ST with built-in flattener

[Coastliner]

Hi All,

Are there any short-tube refractors out there with a built-in field-flattener? Not the Primaluce Lab ones, too expensive!

Thanks,

Neil.

[Guest]

Hi Neil,

 

There are few very good short tube REFRACTORS with built in field-flatteners, like this one.. TSAPO71Q or this one William Optics WO-Star 71mm f4.9 Imaging APO Refractor - 2.5" Focuse

Regards

 

Martin

 

 

[michael.h.f.wilkinson]

Most Petzval designs tend to be expensive. I think Bresser did bring out a Petzval 152mm F/5 some time back, but the newer models seem to be simple doublets. There are several suppliers of smaller quadruplets, some of which initially had problems with pinched optics. but that seems to be sorted, AFAIK

[Guest]

I have this BIEST  TSAPO71Q and it is a light machine (f4.9).. and a lightweight (2KG) also and the best part about this quadruplets are, no need for an extra flattener or reducer and no need to stick to backfocus or calculate the backfocus as you must when you have a flattener or reducer involved, you just attach the CCD or EOS and focus until you have the perfect star and you are done..

  

[Coastliner]

Thanks all, much appreciated. Looking at the Williams Optics ones, why is there a thermometer on the focuser? What use is it?

[Alien 13]

1 minute ago, Coastliner said:

Thanks all, much appreciated. Looking at the Williams Optics ones, why is there a thermometer on the focuser? What use is it?

The thermometer looks cool and I find it useful for judging cool down time..

Alan

[MattJenko]

Also, focus can change as the temperature changes, so if you have an autofocuser, it can use the temperature sensor to either refocus or use preset focus moves dependent on temp changes.

[Louis D]

The first one that came to mind here in the states is the AT65EDQ 65mm f/6.5 ED quadruplet astrograph from Astronomics (Cloudy Nights sponsor).  It's not as fast the others listed above.