41 replies to this topic

[kcl31]

Just by chance, I get a door window that has some prism structure what will split the sun light during noon time everyday. I think this might be a good light source to test my NVD's spectrum response. So here it is:

 

 

I roughly calibrated the wavelength scale with following data for my iphone SE, the visable range is roughly from 410nm to 680nm, if using 15% sensitivity as threshold:

 

Based on this very very crude test, it seems my NVD, which has a L3 Harris filmless WP tube, is approximately matching the curve in navy blue following (450nm to 850nm using 15% QE as threshold):

 

Attached a gif animation as well:

 

Now my question is, if this test has roughly ok accuracy, then what tube has the purple curve(Gen3 GaAsP)?

[Dewbeard]

GaAsP was discussed in this thread:

https://www.cloudyni...-iie/?p=5902175

 

In short: one supplier, hella expensive.

[evan9162]

Interesting that it shows decent response at 500nm, but when I've used my Harris L3 filmless white phosphor PVS-14 with an O-III filter, basically nothing gets through.  

[kcl31]

When I was testing different filters, on o3 rich target such as planetary nebula, I do see some features that are different than Ha. It is not as bright as Ha (I was comparing with 5nm Ha and 3nm O3) but definitely usable.

I guess it has a lot to do with the target and lens used. I was using prime focus mainly, and using AR coated c-mount lens for this test. I assume the mil spec lens of PVS14 which has a “laser shield” kind of bright blue-green coating would reject most energy of o3 wavelength?

[evan9162]

It's possible the PVS-14 has a long pass filter built-in (or lens coatings).  I tried a variety of targets in afocal configuration - the most telling was that M42 was dimmer with NV/O3 than it was visually with an O3 filter.  

 

Another interesting data point - the built-in objective is very poorly corrected in blue-green light - I could not get stars to focus sharply with an O3 filter - But again, that makes since considering these devices are designed around IR light sources/response.

[cnoct]

There are very few NV systems with a built in light interference filter for those nasty YAG targeting lasers, PVS-14's don't have such a filter built into the objective. 

 

The coatings that impart that yellow tint are to maintain contrast, not laser protection, though such coating certainly attenuate wavelengths on the short end.

 

How great of effect these coatings have on blue light?...  

 

Here's two photo's through the same tubes, with indirect room illumination via a 447nm laser, swapping between a standard BBAR 14 lens and a 14 lens with contrast enhancing blue block filter. 

 

^Standard BBAR with 447nm Laser

 

^Contrast Enhancing Blue Block with 447nm Laser

 

^Contrast Enhancing Blue Block on the left, standard BBAR on the right.

 

 

In both the above, through the 14 photos, the objectives were focused for broadband 2856k so focus error is particularly noticeable under 447nm light.  

 

See image below for how the focus looked under 2856k light... 

 

 

^focused with 2856k light source.

Edited by cnoct, 07 December 2022 - 05:44 AM.

[kcl31]

The coatings that impart that yellow tint are to maintain contrast, not laser protection, though such coating certainly attenuate wavelengths on the short end.

That is very good to know! I'll try with my PVS7 on this same test as it has both the yellow tone lens and AR coated Cmount lens available to use.

[kcl31]

Here is the update with PVS7 and a Onmi IV/V era 10130D green tube (thick film tube?)

 

It seems the yellow tone milspec objective lens does show clear cut off of transmission below ~525nm, which could help to explain the poor sensitivity on O3 when using milspec lens alfocal.

 

In comparision with the filmless WP test, it seems the response range are similar between the Onmi IV/V tube and latest filmless, the filmless one maybe a bit better in the range of 450~480nm?

 

Just a quick snap of the yellow tone milspec PVS7/14 lens, vs the normal tone AR coated TV lens.

[kcl31]

Just putting all images into one set

[cnoct]

In regards to laser protection filters for NV, a cheap spectrograph gives some insight into the filters purpose... double the 532nm frequency to get 1064nm...

 

 

[bbasiaga]

Why does the genIII response curve look so much different in this article? 

 

https://www.research..._fig3_258183090

 

Brian

Attached Thumbnails

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[cnoct]

Why does the genIII response curve look so much different in this article? 

 

https://www.research..._fig3_258183090

 

Brian

 

That's the systems relative response, not the tubes so take into consideration that the AN/AVS-6's feature a 625nm cut-on long pass filter (Class "A" minus blue.

[bbasiaga]

That's the systems relative response, not the tubes so take into consideration that the AN/AVS-6's feature a 625nm cut-on long pass filter (Class "A" minus blue.

Ok, a couple of more questions

 

- no filter in a typical PVS14, correct?

- wouldn't you expect the shape of the relative response and QE curves to trend together?  For instance, the curve in post #1 shows at 800nm the genIII tube has very low efficiency, but that is near the peak of the response in the curve that I posted in #11.  

[chemisted]

 

For instance, the curve in post #1 shows at 800nm the genIII tube has very low efficiency, but that is near the peak of the response in the curve that I posted in #11.  

No, the green curve in post #1 is the appropriate one to compare.

[cnoct]

- no filter in a typical PVS14, correct?

 

Depends on the supplier and performance requirements of a particular procurement. 

 

There is no LIF coating applied to or built into the 14 objectives. Same goes for minus blue coating of the AVS-6's, 9's and F4949's, the typical/common/mil-spec/mil-standard 14 objectives don't have them either. 

 

Now there are some 14's from the late 90's that did use reuse the same minus blue optics from the ANVIS'6's cells, those were in ITT's Night Rescue 6015 SAR-1 monocular (see photo's below).  

 

 

[bbasiaga]

No, the green curve in post #1 is the appropriate one to compare.

Ah..I think what confused me is that the OP says his L3 genIII tube was following the blue curve, but if I get my bifocals on I can see that curve is labeled for a gem II tube. I may have to start using these **** bifocals fire often.

Brian

[bbasiaga]

Depends on the supplier and performance requirements of a particular procurement.

There is no LIF coating applied to or built into the 14 objectives. Same goes for minus blue coating of the AVS-6's, 9's and F4949's, the typical/common/mil-spec/mil-standard 14 objectives don't have them either.

Now there are some 14's from the late 90's that did use reuse the same minus blue optics from the ANVIS'6's cells, those were in ITT's Night Rescue 6015 SAR-1 monocular (see photo's below).

ITT Night Rescue AVS6 Minus Blue Lens.png

ITT Night Rescue SAR-1 Thales 1 .jpg

Mine is a from custom night vision/kosher. It's a Carson body and lens. It does look blueish when you look at it. Not sure if that means anything.

Bria

[cnoct]

So you bought a ITT Night Rescue from 20+yrs ago through Kosher, a Night Rescue mislabeled as Carson!...

 

In mentioning the rare PVS-14 type device with minus blue objectives, those specific to the AVS systems, I'm trying to be as specific as possible in that yes there are the oddball systems that came with filters, filters that are not found on the typical PVS-14 objectives.

 

AR coating with enhanced NIR transmission, that's what's giving the blue rejection (reflection). The yellow filter/coating is to increase contrast, one could also say increase MTF. The 14 lenses have quite a bit of focus error across the Vis-NIR spectrum, rejecting blue and some green increases the MTF of the system, unfocused light is noise, all it does is make the scene brighter while degrading contrast so attenuating it improves scene detail.  

 

Optics wise Carson means doesn't mean a whole lot, they source from several manufacturers. In fact, back in the early aught's, Carson CAGE coded optics were not held in high regard. 

[bbasiaga]

So you bought a ITT Night Rescue from 20+yrs ago through Kosher, a Night Rescue mislabeled as Carson!...

 

In mentioning the rare PVS-14 type device with minus blue objectives, those specific to the AVS systems, I'm trying to be as specific as possible in that yes there are the oddball systems that came with filters, filters that are not found on the typical PVS-14 objectives.

 

AR coating with enhanced NIR transmission, that's what's giving the blue rejection (reflection). The yellow filter/coating is to increase contrast, one could also say increase MTF. The 14 lenses have quite a bit of focus error across the Vis-NIR spectrum, rejecting blue and some green increases the MTF of the system, unfocused light is noise, all it does is make the scene brighter while degrading contrast so attenuating it improves scene detail.  

 

Optics wise Carson means doesn't mean a whole lot, they source from several manufacturers. In fact, back in the early aught's, Carson CAGE coded optics were not held in high regard. 

Sorry if I'm a little dense here, I don't have all the history you do as I've only been researching NV for about a year and strictly as it relates to astronomy, and I've only had the unit a few weeks. 

 

I guess I'm just trying to figure out what I have, and what its doing transmission wise.  I had always heard/read that these things couldn't 'see' the shorter wavelengths of visible light, but the curve above suggests otherwise. And since I think I'm hearing that the PVS14 doesn't have any kind of bandpass filter installed in it, then I thought maybe the lens coatings were doing it.  Sounds like perhaps the real answer is that they actually CAN see the whole visible spectrum? 

 

-Brian

[kcl31]

Ah..I think what confused me is that the OP says his L3 genIII tube was following the blue curve, but if I get my bifocals on I can see that curve is labeled for a gem II tube. I may have to start using these **** bifocals fire often.

Brian

Hi Brian,

 

Sorry for the confusion when I call it "Navy Blue". I do mean that green-blue-ish Gen3 curve.

 

Maybe the following is easier to read the whole story of this thread:

[kcl31]

Sounds like perhaps the real answer is that they actually CAN see the whole visible spectrum? 

 

-Brian

Based on my test and all NVD I have, I do think a typical PVS14/PVS7 with milspec lens will miss the purple-blue and A LOT of O-3 green portion of the visible spectrum.

[sixela]

But a lot seems to depend on the objective, at least for OIII. Even if there’s no real filter, the coatings can be optimised differently.

Edited by sixela, 11 December 2022 - 04:00 AM.

[sixela]

There are very few NV systems with a built in light interference filter for those nasty YAG targeting lasers, PVS-14's don't have such a filter built into the objective. 

 

The coatings that impart that yellow tint are to maintain contrast, not laser protection, though such coating certainly attenuate wavelengths on the short end.

 

How great of effect these coatings have on blue light?...  

 

Here's two photo's through the same tubes, with indirect room illumination via a 447nm laser, swapping between a standard BBAR 14 lens and a 14 lens with contrast enhancing blue block filter. 

 

Standard BBAR with 447nm Laser TN.jpg

^Standard BBAR with 447nm Laser

 

Contrast Enhancing Blue Block with 447nm Laser TN.jpg

^Contrast Enhancing Blue Block with 447nm Laser

 

Contrast Enhaned next ti Standard BBAR.jpeg

^Contrast Enhancing Blue Block on the left, standard BBAR on the right.

 

 

In both the above, through the 14 photos, the objectives were focused for broadband 2856k so focus error is particularly noticeable under 447nm light.  

 

See image below for how the focus looked under 2856k light... 

 

 

Focused under 2856k Tungsten light source TN.jpg

^focused with 2856k light source.

Interesting -- but could you do the same test with white light passing through an OIII filter? 447nm is quite some distance away from OIII. I'm sure H-beta is aggressively filtered as well but we really don't care (since anything that radiates in H-beta will radiate in H-alpha). 

 

the photocathode I have is definitely quite sensitive to OIII: I compared Thor's Helmet viewed in prime focus reduced to f/2.8 through an OIII filter, a dual band OIII/H-alpha and a H-alpha and some features were definitely relatively stronger using the dual band filter even though contrast was reduced (in a Bortle 4-5 site there's also a lot of light pollution around 500 nm).

 

I'm trying to figure out whether the Carson/Fujinon I have (which definitely does not pass blue well, a white wall looks yellow through it) hurts OIII badly enough for me to switch to another objective for OIII-rich objects when used afocally (the Zeiss/Tevidon I have has lower transmission in H-alpha and has a slower f/ratio, but is very colour neutral; the Optronics Engineering lenses I have also seem to have fairly generic BBAR coatings).

 

My own tests with a visual spectroscope (but no photometry) are a bit inconclusive. It's clear that the blue of my 460nm laser is very much attenuated (and violet is completely nuked), but 500 nm 'teal' a lot less, and 520 nm green seems unaffected. And I currently don't have the equipment to do a photometric comparison around OIII only.

 

It's clear the blue reflecting nebulae don't like the Fujinon lens. But I'm interested in what to pick for dual-band OIII/H-alpha.

Edited by sixela, 02 January 2023 - 11:14 AM.

[Joko]

the photocathode I have is definitely quite sensitive to OIII: I compared Thor's Helmet viewed in primae focus though an OIII filter, a dual band OIII/H-alpha and a H-alpha and some features were definitely relatively stronger using the dual band filter even though contrast was reduced (in a Bortle 4-5 site there's also a lot of light pollution around 500 nm).

What dual band filter are you using with your OVNI-M ?

I might be interested in buying one to compare with my H-alpha filter.

Edited by Joko, 02 January 2023 - 10:40 AM.

[sixela]

This one (from this store):

https://www.astroart...nd-5nm-filter-2

 

Although I see it's increased in price.

 

Slightly less expensive from Aliexpress (though it's over €150, so they'll subtract the VAT and you'll have to go through customs).

 

When coupled with a broadband 7 nm or 12 nm H-alpha, it behaves pretty much as you would expect a 5 nm H-alpha to behave.

Edited by sixela, 02 January 2023 - 11:12 AM.