Why does my Field Flattener do this?

[TheMan]

I have had my Orion field flattener for a few months and I have been noticing that it is helping but still has some spherical aberration. I have a Nikon d3300 and I use the T-ring to mount it to the flattener, does anyone know why this happens and is there a way I can fix it? Any help is appreciated.

[Demonperformer]

Try enlarging the other corners and see what is happening there. As that is the bottom right corner enlarged, it looks as if the stars are pointing towards the corner. If that is the same on the other corners, then it could be that the distance to the chip is fractionally too close.

[Demonperformer]

As an aside, here is what the opposite problem (distance to the chip too far) would look like:

 

[TheMan]

12 minutes ago, Demonperformer said:

it could be that the distance to the chip is fractionally too close.

How could i make the sensor just a bit further away?

[Demonperformer]

One of these might do the trick (I am assuming T and T2 are similar, but worth checking before you buy).

[kirkster501]

Another possibility is that your polar alignment is not quite right and you are getting field rotation.

[carastro]

Quote

•  the opposite problem (distance to the chip too far) would look like:

 

I am puzzled by this as I was struggling to get my spacing right and all the stars in the corners were a bit like this, so having seen this photo, I assumed the distance was too much, but I spoke to Ian King and he said I needed MORE space not less.  I was dubious about this but tried increasing the distance and now the stars are just right.  So these images somewhat confused me as in my case it seemed to be the opposite way around.

Carole 

[Demonperformer]

Mmm ... I'm going to have to try to track down the original source of these pics before I can respond to that intelligently. I'm guessing I got them from another post, either here on CN probably - will see if I can find where. I know I'm not the only person to have shared these pics on SGL, so maybe someone else will be able to comment.

[Merlin66]

They came from the Baader website.

 

[Demonperformer]

Thanks, Merlin.