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larger aperture lenses

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#1 funkysandman

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Posted 31 October 2017 - 17:23

As a newcomer, I have a couple of questions:
  • Has anyone ever tried the EL NIKKOR 50mm f1.4 for UV ?
  • I see many lenses being tested, is it assumed they are being typically tested with a filter such as a UV bandpass?
thanks

#2 nfoto

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Posted 31 October 2017 - 19:40

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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#3 funkysandman

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Posted 31 October 2017 - 20:55

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.

#4 Andy Perrin

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Posted 01 November 2017 - 01:15

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.

Attached Image: Filter Selection Chart.jpg

Attached Image: Filter spectra (companion to selection chart).jpg

Edited by Andy Perrin, 03 November 2017 - 06:27.


#5 funkysandman

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Posted 01 November 2017 - 17:58

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

#6 Andy Perrin

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Posted 01 November 2017 - 23:27

Beware of the Chinese glass. That's the QB21 and stuff. Also much of the glass on eBay is suspect.

#7 Mark

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Posted 02 November 2017 - 13:25

@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)?

#8 Andy Perrin

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Posted 02 November 2017 - 15:32

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.

Edited by Andy Perrin, 02 November 2017 - 15:34.


#9 Andrea B.

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Posted 02 November 2017 - 15:33

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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#10 Andrea B.

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Posted 02 November 2017 - 15:34

P.S. Can the Baader, Kolari and StraightEdge be added to this chart?
Andrea G. Blum
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#11 Andy Perrin

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Posted 02 November 2017 - 15:37

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?

#12 Andrea B.

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Posted 02 November 2017 - 15:41

Sandman - Here is a post with all our links to Filter info: http://www.ultraviol...ilters-article/
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#13 Andrea B.

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Posted 02 November 2017 - 15:42

Andy - Thanks.

Understood about the brand filters.
Someday I'll hire someone to do that for us.
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#14 Mark

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Posted 02 November 2017 - 16:48

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.

#15 Andy Perrin

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Posted 02 November 2017 - 17:31

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.

Edited by Andy Perrin, 02 November 2017 - 18:36.


#16 OlDoinyo

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Posted 02 November 2017 - 20:28

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...

#17 Andy Perrin

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Posted 02 November 2017 - 21:41

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:
Attached Image: IMG_6696.JPG
Attached Image: IMG_6697.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.

Edited by Andy Perrin, 03 November 2017 - 04:48.


#18 funkysandman

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Posted 04 November 2017 - 21:58

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.

Attached Images

  • Attached Image: 20171104_174721.jpg


#19 Andy Perrin

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Posted 04 November 2017 - 23:03

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.

#20 funkysandman

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Posted 05 November 2017 - 01:09

View PostAndy Perrin, on 04 November 2017 - 23:03, said:

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.