[UV] Noflexar 35mm with Focal Reducer for Ultraviolet Photography

Here after having previously tested that with a quartz / fluorite achromat, now about using this focal reducer method to change the focal length of a Noflexar f3.5/35mm lens, a very well used lens for UV photography, to widen the field of view. This is also known as telecompressor in astronomy and it is the opposite of a (negative) Barlow lens. Here a positive (quartz in that case) element is used which achieves a 0.86x reduction, hence the lens now behaves as a f3/30mm lens. Here some results using some Phalaenopsis orchids.

[click on image to see a larger one]

no reducer full format:


no reducer 100% crop:



0.86x reducer full format:


0.86x reducer 100% crop:


As you may see, the image quality is hardly affected, even by this simple solution. Focus shift is a little increased, but hardly visible. Next step would be to try out a larger reduction factor. The visible vignetting is caused by a too small reducer lens and will disappear once I have a larger quartz reducer lens one on hand.

P.S.: Just made a test with another quartz focal reducer lens, achieving a) a 0.78 reduction factor and b) the vignetting is gone. That now makes a f2.7/27mm lens out of the Noflexar f3.5/35mm.

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

[UV] Focal Reducer or Telecompressor for Ultraviolet Photography

You may remember the recent contribution about using older quartz fluorite parts for taking UV images. It turned out to be a f4/84mm lens.

Here now about a modification of that to change the focal length, specifically using a focal reducer to widen the field of view which also means reducing the focal length. I'm using a focal reducer method, also known as telecompressor in astronomy and it is the opposite of a (negative) Barlow lens. Here a positive (quartz in that case) element is used.

Here some results. I'm showing full format shots here.

[click on image to see a larger one]

without focal reducer:


focal reducer at work:



I measured he reduction factor to about 0.41x and still, there is hardly any focus shift (no adjustments done between shots). In theory the speed of the overall system would change from f4 to f1.6 and the focal length from 84mm to 34mm - we have created a wide angle f1.6/34mm achromatic UV lens now.

Cropped image of focal reducer at work:


BUT, there are downsides which have to be mentioned: the whole projected image of the quartz/fluorite lens system is reduced in size, so the outer, less sharp and well defined image parts will now be visible, which before was cut off by the sensor size and mechanical restraints. If the image projected is not large enough, the vignetting will appear and only part of the sensor will be filled. So this method requires an image size that is at least 2.4x (1/reduction factor) larger before using that focal reducer. And another downside: the back focal distance will also be reduced, so this only works well, if before the system had enough working distance between lens and sensor as in this case 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

[UV] White Clematis in ultraviolet light using a quartz Focal Reducer lens

More shots using my white Clematis hybride I recently got. Here now using that before presented Spectrometer Quartz Fluorite Achromat f4/84mm lens with a 0.42x quartz Focal Reducer lens to make it a f1.7/35mm lens.

[click on image to see a larger one]

This UV image here also uses my standardized false UV color normal + high intensity palette:



White Clematis in UV:


and in visible light (VIS):


Differential VIS-UV:


The VIS-UV differential clearly shows, that despite the Focal Reducer, still hardly any focus shift is present.

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