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UltravioletPhotography

Astrodon Sloan 1.25" U' filters - $100 closeout


lost cat

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This is the cheapest price I've seen, especially for new. Normally they are$190- $200 new and $140 used elseware. These are Gen1 filters but from what I can tell the u filter did not change from gen 1 to 2:

 

Transmission range: 320-385nm

 

post-90-0-86484400-1449081783.jpg

 

http://www.astrodon.com/sloan.html

 

Update: There were indeed some changes in the u' filter in the second generation:

 

NEW! Astrodon introduces Generation 2 Sloan filters based upon ongoing input from research organizations. The changes include:

1.Better out-of-band blocking from Tave<=0.1% to Tabs<=0.03%. This is especially significant for the u' filter.

 

I have since read elseware about a red leak in the Gen1 u' filter.

 

Still at $100 maybe its worth buying more than one and stacking.

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Interesting, but I would want to know the IR transmission details. OD-3 ?? Or, OD-4 ?? Does anyone know ??
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Interesting, but I would want to know the IR transmission details. OD-3 ?? Or, OD-4 ?? Does anyone know ??

 

I emailed the company to see if they have a semi-log version of that graph. I'll post their answer when I get it.

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So it might need a BG or S8612 under certain kinds of UV illumination like, say, sunlight ?
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So it might need a BG or S8612 under certain kinds of UV illumination like, say, sunlight ?

 

I'd expect so. Depending on where the leak was it may not take a very thick additional filter to being the leak under control.

 

Speaking of that what is the minimum VIS/IR OD considered to be acceptable for outdoor use? Especially if the only illumination is sunlight and a good, but not exceptional UV capable "accidental" camera setup is used?

 

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Probably OD-4 suppression is the way to go in strong sunlight because there is just so much more Visible and Infrared light in sunlight. Although it is filter/lens/camera dependent as to how much of that Vis or IR light is going to get through to the sensor. None is preferred, but probably not always attainable.

 

Infrared light wreaks havoc on Visible shots and both IR and Vis wreak havoc on UV shots. However it is very difficult to draw the line between UV and violet or violet/blue and those two wavelengths are somewhat less contaminating for UV shots. After all, it is arbitrary where UV really "begins" and visible "ends" - 380 nm? 390 nm? 400 nm? I have gotten perfectly fine floral UV bullseyes with UV-pass filters which also pass some tiny amounts of violet to violet/blue. But just a whiff of high red or IR can wash them out. Interestingly we usually can block the IR, but it is harder to block green/yellow/red leaks.

 

Perhaps some other folks will weigh in on their blockage preferences. It's really no trouble to add a bit of BG or whatever if you have an OD-3 filter. So I would never rule out buying/owning such. But it is important to know what you are buying and also how to detect the various leakages.

 

You know where this is going, right? You will never own just one UV-pass filter!!! You will have to add IR-pass, IR-block, wide Vis-pass, wide Vis-block filters, Vis+UV-pass, Red longpass, Blue longpass, etc, etc, etc - in other words, filters with which to test other filters and filters to stack on top of other filters and whew !!!

:D :D :D

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Probably OD-4 suppression is the way to go in strong sunlight because there is just so much more Visible and Infrared light in sunlight. Although it is filter/lens/camera dependent as to how much of that Vis or IR light is going to get through to the sensor. None is preferred, but probably not always attainable.

 

Infrared light wreaks havoc on Visible shots and both IR and Vis wreak havoc on UV shots. However it is very difficult to draw the line between UV and violet or violet/blue and those two wavelengths are somewhat less contaminating for UV shots. After all, it is arbitrary where UV really "begins" and visible "ends" - 380 nm? 390 nm? 400 nm? I have gotten perfectly fine floral UV bullseyes with UV-pass filters which also pass some tiny amounts of violet to violet/blue. But just a whiff of high red or IR can wash them out. Interestingly we usually can block the IR, but it is harder to block green/yellow/red leaks.

 

Perhaps some other folks will weigh in on their blockage preferences. It's really no trouble to add a bit of BG or whatever if you have an OD-3 filter. So I would never rule out buying/owning such. But it is important to know what you are buying and also how to detect the various leakages.

 

You know where this is going, right? You will never own just one UV-pass filter!!! You will have to add IR-pass, IR-block, wide Vis-pass, wide Vis-block filters, Vis+UV-pass, Red longpass, Blue longpass, etc, etc, etc - in other words, filters with which to test other filters and filters to stack on top of other filters and whew !!!

:D :D :D

 

Yeah, kinda figured that :D

 

Igor has mentioned the chinese knockoff filters are pretty good. A bit of QB21 might be just the thing to block an IR leak.

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As far as tossing BG type glass on a fire...

Here is a comparison graph I made a while back of S8612 (Schott) and QB21S (Optima), using the latest Optima data I could find.

Although the word 'equivalent' is used liberally, I don't think there is anything exactly equivalent to S8612, at any thickness.

The closest might be CM-500 (Hoya), but not quite, and certainly not any Optima products.

Stacking the wrong BG glass on a leaking UV filter will do nothing, depending on where the leak is.

No BG glass will suppress a blue leak, not much of anything will except changing the U glass type and/or thickness.

 

post-87-0-76726500-1449199251.jpg

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Interesting charts. Thanks, Steve. The 1mm QB passes UV nicely but leaks IR. The 2-3mm QBs block IR but really whack the UV. So no thanks on the QBs for me.

 

Since getting my first S8612, I haven't used any of my BG 38/39/40 glass again for serious documentary work.

 

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Two more thoughts I had, that you may want to think about, and this hypothetical graph illustrates my two points.

1) When you stack a U glass or a UV filter with BG glass, the UV transmission range will be constrained to the limitations of the BG glass, which may or may not make any difference depending on your lens transmission depth, however do not think you are getting the full UV transmission profile of the filter you are stacking the BG with.

2) Filter stack transmissions are not based on the intersection of two filter curves, but are calculated from each filter transmission at every given nanometer, and therefor the peak transmission (UV and Red/IR) is not the intersection of two filter lines, but rather something below, which can only be calculated from data for each glass type, reference thickness, thickness, and reflection factor P.

Just things to keep in mind when putting out the Red/IR fire without losing your UV in the process, which is actually impossible.

 

post-87-0-99915600-1449214035.jpg

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Thank you for the graphs. While I agree neither QB21, s8612, or the other options listed here are an ideal solution any one could do the job if the leak happened to be with a region of strong blocking of the auxiliary filter. Still given the prices I've seen for some of that schott glass - Oy! Pricy!

 

I ended up ordering another sloan u'. Stacked the pair should give an OD of 6 or better outside of UV.

 

I'm still waiting on AstroDon to send me a log chart but given this is a discontinued product I don't know how interested they are in doing so.

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Jim, good glass, whether in filters or in lenses, pays for itself in the long run.

Also remember that stacking filters can bring its own problems: increased exposures (certainly) or reflection/flare problems (sometimes).

 

Steve, another great graph reminding us about the "intersection" of two filter transmission sets and how it is calculated.

Also noted is that anyone wanting to attempt shooting down in the nether regions between 300-320nm most likely isn't going to be able to do too well unless they obtain a dedicated filter - and even then there is the illumination issue.

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Jim, good glass, whether in filters or in lenses, pays for itself in the long run.

Also remember that stacking filters can bring its own problems: increased exposures (certainly) or reflection/flare problems (sometimes).

 

Well we shall see how "good" these filters are. If the manufacturer data in the graph is accurate a stacked pair *should* have a very high transmission over most of the UVA spectrum while rejecting almost everything else.

 

Both surfaces are mirrored (in the visible) so reflection might be an issue.

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Well we shall see how "good" these filters are. If the manufacturer data in the graph is accurate a stacked pair *should* have a very high transmission over most of the UVA spectrum while rejecting almost everything else.

 

Both surfaces are mirrored (in the visible) so reflection might be an issue.

 

Well never mind. Turns out there never were any U filters at this price. It was a pricing mistake :(

 

The good news is I was able to get the raw data for the Gen1 filters. The company is OK with posting the data with the cavet "this was improved considerably in Gen 2 due to input from Las Cumbres, who standardized on our Gen 2 Sloans as well as our UVBRI."

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Here is the filter data plotted from the manufacturers data:

post-90-0-73070800-1450031506_thumb.gif

 

There was data below 250 nm and between 660-725 with nonsensical negative values so these did not plot.

 

Any suggestions on a filter to stack with to plug the leaks enough for daytime use?

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Enrico's AstrodonU is not the same as the UV-Pass from the Astrodon Sloan set. The Sloans are photometric filters for astronomy.

I have no idea how you could block Vis + IR on that Astrodon Sloan U'.

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Enrico's AstrodonU is not the same as the UV-Pass from the Astrodon Sloan set. The Sloans are photometric filters for astronomy.

I have no idea how you could block Vis + IR on that Astrodon Sloan U'.

 

Well I was thinking at least 1 mm of Hoya 340 would do the trick. Its got a window between 700-760 which is blocked well by the Sloan U. Dunno about the visible though as there is no data available within that range.

 

Still even if the 340 has an OD of 2 in the visible that should be enough.

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Take 1mm each of Hoya U-360 and Schott UG11. Block both with S8612 1.75mm or 2mm thick, observe there is no Red/IR through either stack.

However, when I hold the U-340 stack up to certain kinds household lights (some of my CF bulbs show this), I will see a bit of a whitish visual leak, but not with the UG11 stack.

This visual transmission difference seems to be somewhere at and above 500nm, isolated from the Red/IR range using various longpass filters. This is a lower visual leak (lower then Red/IR) exhibited by the 1mm U-340.

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I dunno, blocking one UVpass with another UVpass is a little strange to me. I guess I'll have to think about it.
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I dunno, blocking one UVpass with another UVpass is a little strange to me. I guess I'll have to think about it.

 

I dunno either Andrea.

In this case, it is like using the Sloan filter as a Red/IR blocking filter for the U-glass, and the Sloan graph doesn't look good for blocking Red/IR either.

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I dunno either Andrea.

In this case, it is like using the Sloan filter as a Red/IR blocking filter for the U-glass, and the Sloan graph doesn't look good for blocking Red/IR either.

 

If the ultimate goal is to have an OD 5 does it matter if it comes from OD5+ OD0, OD4+OD1 or OD3+OD2?

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