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N 50mm f1.4 and the mirror on the 5D

 
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MomoInu



Joined: 15 Aug 2006
Posts: 68
Location: Santa Fe, NM

PostPosted: Tue Jul 08, 2008 7:14 pm    Post subject: N 50mm f1.4 and the mirror on the 5D Reply with quote

I've got a question. In the FAQ section, conurus states that the converted N 50mm f1,4 Planar is "not recommended" with the 5D, saying that the rear elements protrudes sufficiently where is might interfere with the mirror.

I'm not sure why this would be the case. The N's 50mm Planar has the same optical design as the RTS 50mm Planar. I've used the RTS Planr with an adapter on the 5D without incident. Why would the N's 50mm be any different, given that the optical design is the same (even the published MTF's are the same). Wouldn't the rear element be in the same place in both lenses?
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conurus
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Joined: 15 Aug 2006
Posts: 795
Location: Vancouver, Canada

PostPosted: Tue Jul 08, 2008 8:33 pm    Post subject: Reply with quote

We have not yet conducted testing, so we chose to make a cautious statement recommending against it.

It is always safe if no part of the lens protrude past the rear bayonets. 7 out of 9 lenses in the N series have no protrusions at all, the 24-85 protrudes too little to pose any threats.

The last lens, 50/1.4, is venturing near the danger zone. The N version is identical to the Y/C version in optical construction, and the latter is known to pose no mirror clearance issues. However, as an AF lens the N version will focus slightly beyond infinity, thus the rear element potentially sits slightly closer to the sensor plane than the Y/C version. If the N lens is actually focused at infinity our experience with Y/C tells us there will be no problems, but we are concerned with the case where the lens is mis-focused and we do not wish to make any commitments until actual testing has taken place.

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John Black



Joined: 24 Jun 2007
Posts: 41
Location: Dallas, TX

PostPosted: Wed Jul 09, 2008 1:42 pm    Post subject: Reply with quote

Bo-ming is correct. The Contax 50mm F1.7 AE & MM and Contax 50mm F1.4 AE & MM are a mixed bag on the Canon 5D. Many variables - adapter thickness, lens is proper adjustment and Canon 5D mirror box are the easy ones.

http://www.pebbleplacephotography.com/forum/yaf_postst22_Contax-50mm-F14-Planar.aspx

http://www.pebbleplacephotography.com/forum/yaf_postst24_Contax-50mm-F17-Planar.aspx

http://www.pebbleplace.com/Personal/Contax_db.html

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MomoInu



Joined: 15 Aug 2006
Posts: 68
Location: Santa Fe, NM

PostPosted: Wed Jul 09, 2008 7:22 pm    Post subject: Reply with quote

Interesting.

Both the 50mm f1.4 MM and the 50mm f1.7 MM that I used on my 5D had no issues whatsoever with my 5D.

I have heard that there may be some variability of the size of the mirror in the 5D. I suppose that is the issue for some people how may experience issues with mirror clearance with these lenses.
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John Black



Joined: 24 Jun 2007
Posts: 41
Location: Dallas, TX

PostPosted: Thu Jul 10, 2008 4:51 pm    Post subject: Reply with quote

When it comes to 50mm and wider, plus Contax RTS manual lenses and the Canon 5D - take nothing for granted. It's about a 50/50 split of people saying X will work or won't work on their Canon 5D. Since the 5D has ~95% viewfinder coverage, it's surprising to me because that would imply the mirror is the same size as the 1Ds bodies, or smaller. People have stated that X lens with an adapter fits their 1DsX fine, but has mirror interference on their 5D. The implied conclusion is that the 5D mirror sits further ahead and/or has a larger support frame.

However, even that conclusion is suspect. To further complicate matters, there have been reports where a given Contax RTS lens & Contax/EOS adapter combo didn't clear on one 5D, but cleared on another. Something is happening at the Canon factory and they are adjusting the mirror box's position.

Looking at the Contax 50mm N, it does have a healthy overhang. The Contax 18mm F4 Distagon (MM) is known problem lens on the Canon 5D. On the left is the Contax 50mm F1.4 N and on the right the 18mm. I suspect Bo-ming's concern is the black collar. It appears to made of plastic, so shaving that down would be fairly easy. However, the rear element may protrude too far into the mirror box.



I do not have a calipers, so I cannot measure anything. This is just a simple illustration to show what Bo-ming is probably concerned about.

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Andi



Joined: 17 Jan 2007
Posts: 27
Location: Europe

PostPosted: Fri Jul 11, 2008 10:41 am    Post subject: Reply with quote

Hope! I have a ZF 1.4 50mm which I normaly use with an adapter which gives me spot on infinity. I just tried it with a very thin nikon to eos adapter, no problem. With this adapter I need to focus at about 8m to set it to Inf, meaning that the lens focused way past inf when set to the mark.

I guess it is a mount and not a lens design problem. Lenses like the 60mm Makro and 2/28mm touch the mirror on the mount and pass the glass IMO

Hope it will be convertable soon, thanks
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conurus
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Joined: 15 Aug 2006
Posts: 795
Location: Vancouver, Canada

PostPosted: Mon May 31, 2010 5:36 pm    Post subject: Reply with quote

We are officially removing the mirror interference warnings for these reasons,

1, it is true that the N 50/1.4's rear element does protrude past the mount by about 0.4mm, but I looked at a Canon EF50/1.2L and its rear element was protruding even more. If the latter had no mirror interference issues there is no reason why the former would.

2, by now, about 100 N 50/1.4 has been converted already but there has been no reports of mirror interference. Yes, we issued a warning but many of our customers are using the N 50/1.4 on the 5D mark II anyway.

3, in the manual focus world, adapter variations lead to unpredictable results, but we are converting each and every single lens one by one here, ruling out the big variable.

I think #1 is a very strong reason, in fact that alone is probably good enough for us to remove our warning.

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