Tal 200k and Hutech Focal Reducer

[avandonk]

In between clouds managed to realign the main mirror of the Tal and using a Hutech focal reducer with the adjustment ring for 800mm as a start took some pictures of Carina as a test.
Details Canon 5DH,3X180sec at ISO 1600,LPR filter,stacked with Registar and adjusted for the usuals in Photoshop.
1.7M
http://users.bigpond.net.au/avandonk/Car_Tal_FR.jpg

The field is noticeably flatter than without the focal reducer see
1.3M
http://users.bigpond.net.au/avandonk/Car_Tal.jpg

There is also a smaller pic showing the latest version of the focuser.

It is now a matter of finding the optimum width of adjustment ring on the FR to suit the Tal.

Bert

[atalas]

Looking real good Bert !

[davidpretorius]

a great "test" photo.

i am unsure of the term "flatter", is it easily explained? I am looking at both images and not sure what to look for?

thanks bert

[avandonk]

It is often difficult to differentiate all the errors an optical system has. An illustration field curvature can be seen in the first picture below. If in a good optical system all aberrations have been minimised as the field of view increases field curvature becomes more obvious. A specially designed field flattener near the image can minimise this. It will not correct tangential or saggital errors(astigmatism).

Bert

[davidpretorius]

thanks bert,

so the same sorts of discussions we have wabout eyepieces and curvature towards the edges applies here.

It is starting to slowly sink in

Thanks again

[ving (David)]

yeah it is flatter with the FR on.
its a nice pic