69 replies to this topic

[overmywaders]

The following photos were taking in bright sunlight. Setting for both the UV shots was the same - f11, ISO 800, and each in-camera white-balanced against PTFE. The focus was not altered between the Baader U and the Neptune U. Lens was a Ludwig Meritar 50/2.9 on a Lumix GF1 converted to full spectrum.

[Added by Editor: The Neptune-U is now called the Precision-U.]

No post-processing was performed, other than a reduction in image size.
Visible


The Baader U


The Neptune U [Added by Editor: Filter now called the Precision-U.]



The Baader was in focus, however it seems to have been blurred by IR or other aberrant light. As you can see from the exifs, the Neptune U required 2/3s of an fstop more than the Baader U.

Regards,
Reed

[kds315]

Well, nothing is really in focus in the Baader-U image, so I seriously doubt that it has anything to do with IR leakage.

Knowing the Meritar and its weaknesses, I would not seriously consider it a good lens to test out the abilities of filters, especially since it is then hard to judge what was caused by the lens and what by the filters. An old engineering rule is that a measuring tool should be at least 10 times better than what is measured...

Oh, and there you have the answer within your text: "The focus was not altered between the Baader U and the Neptune U." So using a lens that has focus shift and knowing that the Neptune-U has about a 15nm shift of its transmission center wavelength as compared to the Baader-U, would clearly mean a decent focus shift between the two shots. I would recommend to re-shoot and at least focus individually.

Further, it is mentioned that the Neptune-U needs 2/3 stops more for reaching the same exposure. This implies that the filter with shorter center wavelength and/or lesser transmission (didn't you want to show the measured transmission spectra?) causes that - but it is neither, is is the substantially decreasing UV transmission of the used Meritar lens at shorter wavelengths that causes that. So again, I seriously doubt that this lens is an appropriate enough tool to show the capabilities of your new filter!

Edited by kds315, 29 June 2012 - 19:56 .

[overmywaders]

Klaus,

I first focused the Baader. It was in nice crisp focus according to the liveview (that may be an important distinction). I let the Lumix determine exposure (P mode) for fairness. The image you see is the best of five. I did not alter the focus for the Neptune. The Neptune appeared on the liveview as in focus and also recorded that way. Go figure.

I'll certainly try again; however, there is not a problem with the Meritar. You prefer other lenses, I understand that. To each his own.

Reed

[nfoto]

Just to clarify, I've tested prototypes of the Neptune-U, and documented a drop in sensitivity around -2/3 EV also with "UV flat" lenses like Coastal APO 60 mm and the UV-Nikkor. Same changes in colour rendition re Baader U2 as well.

[kds315]

It is not about any preference, it is about choosing the right way to measure so as to be able to draw conclusions about the measurement target and not the measurement system - that latter should be out of question. That's why I recommended to use a different lens and only because of that.

But there is a much more important fact that really hits me: The visible shot shows a red (!) transparent glass vase with flowers. Now the Baader-U renders that glass dark, which could have been expected as a red glass should -usually- not transmit UV, but the new Neptune-U shows it transparent (!) and even shows the structure of the chair it stands on. If there is any leakage, I would rather recommend to have a look at the Neptune then.

.

Edited by kds315, 29 June 2012 - 20:19 .

[Andrea B.]

Seriously, it utterly makes no sense that you can't focus the Baader U with Live View !!! The Baader U can be focused with any (UV-capable) lens on any (UV-capable) camera, especially with Live View. I've been focusing it just fine for the last 5 years. Try again !!!

[kds315]

P.S.: I understand that Bjørn and Andrea have (or had) prototypes of the Neptune-U for tests. Would it be possible to see some of their results using a quartz/fluorite lens (UV-Nikkor etc.) ?

Here the transmission of my Meritar 2.8/50mm also showing if used with the Baader-U filter. Maybe it gets more clear from that, why I'm critical about its use for an even shorter wave filter...

[overmywaders]

Andrea,
I have never had a problem focusing the Baader with the liveview and that lens. And today it focused just fine, I used the zoomed focus to make sure, as I always do. However, when I took the shot, the image was blurred.

I went outside a few minutes ago to retest. The difference in light was about two hours; still intense, but the air was much cooler and the haze less. I focused the Baader, took shots, then focused the Neptune -- they both required the same focus; not a hair difference. Again the Baader is blurred but not as much as previously.

I should not have submitted any photos. I need a disinterested third party.

Reed

[Andrea B.]

I don't think that the lens plays any that big a role here. Worst case, exposures with the Meritor would be a bit longer than with the Coastal or UV-Nikkor. So, I don't understand, Klaus, why you are all on about the lens.

The 1st interesting issue is the blurred Baader photo, and the 2nd interesting issue is the difference in the transparency of the glass.
******

Reed, you've never taken blurred photos with the Baader before this. I don't really get this. Were you on tripod? Please tell me you were on tripod. There just is no way you can focus in Live View and get a blurred image unless you moved the camera.

[nfoto]

... or bumped the focus ring on the lens.

[kds315]

Because the Meritar is 1) not a sharp lens for UV and 2) has an overall low UV transmission which makes it unsuitable to draw any conclusions from, about a filter

But again, my major concerns is that I can see through a red glass vase when using the Neptune-U

Neptune-U is left, Baader-U is right, red channel only, converted to bw

 Screen 00579.jpg   35.84K   0 downloads

Edited by kds315, 29 June 2012 - 20:55 .

[Andrea B.]

Klaus, if the Meritor is not sharp for UV, then BOTH photos would be blurred.
So, clearly, it is sharp enough even though it might not be the sharpest tack in the barrel.

[nfoto]

You may have a damaged Baader filter. does it look cloudy or discoloured? Or mounted askew so the image is distorted.

What I don't get is that LV seemed OK but actual images weren't.

[Andrea B.]

And I'm probably fairly disinterested. I don't design any filters, sell any filters, sell any lenses or otherwise make any money from photography. I just love shooting UV. That's it.

[kds315]

Klaus, if the Meritor is not sharp for UV, then BOTH photos would be blurred.
So, clearly, it is sharp enough even though it might not be the sharpest tack in the barrel.

I can agree on that though. Indeed quite a miracle. Maybe Bjørn is right and his Baader-U is faulty. The viewfinder is not as detailed as the final image, so that blur might not be visible (?).

[Andrea B.]

What I don't get is that LV seemed OK but actual images weren't.
Exactly. This cannot happen unless something moved after focus was attained.

Reed, were you stop-down focusing through Live View? I.E., focusing wide-open and then stopping down?? Some lenses do not maintain focus when aperture is changed.

[nfoto]

Here, by the way, are Baader U vs Neptune-U shots to demonstrate the difference between them.

D200, Noflexar 35, straight off the camera with w/b profile from PTFE targets.


Neptune-U

 O1205080424.jpg   418.21K   2 downloads


Baader U 2

 O1205080427.jpg   437.81K   1 downloads


The different rendition holds up also when Coastal APO 60/4 or the UV-Nikkor 105/4.5 replaces the Noflexar, so obviously this is the "true" false-colour of the Neptune-U.

[kds315]

Good idea Andrea about the step-down focusing, but that would apply to both filters, except that there was no "control view done", just a filter change.

Edited by kds315, 29 June 2012 - 21:04 .

[Andrea B.]

OK, now I think I'm stuck in a Kafka movie.......

Bjørn, your Baader U photo looks slightly softer than your Neptune U photo.

[kds315]

Here, by the way, are Baader U vs Neptune-U shots to demonstrate the difference between them.

D200, Noflexar 35, straight off the camera with w/b profile from PTFE targets.

...

Thanks Bjørn, from that I see a sharp and useful new filter with shorter waveband. Looks good to me.

...
The different rendition holds up also when Coastal APO 60/4 or the UV-Nikkor 105/4.5 replaces the Noflexar, so obviously this is the "true" false-colour of the Neptune-U.

Caused by the lack of deeper UV response of the D200 sensor I would guess. If you were to repeat the same test using your Lumix, I bet there would be a difference.

Edited by kds315, 29 June 2012 - 21:13 .