Focal reducer help please

[mickw]

I have been experimenting with a borrowed focal reducer/flattener to get rid of egg shaped and improve FOV.
Here are crops of the bottom left corner of 3 raws straight from the camera with no processing, they are not from the same area of the sky, but I've yet to hear of a constellation where the stars are sausage shaped  
1st is with no FR, 2nd is with FR and 3rd is with FR and 5mm spacer.

No FR

Full size http://gallery.orpington-astronomy.org.uk/albums/userpics/10049/ss-L_NGC6888_No_FR.png

With FR

Full size http://gallery.orpington-astronomy.org.uk/albums/userpics/10049/ss-L_7000_FR_no_spacer.png

With FR and 5mm spacer

Full size http://gallery.orpington-astronomy.org.uk/albums/userpics/10049/ss-L_7000_FR_with_spacer.png


As the star elongation gets progressively worse, I assume that the FR needs to be closer to the CCD by an unknown amount
There also appears to be some vignetting.
Am I right ?
Comments anyone ?

*************Updated with full sized images*****************

[Rocket Pooch]

Not a WO MK3 by any chance is it?

Chris

[RobertM]

Are these all full frames? - the first doesn't seem right for no FR.  If it isn't full frame then can you post it.

[mickw]

Not a WO MK3 by any chance is it?

Nope, it's John's Mk2 that I borrowed

Robert these are crops (bottom left corner) of full frame just converted to PNG.
The full sized images are 15 meg and the gallery doesn't like them, I tried resampling them down to a manageable size but resolution disappeared    I've added links to the full "scale" versions if that's what you mean
All three images are the same scale but not necessarily the same size (crop)

I did have issues with eggy stars in the corners without a flattener which is why I started experimenting

[Rocket Pooch]

Hi,

With John's FR the spacing from the FR to the chip is 55mm which is that FR to a t adapter, no spacer required.

I guess it might not be well matched to your scope?

Chris

[RobertM]

If the four corners are exactly the same and the FR distance is correct then I agree with Chris.  It looks to have overcorrected too much to me.

Robert

[mickw]

I guess it might not be well matched to your scope?

That's what I was thinking.

The corner to corner size is the same on all the originals, the cropped corner distance will be different.

The only option seems to be a universal/adjustable flattener like the Hotech or TS - Or choose smaller subjects and crop out the crap 

I wish that TS quad was more reliable.

[MarkS]

The distortion is not symmetrical in each corner.  So either field rotation is taking place (the 3rd image certainly looks like it) or the optics are not properly aligned (saggy focuser?)

By the way, which scope are you using?

Mark

[mickw]

Mark, the images are crops. Bottom left corner is bottom left of full frame, but top right is roughly centre of full frame - I'll try to upload full frame images.

All taken with the Burgess 91

*****************First post updated with full sized images**************

[RobertM]

Collimation looks out (top-left to bottom-right) bit in any case I think something like the TS flattener may be your best bet (bit pricey though).  Have you checked forums like cloudynights to see what others are using successfully?

Robert

[mickw]

Collimation on a refractor 

I tried CN a few months ago, nobody confesses to owning a Burgess, let alone a flattener for it. but it's worth a shot

[The Thing]

Can't Burgess help?

[mickw]

Burgess are even worse than Pulsar at replying to emails 

There's a Burgess forum, but there's only a couple of 91 owners and only one gave a sensible reply to the question.

Astro Tech seems to be a possibility.