Zero Back Focal Distance like IMAX Lens, How to design such anamorphic lens

<p>Hello ,</p>

<p>While surfing, I learned IMAX lenses have zero back focal distance<br>

and I want to design a water jet cut from single block glass ,<br>

no mount - mount is the glass block,<br>

two elements ,<br>

flat front and rear ends,<br>

anamorphic lens with <strong>zero back focal distance</strong>.<br>

<strong>I want the film slide on rear flat element.</strong><br>

How can I do it ?<br>

What are the formulas ?</p>

<p>Thank you,<br>

Mustafa Umut Sarac<br>

Istanbul</p>

<p> </p><div></div>

<p>"What are the formulas ?" - Complex, time-consuming to calculate by hand and too numerous to list here!<br>

You'll need some optical design software like Zemax. Or one of the free open-source optical design applications.<br>

http://arachnoid.com/OpticalRayTracer/<br>

or<br /><a href="http://www.sinopt.com/">http://www.sinopt.com/</a><br>

<br>

It looks like the rear element of the I-Max lens is more of a field flattener than a focusing group. I believe it's there to equalise the optical path lengths between the x and y focal lengths of the anamorph proper. I think trying to do the job with just two elements is going to result in very poor correction of aberrations, if it can be done at all.<br /><br>

<br>

I've just come across this interesting web-page that shows a number of wide-angle designs, some of which are quite simple, like the Robin Hill Sky lens: <a href="http://www.marcocavina.com/articoli_fotografici/CZJ_Perimetar_Sphaerogon_Pleon/00_pag.htm">http://www.marcocavina.com/articoli_fotografici/CZJ_Perimetar_Sphaerogon_Pleon/00_pag.htm</a><br>

None of them are anamorphic designs, but might be a starting point with the addition of a couple of cylindrical elements.<br /><br>

<br>

Anamorphic afocal attachments can be found occasionally, but they have little practical use now that digital manipulation makes stretching and stitching a simple process. The main limitation of anamorphic attachments is that they can only be used on lenses with a relatively narrow angle. They'll increase the AoV by 1.5 in one direction, but that absolute angle is limited to around 60 degrees. So just fitting a moderate wideangle and cropping does more-or-less the same job.<br /><br>

</p>

<p>It is possible that the cross section that you've shown is actually not two elements but four. The first looks like a positive achromat, while the second looks like a negative achromat. This would give the designer enough degrees of freedom to make a viable lens. Using aspheric surfaces would be a benefit as well but are very difficult to manufacture. </p>