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Finite objective on bellows

 
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AnselAdamsX



Joined: 13 Aug 2011
Posts: 7

PostPosted: Mon Aug 22, 2011 7:40 pm    Post subject: Finite objective on bellows Reply with quote

My first objective and adapter rings arrived today and I was doing some quick tests with different bellows extension. I was expecting that if I used the minimum bellows extension of my bellows with a 160mm objective that it would vignette. But it didn't. How small of an extension can be used and will corner sharpness or IQ go before it vignettes? I'm using a D300 with a PB-6 bellows and a PK-11A extension ring. I measured from the focal plane to the start of the objective and it looks like it's about 107mm. The objective is a Nikon 10x E 0.25 160/-.

Thanks
Chris
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5803
Location: Issaquah, WA USA

PostPosted: Tue Aug 23, 2011 3:40 pm    Post subject: Reply with quote

Unless someone has already tested and reported in with results on that specific objective you will have to tell us! Wink

There can be considerable variability between objective "models" in that regard.

With a (160mm TL) finite objective extended to its mechanical tube length of 150mm you should expect it to just barely "cover" an APS-C sized sensor with a good image. That's not to say you will not be able to "cover " the sensor with less extension, just that you might consider that a happy "bonus". But it is best you check out the image quality produced around the edges and corners before relying on it for making photographs.
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 18913
Location: Richland, Washington State, USA

PostPosted: Tue Aug 23, 2011 8:26 pm    Post subject: Reply with quote

I'm not sure it's exactly the same lens, but I've tested the Nikon Finite Conjugate 10X NA 0.25 160/- currently sold by Edmund Optics as being OK down to 6.9X on an APS-C sensor. See http://www.photomacrography.net/forum/viewtopic.php?p=57815#57815. In that case the IQ held up OK to the corners, but the lens developed significant curvature of field.

Yes, generally objectives will lose image quality far before they vignette. See for example the Nikon CF N 10X/0.30 illustrated at the link given above.

Charlie's comments are dead on, of course.

--Rik
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