![Amazon.com : Lightdow 900mm F8.0 Telephoto Mirror Lens + T2 Mount Adapter Ring for PK K20D K10D K200D K100D K-5 K-7 K-20D Work with Any Pentax/Ricoh DSLR/SLR K-X Adapter : Electronics Amazon.com : Lightdow 900mm F8.0 Telephoto Mirror Lens + T2 Mount Adapter Ring for PK K20D K10D K200D K100D K-5 K-7 K-20D Work with Any Pentax/Ricoh DSLR/SLR K-X Adapter : Electronics](https://m.media-amazon.com/images/I/71oaIZJqgjL._AC_UF894,1000_QL80_.jpg)
Amazon.com : Lightdow 900mm F8.0 Telephoto Mirror Lens + T2 Mount Adapter Ring for PK K20D K10D K200D K100D K-5 K-7 K-20D Work with Any Pentax/Ricoh DSLR/SLR K-X Adapter : Electronics
![optics - With this lens and mirror combination, should there be a third image formed? - Physics Stack Exchange optics - With this lens and mirror combination, should there be a third image formed? - Physics Stack Exchange](https://i.stack.imgur.com/jAyC4.png)
optics - With this lens and mirror combination, should there be a third image formed? - Physics Stack Exchange
![Mirror…Mirror… A guide to choosing and using mirror lenses Part 1 – Wayne John Grundy's PhotoTech Blog Mirror…Mirror… A guide to choosing and using mirror lenses Part 1 – Wayne John Grundy's PhotoTech Blog](https://advancedphototech.files.wordpress.com/2010/05/800px-schmidt-cassegrain-telescope-svg.png)