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In article <1992Aug11.165800.8441@swift.cs.tcd.ie>, mahonj@swift.cs.tcd.ie writes:
> Could anyone recommend a lens of about 50 mm focal length
> optimised for 1:1 reproduction ratio ?
> 
> This would be used with a c-mount video camera with an image
> sensor size of 8.8 x 6.6 mm so a wide angle coverage is not
> important.  What is important is the ability to resolve at
> least 10 microns (preferably much better than that).
> 
> I have already considered enlarger lenses, but I really want
> something for 1:1 which is outside their optimal range.
> 
> It should have an iris, and ideally a focus mount, but this
> is not critical.  Any fitting could be used.
> 

If you really need an optimised 1:1 flat field lens check out the Rodenstock
line. They make the type of lens you are looking for, but I don't have model
numbers. However, you probably don't need a very highly corrected lens, since
you are imaging onto such a small area. Any 35mm macro lens should give a
very good image over a 9mmx7mm square in the center of the field - even a
regular lens would do quite well. 10 micron resolution is only 100 lp/mm 
which is well within the resolution of almost any decent lens as long as you
don't stop it down too far (f11 maybe) and get into diffraction issues. The
optimised 1:1 process lenses will give very wide flat fields - and you will
pay for them! I'd try something like the Nikon 55/2.8 macro to start with.
I actually use a reversed Pentax 55/2.0 lens for in an aplication similar
to yours and find it works very well (certainly 10 micron resolution when
working around f8).

===============================================================
Bob Atkins  AT&T Bell Labs  email (direct)  att!clockwise!rma
===============================================================

In article <1992Aug11.165800.8441@swift.cs.tcd.ie>, mahonj@swift.cs.tcd.ie
writes:
> Could anyone recommend a lens of about 50 mm focal length
> optimised for 1:1 reproduction ratio ?
> 
> This would be used with a c-mount video camera with an image
> sensor size of 8.8 x 6.6 mm so a wide angle coverage is not
> important.  What is important is the ability to resolve at
> least 10 microns (preferably much better than that).
> 
> I have already considered enlarger lenses, but I really want
> something for 1:1 which is outside their optimal range.
> 
> It should have an iris, and ideally a focus mount, but this
> is not critical.  Any fitting could be used.

I recommend the Sigma line of lenses.  They make lenses fitting
all of the popular mount types (with the exception of c-mount).
You might try the Nikon auto-focus mount since I know that 
Nikon-to-c mounting adaptors exist.  The advantage of Sigma is
that they are cheap and every bit as good as the name brands.

I just bought a 90mm f2.8 macro that goes down to 1:1 with the
included life size adaptor lens.  I believe a 55mm version
exists also.  They are about $200 - $250 depending on where you buy
them.

In any case, be sure to specify that you want 1:1 capability
since many macros only go 2:1 or 4:1.  I've even seen
supposed micro lenses that only go 2:1 (figure that out!!)

As for resolution, on an f2.8 lens, the best resolution will
be at f5.8 or f8.  For a decent lens, this is typically in the
80-100 line pairs/mm range.  If you're imaging at 1:1 your resolution
may be limited by your sensor (i.e. 8.8mm /512 = 17 microns).

--
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|Dick Wallingford      | Internet: dickw@iastate.edu                 |
|Center for NDE        | Packet  : wd0anb@n0an.ia.usa.na             |
|Iowa State University | "This river don't go to Aintree" - S.H.     | 
+--------------------------------------------------------------------+

In article <1992Aug12.094518@IASTATE.EDU>, dickw@IASTATE.EDU (Richard Wallingford) writes:
> 
> As for resolution, on an f2.8 lens, the best resolution will
> be at f5.8 or f8.  For a decent lens, this is typically in the
> 80-100 line pairs/mm range.  If you're imaging at 1:1 your resolution
> may be limited by your sensor (i.e. 8.8mm /512 = 17 microns).
> 

The aerial resolution (i.e. lines/mm in the focal plane (surface) of the
lens) should be much more than 80-100 lp/mm for any reasonable lens. The
80-100 lp/mm figure is for the lens+film combination, where the film is
always a limiting factor. A halfway decent lens at f8 should resolve 
around 200 lp/mm (depending on your definition of "resolve"). Resolution
would drop to 100 lp/mm somewhere between f11 and f16.

===============================================================
Bob Atkins  AT&T Bell Labs  email (direct)  att!clockwise!rma
===============================================================

>In <1992Aug11.165800.8441@swift.cs.tcd.ie>, mahonj@swift.cs.tcd.ie writes:
> Could anyone recommend a lens of about 50 mm focal length
> optimised for 1:1 reproduction ratio ?

Another approach -- buy a double-threaded 49mm (or 55mm or whatever) filter
ring and attach two 50mm SLR lenses "head to head". This produces a symmetric
1:1 system that relays very flat, colour corrected image (24mm by 36mm format)
onto the film plane. Such rings are made for this purpose -- they are NOT the
same as reversing rings. Conventional C-mount or T-mount plumbing then puts
the assembly on the video camera or SLR body.

I would go with fast "prime" optics but would avoid using a superfast (f/1.2)
aspheric objective. The slower stock 50mm lenses are increasingly easy to buy
at camera shops -- many 35mm SLR buyers now opt for bodies only (so I guess
they are "non-objective buyers" :-) ) and then add a zoom as their first lens.

   /Alan Paeth
   VE3AWP/KD3XG