UV focus stacking

A forum to ask questions, post setups, and generally discuss anything having to do with photomacrography and photomicroscopy.

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hellmill
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UV focus stacking

Post by hellmill »

Hi,
I have been photographing tiny flowers (<3mm) in UV, but would really like to get greater magnification. Currently I have been using a reversed 50mm El nikkor enlarging lens. This does allow >1:1 but to date I am not really very impressed with the optical quality of the lens and need better resolution if possible.
Does anyone on here know of any microscope objectives (preferably not expensive) that would transmit UV, could be mounted onto a full spectrum converted camera via a bellows?
In other words, some way of carrying out higher magnification UV focus stacking?

Many thanks

Helen

Pau
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Post by Pau »

In fact many (most?) microscope objectives transmit well near UV (365nm-400nm), in special those recommended for fluorescence microscopy like Plan fluorites but most plan achromats and modern plan apos also do well.

For bellows, if you don't want to use tube lenses you need objectives finite corrected (marked 160 or 210) that do nor need compensating eyepieces. Nikon CF series are the most recommended way.
What magnification do you need?
What wavelengths do you use?
Pau

hellmill
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UV focus stacking

Post by hellmill »

I wanted to use finite lenses as any tube lens or eyepiece might not transmit enough UV
In particular I was concerned that any coatings on the lenses would block UV (as with camera lenses) and that the cements used can fluoresce sometimes, if the lens is inteneded for UV use

I am interested in wavelengths between approx. 360 - 400 nm that correspond roughly to those that an insect might see.
As to magnification, X5 to X10 is probably the best starting point, but possibly also X20

I did spot some objectives on ebay, but had no idea if they would work and although not super expensive (for objectives that is) they were still too dear to take a risk.

So Nikon CF series will transmit UV? I hope I understood you correctly?

Pau
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Post by Pau »

So Nikon CF series will transmit UV? I hope I understood you correctly?
Likely most of them will do pretty well*, but because I don't have any of them I can't be sure, this is a guess based in my short experience with other objectives. Maybe other members could post better backed opinions.

* only the ones marked Fluor are specifically designed for UV fluorescence
Pau

Lou Jost
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Post by Lou Jost »

There are some UV lenses available on eBay that are sharper than almost any microscope objective in those magnification ranges, and that have enormous fields of view quadruple those of typical microscope objectives. However they have their practical drawbacks....

These are the microchip-photolithography lenses, of which the Ultra-Micro-Nikkors are the best known to photographers. Those UMN lenses were an early generation and used visible light, but as the need arose for more complex semiconductors, the lensmakers moved to shorter wavelengths, and eventually to UV-A and UV-B and then deep UV. Surplus lenses from this period are available for reasonable prices. Now the technology has moved to extreme UV and electron beams, and immersion lenses, so those earlier UV lenses are obsolete.

The lenses are diffraction-limited and perfectly sharp from corner to corner, and project an image up to at least 125mm x 125m at (most commonly) 5x or 10x when reversed. They are basically enormous UV microscope objectives. And I do mean "enormous". One that I have weighs 20 pounds.

They are optimized for a single wavelength, typically the optimized wavelength is in the range from 405nm to 248nm for the more recent lenses.

There is a 308nm version on eBay right now:
http://www.ebay.com/itm/7608-TAMARACK-S ... 0005.m1851

I like this lens and wanted to buy it but ran out of money. If this is a one-time project for you and you buy it now, I'd be willing to buy it from you for the same price next year...the danger of this one is that we don't know anything about its working distance, image size, etc.

In contrast a bit more is known about the Zeiss UV photolithography lenses. Check out this recent thread (begin on p2):
https://www.photomacrography.net/forum/ ... fee63466a5

Here is a 405nm version available now:
http://www.ebay.com/itm/D124750-Carl-Ze ... SwqXZZzSnU
My guess is you could offer 500 and get it for 900-1000. Note the NA= 0.28 and m=5x reversed. No idea about the reversed working distance, but probably on the order of 12mm.

There are also sometimes Soviet versions of these available for very little money. They are hard to search for an eBay though, since the sellers rarely seem to know what they are for or how to interpret the numbers inscribed on them. I have seen the magnification misinterpreted as max aperture, and the optimized wavelength misinterpreted as the focal length.

Do you have a modded camera?

Edit: Here's the biggest one I've ever seen on eBay, now sold (for $10,000!):
https://www.terapeak.com/worth/canon-ul ... 914734756/
The ones I am suggesting are much smaller and really cheap (I picked up one for $75). But I have to admit to drooling over the one in that link.
Last edited by Lou Jost on Tue Oct 03, 2017 12:04 pm, edited 1 time in total.

enricosavazzi
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Post by enricosavazzi »

For reasonable quality at 365-380 nm and at low to medium prices, there are a few possibilities.

Zeiss Luminar 63 mm is reported to do reasonably well in NUV. This is a photomacrographic lens, so it is used non-reversed. It should perform well to about 5x.

El-Nikkor 80 mm older model (metal barrel) reversed, usable at least down to about 3-5x.

I have not tried in photomacrography, but there are several legacy 35 mm f/3.5 lenses that perform quite well in NUV (e.g. http://savazzi.net/photography/35mmuv.html ). Reversed on bellows or extension tubes, they -should- perform reasonably well.

At higher prices and higher magnifications, there are the Mitutoyo NUV M Plan Apos (especially 10x and 20x), but you also need a suitable NUV tube lens. At least some legacy single-coated 200 mm f/4-f/5 lenses should do well enough in NUV when used as tube lenses, but I don't have concrete data. On APS-C and Micro 4/3, you can use a correspondingly shorter FL for the tube lens.

The Mitutoyo UV M Plan Apos are instead different beasts for use with UV lasers at shorter wavelengths as well as VIS, and are not especially well corrected in NUV.

A good thing with UV is that it is less affected by diffraction than VIS, so at 365 nm you can stop down about one stop narrower than optimal in VIS at the same magnification.

Axial chromatic aberration is a common problem with lenses not specifically designed for NUV (and often also with UV lenses for photolithography, which are corrected only at one specific wavelength). One way to mitigate this problem is using a camera capable of live view in the NUV to focus, and eliminating VIS by filtering.

If you can do with a relatively narrowband UV source (in your case 365 nm UV LEDs), axial CA is less of a problem than with broadband sources like xenon arc, but some legacy lenses that happen to transmit NUV are unfortunately too uncorrected in the NUV for use even with these LEDs.

Then, if you want to really do NUV-only imaging, there is the problem of filtering out VIS and NIR, including both the VIS-NIR emission of the UV source and the NUV-excited fluorescence of the subject in the VIS and NIR. VIS emission is usually a problem even with 365 nm LEDs (their emission tail extends well into the VIS), and many subjects fluoresce in the VIS and NIR. The filtering problem would take volumes to discuss.
--ES

Lou Jost
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Post by Lou Jost »

You might also consider catadioptric (reflector) lenses, which should work in UV and will not have chromatic aberration.
Here's one:
http://www.ebay.com/itm/Newport-50105-R ... SwOyJX5GeM

I have no experience with these, just with their telephoto counterparts for visible light.

Some of these are quite cheap on eBay, especially old ones from Tropel. I'm not sure what this is but it might work:
http://www.ebay.com/itm/Tropel-15x-P-N- ... SwtGlZA1Nx
Last edited by Lou Jost on Tue Oct 03, 2017 12:39 pm, edited 1 time in total.

Lou Jost
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Post by Lou Jost »

Here is the current generation of UV hybrid reflector+refractor microscope objectives:
http://www.corning.com/worldwide/en/pro ... tives.html

I think Edmund and Thorlabs sell reflector objectives too.

enricosavazzi
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Post by enricosavazzi »

Lou Jost wrote:Here is the current generation of UV hybrid reflector+refractor microscope objectives:
http://www.corning.com/worldwide/en/pro ... tives.html

I think Edmund and Thorlabs sell reflector objectives too.
These hybrid reflector/refractor objectives from Corning are corrected for UVC rather than NUV, so I think not in scope for the OP.

Reflector objectives (without refracting elements) are essentially free of CA, so essentially optimized for "all" wavelengths (the next limitation is the reflectivity of their mirror elements and the optimal bandwidth of their AR coatings, which are broad-band but not unlimited). There are a few of these, and worth investigating. They tend to be expensive compared to other solutions, as well as limited in the size of the corrected imaging area because of spherical aberrations.
--ES

Pau
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Post by Pau »

About normal microscope objectives for epifluorescence they are corrected for imaging in the visible range, for UV they act as condensers, a less demanding task, so not sure on how well they could perform for your application (I just guess that modern Plan fluorites could do pretty well)
Pau

enricosavazzi
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Post by enricosavazzi »

Pau wrote:About normal microscope objectives for epifluorescence they are corrected for imaging in the visible range, for UV they act as condensers, a less demanding task, so not sure on how well they could perform for your application (I just guess that modern Plan fluorites could do pretty well)
Good point, and more generally, a lens being transparent to UV and being able to produce a good IQ in UV are very different things. I have seen several legacy camera lenses that transmit UV well enough, but produce very poor IQ in UV.
--ES

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