Sunny spring day test

[Cadmium]

Just a test to see if it really is a sunny spring day.

 

Front yard

 

Back yard

[Andy Perrin]

Those are gorgeous photos, but I no longer believe in sunshine. There will never be sun again.

 

I love the sky there, even though it must be fake because sunshine does not exist. At least not here in Boston.

[Cadmium]

Andy, I understand your thinking. I was convinced the world was flat until I performed this test, but science is science.

[bobfriedman]

it started raining today then it snowed for two hours..

[Andy Perrin]

See, Bob knows.

[Andrea B.]

So pretty!

[Cadmium]

The two shots above were using a UG2A 2mm filter.

Below is a comparison between UG1 1mm thick and UG2A 2mm thick (different time of day than the pic above, morning).

Top row using the same shared in camera preset white balance.

Second row using CNX2 white balance on grass.

Conclusion, perhaps subtle, but UG2A white balances easier, and has a bluer sky and 'cleaner' whiter foliage. UG1 1mm tends to have a bit more 'muddy' color to the foliage that is harder to remove or white balance to 'white'.

I leave this up the the experts Bob and Ulf to experiment with further. I plan to test UG2A 1mm thick in the near future.

 

 

[ulf]

I love the pure colors. Very nice pictures indeed!

This look very promising.

 

I hope my filter will arrive soon!

It will also be interesting to test the UG2A in a stack with a S8612.

 

If I should add to the whining, I can tell that the Swedish customs has changed the rules for all incoming mail, not coming from within the EU.

Now everything has to be processed to extract VAT and process fees. This has saturated the system totally, resulting in very long delays.

 

The filter I hope to get might be stuck for several weeks before I get it.

Some of my other packages got delayed more than a month before I received them.

[bobfriedman]

my initial thought is that the UG-2a produces more reddish skies for my cursory WB - you can also see some green cast in my shot.... at least with the shot i took today after work.. i need to wait until the trees get leafed out to get a proper chance to test this potential improvement to the UG-1

[Cadmium]

Bob, I have to admit, that, looks a little bland... You have enough foliage there to white balance on, but I would do it out of cam with whatever software,

and yes, compare it with UG1 1mm. I guess your white balance above is using some version of your 'scene refereed white balance', but I think you will get cleaner results with NX-D or the like, especially if you are doing it with your newer full spectrum D800, which seems to establish the newer Nikon models don't work as well with 'scene refereed white balance' as did the older models, such as your D200, unfortunately, which has been my experience with every full spectrum converted model of Nikon I have tried the 'scene refereed white balance' with (D90, D7000, D7200). It doesn't sound like it works with the D800 as well as it did with the D200 either, but still better for many filters than any other in camera WB method I have found.

 

UG2A is practically the same as very thin UG1. Specifically, UG2A is 1/3rd the strength of UG1, and follows approximately the same curve in a 1 to 3 thickness ratio.

In other words, UG2A 3mm thick would preform approximately the same as UG1 1mm thick (see graph below).

 

Also, with the comparison I made between UG1 1mm and UG2A 2mm, all settings were the same, except exposure.

Exposure:

UG1 = 1/100s

UG2A = 1/160s

So in other words, the UG2A 2mm doesn't need as much exposure time as does the UG1 1mm.

I assume the exposure time would be the same if the UG2A was 3mm thick, compared to the UG1 1mm thick exposure time.

Using UG2A 2mm thick should perform the same as using UG1 0.66mm thick.

However, handling and even making 0.66 thick glass will be precarious and impractical, thus the UIG2A is a better method, and that is basically all it is, a 1/3rd version of UG1.

 

[Cadmium]

Bob, Your pic, with adjusted contrast...

I see some yellowing around the perimeter, not sure what to think of that.

Still, I would start with a more controlled white balance, out of cam.

 

[ulf]

How wide are the lenses you guys used here?

 

If the image information in the corners are passing the filter at a wide angle to the optical axis it will pass through a longer distance of filter material.

This will shift the filter cutoff at least slightly just as if the filter were thicker.

 

With a corner to corner FOV of 120° it will equal a 4mm, for a 2mm filter.

A slight tone in the white is very quickly visible.

 

This effect is much stronger with a dielectric filter than a filter like the UG2A, but it still exist.

 

Graphs for 2mm and 4mm UG2A:

 

The IR cut on wavelength that will be dominant in these mainly IR-images is shifting 20nm

This might cause both the vignetting and color shift we see here.

 

I guess that the lens Bob is using is the widest of the two.

[bobfriedman]

Bob, Your pic, with adjusted contrast...

I see some yellowing around the perimeter, not sure what to think of that.

Still, I would start with a more controlled white balance, out of cam.

 

 

yes.. the scene referred WB just won't work in my full spectrum D800 (works great in the monochrome cam with BG-38 glass for UV)... so, of course i used the WB adjustment in NXD but i am going for "blue" sky not purple.

[Andrea B.]

Steve: I see some yellowing around the perimeter, not sure what to think of that.

 

Ulf: If the image information in the corners are passing the filter at a wide angle to the optical axis it will pass through a longer distance of filter material. This will shift the filter cutoff at least slightly just as if the filter were thicker.

 

Good reminder about how this kind of vignetting occurs. And, of course, I have a question. :D

 

Ulf, do the microlenses on sensors increase this kind of possible vignetting by capturing more of the light entering the lens at an angle to the main axis?

[bobfriedman]

tried for blue sky... still not real happy with it.. like i said before i need to spend some time with this conversion... the second shot was taken today but a lot more work in post

[ulf]

Andrea: The microlens function depends on their design and shape. This is not really something I know much about, to be able to give a really accurate answer, sorry.

 

I understand that you are referring to the general Cos^2 falloff for vignetting.

The phenomenon I tried to discuss above is something else caused by the different travel length in the filter-material depending on the angle.

A thicker filter have less transmission and different cutoff/on wavelengths due to the slope of the characteristics.

 

In reality the wave behaviour is much more complicated with polarisation effects etc.

The vector analysis math behind that is for me since long forgotten, as I have not needed it in my professional work.

I might even be wrong about that it is that type of math that is used to solve this analytically.

[Cadmium]

All my shots above are using a Nikon 18-55mm VR @ 18mm. 52mm filter.

Bob has an 82mm filter, but I don't know what lens he is using.

There is no color shift in my shots, and I don't know if there is any in Bob's shots, except the one I fiddled with.

 

Bob, I am not adjusting the blue in my shots.

The main difference I see between the UG1 1mm and the UG2A 2mm is that the UG2A has a slightly brighter blue. Also, whites seem cleaner/whiter with UG2A when white balanced.

Both UG1 1mm and UG2A 2mm look almost the same when individually white balanced on the same sample area, but the UG2A still has slightly lighter blue skies.

[Cadmium]

Let's start with these images for comparison.

These are straight out of the camera, they both use identical settings, other than exposure time.

Both share the same Preset White Balance, these are not white balanced out of camera, and are not post processed in any way.

The UG2A shots have bluer blues, and whiter whites, "straight out of the machine".

 

UG1 1mm

 

UG2A 2mm

 

UG1 1mm

 

UG2A 2mm

[Cadmium]

Here are two of the above shots, white balanced from RAW in CNX2 on the same small patch of grass, and also auto contrast using Photoshop.

There is virtually no difference between these two shots other than the UG2A exposure time is less.

 

UG1 1mm, 1/125s, f/9, ISO 200

 

UG2A 2mm, 1/200s, f/9, ISO 200

[bobfriedman]

Bob has an 82mm filter, but I don't know what lens he is using.

 

17-35/2.8D Nikkor