Flattener Distances

[Carole]

As I now have different scopes to what I started out with and also because of the Cooled DSLR box the existing flattener would not pass through the hole, I got myself a new flattener from Bern.  Also hoping it will "iron out" those seagulls in the corners of the images.  It comes with a par focal ring.  

Bernard said that the internal distance from the DSLR sensor to the front of the T ring is 55mm.
I found this chart on another forum and calculated my distance from front of T ring to parfocal ring, (draw tube side) to be between 50 and 55mm (both my scopes are F7.5).  



Just want to check if I've got this right, plus this is a flattener only (i.e. not a reducer).

Not had a chance to try it out yet due to crap skies, holidays etc.

Also not had a chance to try the Cool box out yet as was waiting for the above and now I find my 12V splitter does not work and I need x 3 (it's on it's way - I hope).  
1. Coolbox
2. Dew heaters
3 Cabled DSLR "battery".

Carole

[Rocket Pooch]

Carole,

Flatteners flatten you scopes curvature, so if you move the too far in or out it will introduce curvature.  On the Skywatcher ones it should be 55mm +- 1mm.

Only reducers like the AP67 reduce without flattening so you can use variable reduction and spacing.

Chris

[Carole]

Thanks Chris, I've got it set on about 52.5mm at the moment, so I'll walk it forward and see what I get, weather permitting !!!

Carole

[Mike]

The forecast for tomorrow night and all night is clear!! 

[Carole]

It's Imaging session, and not sure if I'll be bringing all my kit,  It's like moving house, but I guess I could have a go afterwards when I get home. 

Carole

[Carole]

Tried it out last night, no more seagulls in the corners, but top left corner the stars are slightly elongated, but the other corners look OK.

Im thinking if I move the flattener to sort out top left, I may mess up the other three corners.

Any thoughts?

Carole

[mickw]

I believe Mike was experiencing "top left" issues as well.

He was going to try imaging a star field, then rotate the camera to see whether the corners change - if the problem stays at top left that would suggest the camera or mod may be at fault, if the corners change, the scope/focuser could be the cause.

[Carole]

Thanks Mick, will bear that in mind.
It's certainly better than before. 

Carole

[Carole]

This is the test I did last night, this is not a final image as such, as it's not enough data, but just to show the result of the new Flattener.

http://gallery.orpington-astronomy.org.uk/albums/userpics/10047/Bubble_20-8-11_5mins_7_x_5mins_13_degrees_new_flattener_13_degrees_OAS_Forum.jpg

It's only 7 x 5mins, at 13 degrees.  Don't have the Peltier Coolbox working yet as waiting for a 12V splitter to arrive as I can't power everything up without.  

This is an example using the old flattener (examine the corners)
http://gallery.orpington-astronomy.org.uk/albums/userpics/10047/Witches_Broom_2-7-11_Rother_Valley_18_x_5mins_6_-_8_degrees_CROP.jpg


Carole

[Fay]

well the old flattener looks ok to me Carole

[mickw]

The image with the old flattener is a crop - the corners aren't there 

Having said that, the corners do look a bit square/diamond shape and the new flattener is quite an improvement.

[Carole]

The image with the old flattener is a crop - the corners aren't there

It's not a crop, you need click on the image to enlarge it and slide the scroll bar to the corners.

Bottom left and top right and bottom right are the worst they are all dagger shaped.  

Carole

[mickw]

Bottom left and top right and bottom right are the worst they are all dagger shaped.

That's odd, the new flattener seems to be causing the worst distortions in the area that was "better" - perhaps a bit more fiddling with the spacing is needed, but that might just make the spacing a "compromise"

[Mac]

looks like it has four corners to me,  
If it had no corners wouldn't it be a circle?

The bubble looks pretty flat to me.
I agree about the daggers in the old one though.

it could be that its not flat to the focal plane?

Mac.

[Carole]

it could be that its not flat to the focal plane?

Hmmm, I'll re-check I've screwed the parfocal ring on absolutely square, just to make sure.

Anyway, it's a lot better than before, thank goodness, as the new Flattener was NOT cheap!!!

Carole