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[Filter Test SEU Gen2 #8] Dichroic Reflection Detour


Andrea B.

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UPDATE 2018.07.27 5:10 EDT Photos added in Post #7 to illustrate that there is no doubling problem with the Noflexar 35/3.5 or UV-Nikkor 105/4.5 and the SEU Gen2.

I still don't know why my EL-80/5.6 is misbehaving. I'm going to look into the helicoid again as a possible culprit.


[Filter Test SEU Gen2 #1] Introduction to the SEU Gen2

[Filter Test SEU Gen2 #2] White Balance, Raw Histogram & Andrea's "White Signature"

[Filter Test SEU Gen2 #3] Filter Speed & A Windy Bull's-eye

[Filter Test SEU Gen2 #4] Dealing with the Usual Dichroic Effects

[Filter Test SEU Gen2 #5] Landscape Interlude

[Filter Test SEU Gen2 #6] Monochrome Museum Comparison

[Filter Test SEU Gen2 #7] Measured Filter Transmission

[Filter Test SEU Gen2 #8] Dichroic Reflection Detour

[Filter Test SEU Gen2 #9A] Longpass Stack Wandering Discussion. See #9B for results.

[Filter Test SEU Gen2 #9B] Longpass Stack Results

[Filter Test SEU Gen2 #10] What good is a filter test without a Rudbeckia?

[Filter Test SEU Gen2 #11] A Fascinating New Rudbeckian View

[Filter Test SEU Gen2 #12] Summary


 

Dichroic Reflection Detour

 

Some UV-capable lenses and some UV-pass filters may under some circumstances (mostly involving the angle of the light, methinks) combine in some way to sometimes produce an unwanted artifact in a photograph - usually of a reflective nature.

 

UV photography is particularly prone to unwanted artifacts. For example, you might never notice a camera's little light leak through its upper LCD in an Infrared frame, but the corresponding UV frame will be ruined by an IR light smear. Or this -- about every 500th time I use my BaaderU on a 35mm f/3.5 lens I will get lovely concentric rings targeting the middle of my photo. And then there's the one involving the fine Coastal Optics 60/4.0. Use the CO60 too close to a subject and reflections off the rear elements combine to produce that pesky hotspot.

 

We didn't stop using the leaky D610 or the BaaderU or the CO60. We just taped up the camera, changed the BaaderU shooting angle and bought the CO60 its very own set of extension tubes.

 

So I hope you see that I take a practical point of view about these artifact events. That is, what is my work-around when an unwanted photographic artifact occurs so that I can continue shooting? I do care about what causes an artifact problem, but I care more about whether and how I can work around it.

 

During my SEU Gen2 filter tests, when using my EL-Nikkor 80/4.5 (old metal version) in the tests, I discovered that the combination of the EL-80 and the SEU Gen2 could sometimes produce a reflection artifact when shooting a very UV-reflective subject like a titanium white fence or a white metal bar against a UV-dark background in very strong sunlight.

 

Please keep this important fact in mind -->> I cannot reliably reproduce the EL-80 + SEU Gen2 reflection artifact.

 

Aren't those intermittent artifact occurences just the worst kind of things to try to figure out? If I could reliably reproduce the reflection artifact, then I would probably know what is causing it. But I really cannot say for sure. Only that it seems to involve the EL-80, a double dichroic filter, strong sunlight, a very UV-bright subject against a UV-dark background and the angle of the very strong sunlight.

 

Before I show a couple of photos, let me list what I have tried.

  • A lens hood was always used.

  • The problem is not from the D610 upper LCD light leak. That's taped up.

  • The reflection does not always occur with the EL-80 + SEU Gen2 combo. Only sometimes.
    [2018.07.20 23:45 EDT] This remark was reworded for clarity.

  • The reflection happened with both my EL-80/5.6 lenses under the SEU Gen2.
    What is it about the EL-80 that could be causing this?

  • The EL-80/5.6 helicoid has no light leak that I can find. I never fully extend the heli. That's often when I've gotten helicoid light leaks, so I avoid it. Besides which, the artifact does not look like a light leak.

  • I'm pretty sure that the artifact changes depending on where the sun is in relation to the front of the lens. The artifact can appear above, below or to the side of the UV-bright subject.

Here are some examples.

 

UV-bright bridge against UV-dark tree background. The bridge railing is "doubled".

d610_el80_uvSeuGen2_sun_f11_20180716somesvilleME_1201601.jpg

 

Crop from preceding.

d610_el80_uvSeuGen2_sun_f11_20180716somesvilleME_12016.jpg

 

For this photo I was in a position to catch some flare even with a lens hood. This photo was pushed brighter to better see the flare blobs on the left between the yellow bars. Please note: I was trying to make flare blobs and compare them to the doubling over the bridge.

d610_el80_uvSeuG2_sun_f11_withLensHood_20180718somesvilleME_12317pnArrows.jpg

 

 

 

In these next photos you will be looking at the white metal bar of a deck chair. The fabric of the chair is not shiny or UV-reflective. But you can see through the weave to the bricks & mortar behind the chair. Please do not mistake mortar lines for the doubling problem. The brighter area on the bottom right is part of the chair arm showing through the fabric and is therefore not doubling. The doubling is horizontal when present (...horizontal curved, that is).

 

EL-80/5.6-944334 + SEU Gen2 :: Doubling above the white metal bar.

The first EL.

d610_el80-944334_uvSeug2_sun_lensHood_20180720swhME_12473.jpg

 

 

UV-Nikkor 105/4.5 + SEU Gen2 :: NO Artifact.

Also note here that I've not had any reflection artifacts with the Noflexar 35/3.5 + SEU Gen2 combo.

d610_uvNikkor_uvSeug2_sun_lensHood_20180720swhME_12460.jpg

 

 

EL-80/5.6-996454 + SEU Gen2 :: Doubling just below the white metal bar on the right only.

The 2nd EL.

d610_el80-996454_uvSeug2_sun_lensHood_20180720swhME_12519.jpg

 

 

What is the cure for the reflection artifact ("doubling") if occurs with the EL-80/5.6 + SEU Gen2 combo?

[Added 2018.07.21 00:13 EDT]

Either you or the sun has to move so that your illumination is at a different angle. I wish I could tell you what angle works best, but I'm not sure I can say with certainty. I think it might be best to have the sun in back of you to correct this doubling if it occurs. If that is not possible then change the angles between you, the subject and the lens as best you can.

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[Last Update: 2018.07.21 00:15 EDT]

 

In this photo I was shooting with the sun above and in front of me using a lens hood, as always. There is a path going up the hill with wooden steps which are very UV-bright. But there were no doubling artifacts at all above or below the reflective wood in this photo.

D610 + EL-80/5.6 + SEU Gen2

Photo as shot.

NO Artifact.

610_5694.jpg

 

 

Here is the deck chair back photographed with the sun behind me. No artifact with the EL-80 this time.

D610 + EL-80/5.6 + SEU Gen2

Photo as shot.

NO Artifact.

610_5607.jpg

 

 

In the next two photos the sun was to my left. One artifact reflects the circular flat end of the chair back support and the other reflects the horizontal bar on the right side as a streak at the same level.

D610 + EL-80/5.6 + SEU Gen2

Two small artifacts.

610_5661.jpg

 

D610 + EL-80/5.6 + SEU Gen2

Two small artifacts.

610_5665.jpg

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I must continue on to my last two test series. But any comments and suggestions are welcome here. When I complete the last two tests, then I'll come back to this and try to work on it some more.
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A good suggestion! Later I will try other experiments.
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These photos of the Somesville Bridge were added to illustrate that both the SEU Gen2 + UV-Nikkor 105/4.5 combo and the SEU Gen2 + Noflexar 35/3.5 combo perform admirably in flare conditions. No doubling of the bridge rail is seen.

 

 

The UV-Nikkor photo is straight from camera.

d610_uvNikkor_uvSeuGen2_sun_20180727somesvilleME_13601.jpg

 

 

The Noflexar photo was given a rudimentary monochrome conversion to remove dichroic discoloration due to wide-angle use. Some falloff vignetting still shows a bit. But I didn't fix it because I wanted only to do conversion and monochrome so that there was no chance I would inadvertently hide doubling should it have occurred.

You can click this up to a full 1200 pixels width.

There are massive amounts of detail in this photo which is well-handled by the Noflexar + SEU Gen2. This copy of the Noflexar is quite good.

d610_noflexar_uvSeuGen2_sun_20180727somesvilleME_13645mono.jpg

 

 

 

 

 

 

[Done 2018.07.27 17:35 EDT]

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