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UltravioletPhotography

larger aperture lenses


funkysandman

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As a newcomer, I have a couple of questions:

  1. Has anyone ever tried the EL NIKKOR 50mm f1.4 for UV ?
  2. I see many lenses being tested, is it assumed they are being typically tested with a filter such as a UV bandpass?

thanks

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Unfortunately, you have misinterpreted the specifications. This lens is 50 mm f/4, or as commonly presented, 50 mm 1:4.

 

It is not very meaningful to test any lens for UV usage without having a UV bandpass filter over the lens (or inside the camera).

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Ok, thanks for clearing that up. I will soon have the f/4 but I am still looking for a suitable filter for a highly sensitive 2/3" mono sensor.
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The Baader U is the standard, although many stacks produce useful images.

 

A good stack seems to be something (like) 1.75mm S8612 to block IR and 1mm UG11. Many others work, though. I tried a computational model of many possible stacks and came up with this figure. The horizontal axis is a measure of how well the stack blocks IR, by taking the ratio of the area under the IR part of the curve to the UV part. The vertical axis is how well it transmits UV. The transmission values are simulated values (including partial reflections) based on the Schott data and also any other data I could find online for the Chinese glasses. The Chinese data is known to be rather dubious so take the QB21 stacks with a grain of salt.

 

post-94-0-39852600-1509690282.jpg

 

post-94-0-91028900-1509690450.jpg

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wow thanks, I admit I am not qualified yet to fully appreciate this data but I get the basic idea. My first mission will be to learn how to put together a stack that I can mount in/on the camera
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@Andy: Could you clarify for me your "Safety" X-axis in the 1st chart you posted. Is it that higher values indicate greater blocking performance, or higher IR transmission (i.e., lesser IR blocking performance)?
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Mark, more safety means better blocking. It's the ratio of how much UV passes to how much IR passes, so a higher number means one is drowning out the other. If all IR was cut, safety = infinity.
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Andy, love your awesome chart. When you get a moment (!), please give this chart and your data its own topic. That way I can easily reference (i.e., link) it in various places.

 

Via which method did you accomplish "area under the curve"? Way cool to see someone do this.

 

[[[[Apologies for being so busy currently that I cannot perform the topic creation myself.]]]]

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Andrea, will do. The propriety filters can't be added because in order to compute the safety I would need a diabatic plot (or the equivalent numbers) for those. Someone with a really good spectroscope could run them for me I guess?
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Andy - Thanks.

 

Understood about the brand filters.

Someday I'll hire someone to do that for us.

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Thanks Andy. I've never seen an x-axis called 'safety', outside of metrics related to safety ;) (or, do you mean this as a measure of 'safely' making an IR free image?). Either way, now that you explain it, it makes sense. Could you add the Asahi 0340 to the chart (data is posted on their website), as this is in a sense a 'stack' in a single filter.
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I made it up, Mark! And yes, it's meant to be a measure of how safe you are of making an IR-free image. The Asahi 0340 numbers only go to 800nm, so it would not be enough to calculate the denominator in the Safety equation. I'm about to put up a post with the full details so give me an hour or two.
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A possible caveat: since the graph is logarithmic in the y axis and uses nanometers rather than wavenumbers (e.g. cm-1) in the x axis, curve area does not reflect the actual energy flux represented, right? I was always told that one needs a linear plot against inverse wavelength. I realize that if the y axis correlates with photon count rather than total energy, this could complicate the picture, however. Perhaps someone with knowledge of sensor physics could help sort this out...
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The graph is not log in the y axis when I do the integral but your second point is correct. I will redo the graph!

 

(For what it's worth, I don't think the conclusions will change much. But we shall see.)

---

 

Update: So, I initially thought you were right, Clark, but my textbook seems to be saying the original method was okay:

post-94-0-07546600-1509684334.jpg

post-94-0-74761100-1509684344.jpg

(From "Fundamentals of Heat and Mass Transfer," Frank P. Incropera and David P. DeWitt, 4th ed.)

 

That last integral is the one I'm carrying out, assuming that the spectrometer uses a constant G_lambda of incident radiation, so it comes out of the integral.

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I am considering the 1.75mm S8612 + 1mm UG11 stack in a 25mm diameter. Who might sell this pair? I need them to fit inside the c-mount. I've attached a pic of the camera case with an example uv/ir cut filter that fits.

post-166-0-54690000-1509832654.jpg

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You know, at 25mm, Omega Optical sells 330WB70 and 330WB80 filters that are dichroic which you might want to have a look at. The seller is bjomega on eBay. Those are not stacks, they are shiny dichroic filters. They come unmounted so you will have to put them in a ring.
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You know, at 25mm, Omega Optical sells 330WB70 and 330WB80 filters that are dichroic which you might want to have a look at. The seller is bjomega on eBay. Those are not stacks, they are shiny dichroic filters. They come unmounted so you will have to put them in a ring.

thanks, I think I might order the 330WB80.

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Be aware that all dichroic filters have angular color shifts, so if you are using a wide angle lens, those will be more prominent. Also, speaking generally, there can be strange reflections off the back, although I have not observed those with the 330WB70 or -80.
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I intend to mount the filter in the c-mount barrel on the camera so this is perfect. My sensor is monochrome so I'm not sure if I would notice?
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