Help with spacing

[Lee_P]

Hi all,

I'm seeing streaky stars pointing away from the centre of my images -- which I think is a sign that my spacing isn't quite right. I was trying different combinations of spacing last night and made some improvements but couldn't get it quite right. Is there a way to get this right during the daytime, so I'm not wasting precious gaps between the clouds?

Thanks in advance!

[iapa]

Hi,

could you post details of the equipment that you are using please; will make diagnosis much easier.

also, an image showing the effects you are seeing in immensely useful.

cheers

[Lee_P]

Thanks for the reply, I played about today and am currently taking some shots to see if it's better! I'll post some pics if it's still off.

[Uranium235]

Unforunately, there is no way of testing for this during daylight hours. But is possible to make adjustments on a cloudy night by using an artificial star - as long as you are able to place it far enough away from your telescope (thats where it helps to have a really long garden!).

[iapa]

1 hour ago, Lee_P said:

Thanks for the reply, I played about today and am currently taking some shots to see if it's better! I'll post some pics if it's still off.

From your dog, if you are using an ED80 refractor, then One thing we can, probably, eliminate is coma, as that is generally associated with reflectors. 

You mentioned spacing, but no details of and spacers listed in the sig.

ate you using a failed flatterner for example?

[Lee_P]

I managed one picture! It's attached. It was unguided, which I hope explains the slight trailing. 

[iapa]

Again, not knowing all the details of you rig, and, I am no expert in any of this,

how is your guiding?

if your mount is not fairly  level east/west then you can get slightly stretched stars at the edges.

 I am also wondering if this is related to a slight tilt of you camera in the focuser?

Pls see sig.

[Lee_P]

I have an ASI1600 camera; filter wheel; .85x flattener / reducer; and ED80. It's looking a lot better than it was yesterday; I'll have another crack if the clouds clear. Thanks for your help!

 

[iapa]

ive  got  asi1600mm-c, mini efw and the equinox ed80 with  flattener. 

Usually use on AVX Mount

not set up just now, but I could set a rig up tomorrow and see what I get at night?

are you using any spacers between flattened and camera?

i didn’t last time I set that up.

[Tim]

The pic doesn't look too bad. Here is some general advice about spacing:

Normally, there is a critical spacing behind a flattener or reducer to eliminate coma as far as possible. Sometimes it is tricky to get this right. 

For a starting point, you need to know if there is a specified spacing for the flattener.

Next, check the backfocus distance of your camera. This will be the distance between the front edge of the camera and the rear face of the CMOS or CCD chip.

Subtract the camera backfocus measurement from the specified flattener spacing measurement and you are left with the amount of spacers you need.

Bear in mind that:

Sometimes spacers don't screw all the way in and become effectively longer.

Fine tuning can be accomplished using Baader Delrin rings, stocked by FLO and others. These also help prevent spacers welding themselves together.

There are adjustable length spacers available.

A vernier gauge makes it easier to accurately measure spacing.

You can never have enough spacers to muck about with!

Hope that maybe helps somebody....

 

 

[iapa]

Additional items are such as the Baader adjustable extensions e.g. https://www.firstlightoptics.com/adapters/baader-varilock-29-lockable-t-2-extension-tube.html

These also help for the smaller adjustments: https://www.firstlightoptics.com/adapters/baader-t2-delrin-spacer-ring-set.html

 

[Lee_P]

Thanks for all the advice, I think it's sorted now!