> Dear Yuri,
>
> Thank you very much for your clear answer. I'm not an optician, but
> would like to know how about for AP140, AP160, AP130 + AP focal
> reducer? Is it under control for various aberrations such chromatic,
> spherical, astigmatism as well as coma.
>
> If TEC do focal reducer like AP did in the same performance but for
> TEC refractor scope(TEC140). Is it possible? And can you let me know
> (or Mr.Roland) about optical configuration of AP reducer?
>
> If there is no way. I may be have to buy a short focal length
> refractor for wide field imaging like Tak 106 or close focal length.
>
> Thank you very much.
> Best Regards,
> Pornchai POP

Dear Pornchai,
If you take a look on William's images made with APO140 + AP 0.75X
telescopressor - you will see that this combination works, but you may
see elongated stars at the edges for the FOV of his camera Nikon D50.
If we do two-lens telecompressor it will work similar way.
For better result and wider field a min three-lens corrector with ED
element must be done, that will cost ~$2000 ...
So, if the goal is wide field imaging - buy TAK!

A specially designed telescope for imaging could be the answer, and we
are working on such one, it will have F5.6 focal ratio and flat field.
I will not add more details until we finish and test prototype.
But I expect that if it works and be available, some time later people
will ask a focal reducer for that unit too... :-)

Best regards, Yuri