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View Full Version here: : MT-160 - Colour fringing?!?!


Lognic04
02-09-2017, 09:17 AM
I am really confused as to why mt MT-160 newt is showing colour fringing? I am pretty sure it is coming from the flattener, but it is at the correct 61mm spacing. Help! :confused2:
Image attached.
:help:

Atmos
02-09-2017, 10:08 AM
How close to the horizon were you imaging?

LewisM
02-09-2017, 11:14 AM
Atmospheric dispersion/refraction

Bad Bayer matrix in the camera

Problems with the orthogonality of the reducer/gflattener (which would not surprise me judging by the bodgy fitting that was supplied to you)

If that's the corners, you either have a spacing issue, the reducer/flattener is not orthogonal as discussed, or your tracking is not working (but that would show in all corners etc)

I think it will be somewhere in the focuser side of things for sure

Lognic04
02-09-2017, 11:49 AM
This was 30-40 degrees up - might be the reason.
but also, in the corners the stars turn into a 'c' shape, i dont think it is the spacing, but here is my setup: dslr44mm > tring10mm > 6mm t extension > flattener, so within the 2mm sweet spot.
Lewis, how do ensure that the flattener is orthogonal?
PI maps attached, looks like i do have some problems:
:help:

LewisM
02-09-2017, 02:53 PM
Looks like tilt to me, and perhaps a slight spacing issue too.

Lognic04
02-09-2017, 04:19 PM
Lewis, what can i do to fix tilt? all i have seen is to get a better focuser...

LewisM
02-09-2017, 06:14 PM
Lots of ways - getting a proper reducer/flattener adaptor rather than that bodged up one sold to you will help - it looked askew to me just looking at it!

Also, remember to have the camera pointing straight down when imaging with a Newt.

Astrofriend
03-09-2017, 06:33 AM
Hi Logan,
If you rotate your camera 90 degrees you will see if focus at the corner changes and move. Then you maybe have a tilt.

If the corners are out of focus in all corners then maybe the distance between coma corrector and sensor is wrong, can you fine adjust it or is it fixed?

Is your camera sensor bigger than the image circle from the coma corrector?

I can see what telescope you have, but what camera and coma corrector?

If close to the horizone maybe this will help:
http://www.teleskop-express.de/shop/product_info.php/language/en/info/p8504_ZWO-Atmospheric-Dispersion-Korrektor-ADC.html

Takahashi must be the telescopes Rolls Royce.

/Lars

multiweb
03-09-2017, 09:32 AM
hmmm... I don't know. That's a level of colour fringing I could easily live with. That's not fringing really. Likely to be debayering process/sampling. Nothing major here. Correctors depending on quality and any glass will always introduce a little chromatic abberation.

Atmos
03-09-2017, 10:51 AM
It is this kind of fringing that I sometimes see in far more expensive systems from much more experienced photographers. In those cases it is atmospheric but it can be caused by a multitude of other issues as well.

Your best way to test would be to image something high in the sky and see if it is there as well.

gregbradley
03-09-2017, 11:47 AM
Do you have a full sized sample image? Its hard to tell what's going on from that image. Is that a corner crop?

What was the camera setup? Is the scope well collimated?

Tilt can be corrected with spacers. I developed a procedure to handle tilt. Tilt causes one or more corners or even sides of an image to have elongated stars. Not all corners, one or two corners will be sharp and the other 1 or 2 will not be. Sometimes one side is good the other is bad. That's tilt. All 4 corners off would be spacing issues. Comet shaped stars would be collimation.


Greg.

Astrofriend
18-09-2017, 03:48 PM
I rebuilt one of my adapters to let it be both a tilt adjuster and lenght adjuster. It works very well but it's very sensitve to adjust it.

Here is how I did it:
http://astrofriend.eu/astronomy/projects/project-mechanical-construction-adapters-for-apo-refractor/project-mechanical-construction-adapters-for-apo-refractor.html#part08

The cone that holds the adpater in another place is a bit weak to hold this heavy DSLR camera. Have to tight it firmly to not get problem with hang.

/Lars