conurus

aeronation · Joined: 31 Aug 2012 Posts: 7

Did anyone find that your Contax N 24-85 with EOS AF conversion got a wider angle in the full range? The 24mm looks like 21mm, and 85mm even got a wider angle than 70mm @ Canon 24-70L. If need to, I can post comparison photos later

hungmo · Joined: 11 Jan 2010 Posts: 35 Location: Hong Kong

Surprise me...

amhlee · Joined: 27 Nov 2007 Posts: 35

Pls post photo ....

aeronation · Joined: 31 Aug 2012 Posts: 7

I've attached the the lens comparison of Canon 24-85mm F/3.5-4.5, Canon 24-70mm F/2.8L and Contax 24-85mm F/3.5 -4.5 on Canon 5D Mark II body.

The top photo represent Canon 24-85mm, middle one is Canon 24-70mm, the bottom one is Contax 24-85mm with Conurus AF modification.

aeronation · Joined: 31 Aug 2012 Posts: 7

I've attached the the lens comparison of Canon 24-85mm F/3.5-4.5, Canon 24-70mm F/2.8L and Contax 24-85mm F/3.5 -4.5 on Canon 5D Mark II body.

The top photo represent Canon 24-85mm, middle one is Canon 24-70mm, the bottom one is Contax 24-85mm with Conurus AF modification.

all lens set as their maximum focal length, you can see the Canon24-70mm @ 70mm got narrower focal length than Contax 85mm.

amhlee · Joined: 27 Nov 2007 Posts: 35

Did you set it on a tripod ?

aeronation · Joined: 31 Aug 2012 Posts: 7

All those photos are put on a tripod while capturing.

lam · Joined: 27 Apr 2008 Posts: 127 Location: Bangkok Thailand

Good news , thanks for nice comparison.

I used to wonder why my N24-85 was so wide @ 24mm and fit my requirement for wide view that no need to purchase 21/2.8 distagon .

conurus · Posted: Fri Sep 07, 2012 7:47 pm Post subject:

very interesting. Did you experience the same phenomenon for objects at infinity?

aeronation · Joined: 31 Aug 2012 Posts: 7

I haven't tried on the infinity focus yet, I'll give it a try over this weekend. Secondly, I just bought the 70-200 from you and received it today, and do some comparison also. Finding the Contax 70-200 @ 200mm, the field of view exactly the same as my Contax 135/2 CY prime. And I compare with my Canon 70-200mm, it is also indicate closely to 135mm. I'll post the result within this week.

aeronation · Joined: 31 Aug 2012 Posts: 7

Data comparison from Contax official Document and Canon official Document about the 24-85 and 24-70

Contax URL: http://www.contaxcameras.co.uk/assets/pdf/Vario-Sonnar%2024-85_e.pdf

Contax 24-85/3.5-4.5
Angular Field: @Wide 84 degree, @Tele 29 degree

Canon URL: http://www.usa.canon.com/cusa/consumer/products/cameras/ef_lens_lineup/ef_24_70mm_f_2_8l_ii_usm#Specifications

Canon 24-70/2.8L
Angular Field: @Wide 84 degree, @Tele 34 degree

From the data, Contax should maintain the same wide angle as Canon does, but obviously Contax is much wider than Canon. In the Tele end, Data also shown Contax should get a narrow angle than Canon, but in realistic, Canon get a much narrower angular view.

aeronation · Joined: 31 Aug 2012 Posts: 7

Data comparison from Contax official Document and Canon official Document
about the 70-200

Contax URL: http://www.contaxcameras.co.uk/assets/pdf/Vario-Sonnar70-200_e_29-05-02.pdf

Contax 70-200/3.5-4.5
Angular Field: @Wide 31 degree, @Tele 13 degree

Canon URL: http://www.usa.canon.com/cusa/consumer/products/cameras/ef_lens_lineup/ef_70_200mm_f_2_8l_usm#Specifications

Canon 70-200/2.8L
Angular Field: @Wide 34 degree, @Tele 12 degree

From the data, Contax should got a narrower angle as Canon does, but obviously Contax is much wider than Canon. In the Tele end, Data also shown Contax should get little bit wider angle than Canon, but in realistic, Contax got a much much wider angle than Canon, and Contax is much similar to 135mm lens (18 degree)

conurus · Posted: Thu Sep 13, 2012 5:26 am Post subject:

I am no expert in optics... but the object distance is measured from the front principal plane and the image distance is measured from the rear principal plane. Those planes depend on the optical formula and could reside anywhere in the lens - or even outside of the lens! In any case, very unlikely to be the location where you set your tripod. (But admittedly your test shots are taken at a long-enough focusing distance for this effect to be negligible.) Zeiss always publishes this data in their literature but Canon never publicly discloses these parameters.

Also many lenses with internal focus designs have focal length changes as you focus closer, which I think is the primary reason for the anomaly you are experiencing.

Those were the reasons I suggested testing at infinity, since at infinity both effects were eliminated.