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Nikon CF Plan 50X 0.55 inf/- EPI ELWD, initial impressions
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Bob S



Joined: 07 Aug 2010
Posts: 16

PostPosted: Sun Dec 12, 2010 10:14 am    Post subject: Reply with quote

I am surprised that you did not find a decrease in image quality when you changed the focus of the telephoto lens to the near limit. Changing the focus of the rear lens away from infinity is optically equivalent to creating a tube length error in a finite objective, and should give noticeable spherical aberration in a high-NA objective.
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Blame



Joined: 14 May 2010
Posts: 342

PostPosted: Sun Dec 12, 2010 12:37 pm    Post subject: Reply with quote

Are you sure you have reached the limits with this lens?

Try using it with the 120mm lens on its own without the 1.4x.
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morfa



Joined: 12 Oct 2009
Posts: 556
Location: Stockholm, Sweden

PostPosted: Sun Dec 12, 2010 3:09 pm    Post subject: Reply with quote

Bob S wrote:
I am surprised that you did not find a decrease in image quality when you changed the focus of the telephoto lens to the near limit.


Yes, more careful testing is required here. Like I said, I only did a quick comparison using magnified live view. It would be better to compare stacked images side by side.

Blame wrote:
Are you sure you have reached the limits with this lens?

Try using it with the 120mm lens on its own without the 1.4x.


No, I'm not sure of that! I have used it without the TC on the 12cm – no black corners or visible vingetting but corner performance wasn't impressive. That said, the 12cm is very far from impressive in the corners when focused on infinity without an objective in front of it (I've tried it for landscapes and the corners were very soft).

I've also briefly tried using Micro-Nikkor 105mm f4 as a tube lens (without TC). Again – no problem with dark corners as I recall it, but the corners seemed a bit funky upon live view inspection.
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Blame



Joined: 14 May 2010
Posts: 342

PostPosted: Mon Dec 13, 2010 2:10 am    Post subject: Reply with quote

Don't knock poor corners too much.

With the test you did they count, but consider full portrait of a small insect. You might not be able to get it all in with the 200mm, but with 120mm you may, and the irregular shape gives you a good chance of avoiding the corners, or at least avoiding putting an important bit in it.

Poor corners are considered irrelevant or even an advantage (concentrating the viewers attention on the subjects face) with human portraiture. I don't see why a flea should be treated differently.
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morfa



Joined: 12 Oct 2009
Posts: 556
Location: Stockholm, Sweden

PostPosted: Mon Dec 13, 2010 3:31 am    Post subject: Reply with quote

Blame wrote:
Don't knock poor corners too much.


I basically agree with you. In fact I've expressed very similar views a couple of times in the past on this forum. That said, I have experienced that I can become quite annoyed with bad corner performance in real images (as opposed to just test images) even if just some very small part of the subject is affected by this (and this is quite possibly something I've acquired from spending time on this forum).

Besides, at 30-50x magnification I'm most likely to be focusing in on some very small detail of something much larger than the FOV and therefore chances are high that one or several corners will be occupied by something "of value".
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