larger aperture lenses

[OlDoinyo]

Known cure for it is to mount the filter BEHIND the lens.

 

That might help...or not. You can get the effect even with a pinhole, which has no glass. If your lens's rear divergence angle is less than its field of view, rear-mounting might help. If the reverse is true, rear-mounting might actually worsen the problem.

[Andy Perrin]

Wait, I didn't know the rear divergence angle was EVER larger than the field of view. When does that happen?

[Andrea B.]

I am considering the 1.75mm S8612 + 1mm UG11 stack in a 25mm diameter. Who might sell this pair?

 

I think ebay Uviroptics (filter stacks) and website UVR Optics (filters) both will cut filters to size. Links are in the Filters Sticky.

 

[Note: They are both vendor-members here but UVP has no business relationships with any vendors of photographic equipment.]

 

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Omega Optical makes great filters (I have two), but I have a question: why do you all buy 330 nm peak filters when you aren't going to use a lens which has some coverage in that region? This always puzzles me. Wouldn't you get shorter, less noisy UV exposures using a 360 nm peak filter? Just curious, so thought I'd ask.

[Andy Perrin]

Andrea, I don't think Omega sells any non-330nm that don't have vis leaks, and anyway the 330nm "peak" is kind of irrelevant because it's so wide - 80nm! - that it covers the whole band really.

[Andrea B.]

Forgot to put this link in the preceding post.

 

Another example of dichroic edge problems found in these posts:

Lens: Meyer-Optik Görlitz 35mm f/3.5 Primagon #28375XX

Lens: Asahi-Kogaku 50mm f/3.5 Takumar #905XX

 

Scroll down to the versions of the UV photo where I increased saturation to illustrate edge problems.

 

If you combine a BaaderU with a lens which already has some edge problems (although good in the center),

then the dichroic effect can increase. Lens vignetting also adds to it. That little old Asahi-Kogaku 50/3.5 is a charming, well-made (quite heavy for its size!) little bit of a lens, but it stinks in UV.

 

The dichroic problem does not always occur. A lot depends on the distance from subject, the type and location of illumination and so forth.

[Andrea B.]

A UV filter band may be wide but transmission within the band is centered around the peak. By choosing a peak to better match a lens ------ and so forth ----------- I'm pretty sure you all know this well enough, so I'll quit now. :D

[Andy Perrin]

Oh well here is the Omega spectrum:

 

Klaus did the EL-Nikkor 80mm/5.6 here:

http://photographyof...ses-for-uv.html

[Andrea B.]

I thought we were talking about the 50/4.0 EL?

 

^{Edit: I initially wrote 1.4 and just corrected that to 4.0.}

[Andy Perrin]

I only meant it as a generic example of a UV lens, but actually I just noticed it's in the same graph. With the peak shifted to shorter wavelengths, that way you don't have the 400-380nm waves hiding the rest of the curve (because the lens lets so much more of those wavelengths through).

 

Edit: actually, that 50/4.0 EL looks like it cuts off too soon! I didn't realize it was such a poor UV performer.

[Andy Perrin]

If you multiply the transmissions of the Omega 330WB80 and the Klaus data for the 50mm/4 EL, you get this curve:

 

With the 80mm/5.6 you get:

 

(Data assumed...dangerously...to be zero outside 390nm-310nm)

 

A stack would obviously let a lot more light through, but the longer wavelengths would predominate.

[Andrea B.]

I was guess-timating that there is about a 2/3 - 3/4 loss of the filter's UV light passing capability when the 330bp80 is used on the 50/4.0 EL versus about a 1/3 - 1/2 loss when used on the 80/5.6 ?? (Not sure how to word that "UV light passing capability". I was looking at the areas under the curves.)

 

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Don't you think we can say that the 50/4.0 EL isn't really a "poor" UV performer when used in the range it was designed for -- which is probably something close to 370-400 nm? Enlarging lenses, generally speaking, are optimized for "high" UV and perform quite well there. So I'm willing to give the 50/4.0 EL a break. :D

 

But I would pick an unclad StraightEdgeU to use on any enlarging lens. That would maximize UV input. Alternately, I would pick anything with an underlying 360 nm substrate whether stacked or coated. We need all the UV we can get!!

[enricosavazzi]

Wait, I didn't know the rear divergence angle was EVER larger than the field of view. When does that happen?

If you mean rear divergence angle wider than front divergence angle (a.k.a. angle of view), it may happen with telephoto lenses. The opposite usually happens with wideangle lenses designed for SLR/DSLRs, as a workaround to the thickness of the mirror box.

 

In principle, an asymmetrical optical scheme has the potential of having a different (either way) rear and front divergence, so it is a common phenomenon.

 

Focal length multipliers and "speed boosters" also change the rear divergence angle.

[funkysandman]

Looks like I will need longer exposure times with this combo? I have the feeling this won't be my last uv lens and filter :)

[Andrea B.]

Yes, you might see longer exposure times with your lens/filter choice. But we all experience long exposure times in UV work! It is the nature of the beast, as they say. :D

 

Sandy, I don't know what you plan to photograph, but some kind of artificial UV illumination will no doubt be needed. Most of us have both a UV-Led and a UV-flash. Some folks use UV lamps.

 

BTW, sometimes we digress in post comments. As an Owner/Admin/Editor, I have chosen to let topics and comments wander as they will because we all learn from them. ((Well, I do not let them wander completely off course. Comments should remain in the realm of UV photography or tech related to that. ;)))

[funkysandman]

Andrea, I have no specific subject I plan to image but I suppose people, plants and wildlife in sunlight would be the most interesting to me.

An artificial UV source will be useful once I figure out what wavelengths are the most fun, but I'm used to long exposures.

I'm hoping that without a bayer filter on the mono sensor there will be a sensitivity boost as 100% of the photo sites on the sensor will be used.

[Andrea B.]

We get pretty much the same thing with our various wide-band UV-pass filters in terms of light/dark areas. There is some variation in false colours dependent upon the filter peak, but that is not relevant to your monochrome camera. So I can't currently say that any one UV region is more fun than another. Some days I'm just happy to get any UV at all.

 

Dan Llewellyn at MaxMax.com showed that one of his monochrome conversions did indeed increase in UV sensitivity over the corresponding Bayered version. So I would expect your mono UV exposures are to be faster than the equivalent conversion exposures. But I don't think Dan's mono conversion gets any more "reach" into the shorter UV wavelengths below 300 nm (or maybe 290 nm, not sure). ((I need to go re-check this.))

 

The problem we all face when trying to shoot UV in a deeper range like 250-300 nm is primarily one of illumination. Sunlight UV-C is blocked and artificial UV-C illumination is quite dangerous and not to be played with. Shorter UV-B is strongly attenuated in sunlight. So really we are restricted to 300 - 400 nm for these various reasons. And the general consensus is that shooting below 300 nm with a converted mirrorless or DSLR is futile because the sensor just doesn't "reach" that far whether it has a Bayer filter or not.

 

Your sensor may be different, of course. I'm not at all familiar with such industrial UV cameras in terms of their reach.

 

Side Note: I feel I must stress the safety factor to anyone beginning in UV photography! Please remember that when using artificial UV illumination like UV-LED torches or UV-Flashes, you will need some UV-blocking goggles.

[Andy Perrin]

Yes, I was forgetting that with a monochrome camera the peak won't matter as much. So you may as well let all the light in that you can!

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enricosavazzi, thanks, I did not know the rear divergence angle could be larger than the front one. (Is field of view different from angle of view? I thought those were synonyms.) I haven't experienced any situations where rear-mounting the dichroic filter made things worse, but based on this, it seems that was coincidental.

[funkysandman]

I have the icx285 and icx445 which I will test with this combo. Hope I will be able to reach focus!

[enricosavazzi]

Yes, I was forgetting that with a monochrome camera the peak won't matter as much. So you may as well let all the light in that you can!

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enricosavazzi, thanks, I did not know the rear divergence angle could be larger than the front one. (Is field of view different from angle of view? I thought those were synonyms.) I haven't experienced any situations where rear-mounting the dichroic filter made things worse, but based on this, it seems that was coincidental.

Field of view can be defined in different ways. It can be an angle (and then it is synonym with angle of view), or it can be an area, usually measured as height x width or diagonal. The latter is especially useful in macrophotography and photomacrography, because it is useful to compare macro images produced on sensors of different sizes. Magnification alone says little without also knowing the sensor size, while field of view (of the area type) gives information of how much of the subject is recorded even without knowing sensor size and magnification. This measurement is also invariant with respect to the final print or display size (unless cropped of course), while magnification is usually specified on-sensor.

[ulf]

I can verify Andys theoretical graphs with measurements of my 330BW80 (magenta) alone and 330BW80 on my EL-Nikkor 80/5.6 ( old Nippon Kogaku metal type ) (green)

Unfortunately the measurement of the lens with the filter has some gain compared to the measurement of the filter only, due to limitations in my setup.

The filter only-measurement has realistic levels

 

 

The transmission plots from Omega are old and not from the filters sold now.

[Andy Perrin]

COOL! Neat to see how close I got to the peak location. My Omega transmission plot was the one that arrived with my filter, so it is old also.

[JMC]

Dan Llewellyn at MaxMax.com showed that one of his monochrome conversions did indeed increase in UV sensitivity over the corresponding Bayered version. So I would expect your mono UV exposures are to be faster than the equivalent conversion exposures. But I don't think Dan's mono conversion gets any more "reach" into the shorter UV wavelengths below 300 nm (or maybe 290 nm, not sure). ((I need to go re-check this.))

 

Having got one of Dan's monochrome conversions, when I compare it to a UV conversion from ACS I see about 2-3 stops more sensitivity to UV for the monochrome conversion. Granted I am comparing a Baader U filter on the monochrome conversion, to ACS's proprietary filter on the camera from them, which they don't share the details of, but in a real world test the monochrome version is more sensitive, and by about what Dan expected. However, benefits to a lower wavelength, not sure about that. Mine has WG280 glass on the sensor, and Dan mentioned he used that as the sensor is basically blind down there anyway suggesting to me that 300nm and above is what the cameras can see.

[Cadmium]

UlfW, Very nice demonstration of what I call 'truncation'. The El-Nikkor is one of the better 'accidental' UV capable lenses, so unless you have something like a UV-Nikkor, you will pretty much be stuck with the 360nm peak no matter what UV-pass filter you use. The lens limits the filter. I have never seen such a good example of this. I wish I had your spectrometer set up, it is very cool!

Thanks for that post.

 

ADDED:

I think it would be very revealing to test both the El-Nikkor and a UV-Nikkor (or the like) in this same way.

Then also shoot some same UV scene with both of those lenses to compare the actual difference realized between the two photos,

and compare the photos to the differences in the transmission graphs.

I don't think I have ever seen such a demonstration, and I think it would be quite interesting.

[Andy Perrin]

I've been considering playing with a quartz singlet, just to see what I'm missing. They aren't too expensive, but as lenses, the quality may not be so hot.

[Andrea B.]

I think it would be very revealing to test both the El-Nikkor and a UV-Nikkor (or the like) in this same way.

 

With a broadband 350-360 nm peak UV-pass filter like the BaaderU or any filter/stack with a U-360/UG11 substrate, the El-Nikkor 80/5.6 (old) and the UV-Nikkor 105/4.5 are going to capture the same tones and (eventual) false colours. You might find some differences in degree of (native) sharpness or in colour aberrations because enlarging lenses are typically only corrected from about 370 - 380 nm.

 

In the attached lens test link, using a Rudbeckia as the subject, all five of the lenses capture pretty much the same look. The EL-Nikkor 80/5.6 used in that test was, however, the new "metal" version with the aperture window (which does leak light unless covered). If the new EL-Nikkor 80/5.6 tones/colours look the same as the UV-Nikkor tones/colours, then I'm pretty sure the old 80/5.6 will provide the same look. Should we ever get any sun back in this part of the world, I'll try to run an outdoor landscape type test with the UV-Nikkor and the old EL 80/5.6.

 

We need to remember that we are shooting most of our UV photographs in a very narrow bandwidth -- at most 100 nm wide from 300 nm to 400 nm. And that is a bit of an exaggeration because we really aren't getting a lot of UV light under 330 nm or above 380 nm because

(a ) our broadband filters all have sloping shoulders (except for the special StraightEdge with its 380 nm peak ), and

(b ) there just isn't much of the shorter UV light in sunlight.

 

I would say that most non-dedicated but UV-capable lenses are not missing too much compared to the UV-Nikkor if they get down to at least 350 nm, 360 nm. (340 nm ??) [[ I duly note that the UV-Nikkor can reach 200nm but then none of my cameras or filters can handle that, so this nice reach never gets used !! Doesn't seem much point to having it really except that it is a nicely corrected and very very sharp lens.]]

 

I speculate that it is possible that narrowband UV-pass filters could provide differentiation between the two mentioned lenses -- especially on the shorter wavelength end of our UV waveband.

 

http://www.ultraviol...__fromsearch__1