Re: Apo stuff

["Willem-Jan Markerink" <w.j.markerink@xxxxx>]

(started on the Leica list, taken to private mail, but mighty 
on-topic on the IR-list, hence CC'd there....;-))

On 27 Jul 97 at 15:09, Henning J. Wulff wrote:
> 
> 
> >> Willem-Jan Markerink wrote:
> >>
> >> >I might have asked this before, but don't think I saw a confirmation:
> >> >Does the 70-180 still need focus correction for infrared film, or is
> >> >it a true APO in this respect too, just like all other Leica APO primes?
> >> >Does it show a red dot on the DOF scale, or is this mentioned in the
> >> >manual?
> >>
> >> Apo correction does not imply that refocussing for infrared is superfluous.
> >
> 
> We've been through this before, but...
> Apo correction means only that three colors are truly corrected for; these
> usually occur in the visible spectrum. Only the 250 Hasselblad, the
> 'Superachromat', has two correction points in the IR as well as being at
> least apo corrected in the visible region. The ONLY lens. 

Sorry, you are wrong. The UV-Nikkor is in the same league, and there
have been two older Asahi Ultra-Achromatic-Takumars as well (the
85/4.5 corrected from 220nm to 1000nm, the 300/5.6 from 400nm to
850nm). I believe Ken Sinclair has one of these beasts (Ken?).
There has also been a Hassy UV-Sonnar 105/4.3, corrected for both UV 
and IR (no data given in my books).

> Other lenses
> (including Leica's apo lenses, are very well corrected, but not necessarily
> in the IR. 

But this fact is even confirmed in the BAS reports!....8-))

> If you put an 87a filter over the lens, and load up with an
> appropriate emulsion, you will have to refocus virtually every lens made
> for general photographic use, including the Superachromat, as 1000nm is
> beyond its correction. 

My literature shows correction from 400nm to 1000nm....

> As for 1200nm sensitized emulsions, they are imaged
> by apo lenses at times, but these are corrected for three IR points, not
> for visible light. Some lenses are computed for even longer wavelengths,
> but these are sometimes not even achromats; their correction is for only
> one wavelength, and they are quite bad off that wavelength. IRTRAN based
> materials are often used for lens materials, with very sharp cutoff
> filters, or narrow acceptance sensors.
> 
> 
> >In my book, and that of Leica (at least primes!), Zeiss, Mamiya and
> >Angenieux it does.
> 
> I don't have any Leica 'apo' lenses, but I do have a Mamiya 150 which they
> claim is apochromatically corrected. It has to be refocussed for infrared,
> and that includes 800nm stuff. IR settings on lenses are typically computed
> for 750nm, in any case.

I was talking about the RB/RZ APO's, the 150mm for Mamiya 7 does not
have APO in its name, though it is indeed mentioned in the text.
Note that you can only have HIE in 70mm, not in 120/220, and the RB
is the only one with which you can shoot this format. I am pretty 
sure the designers had the combination of APO lens, HIE and 70mm in 
mind at one time. Konica hardly requires it, although even their Hexar 
allows two AF-settings for IR: 750nm and 850nm; the first for Konica 
750 IR, the latter for HIE.

> 
> >> It is unlikely that even if the 70-180 were a true apochromat for all focal
> >> lengths, one of the three correction points would lie in the infrared; and
> >> besides, which wavelength in the infrared is it you want the best
> >> correction for - it extends quite a way.
> >
> >This does apply to all Leica APO primes....I don't think they allow
> >two types of APO....either it complies with Leica standards, or it
> >doesn't, but I doubt they would call it APO in that case.
> 
> Since Apo doesn't have anything per se to do with IR, their lenses don't
> have to focus any IR reasonably; if they do, it is just a bonus. If you
> hold Leica (or any other company to the standard that apo lenses must focus
> IR in the same plane that the three correction points are on, you are
> holding them to a standard which they have not claimed; in fact, you are
> holding them to 'superachromat' standards, and only Zeiss has claimed, and
> achieved that commercially on one lens. Leica, and the other companies, are
> definitely capable of producing more such lenses, but have chosen not to
> for economic reasons, most likely.

It is not a bonus, both Leica and Zeiss are quite proud of this 
performance. I am quite sure this was intended from scratch.

 
> >I am pretty sure the above mentioned brands go up to 950nm at least,
> >otherwise they wouldn't claim perfect focus for infrared film. I even
> >don't rule out the possibility that it goes higher; there are some
> >special infrared films that go up to 1100nm, but those require
> >special handling (very cold storage, immediate processing).
> >
> >> It might need very little
> >> refocussing for most infrared photography, but the Apo designation goes not
> >> guarantee it.
> >
> >For the better brands it does....someone has to put the benchmark if
> >APO doesn't have a decent definition....;-))
> >
> 
> It does have a perfectly good definition. It has just been abused by
> companies from Rodagon to Sigma.

I was recently even more confused, as you might have read on the IR 
list....a Sigma rep claimed perfect focus for IR with their 
APO's....but until I get sufficient proof, I tend not to believe 
it....:-))
 
> Anyway, I thought this was better put on private e-mail, so as not to clog
> up yet another list with these minutae :-).

Aw, but this is fun stuff! 


- -- 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand


<w.j.markerink@xxxxx>
[note: 'a-one' & 'en-el'!]
*
****
*******
******************************************************
*  To remove yourself from this list, send:          *
*         UNSUBSCRIBE INFRARED                       *
*       to                                           *
*         MAJORDOMO@xxxxx                            *
*----------------------------------------------------*
*   For the IR-FAQ, IR-Gallery and heaps of links:   *
*  http://www.a1.nl/phomepag/markerink/mainpage.htm  *
******************************************************

------------------------------