Topic:	Rodenstock Apo-Rodagon-N 4/75
Author/Copyright:	John Jovic

The Rodenstock Apo-Rodagon-N 75mm F4 is not a very common lens. The exact period that is was sold is uncertain but it appears the lens was sold from approx 1998 to approx 2008[1].

Specifications

The engineering drawing and test report for the Apo-Rodagon-N 75mm lens have been kindly supplied by Rodenstock (Germany) and are reproduced here with permission.

The data in the table below has been extracted from the above drawing.

Rodenstock Apo-Rodagon-N 4/75 Focal Length (mm): 75 Maximum aperture (F): 4 Lens construction (elements - groups): not stated Angle of coverage: 53° Recommended negative size (mm): 60x60 Minimum aperture (F): 22 Number of aperture blades 5 Designed magnification: 1:10 Useful magnification range: not stated, at least 1:2-1:10 Achromatized wavelength range (nm):   Distortion at basic magnification (%):   Focal length design value (mm): 74.7 Barrel outer diameter A (front) (mm):   Flange mount thread size: 39x1/26 Filter size (mm) M40.5x0.5 Barrel outer diameter B (rear) (mm):    flange focal length (mm):  68.7 Back focal length (mm):  59.3 Distance from flange surface to the second principal point (mm):    Principal point spacing (mm): -2.5 Total length (mm):   Weight (g):   Coating:

Application Notes

The lens has a Leica or M39 x 1.0 mount and can easily be mounted to a camera using a helicoid or bellows, depending on the intended application and magnification required.

The filter thread is the common (for enlarging lenses) M40.5x0.5 and allows lens hoods or reversing rings to be used. A lens hood should be used whenever possible.

Sample Images

Unless stated otherwise all the sample images below were photographed using a Canon 5D2 and a Nikon PB-4 bellows. A lens hood was used in all the images below.

This lens seems to have very high resolution and excellent colour and contrast even wide open.

Like most enlarging lenses it shows some axial or Longitudinal CA but not enough to be objectionable.

Although probably intended as a machine vision lens this lens may not have been designed to photograph three dimensional objects so bokeh was probably never a consideration in it's design. None the less this lens shows relatively soft and smooth bokeh behind the focus plane and quite harsh bokeh in front. The bokeh is typical of a lens which has been under corrected for spherical aberration.

	Computar dL 5.6/135mm enlarging lens photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera.
	Computar dL 5.6/135mm enlarging lens photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera.
	Computar dL 5.6/135mm enlarging lens photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F16 on a Canon 5D2 camera.
	Computar dL 5.6/135mm enlarging lens photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F16 on a Canon 5D2 camera.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid for focusing.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid for focusing.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid for focusing.

Hot Spot or Flare Spot

The sample images below were photographed using a helicoid and the same lens hood as all other sample images shown on this page yet some of these images show a bright spot in the centre of the frame called a Flare Spot or Hot Spot. Whilst this may not be entirely attributable to the lens itself, which seems to show excellent flare resistance and very high contrast in normal use, the use of helicoids and other focusing mechanisms may contribute or even cause these issues when used in certain circumstances. Whilst more testing is in order it is none the less worth noting that the potential for a hot spot does exist under certain conditions.

	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid for focusing. This image shows a Flare Spot in the central area of the frame. This image was taken with a very bright reflection to one side of the image, and also just outside the frame, even though the subject itself was quite dark. It is likely that this Flare Spot was only visible because the subject itself was very dark relative to the Flare Spot created by the bright light outside the frame.
	This is the exact same subject as in the above sample, using the same camera, lens, helicoid and lens hood yet there is no sign of Flare Spot or any Veiling Glare at all. Unlike the previous sample image there was no bright light outside the frame to cause the flare.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid for focusing. A mild but significant Flare Spot or Hot Spot can be seen in this sample image for the exact same reason as the previous example. The subject itself is very dark yet the area outside the frame is very bright, in this case a white engine bay and car body with enough stray light to contribute to a Flare Spot.
	Here the same subject is photographed with negligible if any Flare Spot or Veiling Glare at all, possibly due to less stray light at the periphery of the frame. The exact same camera, lens, helicoid and hood were used as above.

Sharpness at Infinity

The images below show wide open centre and edge sharpness at Infinity. It's common to see poor edge performance with enlarging lenses when focused at Infinity however this lens seems to perform quite well.

	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid to enable infinity focus. See centre and edge crops below.
	Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 focused at infinity. 100% unsharpened crop from the centre of the frame.
	Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 focused at infinity. 100% unsharpened crop from the left edge of the frame. The lens was focused in the centre of the frame and was not refocused for optimum focus at the left edge.

Although this lens is not optimised for infinity there does not appear to be any significant deterioration in image quality even when used wide open. Rodenstock Apo-Rodagon-N lenses are typically intended to be used stopped down one or two stops depending on the lens in question.

	Photographed hand held (at 1/125th sec, ISO200) with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid to allow infinity focus. See unsharpened 100% centre and corner crops below.
	Unsharpened 100% centre crop from the above image.
	Unsharpened 100% crop from the above image from the bottom left hand corner.
	Photographed with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid to allow infinity focus.
	Photographed handheld (at 1/100th sec, ISO200) with a Rodenstock Apo-Rodagon-N 75mm F4 lens at F4 on a Canon 5D2 camera using a helicoid to allow infinity focus.
	Unsharpened 100% centre crop from the above image.

 

References
[tbc]	To Be Confirmed. The information has not been confirmed by a credible source.
[pc]	Photo Cornucopia. Measured or personally observed by the Author.
[1]	"Linos Präzisions-Objektive". http://www.stemmer-imaging.de. accessed July 29, 2015 http://www.stemmer-imaging.de/media/uploads/websites/documents/products/optics/Qioptiq/de-Qioptiq-Rodagon-OLIN1-201311.pdf

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