Schneider-Kreuznach Xenoplan 5.6/26-001 prototypes, initial tests and strange results

[enricosavazzi]

I am testing three prototypes of the Schneider Xenoplan 5.6/26-001, possibly manufactured for a customer in 2002 and afterwards never produced on a larger scale. As the name indicates, this is a 26 mm f/5.6. They have a number of peculiar characters, including a (likely) very expensive construction and non-standard lens and filter attachment threads (one prototype has a different attachment thread than the other two), among a sleeve of other oddities. A Schneider representative confirmed to me that these are prototypes and sounded curious about how I got my hands on them (an eBay Israel-based second-hand seller of mostly high-tech items), but added that he could not provide any information about the customer and the use of these lenses. I am writing a page for my web site where I discuss these peculiarities more in detail.

 

It is taking a long time to find practical ways to use these lenses (two months so far, mostly waiting for both standard and custom-made adapters to arrive), so I thought of publishing some preliminary results. First of all, these lenses do not cover full-frame, but seem to cover APS-C (possibly except for a loss of resolution in the extreme corners) and of course Micro 4/3. Resolution in VIS is extremely high, they easily out-resolve 24 Mpixel full-frame and 20 Mpixels Micro 4/3, and quite possibly 40 Mpixel full-frame. They are excellent at infinity focus and down to 0.5x macro. They perform quite well in NIR up to 900 nm, but with a hint of a central flare spot. They came with rear-mounted dual-band blue- and NIR-pass filters that completely block UV, so I did not have high expectations about their NUV performance. Instead, NUV transmission is decent, as shown by the samples below, which are straight out of camera except for reducing and cropping.

 

Godox AD200 flash without plastic window, + Convoy S2+ LED torch for framing and focusing (left on while shooting), Baader U.

 

Daylight on an overcast day, front-mounted Baader U. There is a strange yellow flare at the bottom and right. I am not sure about the light blue sky (obviously overexposed), which I suspect might be in part NIR forcing its way through the Baader U. The sun umbrella in the garden reflects a lot of the same light blue.

 

1:1 pixel crop of the sitting bench in the garden. Image resolution is obviously very high.

 

Same scene with rear-mounted Baader U. The yellow flare is gone.

 

1:1 pixel crop with rear-mounted Baader U. Resolution is much worse. It is still not a bad image compared with those produced by some low-price accidental UV lenses, but obviously this lens does not behave well with a rear-mounted UV-pass filter. All the more odd, since the lens came with a thick (2 mm) rear-mounted filter that I had to remove for these tests.

 

Rather good false-color in sunlight, except for the yellow flare. There was a strong wind whipping the trees. A lake with distant islands in visible between buildings.

 

Still good results at dusk with overcast sky, in spite of the long exposure time (a few seconds).

 

1:1 pixel crop of above picture. The terrace at the bottom has venetian blinds (as verified with binoculars) that cause a color moiré, probably the first time I see this in NUV. This is a type of interference at the scale of single pixels, caused by the lens substantially outresolving the camera sensor. The terrace two floors higher has a cloth curtain, which causes no moiré.

 

I bought these lenses on a hunch even though they were in no way cheap, expecting an excellent VIS resolution when reversed in photomacrography (which they also provide), but the above results seem to indicate a relatively rare case where UV performance largely exceeds expectations. The yellow flare with front-mounted filter is a peculiar problem with no easy solution. There is no such flare when the image contains no sky, so still a very good lens for UV macro. The flare cannot be eliminated with any lens shade I tested. The yellow flare only disappears when the sky is entirely left out of the image, even though oblique sunlight still hits the front element.

 

The seller has no more stocks, but I know that there exists at least a fourth prototype that sold before I bought mine.

[Andy Perrin]

Yellow flare looks like a leak perhaps?

[enricosavazzi]

2 hours ago, Andy Perrin said:

Yellow flare looks like a leak perhaps?

I thought so initially, but there is no yellow flare at all if I shoot with a lens cap on the front-mounted filter, all else being the same. Just a completely black frame.

[Andy Perrin]

So you think it could be reflection from the shiny rear of the Baader?

—-

One really wonders just whom these were made for! An impressive trio of lenses. 

[colinbm]

Looks like a nice lens.

[enricosavazzi]

14 hours ago, Andy Perrin said:

So you think it could be reflection from the shiny rear of the Baader?

[...]

I made another test today after reversing the Baader U in its mount (now it has the purple side outwards), and the yellow flare is largely gone! Only a slight hint along the right side. I made other tests shooting directly against the sun and the yellow flare came back, but not as strong as before. I then shielded the filter from incident sunlight with a hand, and the yellow flare went away. Nothing I did with my hands and by testing different light shades yesterday made the yellow flare go away. Not even with a lens shade that clipped the field of view to one-quarter its diameter.

 

I believe I said once or twice in this forum that the way the Baader U is oriented should make no difference, and in fact, until now, I had not seen any difference with the filter turned either way. Now I know better. Sometimes it may make a difference. I don't know exactly why (it might have something to do with light reflected multiple times between sensor and rear of the filter).

 

Either that, or the shooting conditions are so different (overcast and near sunset yesterday, full mid-day sun and clear sky today) that they do make the difference.

[colinbm]

That is a good result Enrico.

[nfoto]

Purple-side out is how I orient my Baader-U and yes, although differences can be small to the results obtained with the opposite orientation, they also can be pretty obvious. Like what you described here.

[Andy Perrin]

“When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” — Sherlock Holmes. 

[Andrea B.]

I believe I said once or twice in this forum that the way the Baader U is oriented should make no difference, and in fact, until now, I had not seen any difference with the filter turned either way. Now I know better. Sometimes it may make a difference. I don't know exactly why (it might have something to do with light reflected multiple times between sensor and rear of the filter).

 

Baader recommends pink-side "out" (facing the subject) because that is the side which has the best flare-preventing properties. The orientation of the BaaderU makes no difference to the tonalities recorded in non-flare lighting situations.

 

About that cyan sky....

I have noticed that some converters which cannot properly process a blown-out area in a reflected UV photo often produce that bright cyan result. It isn't from leakage or flare. It is just blowout. After all, we are using our software apps outside their specs for this kind of work. 

 

Thank you for the report about the interesting prototype lenses. I will be checking out your site for more details.

[enricosavazzi]

A couple of news about the "mystery" lens:

 

1 - I published a page on my site about the physical characteristics of these lenses: https://www.savazzi.net/photography/xenoplan26p1.html

I will publish lens tests on a separate page, but it will take some time. You can check my posts earlier in this thread for preliminary tests.

 

2 - There is right now at least one more lens of the same type available from the same seller, if anyone wants to take a bite. Search for eBay item  275349222529 . A word of caution is that the picture of the lens in the ad is not of the actual lens for sale, it is instead one of the specimens I own. Since my specimens have two different types of lens mount, contact the seller if you need to make sure what exactly they have available. I have no connections to the seller, other than purchasing three of these lenses in the past.

 

3 - I am posting this information only here and on photomacrography.net.

[Lou Jost]

Thanks Enrico for this information. I just now grabbed the copy you mentioned. It sounds very interesting, especially if there is no focus shift from IR to UV! One can always hope....

 

The link to the page on your site does not work for me.

[enricosavazzi]

6 hours ago, Lou Jost said:

Thanks Enrico for this information. I just now grabbed the copy you mentioned. It sounds very interesting, especially if there is no focus shift from IR to UV! One can always hope....

 

The link to the page on your site does not work for me.

Somehow a dot ended up at the end of the URL. After writing the URL in the post editor of this site, the editor does not recognize the end of the URL and goes on adding to the URL the rest of the text I type. I don't see the dot when I edit my post, so I cannot correct it. In the end I corrected the link by deleting it in the above post and then re-entering it as plain text.

 

The correct link is https://www.savazzi.net/photography/xenoplan26p1.html

[Lou Jost]

Thanks for the repaired link. Your odyssey to get this lens up and running is quite impressive. I also use 65mm helicoids for this purpose, so maybe I have enough parts to get it to work on my cooled monochrome astro camera. That's my hope.

[Lou Jost]

Enrico, what is the aperture you used for the above tests?

[enricosavazzi]

I don't have any records, and of course there is no information in EXIF, but I think most likely f/5.6, or at maximum f/8. Anything more than this would not be compatible with the amount of detail recorded in the images.