Mickyj's Mindspillage

** Companion Video for this post is up on YouTube at http://youtu.be/UrvViq2Y7OE 

The first question I get is .. why?
Then I get told “Don’t Bother”.

The “Don’t Bother” is understandable. Almost anyone who takes UV photos uses a Nikon. Those that tried Canon got low contrast images, stopped down with large exposure times. Nikon exposures look great. I am a Canon man and I am going to see what I can do with Canon (Although I concede that Nikon may do this better and faster).

The “why” is simple. I want to see a part of the spectrum and patterns on items, outside of our normal view. Bees as an example, can see down to 300nm in near UV. Bees can see Nectar guides on flowers and navigate using images we can’t see. http://en.wikipedia.org/wiki/Nectar_guide

Living in Australia, beaten and sunburnt by the sun, I have a great opportunity to photograph in UV almost all year round. To help with the why, check out some sample photos. These are from LifePixel. A company that will modify your camera for you. http://www.lifepixel.com/galleries/uv-ultraviolet-photography-gallery�
(There are a few other options for ordering modifications throughout this post).

Here is one of my own images. This is a pure yellow flower.

More examples of UV photos and their Visual comparisons are available on Flickr

In the end, I want to photograph flowers in UV. They will not nessessarily be the best photos I have ever taken however will show items in a different light. This is going to be a challenge.

Modern camera’s and lenses are designed to reduce/remove UV from photos. UV also has different focus to visible light. Digital camera’s have limitations in their CCD / CMOS sensors. The sensors are covered with pass/block filters. Camera lenses are made from glass elements that can block UV and lenses can have multi coatings to remove UV. Everything is designed to prevent UV from getting into your photos. On top of these issues, camera response can be slow due to the lack of light entering the sensor and framing via the viewfinder is impossible. Live view can help somewhat.

So what is Ultraviolet (UV) and what am I trying to photograph? It is called Near UV. The Spectrum between 300nm – 400nm.
http://en.wikipedia.org/wiki/Ultraviolet�
http://en.wikipedia.org/wiki/Ultraviolet_photography

Only near UV is of interest for UV photography. Ordinary air is opaque to wavelengths below about 200 nm, and lens glass is opaque below about 180 nm. UV photographers subdivide the near UV spectrum into

• Long wave UV that extends from 320 to 400 nm, also called UV-A,
• Medium wave UV that extends from 280 to 320 nm, also called UV-B,
• Short wave UV that extends from 200 to 280 nm, also called UV-C.

So what can we do from here? Starting with the Camera.

The Nikon CCD camera’s, like the D70, are great for UV photos (Without modification). These and others in the range are recommended. I am using a Canon EOS 600d. Why am I not just going with a Nikon? (People have tested the Nikon and it works. People have tested the Canon and it was terrible!) I have an investment in Canon. I aim to use this camera with my other accessories. A full spectrum Camera would be of most use. I can use it for UV, IR or other. I can’t find people posting information on current Canon camera’s so I am taking the plunge. Most Nikons have moved from CCD to CMOS so now the brand is not a real differentiator. Silicon is the limiter.

This will be the first real web post/discussion on Canon and UV from an exploratory point of view, where the Canon will not be straight out dismissed.

Limitations in the SiCmos

So the first place to look at is the Silicon CMOS (SiCMOS) sensor. I have seen reports that the Canon EOS 1000d sensor can image the spectrum down to 380nm. The Canon EOS 60a apparently goes down to 200 nm (I was unofficially told by Canon technical support) but I doubt you can take a photo of anything that low. The EOS 7d, 60d, 600d, 550d all have the same sensor and reportedly go down to 305nm. I am picking the 600d, being the cheapest that is readily available to me in this range.

IR Block Filters

Now in front of the CMOS are the IR block and UV block filters (ICF/AA) and the sensor cleaning assembly. These need to be removed.

Choices for replacement of the filters (To maintain focus) include the Astronomik MC clear glass, Baader Clear glass, WG280, Schott WG-280, BK-7 and many others. All of these replace the block filters and make the camera full spectrum. The issue is that no matter how good the glass is, it can block some of the spectrum. Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths, whereas silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm When getting a conversion/modification, make sure to do your research.

There are many good modders out there and many dodgy ones. Take a look at these examples of bad work http://www.lifepixel.com/wall-of-shame

There are some good professional outfits like MaxMax, LifePixel, Spencers Camera and photo, HyperCams and many more. They can all mod your camera. For general mod’s of existing cameras or 2nd hand ones (IR, Full spectrum) look up cptconforti (Marcelo) on eBay.

To give myself the best chance, I want to go with a full spectrum clear medium in from of the CMOS that far exceeds the capabilities of the CMOS. I have selected Spectrosil fused silica (Quartz) which goes down to 180 nm.

This rules out the qualities of the Glass/polishing and means that the limitations are then the lens and CMOS sensor. http://heraeus-quarzglas.com/media/webmedia_local/downloads/broschren_mo/Spectrosil_syntheticfusedsilica.pdf 

http://optik.heraeus-quarzglas.de/en/productsapplications/productdetail_14208.aspx?psMarketId=1284&psApplicationId=12119

If you want to do the same, look up eeassa (Ehab) on eBay. http://stores.ebay.com.au/Digital-Landscapes  I can’t recommend eeassa and cptconforti enough. They have listened to my questions and tried to find solutions. They are both very proud of their work. cptconforti is also a photographer.

Here is one of the listings and it uses the Spectrosil

Many of the professional modders have offered to convert the camera to UV. This would leave me with a camera I can use by viewing through the viewfinder and snapping images but I am limited in spectrum. Going full spectrum I need to fit a UV filter to the lens and I can’t line up my image through the viewfinder as all visible light will be blocked.

MaxMax convert some cameras to monochrome removing the CFA and microlenses which greatly increases the UV sensitivity. They have done this with Canon.

The lens

Now I need to worry about the lens. Lenses contain glass. I can spend a huge amount of money and hunt down a purpose built Nikor Quartz lens (UV-Nikkor 105mm f/4.5s )

http://www.company7.com/nikon/lens/0105f4.5uv.html or get a lens that will not be as good as the Quartz lens, but will work enough for my amateur needs. Modern Standard lenses normally have many elements which block UV. They also have coating’s to prevent UV transmission. The Canon lenses with very few elements might allow light down to 350 nm through.

You can get a normal lens and remove the coating on the front/rear element (A quick way to destroy a good and expensive piece of glass). You need some material, plenty of abrasive polishing cream, and loads of time. The side effect might be a low contrast image. You end up with a nice soft focus lens. If you want to do this, take a look here

http://www.naturfotograf.com/UV_IR_rev05.html

Alternatively to destroying your lens, you can setup a bellows system and get some Nikkor EL enlarger lenses. These were used in the film days for enlarging images onto film from negatives. They pass a considerable amount of UV. Here are some reviewed for you

http://savazzi.freehostia.com/photography/el-nikkor_uv.htm

If you do this, make sure your bellows does not leak IR etc.

Focus

The next issue is focus. Camera’s are set to focus in the normal visible light spectrum. UV focuses at a slightly different position.

That is why older lenses have UV markings in red on them. This focus shift is an issue. Some Nikon lenses have very small Focus shift.

e.g. Nikon EL-Nikkor 80MM 5.6 Enlarger Lens

Filter

As this is a full spectrum camera (my reference camera for this exercise) I need to now block all light except UV. I need a UV pass, all other light block. Many of these types of filters leak IR. You can get filters from MaxMAx. Also there is Schott UG1, UG11, UG11x, Hoya U-360, B+W 403,Baader U “venus” filters.

I have gone with a Baader U telescope filter. This passes 320nm – 390nm. Another good choice is the Astrodon

http://www.astrodon.com/products/filters/uvenus_filter/

Just be sure to get the stepup/step down filter rings you need to mount the filter. The best responce is with the yellow side to the CMOS sensor 

Setup 

Now my setup is

• Full spectrum Canon EOS 600D with a Spectrosil fused silica modification
• Canon EF Macro lens bellows (And some Macro tubes)
• M39 lens to Canon EOS Adapter
• Nikon EL-Nikkor 75mm f/4 Enlarging Lens, filter size 40.5
• Nikon EL-Nikkor 80MM 5.6 Enlarger Lens, filter size 40.5
• Nikon El-Nikkor 1:4 50mm Enlarger Lens
• 40.5mm-48mm Step-Up ring adapter filter size 40.5 to 48
• 2″ Baader U-Filter 300-390nm UV Venus (Original version)
• Kood Plastic clip on lens cap for 40mm lens

Tricks

• Reverse-mounting the filter to get the yellowish side pointing towards the film/sensor plane is desirable.
• An artuiculated LCD is helpful in bright sunlight
• A towel over the head helps with glare on the LCD
• If you are worried about IR leak in your connections, take a test shot with the body or lens cap on
• Use metal macro extensions to try and mount the lenes different distances to the body to acheive focus of different lengths
• Make sure you use a custom white balance
• If the object is in the wind, you will get blur due to the exposure time. Pick your subject caefully and maybe move it ?
• Remember you are using UV. Wear a hat, glasses and suncream  

Focus experiments

I found using the 75mm lens I could get the lens base  mounted 22mm from the camera using Macro tiubes and could focus on items at 184 cm. Using a Bellows the lens base mounts at 36 mm from the camera and focus is at approx 16 cm.

 Additional material

Klaus is a well respected person working with UV. Check out his pages http://photographyoftheinvisibleworld.blogspot.com/2011/01/simple-tutorial-for-reflected-uv.html

David Kennard has some good information at http://www.davidkennardphotography.com/blog/811-ultraviolet-and-multispectral-photography.xhtml

 Learn more about UV black and White conversions and the removal of the CFA and microlenses with MaxMax http://maxmax.com/b&w_conversion.htm

Learn more about UV with Enrico Savazzi http://savazzi.freehostia.com/photography/uv.htm and check out the lenses he has tried http://savazzi.freehostia.com/photography/el-nikkor_uv.htm

Update 13 Jan 2013

I fitted the El Nikkor 50mm F/4 (34.5mm front filter thread) to the M39 adaptor today. The Canon Full spectrum camera was calibrated to focus at 50 mm. The M39 adaptor and lens fitted direct to the front of the Camera.

This gave pin sharp focus at infinity in the visual spectral range. As I do not have a filter stepup/step down for a 34.5 mm thread, I had to hold the Baader U 2″ over the front of the lens. I could not see if there was any focus shift in UV but I assume it is there.

Viewing the photos later did not show a focus shift with this lens. If the photo was not taken at infinity, there might be a different story.

I also tried the Nikon EL-Nikkor 80MM 5.6 Enlarger Lens. Screwing this to the M39 adaptor and then mounting to macro tubes and then the camera, did not acheive focus. Unscrewing the lens from the M39 a few turns, gave me focus. I will need to work out a  plan for focus. I only need the lens to be a few mm further from the camera to get focus.

Tags: Camera, Canon, DSLR, Ultraviolet, UV