Why do UV-imaging? What do you need?

Discussion in 'Black and White' started by tbyork2012, Mar 23, 2013.

  1. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    Hi,
    Different people get into photography for different reasons, be it to take pictures of children (theirs or other people's), pets, a sports event, or holiday memories. Some only shoot specific types of subjects, while others shoot varied subjects (portraits, landscape, macro, infrared or others). I do like to take portraits, and sometimes landscape and most of the time this is fairly straight forward depending on available light.

    But what drew me to UV-imaging was that it is completely different from conventional imaging - the camera and lenses were made to image in visible light rather than UV or IR spectrum. It is a case of diminishing returns as: 1) the camera sensor is less sensitive to UV light than visible or IR, 2) there is less UV light available than visible or IR from the sun and 3) the lens unless specifically made for UV-imaging, will contain glass which absorbs UV to different extents, which further reduces the amount of UV hitting the sensor.

    Each piece of equipment in the imaging chain needs to be able to work in the UV-spectrum (up to 400nm) in order to produce the end image, which just happens to be invisible to the naked eye. I would like to think that I can overcome the limits of the equipment in order to extract the amount of UV-light needed to create the images in UV - there is more to this than art, as there is also the science behind it.

    Many have been put off UV-imaging, by the thought that it is very expensive to achieve. Previously it was thought that you required a DSLR which costs $$$-$$$$, needing conversion $$$, UV lens $$$$, UV-pass filter like Baader U $$$, and perhaps a powerful light source to produce the UV-light (studio Xenon strobes with uncoated bulbs or modded camera Xenon flash $$-$$$), which adds up to $$$$, with the lens being the most expensive component to buy (and some of these lenses can be hard to find).

    Perhaps that need not be the case any longer, as it should be possible to do this on a budget. For example if you used a cheaper previous generation mirrorless camera low $$$ and mod it yourself (free - I may do a thread on how I modded my Oly's further down the line), UV-capable lens (with or without helicoid focuser) $$, UV-Pass filter $$, and sunlight for UV light source (free) if you can handhold (with good high ISO and IBIS) or mount on tripod. So for low $$$ you can do UV imaging.

    I shall talk about each piece in the imaging chain separately in turn soon.

    Boon
     
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  2. kds315

    kds315 Mu-43 Regular

    149
    Apr 6, 2010
    Weinheim, Germany
    Looking forward to reading about your experiences! I may share some of mine too, if that would be liked.
     
  3. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    Just some examples of UV. Although this is most interesting in flowers, like IR it can show landscape/objects in a different perspective:

    Car at the showroom:
    8583092963_36735fa50c_b_d.

    Something fishy:
    8583100939_35e8b59bcf_b_d.

    Flower macro (visible):
    8584207194_c334a6beac_b_d.

    (UV):
    8583111323_0dd6864133_b_d.

    BT
     
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  4. kds315

    kds315 Mu-43 Regular

    149
    Apr 6, 2010
    Weinheim, Germany
    Nice ones, but I hope no moderator will be ticked about showing "color" images in a "black and white" section...
     
  5. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    Camera/Sensor for UV

    The camera/sensor:
    Digital cameras have sensors which are sensitive to UV, visible and IR light; this is true of many current CMOS and previous CCD sensors. Fortunately for us the Panasonic, Olympus and Sony sensors (in OM-D, E-PL5 & E-PM2) are sensitive to both UV and IR, although the sensitivity to IR is many magnitudes more than to UV. But in order for these sensors to be used for visible light imaging, manufacturers have to place an internal cut filter (ICF) in front of the sensor to block the UV and infrared spectrum of light. This filter while useful for normal imaging, stops the sensor being efficient for imaging in UV and IR. Hence the need to convert the camera by either removing the filter or replacing it with a quartz filter.

    There are companies who do provide the conversion service for either full-spectrum cameras capable of imaging in UV, Visible and IR (when paired with the correct spectrum filter on the lens), or IR-only camera where the ICF is replaced with an IR filter. I could not justify having to send the camera away for the conversion and the cost (at least $200). Hence I have gone down the DIY route - with the Sony Nex-5N, Oly E-PM1 and E-PL5 (and perhaps the OM-D one day - but currently it is my main camera).

    BTW, the E-PM1 and E-PL5 took me only a short time to mod each of them, but the process is definitely not for the faint hearted. The only down side is that by removing the ICF and not replacing it with a quartz window, the focus distance to the sensor has been affected so that some lenses cannot achieve infinity focus i.e. can only focus up to a distance of a few meters away at most (shorter focal length lenses are more affected). But fortunately some lenses have enough focusing capacity to compensate for this - this includes Oly 14-42 ii, 75/1.8, and Pan 100-300/4-5.6, so autofocus in IR is still possible with these lenses.

    Just to say that it may be worth considering Olympus cameras for the benefit of their IBIS as the lenses which are useful for UV-imaging will be older manual focus/enlarging lenses and not have IS. If using the sun as the light source, you will most likely have to use high ISOs and slow shutter speeds, where the IBIS can help to get sharp images handheld. Otherwise a tripod will be needed. The E-PM1 and E-PL3 would probably be the most cost effective, but will not have the High ISO capability of the current cameras (E-PM2 + E-PL5), which is at least 1-stop better than the previous generation sensor.

    Also, with mirrorless cameras you can liveview focus for UV (or autofocus with IR), which can help with getting sharper images and negate the phenomenon called focus shift (which will be covered in the lens discussion).

    BT
     
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  6. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    UV-Lens

    Lens:
    I thought it would be a good idea to talk about budget lenses which can be used for UV-imaging, rather than the rare and expensive quartz-fluorite ones. There are some old manual focusing camera lenses which are useful for UV-imaging, as well as some enlarging lenses which do not have a focusing mechanism. I thought it would be simpler to explain in terms of questions and answers.

    Q1) What qualities should the UV-imaging lens have?
    Answer: It should transmit as deep into UV as possible, it should produce sharp images in UV-light, [have reasonable contrast, flare resistance and absence of hotspot (added 26/3/13)] and preferably have minimal or no focus shift. Do be aware that there are uncorrected quartz-only lenses which do transmit deeply into UV, but the bandwidth of UV being imaged will not all focus at the same point which results in an image which is not very sharp, unless a narrow bandwidth UV-pass filter is used.

    Q2) What is focus shift?
    Answer: [Focus shift is the phenomenon of lenses where different bandwidths of light (UV, visible, infrared) passing through the lens do not all focus at the same point on the sensor. Some bandwidth could be focused in front of or behind the sensor and be out of focus), while the bandwidth which is focused on the sensor will be in focus. (Added: 26/3/13)] The ideal UV-lens should not have any focus shift i.e. if you focus on a particular point on a subject in normal visible light, that same point will also be the point in focus in UV-light (the focus point stays the same in both UV and visible light). This used to be important as it was not possible to focus under UV-light. But this has changed with the arrival of liveview focusing as you can see the image in UV-lighting on the liveview screen and adjust the point of focus on the subject to where you want.

    Q3) What characteristics of lenses do you look for in UV-capable lenses?
    Answer: It should have a simple coating (i.e. not multicoated), as few optical elements as possible, uses glass which absorbs the least amount of UV (this is the characteristic which you will not be able to tell by looking at the lens) and preferably use no optical cement or at least uses optical cement which does not block UV. The optical cement is the adhesive used to fix optical elements together e.g. a lens described as 4e 3g construction has 4 optical (e)lements arranged in 3 (g)roups, with 2 of the optical elements glued together with optical cement.

    Q4) How do you use an enlarging lens for UV?
    Answer: There are some enlarging lenses which have been confirmed as very good for UV-imaging, such as Nikon El-Nikkor 80mm f5.6 and 105mm f5.6 (look for the older version with the silver metal barrel). One lens I found for under £10 is the Paterson 50mm f3.5 3-element, also does reasonably well for UV, especially if you are on a budget. For other suitable enlarging lenses, it would be worth looking up Klaus Schmitt's UV blog, as he has probably tested more lenses for UV than anyone else.
    The things to consider when using an enlarging lens on your camera is: How do you mount the lens and adjust focus? How do you mount the UV imaging filter? Some enlarging lenses like the Paterson do not have front filter threads to mount filters on while others like the El-Nikkor 80mm and 105mm have non-standard filter threads (34.5mm)? There is a simple solution I've found which will help solve both of these problems, and is much cheaper & lighter than previous generations of helicoids. Plus it allows for the use of cheaper UV-pass filters.

    On eBay, you can find a 17-31mm focusing helicoid which has a separate Micro 4/3 to M42(42mm)/C-mount adapter. This Micro 4/3 adapter mounts to your camera, has female M42(42mm) thread to mount a M42(42mm) to M42(42mm) helicoid, as well as female C-mount thread to mount a 25.5mm filter. So all you need is a UV-pass filter that mounts on the 25.5mm threads (this I will cover in the section on UV-pass filter). As most enlarging lenses have male 39mm lens mount, you will need a female M39(39mm) to male M42(42mm) step-down ring to mount this to the helicoid. For convenience and ease of focusing I tend to use this adapter/M42(42mm) helicoid combo to attach M42-mount lenses for UV imaging as well.

    Q5) What are some useful non-enlarger lenses for UV-imaging?
    Answer: The best transmitting lenses are the Nikon UV Nikkor 105mm f4.5 and the Coastal Optics 60mm f4 Apo Macro (both $$$$). Then there is the Novoflex Noflexar 35mm f3.5 which does reasonably well in UV, and highly sought after by UV-imagers (hence now $$$). But one lens which is less well know and seems to be in good supply is the Soligor 35mm f3.5 (there are numerous versions), which also does reasonably well in UV. It is worth considering this as they are fairly sharp, and transmit fairly deep into UV and costs low $$ (currently). I've found the versions with serial numbers 9xxxxx to perform better than the 'KAxxxxx' or other versions.

    If you do not wish to invest in the helicoid, then the other way to use that Micro 4/3rds to M42(42mm)/C-mount adapter is with an extension tube (longer for macro and shorter for infinity-focus), as these lenses all have focusing mechanisms.

    Photos of this adapter to follow.

    [Edited: 26/3/13 in response to Kds315 post - thanks for the corrections, further info added 4/4/13]
    BT
     
  7. kds315

    kds315 Mu-43 Regular

    149
    Apr 6, 2010
    Weinheim, Germany
    Boon, thanks for that.

    I would not write M39, M42 and M43 as the former denotes a worldwide standardized diameter and type of thread mount with 39mm resp. 42mm diameter and with M43 you most obviously mean the m4/3 or micro four thirds bajonet mount as defined by the Four Thirds Consortium.

    Further, in Q1 just sharpness for lens in UV does not do, suitable contrast, flare resistance, lack of hotspots at least I would have added.

    Further you haven't answered your own question Q2, what focus shift really is, but provided an answer "how to deal with focus shift".
     
  8. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    Thanks, Klaus. I have updated thread as per advice. I also noted that I had mentioned M39-M42 step-up ring but actually it should read female M39(39mm) to male M42(42mm) step-down ring. I have corrected this point in the thread.
    Boon
     
  9. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    As promised pics of the adapter:

    Mounted on E-PL5 with my 25.5mm UV-pass filter (which I have adapted to fit the filter mount of a Pentax 25.5mm skylight filter) mounted on the C-mount threads of the Micro 4/3 adapter.
    8510360676_98c7444742_b_d.

    With the focusing helicoid mounted on this adapter.
    8591297941_b9e78f7423_b_d.

    BT
     
  10. kds315

    kds315 Mu-43 Regular

    149
    Apr 6, 2010
    Weinheim, Germany
    Thanks Boon.

    Just a hint to avoid possible confusion for interested readers: That M39 - M42 ring you mention is not a classic step down ring as known from filters (nor is that term used for that, as it is for a lens thread mount). Technically it is a M39 x 26tpi (female, also called Leica thread mount) to M42 x 1 (male, also called Pentax thread mount) adapter ring [don't confuse with T2-mount, which has M42 x 0.75].

    Filter step up/down rings have usually a pitch of 0.75 or 0.5 (the smaller ones), not 26tpi or 1.0 as the ones above.

    It is a bit confusing, admittedly.
     
  11. slothead

    slothead Mu-43 All-Pro

    Aug 14, 2012
    Frederick, MD
    Hi Klaus! I know you from Nikonians and the Nikon Cafe (where you also use the exact same username - that's convenient isn't it - I am slothead on the other two also). I'm glad you are here too.
     
  12. kds315

    kds315 Mu-43 Regular

    149
    Apr 6, 2010
    Weinheim, Germany
    Great to also see you here Tom!
     
  13. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    UV-Pass Filter

    For UV-imaging, you will need a UV-pass filter which allows UV-light through to the sensor, but blocks all light from the visible and infrared spectrum. The current reference filter which does just that is the 2" Baader-U filter (note: the 1.25" version is not suitable), which at over £200 is not for the budget conscious or those who just wish to experiment periodically with UV-imaging.

    One important point to note: unlike film, digital sensors are highly sensitive to infrared light, being many magnitudes more sensitive to infrared than to UV-light. Hence the older generation of UV-pass filters from Schott (UG1, UG11) and Hoya (U340, U350, U360) cannot be used alone for UV imaging with digital sensors, as they do not block the infrared light sufficiently. It will need to be stacked with an additional (IR-blocking/hot-mirror) filter to stop the remaining infrared light getting to the sensor e.g. BG38/BG39/BG40.

    In the search for alternative UV-pass filters, some of us have experimented with various filter stacks as well as certain available wideband UV-pass filters. Many of these will block sufficient IR to work for UV-imaging. But mounting these stacks may not be as straight forward or require costly special mounts.

    But there are useable filters which can be economically adapted. There are some wideband UV-pass filters measuring 22mm diameter; one of these wide-band filters can be seen mounted on the Micro 4/3 adapter on my E-PL5 in the pics of the adapter. These filters can be adapted to fit in a 25.5mm filter mount. You will need to replace the filter glass from the 25.5mm filter with this UV-pass filter.

    Fortunately for us this filter fits onto the C-mount perfectly, so you can mount the filter onto the C-mount female threads of the Micro 4/3rds to M42(42mm)/C-mount adapter. This also serves to 'hide' & protect the filter within the adapter and helicoid assembly, so there is no filter sticking out at the end of the lens. The cost of this filter + a used 25.5mm filter to mount in will set you back less than 1/4 the cost of the 2" Baader-U.

    I have successfully custom whitebalanced with 2 of these filters on the E-PL5, so I can shoot UV-images in jpeg. I will cover the custom whitebalancing for UV-imaging later.

    BT
     
  14. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    Lighting for UV-imaging

    The cheapest lighting for UV-imaging is sunlight (free), bearing in mind the limitations. These are:
    1) You can only shoot UV in the daytime.
    2) You will most likely require a tripod as it will require slow shutter speeds (which can be an issue if it is windy as the subject will not stay still for you - so High ISO ability may still be important even when using the tripod).
    3) It is not an indoor lighting - you will need an alternative (usually UV-torch) to light the subject for adjusting focus, and a wideband light source (usually a Xenon flash) to illuminate the subject for actual imaging.

    But there are benefits to using sunlight. It is free, is a good source of UV lighting and provides an even lighting to both the subject and the background. It also has a constant lighting ability largely independent of the distance of subject from the camera, unlike with a flash where the UV-lighting ability drops off the further it is from the subject. Let me explain why.

    The light power output from a source is expressed in meters (its guide number). This reflects the effective distance to which the source can provide sufficient illumination of a subject. The light has to travel from the source to the subject, and then be reflected back to the camera sensor, which when using a flash is usually double the distance from flash to subject. As the UV-lighting reduces with increased distance from subject, this can significantly reduce the lighting ability of any light source (with the need to use larger aperture/higher ISO).

    But as the sun is so much further (over 90 million miles) from the subject than the distance between subject and sensor (usually cm/m). Any change in distance between sensor and subject will be negligible compared to the over 90 million miles it has already travelled to reach the subject. Hence the distance of sensor from subject will not reduce the intensity of actual UV-light illuminating the subject.

    Now to consider the alternative light sources. I have experimented with many different UV-light sources and these are the ones I've found to be useful.

    UV torch (narrowband) for aiding liveview focus adjustment (if using this as the source of UV for imaging, it will result in a less colourful/more monotonous image):
    Budget: TANK007 3W 365nm UV torch [$$]
    Ideal: 5W Nichia-chip 365nm UV torch [low $$$]
    I would not recommend any lower power torches as they will not be strong enough to light the subject for focusing in liveview in UV. Ensure safe use of these torches by wearing appropriate eye-protection to prevent eye damage from the UV (don't look directly at the UV light)

    Xenon flash with uncoated Xenon tube (wideband):
    Most compact: Olympus FL-300R [~£100] (will need the fresnel lens removed which is relatively easy to do. It can be angled down by 30 degrees for macro and can even be triggered wirelessly - for more power use 2 or even more of these)
    Normal size: Canon Speedlite 199A [low $$] (has safe triggering voltage, also needs the fresnel lens removed, easily found on eBay and gives powerful UV output - even more than the Vivitar 283 & 285)
    Larger flash: Quantum T2/T4/T5s [high $$$] (including the D and DR models) with 150Ws output, and the Quantum X2/X4/X5s [high $$$-$$$$] with 400Ws output (very powerful UV output although at the expense of portability)

    Be aware that you should not use an old camera flash unless you confirm that it has a safe low trigger voltage, as some old flash have high trigger voltages which can damage digital camera circuitry. The above flashes are safe to use on digital cameras. Again remember to protect your eyes - I wear glasses which block UV but I still close my eyes before shooting with flash, to be absolutely safe.

    BT
     
  15. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    How to do custom whitebalancing for UV?

    The benefit of the Micro 4/3rds cameras is that they offer 2 custom whitebalance (CWB) settings (Sony Nex only has one); one of these can be set for the UV-pass filter, and the other can be used for visible light or IR whitebalancing.

    Q1) What do you use as the custom whitebalance reference for UV?
    Answer: There are UV whitebalance reference standards which can be bought, but they are expensive $$$. Hence it would be useful to have alternatives if you are unwilling to spend that money on a WB reference. I have tried various white material for this, including white sheets and WB lens caps which can be bought on eBay, but I've not been entirely satisfied with them (note: the WB lens caps will not work for UV WB).

    So my suggestion is one thing which is free (if you have them lying around at home) and does not need preparation. It is white polystyrene sheet/chips - it has worked well for me so far (in fact my preferred CWB is one done with white polystyrene chip). They are light so will not add weight to your camera kit, and when dirty can be discarded and replaced at no cost.

    For something sturdier but which requires preparation, you could buy white PTFE sheets £/$ on eBay which are cut to various sizes (buy one large enough to fill the sensor when the lens is pointed at it). Due to how these sheets are cut, the surface needs to be 'smoothed down/evened out' by rubbing the surface in a circular motion under a running tap with a piece of sandpaper. I learnt this cleaning technique from the manufacturer of the ultimate (i.e. expensive $$$) UV WB reference. I do use the white PTFE when testing lens/filter combos. Note: these WB references will need periodic cleaning.

    But be aware that while the polystyrene and PTFE sheets will get you pretty close, for the most accurate WB you will need to use the true UV WB reference.

    Q2) How do you do custom whitebalance for UV?
    Answer: Follow the manufacturer's instructions for doing custom WB, but with your UV-pass filter on the lens. Ensure that your whitebalance reference fills the entire screen and is evenly illuminated by sunlight (works even when the sheet is out of focus). This is what Panasonic and Olympus suggest for custom whitebalancing; Sony Nex only uses the center circle portion for CWB.
    I would try this in Aperture-priority mode first and let the camera choose the shutter speed. But if this is not possible and you keep getting an error message, then it is most likely that the lighting is too dark and you need to set a longer shutter speed (can be done in Shutter-priority or Manual mode). Once the CWB is set, it will give consistent results with the same lens/filter combo even with different subjects.

    Now with the right equipment and the know-how to do CWB, it is time for happy UV-imaging.

    Note: Credit for finding the PTFE white balance reference should go to Klaus Schmitt.
    BT
     
  16. kds315

    kds315 Mu-43 Regular

    149
    Apr 6, 2010
    Weinheim, Germany
    Please mention that fumbling with such Xenon flashes (removing front filter glass, removing coating etc.) is quite DANGEROUS, can cause life threatening electric high voltage shocks, so should only be done by experienced people after full flash discharge and prevention from recharging (batteries out, ac disconnect). Further there is a risk of breaking the high pressure Xenon tube which may cause eye damage!
     
  17. kwalsh

    kwalsh Mu-43 Top Veteran

    775
    Mar 3, 2012
    Baltimore, MD
    +Many.

    I am an experienced electrical engineer and despite that and taking extreme care when disassembling a disposable camera I managed to have the flash accidentally recharge and my finger hit the storage capacitor. That hurt - a lot. Besides removing a chunk of flesh from my finger I also nearly broke my hand on the desk behind me due to involuntary muscle contraction (imagine pivoting your arm in a windmill fashion with more force and velocity than you could ever voluntarily achieve and then encountering a hard desk with your hand). And of course I was very lucky, it could have been much, much worse - to the point I wouldn't be around to write this.

    On a related side note when I took a laser safety class years ago the instructor observed that the organization I worked for had never actually had any laser injuries in the many decades of laser work done there. On the other hand there were multiple fatalities from laser power supplies.

    In general, don't screw with anything that generates high voltage unless you have a very, very good reason to do so. It is rarely worth the risk and even experienced people make mistakes.
     
  18. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    I too had a jolt when I accidentally touched the electrical connector of the Olympus clip-on kit flash. This happened when I was replacing the fresnel lens back onto the flash after testing it for UV-imaging. I know to be more careful in future.

    Fortunately the Canon 199A flash and even the Olympus FL-300R do not require you to get close to the electrical connections. Hence it is much safer than modding the Olympus clip-on kit flash. In fact these are probably two of the easiest ones to mod for UV.

    BT
     
  19. tbyork2012

    tbyork2012 Mu-43 Veteran

    213
    Nov 14, 2012
    Oxford, UK
    I have updated the UV lens thread with further information.

    BT
     
  20. kds315

    kds315 Mu-43 Regular

    149
    Apr 6, 2010
    Weinheim, Germany