Sigma Dust block filters, BW486 and my Venus 2 Spectra

[dabateman]

Hello,

 

I thought that I would share the spectra for the Sigma SD14, Sigma SD15 dust block filters that are removable from these cameras. I collected the data using a Genisys 5 UV/Vis spectrophotometer, that I used to have access to in my old lab. The instrument prints out the obtain curves and then I photographed them. So they look a little odd. I labeled the images so we know what we are looking at. For comparison I also included my B&W 486 filters in 58mm and 72 mm sizes and my 48mm Venus Baader 2 filter.

 

Hope this helps people interesting in picking up a good used Sigma camera. Unfortunately, I broke the SD14 filter when I tried to place it back into the camera. So I only have the SD15 filters. I ordered two from Sigma back in the day and they were both the same. With the broken holder I was able to make a 830nm drop in IR filter. However since the filter is just behind the lens, the viewfinder is still blocked. So this only works well for lenses which can not take filters, like the 8-16mm.

 

David

[Andrea B.]

Over the years I've not seen many users of Sigma Foveon cameras for UV/IR work. So it will be very interesting to see some more photographs made using them. I once had a chance to look at a raw Sigma file (forget which model, probably the 14) and was very impressed with the way that sensor handled detail.

 

Our member Colin (colinbm) uses a converted Sigma. I think his are the only posts here on UVP about Sigma.

 

So the internal Sigma blocking filter is totally easy to remove? And you do not have to send a Sigma 14 or 15 off for conversion? Thus saving something like $250-350? I like that!! Assuming a person could get filter glass of the right size, it would be so easy to home-convert one's Sigma for different UV or IR shooting. (And I don't think it is too difficult to get pre-cut filter glass. We know here of one source already.)

 

I have a small question about the first 3 charts. The first big tick on the horizontal scale is at 400nm, yes? What else could it be, smile. But I just want to double-check.

 

It's interesting that the 14 blocker covers a 400-660 nm interval and the 15 blocker covers 410-670 nm. The second filter appears to cut a lot of violet.

 

I note that the B+W 486 UV/IR blockers are a bit more lenient on the short end there, starting at about 380. I've always thought that region between 380-400 nm was a kind of no-man's-land -- not quite UV and not quite Visible. The 486 looks to be good for Visible work with a converted camera. I might worry a bit about using it for UV-induced visible fluorescent work depending on what the fluuorescent subject is.

 

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David, when you get a moment, I wonder if you would please also post the 486 charts and the BaaderU chart in this topic: Filter Transmission Charts

 

We are trying to maintain a collection of transmission charts for reference there. (I'm woefully behind in collecting transmission charts scattered among our topics!)

[OlDoinyo]

I used to have a Sigma SD14 and have posted a few shots taken with it (my avatar was taken from one such, and my Callanish standing stone shots were also taken with this camera.) They are eccentric beasts outside the visible, and cannot give real UV false color the way Bayer-mask systems can--almost all the UV image info is contained in the channel from the top sensor layer. I remember that I had to remove the hot mirror to do UV--it is a very efficient UV blocker, unlike some camera hot mirrors.And yes, in these cameras the hot mirror is in front of the mirror box and is hand-removable. "Conversion" requires about 60 seconds.

[dabateman]

Andrea, yes the first big tick is 400nm.

What was more interesting is the SD14 filter lets in IR. This is a problem for these earlier Sigma cameras as these cameras are really IR cameras with block filters to be usable in visible. The SD14 conversion is quick, reversible and yes if your not careful can easily break the dust block filter. I bought a 32mm glass 830nm filter and glued it into the broken dust filter. But in hindsight cutting ir sheet, may have been better.

Its hard to set focus, as there is an OVF and no live view. But the uv sensitivity is quite good. I also have a full spectrum Olympus E510.

In a test last year with pentacon 6 80mm f2.8 lens, baader venus 2 and fluorescent grow light in my basement. The subject was a dandelion, the E510 setting ISo 1600, 15 sec. My stock Olympus E3 was Iso 1600, 30sec. The SD14 Iso 200, 30sec and my Kodak slr/n was Iso 160, 30sec. All about equivalent, but Slr/n was really noisey.

My stock Panasonic Gm5 saw nothing, I think the uv block filter is very strong on Panasonic cameras. I think this helps reduce chromatic aberrations and prevents the purple blobs people see with Olympus cameras.

Now that I have other lenses I still have to do a lens test.

I also since learned that the Kodak Slr/n just has a 0.7mm S8612 filter cemented onto the sensor. It too is a pain to focus but will be interesting to test more.

 

[Andrea B.]

I did not know that the SD14 had no Live View. I think I would be lost without LV after becoming so accustomed to using it. :) And it certainly does pass enough IR to contaminate any photograph! Did users complain about that??

 

You made a good comparative test, but those are fairly long exposure times and high ISOs so I'm not surprised that noise occured. Perhaps you might enjoy a UV-Led torch or a UV-flash to reduce both ISO and exposure length?

 

We have noticed that over the years the internal blocking filters have become much better on DSLRs and mirrorless bodies after the first few years. So it would require very strong UV illumination to record anything UV with your stock G. I had similar results with my stock Nikon D810 and D610. In the "olden" days of digital cameras with those weak internal filters, there were some strange results for certain synthetic fabrics due to the IR around 700-710 nm getting through to the sensor. I remember when Leica had to issue external IR hot mirrors to M8 owners. It was always quite a mystery to me why Leica and other manufacturers didn't notice this phenomenon when testing their cameras??

 

Looking forward to seeing some lens tests!

[OlDoinyo]

The SD14 is an SLR--that kind tend to have swinging mirrors, old-school pentaprism viewfinders and focusing screens rather than live view. But they work even with the camera turned off, unlike more recent hardware! Invisible photography is of course a challenge, as framing cannot be done in real time. Live view is found on pellicle-mirror (DSLT) cameras and on mirrorless cameras.