What is everyone doing with their 8mm ZWB1

[Andrea B.]

Yes, I know that stuff.

What I was wanting to know was how you use glycerol to "glue" (so-to-speak) two filters together. Like, can that be done temporarily and actually used? Or is it way messy?

[Andy Perrin]

I'm betting it's messy but since glycerol is kinda sticky, you might be able to paint it on there and squeeze out the excess? Then seal the edges somehow? I'm curious to know also!

[ulf]

It can be used temporarily and actually used with some care, possibly by putty-mounting the stack in a suitable filter ring.

 

It is messy and I have no good solution how to seal the edge more permanently, keeping the glycerin in place.

I think it will creep and possibly affect the adhesive of the tape.

 

I used 3M "Magic" tape, first adding some thickness to the glass locally at the edges by covering two surfaces at opposite side of the circle with secant shapes of tape. (That shape after cutting the excess tape with a scalpel)

The was done on two of the three 3mm thick rounds. (four tape patches.)

https://www.mathemania.com/lesson/the-definition-and-basics/secant-2/

 

Then I made an air-spaced stack of the rounds, with all the spacer tape secants aligned on top of each other.

On the edges of the stack, outside the spacer tape, more tape was used to hold the stack together, again cutting the excess tape with a scalpel)

 

=> Air-gap measurement

 

Glycerin was then applied in small amounts at one edge between the spacer sections.

Due to the high viscosity of the glycerin I had to work it in by squeezing the stack a bit until I saw the first sign of glycerin reaching the opposite side of the stack.

Excess glycerin was the wiped off at the edges.

 

=> Glycerin-gap measurement.

 

It is a lot of fiddling and IMHO not worth the trouble in most cases.

For a two-glass stack the gain of transmission will be smaller.

Here I improved the transmission at four surfaces.

 

This was just a test of concept and a demonstration of the effect.

The resulting gain is reasonably matching the expected theoretical value.

 

I did this to get an idea of how the 8mm ZWB1 would perform.

[dabateman]

Mine arrived today. About 8.04 to 8.08 mm thickness. I am not sure the error on my calipers, they typically read about 0.05 to 0.1 lower than I expect. So the filter is thick.

 

I used my halogen bulb and could see a nice 350nm peak without anything in 700s.

 

I then popped new batteries into my halogen spot flashlight and focused through the filter and culminated it to the fiber. Then I could actually see a 370nm peak from the flashlight and a 700nm peak. Very impressive blocking.

 

For context of the flashlight brightness, if you looked at the flashlight, you would be blinded almost instantly. Even the bounce back spot from a Black 2.0 painted surface is too much to look at.

 

I am currently using 52mm to 55mm step up ring, then 55mm to 52mm step down ring, and then cheap 52mm UV ring with narrow pass, to hold it. I need to see if I have a 55mm UV filter to sacrifice, as it thick and needed tape to hold that all comfortably together. They aren't all tight together. Even my really thick 52mm ring wasn't deep enough.

[colinbm]

Good on you Dave

[dabateman]

I think I will share this anyway even though Johnathan and Ulf can call me foolish.

 

Kind of like standing on the surface of the sun and saying there is too much IR there, but really that is the least of your concerns!

 

This is the raw spectrum, there is no way for me to obtain a transmission spectrum, of a uncoated 75W halogen light bulb through the 8mm ZWB1 filter.

 

This is my spot halogen flashlight about 2mm from the surface of the glass, focused through the filter on a culminating fused silica lens behind into the fiber optic. I had no idea you could even get any UV off this flashlight, interesting to see a 370nm bump. The IR peak is 711nm

 

 

So yes with at least 8mm thickness of ZWB1, and an uncoated halogen bulb, you actually can get some UV. But I wouldn't recommend that as lighting source.

 

I hope Ulf gets his soon and can actually show us a log plot for the real blocking.

[Andy Perrin]

As a lens filter, I have to say the ZWB1 8mm is not too hot. Here is my comparison to UG11 2mm + S8612 1.75mm using the EL-Nikkor 80mm/5.6 at F/5.6 3.2" ISO100. Tested on the converted NEX-7.

 

Contrast/Exposure were adjusted on the UG11/S8612 photo and copied to the ZWB1, and white balance was done off the road in the same spot for each photo. These were shot semi-handheld (I balanced on a window sill) so some blur is probably hand movement. Still, there is a clear loss of resolution and additional scattering in the ZWB1 8mm, presumably due to the glass being so thick.

 

ZWB1:

 

S8612+UG11:

 

ZWB1 crop:

 

S8612+UG11 crop:

[dabateman]

Interesting Andy

The Zwb1 doesn't see through the license plate cover or maybe there isn't one and just mush.

But the S8612 stack has green loca on the Jeep grille, while the Zwb1 has magenta.

 

How dar off where the exposure settings?

 

If both were 3.2 seconds, I would be surprised.

[Andy Perrin]

Both the same. 3.2 seconds. Note that one image is darker though.

 

Can’t see the magenta.

[ulf]

As a lens filter, I have to say the ZWB1 8mm is not too hot. Here is my comparison to UG11 2mm + S8612 1.75mm using the EL-Nikkor 80mm/5.6 at F/5.6 3.2" ISO100. Tested on the converted NEX-7.

 

Contrast/Exposure were adjusted on the UG11/S8612 photo and copied to the ZWB1, and white balance was done off the road in the same spot for each photo. These were shot semi-handheld (I balanced on a window sill) so some blur is probably hand movement. Still, there is a clear loss of resolution and additional scattering in the ZWB1 8mm, presumably due to the glass being so thick.

I think it might be too soon to draw conclusions if it is just the filter to blame for this, based on a pair of semi-handheld images.

 

With such a thick filter I would also expect added blurriness at wider apertures due to spherical aberration that affect resolution like this.

I also think an added reason is that the lens is less chromatically corrected at the deeper UV-A spectra.

It is simply not so easy to take really sharp pictures in this wavelength-band without a lens designed for this.

 

The magenta is not supposed to be there much as the transmission closer to 400nm is very low

 

Could you please take new pictures with the camera on a tripod and the lens stopped down to both 8 and 11?

[Andy Perrin]

I really doubt it was the hand-shake, Ulf but I’ll give it another go when there is daylight. Say what you like about lens effects, but the crops are the same location with the same exposure and the same images. I will try to do a better white balance also.

[ulf]

I am just speculating, but I do not think the thick glass is the entire cause of the difference.

My experience with my U-340 4mm x 2 stack is very limited.

 

Eventually when I have my ZWB1 8mm set up I could try to inspect them internally for flaws with camera and U-340 4mm x 2 stack.

My ZWB1 glass has finally arrived and can be measured too.

[Stefano]

The magenta is not supposed to be there much as the transmission closer to 400nm is very low

Talking about colors after a white balance, based on photos posted on this forum (such as Steve's photo with a comparison between the Moon-U and another filter which I can not find now, and his 8 mm thick U-340 photos, I deduce that the lavenders become redder with a deeper filter and bluer with a filter that passes some violet, so you should see magentas with the 8 mm thick ZWB1 filter. Lavender surfaces should appear darker with that filter, but if visible they should appear magenta.

[Andrea B.]

you should see magentas with the 8 mm thick ZWB1 filter

 

?? I don't get any magenta from 7.0 mm of U340 (which has a raw orange color).

[Andy Perrin]

Well, I redid the test, with a lot more attention to detail, and the conclusions are mostly the same but get more puzzling the more I think about them! Behold, I shew you a mystery.

 

This time I used a very sturdy tripod with the camera fully rigid. I used a 10 second timed exposure to reduce any shaking. I white balanced with separate photos of a piece of PTFE beforehand, and used those photos in PhotoNinja to make the white balances. I discovered that it's extremely difficult to white balance that ZWB1 8mm for some reason - it seems strangely sensitive to little changes. When I white balanced in camera, for the first time ever on the NEX-7, the camera liveview colors did not match the resulting photos' colors. I forgot to mention before in the last post but, I used a tightly fitted lens hood in all the tests, so no light is coming in from the sides of the filter.

 

First the normal stack, same as the first test (S8612 1.75mm + UG11 2mm). F/8, 1", ISO100:

 

S8612 1.75mm + UG11 2mm, F/11, 2", ISO100:

 

Next, the ZWB1 8mm. F/8, 1", ISO100:

 

ZWB1 8mm, F/11, 2", ISO100:

 

------------

 

Here are the cropped images.

 

S8612 1.75mm + UG11 2mm, F/8, 1", ISO100:

 

S8612 1.75mm + UG11 2mm, F/11, 2", ISO100:

 

ZWB1 8mm, F/8, 1", ISO100:

 

ZWB1 8mm, F/11, 2", ISO100:

 

-----------

 

Obviously the ZWB1 is not winning this contest, but it isn't very clear (heh heh) why. The crops I chose show the blurriness relative to the S8612/UG11 stack well, but I noticed that if you look at the bottom left corner of the ZWB1 full size images, the sharpness there is pretty decent. At first I thought maybe the camera focus had shifted, but trying to refocus the camera did not bring the top left into sharper focus.

 

At the moment my conclusion (don't use this particular ZWB1 8mm as a photo filter!) seems pretty firm, but the reasons why it is misbehaving are as muddy as the images it produces.

[dabateman]

Well the left side of the Zwb1 is definitely sharper than the right side.

How did you mount your filter?

Is it loose or shifted?

 

I ended up mounting mine in 52-55mm step up ring, 55 empty filter, 55-52mm step down ring and then 52mm retaining ring to hold it together.

[Andy Perrin]

Took apart an old Kenko filter, removed the retaining ring, coated the inside with Ultra Black Gasket Maker (a stuff that's black and sticky and dries into a rubbery mix), and literally just stuck the filter in and pushed it down. Waited for it to dry. The filter isn't noticeably askew that I can tell, but if it's a fraction of a millimeter I might have a hard time noticing.

[dabateman]

Tomorrow,

Try taking an image with the filter fully screwed on to your lens. Than take a second image 180 degree rotation off. That should shift the sharp part to the other side.

That might tell you if its a mounting problem.

[Andy Perrin]

Yeah, a good thought. Although if the problem is that the glass is uneven thickness, you would also see the sharp part shift.

[ulf]

I measured my ZWB1 8mm. It is evenly thick within ±0.001mm

You might have some internal flaw in the glass.

 

If you take a close up of/through it with a PTFE sheet as background and with the UG11 stack on the lens you might see something.

[JMC]

To answer the opening question of the thread - I am currently waiting for my 8mm ZWB1 to be delivered (very envious of your all for getting yours)........

[colinbm]

I am finding my 8mm ZWB1 is working well with UVA lights & blocking 390nm & above, which was one of my goals.

For UVA photography I am finding that it is blocking too much around the 390nm for coloured UVA photography.

Perhaps 6mm maybe a better choice for UVA photography & but 8mm is better for UVA lighting ?

[dabateman]

Colin 6mm wouldn't have blocked the IR. The UV would look brown.

[colinbm]

Colin 6mm wouldn't have blocked the IR. The UV would look brown.

 

I did a UVA Sparticle today With a BaaderU & the 8mm ZWB1, with 130mm quartz lens.

 

Baader U

 

 

 

8mm ZWB1

 

[Stefano]

Same white balance?

 

This is what I would expect. No 390 nm, and more green at 340 nm. You can really see how the curve shifts towards shorter wavelengths with the 8 mm thick ZWB1.