Nikon Z6/Z7 as a UV/IR Conversion: the Bad News

[nfoto]

Well, "bad" in the sense that the underlying issue still remains unsolved. Even though it is mitigated to some extent.

 

 

Strangely there is a "striping-free" margin, as evidenced by the 100% crop below (portrait mode capture),

 

 

These artifacts are difficult to get rid off, despite judicious processing. So yes, Z6 is like being between a rock and a hard place.

[nfoto]

One has to soldier on with what gear is available, I suppose.

 

For long lenses, there is always an old Nikkor available. I mean really old. like the 35cm f/4.5 Nikkor-T from the '50s. It certainly makes a rather "big" impression.

 

 

The ancient "cannon" does surprisingly well in UV. I used a rear-mounted Baader U. Not too much "UV colour" in the drab late-winter scenery outside, but at least I get a decent UV exposure at f/11, 2.5 sec @800 ISO under grey overcast skies.

 

 

The NEF comes out with moderate-low contrast so needs some additional tweaking. Otherwise it runs smoothly enough through Capture NX-D. Even the infamous striping was kept on a leash for once.

[colinbm]

Very nice Birna

Why isn't the boat the focus of the photo....

[dabateman]

Very nice Birna

Why isn't the boat the focus of the photo....

 

Colin are you Amercan? I though football (soccer) was the focus of the world.

 

[colinbm]

Australia & an ex yacht & dinghy sailor....;-)

[nfoto]

Actually the goal nets are from an ice rink and meant for ice hockey. No longer any ice as the winter has been unusually mild, thus neither snow nor ice any more.

[dabateman]

Actually the goal nets are from an ice rink and meant for ice hockey. No longer any ice as the winter has been unusually mild, thus neither snow nor ice any more.

 

That mkes sence based on scale. I grew up in Canada, so understand why hockey would be the focus.

[nfoto]

For special purposes one might need a rear filtration system. I'm using this approach for much of the "invisible light" kind of photography, ie. UV and IR. The advantages are many, for example, dichroic filters which tend to be very expensive in larger sizes, if at all available, can be used in a much smaller size. Plus the tendency to colour shifts towards the periphery is greatly reduced or eliminated. The same filter can be used for a variety of lenses ranging from wide-angles to long focal lengths. And so on.

 

Due to the short register distance of the Z system, making a rear filtration box is not difficult if non-native lenses are to be used. The example below is a quick and easy solution made in

 

From the Z-mount side

 

 

From the F-mount side. I opted for this mount as I have many candidate lenses for UV or IR in this mount.

 

 

I have verified even my 21mm Panagor and Tamron wide-angles do focus to infinity in conjunction with this rear filtration box.

[dabateman]

That looks quick. I am playing with 2 options for M43rds. First is a 9 wheel that uses 1.25" filters. My 25mm filters fit by compressinto a 1.25" ring.

The option that is working best is a slim dual c-mount/M42 adapter to M43rds. A 25mm filter or a 5mm c-mount tube holds a filter an screws near the sensor. Then 10mm to 15mm helicoid connects to M42 lens, Ef mount or nikon F mout lenses. With adapters.

[Andy Perrin]

My quick-and-dirty method is to use 3M poster putty to wedge the filter at the rear of the lens. This system has proven to be surprisingly secure (provided you use sufficient putty and test it a little). The only drawbacks are that one cannot change filter without removing the lens, and the putty leaves a thin residue behind, which can be removed with a microfiber cloth thankfully.

[nfoto]

I'd guess having the puttied filter perfectly normal to the optical axis would be of concern as well? Wedge distortion and peripheral loss of sharpness would be expected otherwise.

[Andy Perrin]

I haven’t noticed any such issues? The filter has to be larger than the rear part of the lens, and the putty touches mainly the edges of the filter. No putty is blocking the light. It doesn’t seem to be as sensitive as you are imagining. It’s true I have only tried this with 25mm filters, though, not with anything larger.

[Andy Perrin]

For example, all the photos here are made with the putty technique:

https://www.ultravioletphotography.com/content/index.php/topic/1863-buzzards-bay-wareham-massachusetts/page__view__findpost__p__12823

 

There is a lot of dichroic shift but that isn’t due to the putty

[nfoto]

The main advantage of rear filtration, apart from getting away using smaller filters, is dichroic filters no longer tend to make those nasty peripheral colour shifts. At least that is my experience with the Baader U on wide-angle optics.

 

The downside is increased sensitivity to misaligned filters (being not normal to the optical axis).

[ulf]

It would be interesting to know how theoretically "perfectly normal" a filter must be to avoid any visible effects.

 

That must depend on the optical system in the lens too.

If I remember correctly a less parallell beam profile leaving the lens is more sensitive.

 

So far I have not seen any problem with the images I have taken with putty mounted filters.

 

No optical elements are ever mounted absolutely perfectly normal.

One advantage with filters is that there is no need for careful centring to the optical axis.

[Andy Perrin]

It wasn’t a Baader, and indeed I notice less dichroic shift with that filter on the rear than on the front. But less isn’t none, especially when I boosted the saturation enormously in those images.

[Bill De Jager]

Birna, very nice result!

 

I noticed that lens, and its promising age and optical formula, long ago. I did manage to acquire one, but it has a weird converted mount by Photo-Sonics. A number of these have shown up over the years; I think that company acquired, converted, and used them for some sort of industrial or defense-related purpose back in the 1960s or thereabouts. I haven't tried to do anything with the mount yet but I don't see any way to remove it. Maybe this is a job for SK Grimes.

 

As for the Z6 problem, I looked into having a Canon RP converted instead, if the dual-pixel technology would avoid the banding issue. However, reviews indicate that both the R and RP have relatively low dynamic range and high noise compared to other current sensors. The RP also shows banding when exposure is pushed enough, something that's likely in UV post-processing. So I nixed that idea. I think there will be a technological solution in time but it may be quite a wait.

[nfoto]

The 35cm f/4.5 lenses were customised to be used on high-speed film cameras, used for documenting nuclear tests etc.

 

I have three of these lenses, two with the Photo-sonic mount and one (shown here) in the original Nikon(RF) mount. I managed to fit one of the two converted lenses to a bellows device, thus knew this lens could do UV, but the rig was a little on the awkward side for field use. Thus I had no hesitations acquiring a third, complete lens, and as far as I recall, asking price was very modest as well. Shipping was more than the lens itself. I already had several of the N-F Tube adapters linking long-focal rangefinder lenses to F-mount in my possession.

 

The Z6 striping problem will be solved, either by firmware or a combination of firm- and software. NX-D does a much better job with the NEFs after I upgraded the Z6/7 bodies to firmware 2.2. Sometimes I can see striping in Liveview, sometimes they are gone, thus there must be some triggering parameters at play for the striping to occur. Pretty elusive at present, though. Even at this stage, the NEFs are very malleable and the output files can be excessively tweaked. Just what is required for UV.

[Bill De Jager]

Thanks for the information, Birna. Could you share the aperture you used? How much stopping down is needed to get optimum sharpness with this lens in UV?

[nfoto]

I shot the test images at f/11.

[nfoto]

The confusion continues. I updated to firmware 3.0, which might have reduced the striping tendency a wee bit further. Or perhaps I'm suffering from an overactive imagination.

 

The rear filter box is completed. I did decide to make it Z-mount only thus used epoxy glue to ensure the mount would stay put permanently. A potential tiny light leak from the Z bayonet was cured by a piece of black shoestring that conveniently had put itself on my work table I tied the string around the inner bayonet and glued it in position. No more light leaks.

 

I then found the original "FF" filter which Nikon shipped with the UV-Nikkor in its film days. This filter is quite thick and is related to Kodak 18A, being 18B according to information I received back then. It certainly leaks a lot of IR, but the images surprisingly enough come out entirely free of those nasty stripes. Here is a quick test shot at ISO 800. Hand-held by the way as shutter speed was 1/500 (!) sec. at f/5.6. UV-Nikkor 105mm f/4.5 lens.

 

 

Instead of UV, one get something pretty similar to false-colour emulated IR Ektachrome. Horses for courses.

[dabateman]

I think your full spectrum z6 was the best purchase you ever made.

It keeps you surprised every use and is full of potential and adventure.

 

Keep having fun. Seems like the Z6 is an endless toy.

[nfoto]

Certainly the item causing the most greying of my hair .... that's why I decided to colour my hair red !!

 

[colinbm]

Mighty fine image Birna....

[dabateman]

Cool,

I just thought that was an IRchrome image of you. I rarely take selfies. Actually never. I think there are very few photos of me in existence.