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Snag with Sony A7R in UV

Camera TriColour
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#1 Bernard Foot

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Posted 31 March 2021 - 10:13

In this post I bemoaned the demise of my full-spectrum Sony A6000:

https://www.ultravio...4120#entry44120

I decided to buy a replacement from infraredcameraconversions.co.uk (Alan Burch), and took the opportunity to upgrade to a Sony A7R. I was excited at the prospect of having a full-frame full-spectrum camera and the prospect of post-processing being slowed down by having even more megapixels to move around and manipulate.

The A7R arrived yesterday. Initial tests showed it worked fine in IR and with a Baader U. But when I used my UV bandpass filters it was clear that the camera could not reach deeply into the UV. At 345nm it semed about half as sensitive as the A6000, and at 320nm about 1/6 as sensitive. This makes it unusable for UV TriColour as the sensitivity of the A6000 at 320nm is already pretty low.

Not clear what the reason is. The A7R is unusual in not having an Anti-Aliasing filter, and so the sensor cover plate may have ben modified in some way to compensate. Also Alan says the A7R sensor has an AR coating (which may be another result of having no AR filter).

So sadly I am returning the A7R and getting another A6000. It's a bit boring having two A6000s (assuming I get the old one fixed), but at least I know it works down to about 305nm.

BTW - I have updated the other post on the problem with the A6000. This may be of interest to you if you are using a Sony A6x00 camera.
Bernard Foot

#2 dabateman

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Posted 31 March 2021 - 11:09

Jonathan was also having issues.
He posted that the actual cover glass above the color filters is the problem. But only MaxMax is the place to switch that out for you.

Your other option is to get an Olympus Em5mk2. I don't like the flippy screen. But everything else is great.

Also now you can show me if the SvBony works in the dual mount adapter with your lenses. I am curious if it only covers m43rds or if the dual adapter stretches out to the ever so slightly larger APSC.

Edited by dabateman, 31 March 2021 - 11:11.


#3 Bernard Foot

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Posted 31 March 2021 - 11:35

View Postdabateman, on 31 March 2021 - 11:09, said:


Your other option is to get an Olympus Em5mk2. I don't like the flippy screen. But everything else is great.

Also now you can show me if the SvBony works in the dual mount adapter with your lenses. I am curious if it only covers m43rds or if the dual adapter stretches out to the ever so slightly larger APSC.


Having 2 sets of adapters is enough for me, so I'll stick with Sony for full-spectrum.

Looking at the SvBony is next on my list (I'm just finishing an assessment of the Meritar). I can't judge the SvBony for distant shots because I'm awaiting the thin helicoid. But I've done some initial playing at the sub-metre range. I can get full APS-C coverage using the 28mm Lithagon, but the 50mm Focotar 2 gets clipped at the extreme corners. The Lithagon lens at the rear protrudes quite a bit so it is nearer to the SvBony than the Focotar is, and that probably explains why it is better in terms of coverage.

Image quality doesn't look very good though - but watch this space. Haven't looked at UV reach yet.
Bernard Foot

#4 dabateman

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Posted 31 March 2021 - 11:51

Interesting,
I look forward to seeing what you get. Also the further away from the sensor the SvBony is, the greater the reduction. If its 10mm away from the mount, it will push 0.4x

I think my dream full spectrum camera now might be the Pen-f. It has absolute color control with the color wheel and curves. Black and white with it is also quite fun with grain and vignetteing control. One day I might converted it to full spectrum. I just don't like flippy screens, much prefer tilting in axis screens. Also don't know how it will perform, as different 20Mpixel Sony sensor than the 16Mpixel I am used to.

Edited by dabateman, 31 March 2021 - 11:59.


#5 Stefano

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Posted 31 March 2021 - 12:35

I hope my Canon EOS M is useful down to about 310 nm, as deep as the Soligor goes. I only have the sensor coverglass above the sensor. But first I have to upgrade my cardboard/black tape filters and get some S8612.

#6 JMC

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Posted 31 March 2021 - 13:14

Bernard, the A7III cover glass on the sensor is a huge blocker of UV, and it wouldn't surprise me if the A7R is the same. If Alan Burch has a broken A6000 sensor (with the coverglass present) I'd be happy to test it and measure the transmission of the coverglass. I'm guessing it is simply a thin glass one, which would explain why it is blocking less of the UV, but it would be nice to test that.
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#7 Bernard Foot

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Posted 31 March 2021 - 13:52

Thanks, Jonathan - I've passed the mesage to Alan.
Bernard Foot

#8 Bernard Foot

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Posted 31 March 2021 - 14:00

View PostStefano, on 31 March 2021 - 12:35, said:

I hope my Canon EOS M is useful down to about 310 nm, as deep as the Soligor goes.

I looked through my oldest TriColour photographs, but it looks like I'd already switched to the A6000 by then, so unfortunately I can't tell you how the EOS M would perform through the 315BP20 filter.
Bernard Foot

#9 OlDoinyo

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Posted 01 April 2021 - 14:40

I have noticed that my A900 (Lifepixel conv.) is also very weak below 340. I wonder if it could be a similar issue. Just what is this cover glass? I gather it is different from the reseau, the anti-aliasing filter and the hot mirror--there seems to be quite a stack of stuff on these sensors!

#10 Bernard Foot

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Posted 01 April 2021 - 15:30

View PostOlDoinyo, on 01 April 2021 - 14:40, said:


Just what is this cover glass? I gather it is different from the reseau, the anti-aliasing filter and the hot mirror--there seems to be quite a stack of stuff on these sensors!


As I understand it, it's to physically protect the sensor. It's an integral part of the sensor unit and can't be removed. If I'm wrong, I'm sure there'll be someone along soon to corect me.
Bernard Foot

#11 Stefano

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Posted 01 April 2021 - 16:17

MaxMax does remove it, but it isn't normally removed. It is glued on top I think, with a narrow gap between it and the actual sensor.

#12 colinbm

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Posted 02 April 2021 - 02:49

The cover glass is to hermetically seal & protect the sensor with its CFA & microlenses & the very delicate gold wire connections. It is adhered to the ceramic sensor base. Some cover glass, like Canon are easier to remove, while Sigma Foveon have been very difficult to remove.

#13 dabateman

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Posted 02 April 2021 - 04:11

Yes the cover glass is the layer that isn't removed really. People whom monochrome convert their cameras try to remove it with solvent or blow torch.

The newer cameras seem to have anti reflectance AR coatings on the coverglass which block UV below 350nm.

Seems like very few cameras see into UVB. Sony A6000 and Olympus Em5mk2 and Em1mk1 are exceptions.

My old E510 can't see 300nm very well.

Edited by dabateman, 02 April 2021 - 04:14.


#14 Stefano

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Posted 02 April 2021 - 04:48

View Postdabateman, on 02 April 2021 - 04:11, said:

The newer cameras seem to have anti reflectance AR coatings on the coverglass which block UV below 350nm.
That’s a problem for us. Does this mean that removing the coverglass will be necessary for converting future cameras? It is a very delicate operation.

#15 UlfW

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Posted 02 April 2021 - 05:13

View PostStefano, on 02 April 2021 - 04:48, said:

That’s a problem for us. Does this mean that removing the coverglass will be necessary for converting future cameras? It is a very delicate operation.
I don't think so, at least not for most of us.

This is mainly an issue when doing very special photography with dedicated narrow-band filters and light-sources below 345nm.
Then the best option is a monochrome converted camera to get the most of the sensor's declining sensitivity.

The coverglass-coatings rob the sensor's efficiency, but not that much in the bands mostly important for most UV-photography.
As the sensitivity is dramatically higher in the upper end, all light there will drown any image components in the shorter end.

It can be a problem if you seek to take proof of concept-pictures of short wavelength LEDs, but such motifs quickly become rather boring.

It is good to know that there are some cameras like the Sony A6000 and Olympus Em5mk2 and Em1mk1 that are exceptions.
Those are useable for a few of us like David and Bernhard that are doing interesting things with narrow band filters.

For most of us the benefits of low noise as from modern BSI-sensors is likely much more important.

Edited by UlfW, 02 April 2021 - 05:14.

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#16 Stefano

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Posted 02 April 2021 - 05:45

I know my camera can see at least down to 345 nm, since my 340-345 nm LED is visible and appears green as expected. My Chinese BG39 filter doesn’t go that deep anyway, so for now it’s the limiting factor (my Soligor, if it’s the same as yours, should reach 310 nm, and I think the sensor too with the coverglass should go that low).

#17 Andy Perrin

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Posted 02 April 2021 - 18:17

If the issue is an anti reflective coating on the cover glass, it may be possible to dissolve the coating without removing the glass itself (which is there for good reason!).

#18 Stefano

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Posted 02 April 2021 - 18:19

Dissolving coatings could be useful for lenses too, instead of polishing them off.

#19 Andy Perrin

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Posted 02 April 2021 - 18:22

On lenses it is problematic because the surface quality matters. I’m not sure if it matters so close to the sensor, though.

#20 Stefano

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Posted 02 April 2021 - 18:26

The closer you get to the sensor, the sharper the shadows projected by dust/imperfections are. So I think quality does matter, at least up to a certain point.