Wednesday, March 6, 2013

Reducer Flattener Testing

I've been on a quest to find a well-matched reducer/flattener combo for my SV4.

This scope is a F6.41 fl 655mm 102mm diameter apo, LOMO triplet with OK4 glass.  It's a rareish beast in that it falls between the short astrographs and long triplets.  

It's already pretty well corrected and the SSF6 flattener does a good job of controlling the star images out to the edges of the field on an APS-C sensor.  I've always wanted a little bit more, though.

So, everytime I can see a new reducer design available in my price point, I try it out.

  • I've tried the Televue TRF 2008 - with ugly results.
  • I've tried the WO Type II - also with ugly results, although not as bad as the TV.
  • I've also tried the Astronomics one for ED F6 scope - and this has been the best so far.
  • I recently tried the WO Type 6 for F6 scopes.  It also is not so good.



Here is the image from CCD inspector for the WO Type 6:

Not so great. 

Compare with the Astronomics:

Both were taken under similar conditions - 30 second exposured at 100 ISO of the beehive.  Focus was at 1/3 out from the edge.  The astronomics exhibits some interesting coma shapes - the star images are not radial.

See how the upper left and right are radial and the lower left and right are not.  Very strange.  Most likely either a centering or collimation issue.  Centering can be fixed.  Collimation can't.

When I get the chance, I'll do another run of the SSF6 flattener for comparison.

The only processing that I've done with these images before sending them to CCDI was to platesolve and run the bad pixel map on them.  Incidentally, the run of the bad pixel map made a massive difference in showing real star images.  Exposed a lot of the failures of the system.