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Baader U, U-360, UG11, ZWB1 stacks compared


Cadmium

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Exposure and white balance comparison of Baader U, U-360 stack, UG11 stack, and ZWB1 stack.

Nikon D7000 UV/IR, Kuribayashi 35mm f/3.5, filters front mounted.

Settings: Aperture Priority, Matrix Exposure, f/11, ISO 200.

Exposure info posted from RAW files metadata.

 

1) This comparison group uses the same white balance for all 4 filters with no adjustments from the original RAW file shots.

post-87-0-15816000-1452316896.jpg

 

2) Each shot in this group has the white balance individually set using CNX2 full frame marquee from RAW file.

post-87-0-65137500-1452316919.jpg

 

3) Each shot in this group has the white balance individually set using CNX2 full frame marquee from RAW file, with Auto-Levels in Photoshop.

post-87-0-80584900-1452316932.jpg

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Did the sun set before you could take the ZWB filter picture? :rolleyes:

 

Seriously, this is very useful data, thank you. To clarify what we are looking at I humbly suggest adding in the spectra of the filter stacks for a side by side comparison. As I remember the U360/BG40 stack has an IR leak.

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The lighting condition was the same for all shots. All use Aperture Priority mode, there is no different setting or adjustment for the ZWB1 shot.

If by "the spectra of the filter stacks" you mean calculated graphs, then I only have calculated graphs for the U-360 and UG11 stacks.

I have no way of plotting a calculated ZWB1 + QB39 graph from the data they provide.

 

The longer exposure time of the ZWB1 stack is no surprise to me, given the thicker U glass than the other stacks, and the thickness of the QB39 glass,

this all ads up to a longer exposure. Why it is also darker using Aperture Priority, I can not explain.

I used ZWB1 1.5mm thick because I didn't trust the graph for blocking the visible range using 1mm like the other stacks.

Although the QB39 graph looks almost identical to a Schott BG39 graph, I am not convinced of accuracy with the QB39 graph,

however, if we were to trust the QB39 2mm graph, then it has close to the same suppression profile as does BG39 2mm and S8612 2mm (but without as much UV transmission compared to S8612).

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NOTE: Using an exposure compensation of +1.25 in CNX2 with the RAW file adjusts the ZWB1 shot to look like the others.

I will re-shoot these tests again in a few days weather permitting, and try to compensate using manual exposure mode.

I shot these in sets at three different aperture settings, f/3.5, f/8, and f/11,

meaning for example f/3.5 with all 4 filters, then changing aperture and shooting with all 4 filters again, and so on...

and I have looked at the others, and with all of them the ZWB1 stack shot looks consistently darker.

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Something that might be a factor here - how old are these Chinese filters? Supposedly the quality on the Chinese products has tightened up on the most recent products
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Brand new glass straight out of the hopper, freshly cut and polished.

The fact is that this stack needs more exposure time to compare to the other three examples. Up to 3 or 4 times the exposure time. It is already 2x the exposure time of the first to examples, and is still darker.

This is partly a result of the stack formula itself, using a BG type glass that has less UV transmission, and thicker U glass, the longer exposure is to be expected.

For whatever reason, the camera's auto exposure system is thrown off by this stack, which is not unheard of, but with more exposure time, or + exposure compensation, this filter is usable for UV and quite cheap to acquire.

When I adjust the exposure compensation on this shot to resemble the exposures of the other examples, I find that it shows less UV 'false color' richness than the other three, which is probably due to the fact that this glass/stack has less UV bandwidth than the other three. The UV bandwidth might be enhanced if stacked with S8612 instead, depending also on the ZWB1 itself, however, this would increase the price of the stack.

 

"the spectra of the filter stacks"?

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If by "the spectra of the filter stacks" you mean calculated graphs

 

 

That or actual measurement of the stacks if you have easy access to a spectrophotometer. I used to have access to a couple of nice HP 8452A but no longer :(

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Or as Shane once said - a spectrophotometer (dual beam) and an integrating sphere and a monochromator and a stable UV source.

So several thousand dollars later....

 

Anyway, Steve, those ZW filter results are weird indeed. Why do they take twice as long an exposure? Not particularly desireable in the UV game.

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Or as Shane once said - a spectrophotometer (dual beam) and an integrating sphere and a monochromator and a stable UV source.

So several thousand dollars later....

 

That would be the gold standard for lens transmission measurements where the exiting light is no longer collimated. For filter transmission a spectrometer will do the job just fine.

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Andrea, the darker ZWB1 shot is a result of how the camera's exposure system reacted to that one filter, differently than to the other filters.

The exposure system was set up for Matrix, Aperture Priority, and there are subtle differences in exposure between the other three filter shots also, but not as much as with that one.

I tested all of those using different lens apertures, f/3.5m, f/8, and f/11, and those were not all shot at the same time per filter, so I know it was not a mistake, they were all darker for that one filter.

I didn't alter the test for that filter, I am interested in truth and sharing here not in anything else, so I try to make these as accurate and fair as I can.

The ZWB1 stack obviously needs more exposure time.

I will test these again using manual mode to try to pin down a more precise example of exposure time needed to make them all look the same.

It is simply the way the exposure system dealt with that one stack, and still it is twice as long of an exposure.

 

This is intended to be an exposure and white balance test. Not a spectrometer test.

Spectrometer tests are quite useful, but I seldom see spectrometer tests showing diabatic type scaling, and a linear graphs will seldom show Red/IR leaks that might show up in actual UV photos,

and spectrometer graphs will not demonstrate white balance or subtle false color palette differences either.

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The manifestation of a transmission curve is the ensuing photograph.

 

Somewhat a parallel to an MTF graph and the image delivered by the lens.

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Yes, as scientists we want the transmission curve.

And as photographers we want the photograph made with the filter.

 

BOTH are needed in order to evaluate photographic equipment, I would say. :D

 

I gotta say I become ever more tempted to indulge myself in some spectrophotographic equipment. Surely it could be accumulated over the course of a year or two and I could learn it and could make some transmission measurements for filters and lenses.

At the very least, I think I will contact members John and Shane for some suggestions as to what might constitute good enough equipment and make a list.

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I disagree. You need to shoot a photo to 'do just fine'.

 

Which is rather interesting case here. Your Baader and U360+BG40 filter images look identical but I know the latter stack has a rather significant light leak at 720nm (~OD 3.2).

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Somewhere out there, there is Spectrometer topic. I encourage someone to go start one. ;-)

 

I will have some updated exposure tests tomorrow. Tried them again last night indoors. The ZWB1 stack needs considerably longer exposure than the other three.

Tried this using center weighted exposure mode this time, and compared that with manual mode.

I will post some pics and settings tomorrow.

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  • 3 weeks later...

Which is rather interesting case here. Your Baader and U360+BG40 filter images look identical but I know the latter stack has a rather significant light leak at 720nm (~OD 3.2).

 

Works for me.

Of course if you want to use thicker suppression glass that is an option.

 

post-87-0-36345500-1454216214.jpg

 

post-87-0-87375900-1454216233.jpg

 

post-87-0-37524200-1454216246.jpg

 

Weather has been rainy here, so I have not yet re-shot this set. The ZWB1 filter I have tested indoors, and requires considerably more exposure time using that stack (ZWB1 1.5mm + QB39 2mm).

 

Here are some excellent example tests of UV stacks, thanks to Boon:

http://myphotojourney.co.uk/uv-pass-filters-a-comparison/

 

Also, as I posted in a different topic:

Here is another example of U-360 2mm + BG40 2mm, laminated, using the Kuri 35mm in better weather.

http://www.nikonians.org/forums/dcboard.php?the-white-horse&forum=214&topic_id=6171&mesg_id=6171&page=2

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Which is rather interesting case here. Your Baader and U360+BG40 filter images look identical but I know the latter stack has a rather significant light leak at 720nm (~OD 3.2).

 

You are welcome to post your results. Saying you know something opposite my results seems a bit lacking?

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Ok guys.

Photos, test & charts tell the tale. Post 'em all.

 

If the chart is not proof enough that the combo works, then how about stacking a U360 + BG40 + IR695 to see if any IR gets thru?

 

Hmmmmmmm.......I gotta check the filter box. I might have this combo. I'm in the middle of a filter reorg and relabeling of the filter boxes currently so everything is strewn across the room and tables.

 

Anyway, to that reorg end I actually just paid 4.95 per box for empty B+W filter boxes to satisfy my apparently OCD need for uniformity in the already crammed filter case. Yikes!! Then I felt doubly stupid when B&H packed these 4 small filter boxes in an enormous box to send them 18 miles to my house. Really I totally promise never to do that again.

 

I also have a nifty little IR-LED thinger which sits in the flash shoe. So I can perform this leak test indoors if need be.

 

I'll get back here eventually with a shot.

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OK, here ya go - a quick test with a U360 + BG40 stack in Sunlight.

 

Equipment: Nikon D600-broadband + Coastal Optics 60/4.0 + Sunlight

Settings: f/5.6 @ ISO-200

Scene: Chicken pot containing Christmas cactus. A plant was needed for its IR reflectivity.

 

 

Visible: Baader UV/IR-Cut filter for 1/320"

Cluck-cluck.

testFilter_vis_sun_20160131wf_41936pn.jpg

 

 

Ultraviolet: Hoya U360 (2mm) + Schott BG40 (2mm) for 2.5"

As shot version followed by converted version.

Because it's pretty with that dark blue.

testFilter_u360-2_bg40-2_sun_20160131wf_41942.jpg

testFilter_u360-2_bg40-2_sun_20160131wf_41942pn.jpg

 

 

Infrared: B+W092 IR-Pass (695nm) for 1/640"

As shot. To give you a feel for how much IR was out there today.

A lot.

testFilter_ir092_sun_20160131wf_41960.jpg

 

 

The Test: Hoya U360 (2mm) + Schott BG40 (2mm)+ B+W092 IR-Pass for 5"

As shot. Leakage can be forced through the U360+BG40 stack with long enough exposure.

There are almost 12 stops difference between this and the actual IR version.

I do not know if this is Red+IR leakage or only IR leakage.

testFilter_u360-2_bg40-2_ir092_sun_20160131wf_41945.jpg

 

 

 

CONCLUSION: This test nicely illustrates that you can force some OD3 leakage in Sunlight with a long enough exposure. This is not news if you are well-read here on UVP (which might take a while). Under artificial studio illumination (not shown) it might be more difficult to force this leakage. The OD3 for this particular combo is enough blockage to get a good UV photograph in Sunlight.

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Andrea, could you do a comparison of the, Ultraviolet: Hoya U360 (2mm) + Schott BG40 (2mm) for 2.5" As shot version followed by converted version, & the The Test: Hoya U360 (2mm) + Schott BG40 (2mm)+ B+W092 IR-Pass for 5", but for 2.5", like the, Ultraviolet: Hoya U360 (2mm) + Schott BG40 (2mm) for 2.5", shot please. This should show the relative amount of IR in the Ultraviolet: Hoya U360 (2mm) + Schott BG40 (2mm) for 2.5", shot.

Col

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Such attention to the U-360 stack.

My 'intent' of this topic was to introduce and compare the ZWB1 + QB39 stack.

The ZWB1 stack is interesting because it is dirt cheap, but I would not use it personally.

 

Remember to never confuse BG40 with BG38. Way back when, BG38 was often used as a UV-only IR suppression filter, but BG38 2mm - 2.5mm is a sure way to leak IR into a UV shot.

The only thing I use BG38 for is visual shots. It is a mistake to use it for UV-only stacking.

That being said, what I look for in a UV-only shot is foliage color and some parts of a flower pattern. In real life shots outdoors, foliage will either be dark or warm/brown/etc., showing IR.

If you push the test by stacking with longpass filters you will see Red/IR with almost any stack, and White/Gray with a Baader U, and I have numerous examples of this.

I guess I can post some again (below), but not specific to the U-360 stack, but just showing a general example of Red/IR isolation with UV-only filters/stacks.

 

Anyway, back to my point of the topic, my tests show me that the ZWB1 1.5mm + QB39 2mm stack requires exactly twice the exposure time as does the UG11 1mm + S8612 1.75mm stack,

which is already slightly more exposure time than the Baader U.

So for example, @f/8, indoor tests:

Baader U 13s

U-360 stack 13s

UG11 stack 15s

ZWB1 30s

 

post-87-0-85296600-1454317630.jpg

 

post-87-0-66703400-1454317689.jpg

 

Here is a U-360 2mm + BG40 shot outdoors on a sunny August afternoon, last summer.

post-87-0-69719600-1454317979.jpg

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Thanks Steve for all the additional test panels. You have given us so many great charts and tests!!!

 

I like this last UV shot. An interesting sculpture in the midst of the UV bullseyes. Cool stuff! (I want this to be Don Quixote tilting at UV windmills.)

 

Col, I'd be happy to repeat my test with your suggestion of matching times. Today we have such low light that I may have till wait until tomorrow (or whenever) to do so.

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..........CONCLUSION: This test nicely illustrates that you can force some OD3 leakage in Sunlight with a long enough exposure. This is not news if you are well-read here on UVP (which might take a while). Under artificial studio illumination (not shown) it might be more difficult to force this leakage. The OD3 for this particular combo is enough blockage to get a good UV photograph in Sunlight.

 

This does remind me of an earlier thread Optical density has its limits. One point from this earlier discussion was that of the "relative" OD. The OD of out of band blocking must be considered relative to the OD of the passband. A filter's out of band OD may be 3 but it the passband is only 50% then your relative blocking OD is at best only half as good. This is why I am of the opinion, for what it is worth, that optimal relative out of band blocking should preferably be ≥4.

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