First shots with the 60 mm f/4 UV-Vis-IR APO lens

[nfoto]

Did a quick break from the dreariness of writing the D3 review when Fedex at last delivered my 60/4 APO from Coastal Optics. This is the pet design of Brian [Caldwell] and a lens that I really looked forward to put to good use.

Still some flowers left on my sole pot plant, the Moth Orchid (Phalaenopsis) so that specimen was the obvious victim for a first test series with my modified D200. I did UV, UV fluorescence, visible, and tricolour IR. Not much to gain from IR with this subject though, since it appears almost identical all along the IR band. I had too much movement between the fluorescence shots and the remaining captures to allow me to do a multispectral composite (the plant responds very fast to UV-light stimulus leading to movement of the flower and stem).

Here is the Moth Orchid in visible light:



D200, Baader UV/IR Cut filter, SB-800 flash, ISO 200, 60mm f/4 APO at f/5.6, 1/250 sec, 8 frames stacked in Helicon Focus (to get extended depth-of-field)


This is the UV fluorescence shot



D200, Baader UV/IR Cut filter, Sylvania Blacklight, ISO 800, 60mm f/4 APO at f/16, 5 sec

And finally, the "pure" UV capture



D200, Baader U2 "Aphrodite" filter, SB-140 UV Flash with SW-5UV filter, ISO 200, 60mm f/4 APO at f/16, 4 times multi-exposure


The lens is super sharp. Epidermal structures are well defined and can be seen even in visible light.

[annedi]

hot damn, I must have this jewel !!!
i'm going to cancel the D3 order first thing in the a.m.
that money needs to go towards this lens, yesssssss.

Bjørn, have you tried any close close-ups yet with extender, etc.?
How close will it focus ?

[nfoto]

Mind your wording, Andrea 

Cancelling your D3 order won't give you this lens - yet - since production samples are expected in Q1 2008. But then you will get a nice sky blue finish instead of the black of the prototypes.

The lens focuses to m=1:1.5 at a distance of 0.26 m.  Free working distance then is about 0.1m which isn't much but sufficient (the front element is recessed so you can work without a hood and for filter use a hood would be awkward anyway).

I've just have had the lens in-house a couple of hours, so *some* answers are yet not found 

The lens comes with a CPU since I convinced Brian in an earlier stage that was a good idea. I still think it is.

TCs probably won't work well because the rear lens element sits almost outside the lens mount (it is stationary however, which means the lens won't pump dirt into the mirror chamber). Extension tubes should go well. But the 105 UV-Nikkor or similar would be better for 1:1 work due to the working distance.

If the weather miraculously clears tomorrow, I'll do some landscapes with the 60 APO and tri-colour IR filters.

[brianc1959]

Bjørn:
Beautiful shots!  Its really a treat to see this lens get a field tryout after more than a year of design, development, and fabrication. 

Your extended depth of field technique is very interesting, and I'm glad to see you chose the optimum aperture for the lens (f/5.6).

The production lenses will only have a narrow blue ring near the front, similar to the gold ring used by Nikon on their ED lenses or the red ring used by Canon on their L lenses.  The rest of the lens will be black, like the prototypes.

The question about teleconvertors is interesting.  The lens should work with compact TCs like the TC14a, but I still need to try this combination.  However, the UV and IR performance would be seriously impaired by the use of a normal teleconvertor.  Off and on I toy with the idea of a broadband (UV-IR) teleconvertor, but so far have not come up with anything that I really like.

You can get to 1:1 by focusing to 1:1.5 and then adding 27mm of extension. 

Adding the CPU was a great idea, and I really appreciate your encouragement and assistance in this.

[nfoto]

Thanks for the update, Brian. A blue ring is of course appropriate for a Coastal lens 

So a PK-13 or similar would be the ideal way of going to 1:1 then? (PK-13 or M2 ha 27.5 mm extension). Since I prefer not to lose the CPU feature (for use of the lens on my D40 and Fuji S3), I'll make a special extension tube with a custom-programmed CPU in it. If you could provide the pupil factor, or alternative, the exact effective aperture at m=1:1.5, for your lens  I would be much obliged. Then my lens-recognition software should be able to identify not only the 60 APO on its own, but also that an extension was used.

When you shoot subjects with a flash illumination up close, it's difficult to get perfectly even lighting of the scene. So close-ups in UV will likely not benefit from the stacking method unless a better UV flash is available (because you then could put the flash in a bounce mode and get better distributed light). With the current available units, multiple exposures is the only way of getting a "softer" lighting to the subject in the close range, but the logistics of adding stacking to this becomes troublesome.

[brianc1959]

Bjørn, I'm not sure what you mean by pupil factor.  However, the effective aperture (wide-open) at 1:1.5 is f/5.62, and the effective aperture at 1:infinity is f/3.99. 

The blue color of the ring (actually its more of an aqua color) is actually a nod to Coastal's parent company, Jenoptik, rather than a reference to the ocean.  However, it is true that the waters near West Palm Beach do have a strikingly similar color!

[nfoto]

Pupil factor P =  exit pupil/entrance pupil, according to the books I've tried to comprehend  over the years and Neff=N*(1+m/P) for the effective aperture.

Thanks for the details on the effective apertures, Brian. Now I only have to find a suitable tube to add the CPU to. By the way, does the focal length change when the lens is focused closer? I noticed that the spacing betewwen the elements must change since the lens extends and the rear element(s) stay put.

[brianc1959]

Bjørn:
I made a mistake in my earlier post - I did calculations based on 1:2 magnification rather than 1:1.5.

Here are the correct numbers:
To go to 1:1 magnification it is best to focus to 1:1.5 and then add 18.2mm of extension.  Of course, you could still just focus to 1:2 and add 27mm of extension, but you will get a little less aberration (coma in this case) by using less extension.  The effective wide-open f/# when focused to 1:infinity, 1:2, and 1:1.5 is f/3.99, f/5.62, and f/6.13, respectively.

The front and rear groups do change their separation in order to correct aberrations as you focus closer, and as a result the focal length of the lens does get shorter at close focus.  At infinity the focal length is 60; at 1:2 the focal length is 54.6mm, and at 1:1.5 the focal length is 53.1mm.  This drop in focal length corrects about 30% of the focus breathing you get in a simple non-CRC lens.  At one point I considered trying to fully correct the breathing to make the lens more suitable for cinematography, but decided it would add too much cost and might piss off photographers who don't care about breathing.  I also got blank stares from the cinematography people when I asked them if they cared about UV or IR!

[LBravo]

Wonderful photos, Bjorn!
What are your first impressions compared to a Micro Nikkor UV in terms on UV transmittance and usability?
And compared to a glass lens like the EL Nikkor 63mm?

I am very curious about this lens and it is already in my "buying list"!

Cheers

Luís B.

[nfoto]

They are about equal in UV, since they do some 80% transmission in the UV band captured by the camera, and both are very sharp. The main differences are that the working distance for close ups is better for the 105UV (because it has a longer focal length, of course), and that the 60 APO keeps a consistent focus across the entire range UV- Vis- IR, whilst the 105 UV only is parfocal for the UV and visible bands. Thus, the 60 APO is much better suited for multispectral applications.

It is only fair to say that the 60 APO will replace the 63 EL in my field kit.