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UltravioletPhotography

[Filter Test] Hoya U340 vs BaaderU :: crocuses in the wind


Andrea B.

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OK, these are terrible crocus fotos because the force was not with me. In other words, the breezes were against me. :D Breezes are not good for 5-10" exposures for sure.

 

And I had a horrible time trying to focus the UAT 85/4.5 on the Pentax K5. Time to get that camera some kind of Hoodman LCD shade or whatever.

 

But this is why we go out and practice - to discover what needs to be dealt with prior to real field work.

 

I'm going to show you the results anyway because I thought that it was interesting that the Hoya 340U + BG39 stack produced a difference between the white and purple crocus that I did not see when using the BaaderU.

 

First Set: This is the Demosaic Only version of the fotos which is about as much raw PEF as I can present to you short of posting Raw Digger charts. I present these because I'm hoping it shows how the camera+lens+filter combo records in each channel. This is, of course, best seen when viewing the raw file in a converter, but you do get some idea here.

 

Hoya 340U + BG39 :: Demosaic Only

The exposure was f/11 for 10" @ISO-160 under the stacked filters, but it could have gone another second or two as it is slightly underexposed.

PNTX0105demOnly.jpg

 

Hoya 340U + BG39 :: Histogram from Photo Mechanic

PNTX0105_Histogram.jpg

 

BaaderU :: Demosaic Only

This exposure was f/11 for 8" @ISO-160.

PNTX0101demOnly.jpg

 

BaaderU :: Histogram from Photo Mechanic

Under the BaaderU a tiny bit more is recorded in the green channel. Given the somewhat orange cast seen in the BaaderU raw foto above, this makes sense.

PNTX0101_Histogram.jpg

 

 

Second Set: This is a properly colour profiled version of the preceding photo with the K5 camera curve applied. The colour profile for the K5 + UAT 85/4.5 was made in Photo Ninja with a Color Checker Passport and a white standard.

 

Hoya 340U + BG39 :: Exposure and Color Adjusted

Note that all the flowers look the same in the foto.

PNTX0105demColprofExp.jpg

 

BaaderU :: Exposure and Color Adjusted

Note that all the flowers look the same in the foto.

PNTX0101demColprofExp.jpg

 

 

Third Set: The final set has had "True False Colour White Balance" applied. You know how much I enjoy using that phrase. Please forgive me. :D

 

Hoya 340U + BG39 :: Final Edit

Compare the middle crocus and the lower right crocus to the rest of the flowers. There is more green in their false colour compared to the other flowers.

PNTX0105demColprofExpWB.jpg

 

BaaderU :: Final Edit

Under the BaaderU the middle crocus and the lower right one look the same as the rest of the flowers.

PNTX0101demColprofExpWB.jpg

 

Hoya 340U + BG39 :: Final Edit + Brightening

Here's the Hoya 340U foto again, but lightened up quite a bit so you can really see the differences.

Interesting I think. When I first noticed this, I had thought that maybe the filter stack had caused a hotspot before I realized that it was the white flowers which were different under the 340U.

PNTX0105demColprofExpWB_liter.jpg

 

 

Fourth Set: The Crocus in Visible light.

The middle crocus and the lower right crocus were the white ones.

PNTX0098pn.jpg

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That is fascinating that the flowers are different coloured in visible light, but are so similarly coloured in UV. It is in the processing that brings out the slight differences.

Col

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Alex, there are some examples of flowers which have a different UV appearance depending on their colour or their age. So it is not particularly surprising that there is a difference between white and purple crocus under the 340U/BG39 stack. Different pigments can respond differently in ultraviolet light.

 

But this is the first time I have seen that pigmentation difference brought out by a non-BaaderU filter, yet not seen under the BaaderU filter. Of course I have not done all that much work with other UV-pass filters. Finding this crocus example gives me some impetus to re-photograph some flowers with different UV-pass filters. Just to see what is there -- :D.

 

Example of UV signature variation because of flower color:

Hesperis matronalis [Dame's Rocket]: A UV Variant Example

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Also noted is that a bee would see the UV-absorbing, human-white crocus with its G+B receptors. You could call that cyan and almost think that the 340U/BG39 shot is showing us that bee version after the white-balanced, false colours have been brought out during conversion.

 

The bee would see a UV-absorbing, human-purple part of the striped crocus with its B receptors. Call it blue and also see it in the foto.

 

I do not like to read too much into false colours (as I've been careful to caution about before), but this was an interesting example.

 

*******

 

I wonder if I can reproduce this with the D600?

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Sorry, Andrea, for not being clear. But I am not interested in age- or variety- or species-related differences in UV-reflectivity between flowers. My question was about the filters.

 

What are your conclusions about the difference in color rendition between two filters? Do you happen to have a transmission chart for that particular Hoya/BG stack to compare it with Baader-U2 transmission?

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Here is a kludged up chart. Moves the 340U peak about 10nm or so to maybe 350?? No wait, looks closer to 360nm. Too funny - this stack turns the 340U into a kind of BaadU. :D ;)

 

Andrea needs to find a better IR blocker, methinks.

 

u340bg39.jpg

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OK, here's slightly better charts. I took these from Steve's Ebay site. (He makes them with the Schott chart tool I think. I used to have that set up on my other machine but lost the link.) I superimposed the U chart with the blocker chart.

 

The S8612 looks like a better choice. (This is already known if anyone recalls all the filter discussions of yesteryear.)

 

The S8612 + 340U is the grey area (for the 2mm thickness). Peaks around 360nm?

Looking at this, perhaps the BG40 is the one to try with the 340U.

340U+S8612.jpg

 

Here the BG39 + 340U is the grey area - much less. Peaks around 370nm?

340U+BG39.jpg

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So why did I get lighter, cyanish crocus using the 340U + BG39? Beats me !!??!! ;) :D

 

I love this stuff.

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Hi Andrea

Calling a Hoya U-340, 340U, could make it difficult for anyone using the search function to find this discussion ?

Does the thickness of the filters make any difference to the results ?

Col

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Yes, thickness of the filters matters. You can see on the graphs where the thicknesses are noted. Thicker filters have less transmission.
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I have a BG39 from B+W.

Their "F-Pro" filters are listed as being between 1.8-2mm thickness, so I'm going with 2mm. :D

My S8612 is 1.75mm.

 

(The initial post has complete labeling for the 340 so no worries about search.)

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Andrea: perhaps you should plot the actual transmittance of the filter combination(s) instead of overlaying the graphs? That'll make the task of interpreting the filter (pack) response much easier.
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oh please! You know how long I would last trying to plot graphs ?!!!? Probably 1.5 minutes before losing all patience. :P :D ;) B) :P

 

Aside from which I have no actual transmittance measurements for the filter stack as I own no spectral measuring stuff.

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Nah. More thinking of retrieving the underlying data for each filter then multiply and plot the result as a function of wavelength. I assume the filter maker can deliver the tabular data you need if you look for the information.
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Here is the Hoya U-340 Transmittance spectrum with data. http://www.hoyaoptics.com/pdf/U340.pdf You can take the data and load it into the Schott program. As you can see, the Hoya is markedly different than the Schott UG-11 both in terms of peak transmission (>) and 700nm bump (<). That is with a 2.5mm thick U-340.
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Could you re-shoot and use S8612 as IR blocker stacked on Hoya U-340 and see which result you get then compared to using Baader-U?
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Here is the Hoya U-340 Transmittance spectrum with data. http://www.hoyaoptics.com/pdf/U340.pdf You can take the data and load it into the Schott program. As you can see, the Hoya is markedly different than the Schott UG-11 both in terms of peak transmission (>) and 700nm bump (<). That is with a 2.5mm thick U-340.

 

Yes, it is not an exact match, just the nearest industrial cross reference according to KOPP and and NEWPORT INDUSTRIAL GLASS.

I forgot you could load your own transmittance data into the Schott spreadsheet. Do you have to input spectra in standard 1mm thickness or is thickness a variable one can also input in the Schott spreadsheet?

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I have some crocus left so I'll reshoot with the S8612.

 

Problem with these filter stacks is that there does not seem to be a good BG IR-blocker that doesn't cut out a lot of the UV.

 

The Pentax K5 + UAT 85/4.5 (used above) is working out well. I learned that it is necessary to turn off the K5 stabilization when on tripod. My shots got a lot sharper. I know to do this with Nikon's in-lens stabilization, but had not paid too much attention to the K5 in-camera stabilization setting.

 

Here is a crop from a visible shot of a Lenten Rose made with the K5/UAT. This photo was edited for colour profiling and a bit of sharpness, then cropped & resized. So you are seeing it as I would normally present a foto here on UVP. I'm pleased with the colour and detail from the K5/UAT. I'm trying to learn to use this combo as well as I can use my Nikon + UV-Nikkor combo.

 

Cropped & resized to 800px max. Should display within page.

Colour profiled. Detail slider=15. Sharpening = 100/.6. Shadows = .85.

PNTX0101pn_Det15_Shp100.6_Shadow8503.jpg

 

Uncropped & resized to 1000px max. Click up in an expanded browser

Colour profiled. Detail slider=15. Sharpening = 100/.6. Shadows = .85

The yellowish area on the white standard is, I think, supposed to be there because there was an incandescent lamp on a table to the left of the flower - otherwise ambient room light, no flash.

PNTX0101pn_Det15_Shp100.6_Shadow85_fullSizeto1000.jpg

 

Unresized extract 959 x 846px, so you'll need to click it up and maybe expand your browser.

Focus was on the crinkled flower stem.

There is some noise on the lower right leaf which came up when the shadow was lifted. The flower area, while blotchy looking, is not showing noise - that is how it looks.

I like this K5 sensor.

PNTX0101pn_Det15_Shp100.6_Shadow8501.jpg

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COMPLETELY annoying fact: Using a manual lens on the K5 you cannot move the focus point. You are stuck with the center focus point. I really hate that.

 

I went out to shoot crocus and found this early bee who eventually crawled into the crocus.

beeOnCrocus_visSun_20150404wf_032pn.jpg

 

Here is an unresized 637x637 extract from another photo in the sequence showing the good detail possible with the K5/UAT.

A one-pixel hi-pass overlay was applied to the luminance layer for sharpening after the Photo Ninja conversion (which applied a bit of standard sharpening and a bit of detail slider).

beeOnCrocus_unfilteredSun_20150404wf_047extract.jpg

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White & purple crocus again. The false colour difference in UV is slightly less obvious this time because the sun was more direct and was causing the UV iridescence well-known with crocus, the shiny little devils. But you can still see that the combo of U340 + BG39 photographs differently from the BaaderU and the combo of Hoya U340 + S8612.

 

White balances in the UV fotos were set on the same area in each foto and the K5 colour profile was applied.

 

 

Visible f/11

When I started out everything was actually in focus now that I know to turn off the K5's in-camera stabilization.

crocus_visSun_20150404wf_016.jpg

 

BaaderU f/4.5

Being in focus did not last in these March winds. It is absolutely crazy to try to shoot outdoors today.

crocus_uvBaadSun_20150404wf_021.jpg

 

Hoya U340 + BG39 f/4.5

Now you can see the hints of cyan, green and yellow.

crocus_uv340bg39Sun_20150404wf_025.jpg

 

Hoya U340 + S8612 f/4.5

The petal on the left is flapping in the wind.

crocus_uv340s8612Sun_20150404wf_031.jpg

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John,

 

"Reference Thickness" is a variable that you can input to the Schott spreadsheet. Also "Reflection Factor."

 

Regards,

Reed

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