330WB80. Manufacturer's spectrum is: Is there any way to see how much of the shorter wavelengths I'm actually getting in the image? Even qualitatively, I mean, not necessarily quantitatively. I do not have one of those nifty sParticle arrays. Link to comment
JCDowdy Posted April 15, 2016 Share Posted April 15, 2016 You can stack another filter which cuts off part of this one it to see what goes away. Link to comment
Andy Perrin Posted April 15, 2016 Author Share Posted April 15, 2016 Hm. Well, used in conjunction with my UG11 2mm/BG39 2.5mm, just holding it up to the light, it looks like the other stack is blocking quite a bit more. Holding up just the BG39 alone is transparent, however. So the UG11 must be blocking a lot more than the 330WB80, then. And holding up my prior 330WB70 gives this result: Link to comment
JCDowdy Posted April 15, 2016 Share Posted April 15, 2016 Interesting, you will want to try different combinations taking into consideration the UV cutoff of the known filters. Also, depending on the white balance used the false color response will often skew toward the yellow/green for shorter wavelengths or magenta for longer wavelengths. Link to comment
Andy Perrin Posted April 15, 2016 Author Share Posted April 15, 2016 Daffodil attempt. (Omega 330WB80 rear-mounted, Novoflex Noflexar, F/8, ISO3200, 0.1") Link to comment
Cadmium Posted April 16, 2016 Share Posted April 16, 2016 Andy, Nice Daffodil! Here is an overlay I did to try to compare and understand these filters. I used T for these.The Noflexar 35mm and the Kuri 35mm have a similar UV transmission profile and cut-off. Link to comment
Andy Perrin Posted April 16, 2016 Author Share Posted April 16, 2016 Cadmium, the BG39 2.5mm was pretty much transparent when used in conjunction with the 330WB80 and the Noflexar, but the UG11 looked like it was blocking the light. I wonder if I grabbed the wrong filter when I did that test! Either way, with the 330WB80 alone, it seems like the lens is the limiting factor there. What's confusing is that I also tried the 330WB80 with the Steinheil EDIXA auto-cassaron, which is supposedly good down to 320, but it sure didn't seem to be behaving that way! I got even less than I did through the Noflexar. Link to comment
Cadmium Posted April 16, 2016 Share Posted April 16, 2016 Yes, I understand, what you describe is a bit confusing in my mind, that is why I put the comparison graphs here to ponder.In my opinion, the limiting factor in any of these filters should be the BG39 2.5mm filter, because it limits the transmission amplitude and UV range-depth of any U glass you stack it with. Would there be any possibility that the UG11 and BG39 might be ZBW1 and or QB39 instead? Sometimes people use 'equivalents' to mean the same thing. Link to comment
Andy Perrin Posted April 16, 2016 Author Share Posted April 16, 2016 Cadmium, no idea! It certainly SAYS UG11 and BG39, respectively, on the sides... But regardless, the 330WB80 doesn't seem to have a red leak (or at least not enough of one to matter in sunshine), so I don't have to stack it, I don't think. The test was just to find out what exactly the 330WB80 was passing. I really need a narrow band pass filter at a short wavelength to determine that, I think. Link to comment
Cadmium Posted April 16, 2016 Share Posted April 16, 2016 Right, it doesn't have a Red/IR leak. I have a 330WB80, but it may not be exactly the same as yours, I think mine is smaller diameter, here is the Sparticle test I did with mine, which shows no Red/IR leak.(disregard 460DF20, it has an IR leak, since replaced) Here on Kuri 35mm lens. Link to comment
Andy Perrin Posted April 16, 2016 Author Share Posted April 16, 2016 Ooh, that is a help, assuming the filter passes the same spectrum. It certainly looks like it corresponds to the curve I was given (to within eyeball approximation, anyway) assuming the Kuri behaves the way your curve describes. Link to comment
Cadmium Posted April 16, 2016 Share Posted April 16, 2016 Yes, I think the Kuri and the Noflexar have similar performance.This Sparticle comparison is even more informative. Also, note now the BG39 is clear(white) like you described? I have to rethink that each time.By the way, I am using a UG11 2mm + BG39 2mm stack here, because at that time all my filters were generally 2mm thick. Link to comment
JCDowdy Posted April 18, 2016 Share Posted April 18, 2016 I am fairly certain the 330WB80 is one of Omega's approximations of a Schott DUG-11 or DUG-11X, a red reflecting layer deposited on top of a UG-type substrate. The original filters from Schott are hard to find and seem only available as special order. I have the Omega 25mm 330WB70 and it is an interesting filter. It white balances a little different than a Baader-U or a stack. Link to comment
Andy Perrin Posted April 18, 2016 Author Share Posted April 18, 2016 JC, I have the 330WB70 also! This one behaves slightly differently than that one, though they are similar. (Edit: Actually, I posted a pic above holding it up, so you can see the effect, I guess.) Here's the manufacturer's spectra that I have for them. I replotted the data in Excel after extracting it with GraphClick. Link to comment
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