Jump to content
UltravioletPhotography

IDAS 1.25" UV-pass filter


enricosavazzi

Recommended Posts

enricosavazzi

This has likely been available for some time, and therefore it may not be news to some of us. Price is roughly the same as 1.25" Baader U. I have not tested it. I know that Klaus has shown some results with the IDAS filter on his web site.

 

Judging from the transmission graph on the web page, it is likely yet another U340-based filter with added IR-reject dielectric coatings, like the Asahi Spectra XRR0340 (which I already have).

 

The PrimaLuceLab U is another of these U340-based filters (and I have it too), but unfortunately has a significant NIR-leak that makes it problematic to use in sunlight. No such leak is seen in the (linear) diagram on the web site, which is encouraging but not a guarantee. The Asahi Spectra XRR0340 seems to have no damaging NIR leak, but is quite expensive and available only in a couple of sizes.

 

https://www.astrosho...r-1-25-/p,51956

 

Edit - another open question is whether both surfaces of the IDAS filter are dielectric coated. If only one surface has the dielectric coating, the U340 glass might still be vulnerable to atmospheric degradation.

Link to comment

I have one of the IDAS UV372-80 filters, but haven't got round to doing much testing with it yet. One side is dielectrically coated as far as I can tell, and the other side may well be uncoated, as I've just checked mine and it already looks like it needs a clean.

 

In terms of transmission it was about 0.2% at 400nm, dropping below 0.1% at around 414nm. In the IR it remained below 0.1% up to 850nm which is far as I trust the data.

 

If I get the chance in the next few days I'll get some shots done with it.

Link to comment

Looks interesting.

I was confused, however, as to why the filter is labeled UV 372-80 ?? I'm thinking that must be a stock number, but was temporarily mislead into thinking that it referred to the transmission peak. :rolleyes:

 

A Canadian importer of this filter offers the following leakage specifications:

  • Leakage of Visible Band:
  • Leakage from 680nm to 1,000nm:
  • Leakage from 1,000 to 1,200nm:

https://focusscientific.com/product_info.php/manufacturers_id/65/products_id/1086

Link to comment
Andy Perrin
This filter is looking very encouraging, although it lets through more violet than the Baader I think? So maybe it will be a good choice for people who like a more visible-leaning filter.
Link to comment

This filter is looking very encouraging, although it lets through more violet than the Baader I think? So maybe it will be a good choice for people who like a more visible-leaning filter.

 

No actually looks to be quite less.

 

https://www.ultravioletphotography.com/content/index.php/topic/3708-ill-show-you-my-baader-if-you-show-me-yours/page__view__findpost__p__33009

 

This may look similar to 2mm U340 + 2mm S8612. More yellowish, less blueish.

Link to comment

Indeed, compared to Shane's graph of the Baader U (either generation), the graph above seems to show a slightly better violet suppressing threshold.

 

David, Thanks for posting that link, I was trying to access Shane's Baader U graphs earlier, but his website wasn't working,

Link to comment

A rather quick and dirty test this morning. Two filters, Baader U and IDAS 372-80. Lens was UAT 85mm (f8). Camera multispectral 5DSR (ISO2000). Sunny day but windy, hence the movement. Whitebalanced in Darktable using a Spectralon 20% DR standard in the same light.

 

Baader U, 1/4s

post-148-0-56171800-1589451851.jpg

 

IDAS 372-80, 1/4s

post-148-0-71867600-1589451855.jpg

 

Also some IR leak tests.

 

Baader U + Heliopan 715, 1/4s

post-148-0-50979600-1589451856.jpg

 

IDAS 372-80 + Heliopan 715, 1/4s

post-148-0-33867800-1589451857.jpg

 

And pushing the IR leak

 

Baader U + Heliopan 715, 2s

post-148-0-35562200-1589451858.jpg

 

IDAS 372-80 + Heliopan 715, 2s

post-148-0-48397900-1589451859.jpg

 

They certainly white balance differently. IR leak looks similar between them (keep in mind I was holding the Heliopan 715 in contact with the front of the test filter).

 

Let me try and dig out some transmission spectra of the 400nm region. EDIT - turns out I haven't run the Baader U for transmission since recalibrating my spectrometer, so I'll redo them both when I get the chance.

Link to comment
Andy Perrin
Huh, yeah that does not agree with my memory of the Baader curve so I’m obviously mis-recalling. I had thought it turned on at like 395.
Link to comment

Hmm, Interesting, Jonathan, I would have expected the IDA to have less 'leak' than the Baader U based on the OD graph.

Not sure what to think of the white balance false color content.

Link to comment

Steve, yes that white balance is rather odd, and not very pleasant (to my eyes at least). Suns out more today, and less wind so I'll try and get some more shots just to make sure I did everything right.

 

I've got very wary about trusting provided charts when it comes to blocking. Tiny variations batch to batch can easily make large differences in blocking.

 

EDIT - just repeated it, and I'm still getting that weird, blue/purple colour cast with the IDAS filter. I think what might be happening is this. The IDAS cuts most of the light in the 380-400nm region, while the Baader U is still letting light through from 380-400nm. In the 380nm to 400nm region, the blue channel is still very sensitive. So, if you remove that information from the image, when the white balance is done, presumably blue is dialed up to try and balance the colours. Hence the IDAS has a bluer colour cast.

Link to comment

As promised scans of my Baader U and IDAS 372-80 filters. Ocean optics FX spectrometer, immediately after a recalibration and DH200 Balanced light source. Combined data from deuterium and halogen light scans run separately.

 

Firstly, a full scan.

 

post-148-0-42503500-1589796032.jpg

 

Ignore the tails at the short wavelength side of the lines. This is a side effect of the stray light in the spectrometer.

 

Also, zoomed in around the baseline to try and shown any leakage.

 

post-148-0-27881700-1589796035.jpg

 

I see no evidence for better OOB blocking by the IDAS 372-80 compared to the Baader U, for my samples at least and up to 800nm. OD4 (0.01% transmission) is the best I can get with my system.

Link to comment
So is the IDAS 372-80 filter a better filter to use if you want to avoid the 395nm fluorescence, please ?
Link to comment

Here's a plot around 395nm Colin.

 

post-148-0-18003200-1589802652.jpg

 

The IDAS 372-80 lets a lot less light through at around 395nm than the Baader U. Whether the difference is significant in real life usage, I don't know.

Link to comment

Wow very hard to interpret that spectrum based on your image.

After I saw your bluish IDAS image, I thought for sure that the spectrum Andrea posted was a one off from a batch a decade ago. But now it seems the tale from 450nm to 400nm is the real problem. The IDAS lets in more light there than the Baader. So even though there is very little in the 380nm to 400nm range compared to the area under Baader. The area looks much more to me in the 400nm to 450nm for IDAS, which may account for your very blue image.

 

The best test would be a glass test. Can the IDAS see through glass and the Baader can't. Like your canopy test with the SEU version 2. That indicate how much violet rather than UV was getting through.

Link to comment

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
×
×
  • Create New...