Flare reduction and sunshade use in reflected UV ultraviolet photography

Today about flare redction when shooting reflected UV and the dedicated UV transmitting filters, like the Baader-U filter, my "work horse", for that. I'm using here my CERCO 94mm quartz fluorite lens, but in principle this method is applicable for any such lens. However, keep in mind, that quartz fluorite lenses for reflected UV are often single or even uncoated or show hotspotting, so it gets even more important to control flare efficiently, resulting in much higher image contrast and sometimes even removal of the hotspot. All images have been done at identical manual exposure settings, which were tested for correct exposure upfront.

Similar methods using such hoods have been used by others, I'm not claiming anything here, this just documents what I have done to further optimize my own setup.

[click on image to see a larger one]

Test images at nearly infinity (left to right) using (optimized for my camera's sensor size, other sensor sizes will require different sizes)

1) just the UV filter, no sunshade at all

2) a 40mm long sunshade with 50mm free diameter

3) a 50mm long sunshade with 21mm free diameter

The difference gets quite obvious, the longer and narrower the sunshade is, the better flare gets controlled.

Now some closeup shots, using the same method and sequence:

Also here shooting flowers at closeup, it gets pretty obvious, how much flare is present if using no or a simple sunshade, whereas a specilized deep and narrow sunshade results in much improved flare control, hence greatly improved image contrast.

Let me summarize:
Whenever shooting reflected UV (or other multispectral work), make sure to use the deepest and most narrow possible sunshade, that does not vignette, to achieve the best flare control and resulting in best possible image contrast. It is also suitable to control or even remove the effect of hotspots, some of those highly specialized lenses unfortunately show.

I have previously written about filter leakage HERE.

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos

A new apochromatic 60mm UV lens

Just today Coastal Optics has officially announced that they will release soon a new "UV-VIS-IR 60mm 1:4 Apo Macro high performance UV-VIS-IR lens for forensics, science, and fine art" in Nikon F mount (w. built in chip) for UV-VIS-IR covering a wavelength range of 315-1100nm.
It also sports an advanced floating element design for excellent close-up reproduction up to 1:1.5 magnification and consists of 10 lens elements in 9 groups. The chromatic error in the 315-1100nm range is said to be virtually zero. The design covers the full 24x26mm format which would make it suitable for all available UV capable cameras like the Nikon D200, D40, D70(s), the Fuji S3UVIR and S5UVIR. [Lens Image (C) Coastal Optics]


Informed sources mentioned, that the lens will be available in production quantities first quarter 2008.

Here is the link to download the published document on that new lens:
http://www.coastalopt.com/index.php?option=com_docman&task=doc_download&gid=29&Itemid=68


****** NEWS as of June 2009 ******
It has turned out a few days ago, that this high rated lens has a  serious hotspotting issue (UV+IR) from 1:1.5 to about 1:3 magnification especially at small apertures. It hasn't been noticed before by Pro's and ambitioned amateurs, so that comes as a big suprise. Coastal Optics made this issue public and is working hard to get that issue fixed which hopefully turns out not to be a design issue.
It will be reported here as soon as a solution has been found, so stay tuned!
****** NEWS as of January 2010 ******
Informed sources have stated that a solution has been found, yet officially Jenoptik (Coastal Optics new owner) was not willing to make a statement (yet),  if and when a lens without that hotspot will be available.
*********************************
In case you wonder about that hotspot and how that might look like, here an image shot at mag 1:1.5 and f11  (that hostspot is most prominent between 1:1.5 - 1:3, stopping down makes it more prominent)
Read more about it here.

(c) Andrea G Blum

 ****** NEWS as of  July 2013 ******

It has been found out that a very narrow sunshade is able to solve the hotspot issue satisfactory. The lens has not been modified in any way by the manufacturer so far.


Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos>