stargazermanc

So this evening I managed to set up and the collimation was indeed out so I spent some considerable time making alterations at different focus and as you can see from the pictures, the collimation is as good as I can get it with a camera versus a high powered eyepiece.

I checked several times going out of focus and back in so pretty confident that it is now sorted. Unfortunately the clouds rolled in so I didn’t have time to take any proper test stacks but from the test shot I did get, it does look like a tilt issue which could be my next headache.

5 minutes ago, michael8554 said:

 

What magnification are you using for those Airy disks ?

You need around x400 for the final tweaks.

Michael

None, it is being done using a camera as I said in a previous reply. 

In terms of the tilt, I don't think this is the camera side as I use it regularly on my redcat and zs73 with zero tilt. It could be my mirror which has been suggested on another forum.

4 minutes ago, catburglar said:

I platesolved the middle image at 109.5mm spacing- it works out at 0.603 arcsec per pixel and an effective focal length of 1286mm which is almost exactly on spec for a 2032mm fl and 0.63 reducer- which should give an effective focal length of 1280.

Still not sure what's causing the dodgy star shapes.

So you think the second image is the more accurate back focus distance?

I am going to check the collimation. Once I have sorted that and got as close as I can on the backfocus then I can start looking at the tilt.

1 hour ago, Same old newbie alert said:

I always approach focus from one direction, same with collimation I approach from the same way, go through focus and get my donut..The reason I do this is because on my scope my donut is different either side of focus,as you can see... So I focus in the + direction on my XLT version, go through focus and collimate from there

 

 

Thanks for the tip.

34 minutes ago, jacko61 said:

At face value, the third photo looks to be closer to the correct back focus than the other two. Looking at the first one, the stars on the left of the pic all seem to be rushing away from the centre which is what we'd expect if the sensor is too close.  However, the stars down the right hand side don't seem to show anywhere near as much distortion.  It's possible that this is due to poor collimation but it could also be caused by some tilt somewhere in the imaging train. While the third image seems to have better back focus, the focus overall is poor. What are you using to focus?  If you're using a bahtinov mask, I've read it's best to focus on a star in one of the thirds rather than a central object. 

Graeme

 

Hi the focus is handled by the eaf and asiair pro. I am going to check the collimation again on the next clear night

No. I'm using my camera and defocus inwards and outwards to ensure its good in both directions. 

Which backfocus would you say is the closest?

So last night I managed to do some testing before the clouds rolled in. I managed to take 10 x 60sec exposure of Capella at 3 different back focus lengths (105 mm, 109.5 mm & 126 mm) based on the spacers I had available, each time I refocused using the ZWO EAF. Each image is the stacked output and stretched.

There is definitely something not right, I am going to recheck my collimation but what do people think?

No other focuser is compatible with ASIAIR. Yes I have an eaf attached to each of my scopes as it's easier and not a quick job to change between scopes, especially when using an SCT and a refractor.

After reading everyone's advice, I have decided to abandon taking a test stack without the reducer as I don't think I have a mirror issue and I think my collimation is good, I think my issue is the back focus distance which in my case is not the 105mm as stated in multiple sources but probably longer...

I need to take some new test images as I have messed about with that many combinations now that I have forgotten where I got up to. So on the next clear night, I will setup with 105mm back focus, take a test stack of Capella, review and take it from there.

4 hours ago, jacko61 said:

According to this review, the Antares 6.3 only needs a back focus of 49mm...    f/6.3 Antares Focal Reducer for SCTs- Awesome Astrophotography   

Surely he must be mistaken in the backfocus being 82mm!

10 hours ago, Same old newbie alert said:

I'm slowly solving some issues with mine..

Can you confirm what version you have, are you using a reducer and which one? 

Using the Celestron 6.3 reducer and the recommended 105mm doesn't give you the spec'd focal length of 1280mm , 105mm gave me a focal length of 1320mm... I can't remember what back focus distance I'm using but my focal length is now very close to 1280mm and my stars are certainly better..( it's further out than that,further out gives you a reduced focal length)

So for me it's a combination of backfocus distance, good collimation.. I'm using a XLT version, Celestron 6.3 reducer, atik 460ex mono, oag with filterwheel

If you could measure your back focus then I would really appreciate it as it is possible that there isn't anything wrong with my mirror or reducer, its just the 105mm back focus is incorrect. I think my collimation is spot on so the poor star shapes are down to the back focus.

My version is also the xlt version, with the antares 6.3 reducer, asi2600mc pro. I am not planning to use a filter wheel / drawer as I will be only shooting galaxies in RGB.

6 hours ago, jacko61 said:

google is your friend..

What are the optimum back focus distances for Celestron SCTs? | Celestron

so 127mm

Graeme

Thanks but I was looking for real world examples.....

I hope someone may be able to give me the correct figure.

I have been trying to image using my C8 with fr and asi2600mc pro. I appear to have really bad coma at 105mm backfocus. I have checked collimation and that appears to be fine so someone has suggested there might be a problem with the mirror but to narrow done the issue, he has suggested that I remove the focal reducer from the equation and take a stacked image of capella at the native fl. I will do this on the next clear night but does anyone know what back focus distance I need when not using a focal reducer on this scope?

I have no way to add as the all the adapters are fixed in length.

Does anyone have any thoughts on how to fix this? Everywhere I read it says 105mm back spacing which I have achieved using the following:

Celestron T Adapter (50mm) + 16.5mm Spacer + 21mm Spacer + ASI2600mc (17.5mm)

I thought it might be collimation so last night I again used Deneb to check and whilst it isnt perfect it was the best I could get it.

Well I tried 105mm and I am struggling with round stars throughout the image. The attached image is Deneb, 180 second exposure guided. I thought it might be collimation but whilst it isnt perfect it is good enough.

Hello all, in preparation for galaxy season I have decided to resurrect my C8 to use with my ASI2600mc Pro, I intend to use my Antares f6.3 reducer. Can I confirm that the back focus to the sensor from the reducer is 105mm?

Thank you all for your responses. I have just taken some test exposures after making a change to the back focus and that has cured the issue, the artifact has gone and the stars are nice and round throughout the image.

I am going to check the back focus measurement and take a new exposure. I am also going to take another exposure without the filter drawer as someone has suggested it might be light leak which has caused like a lensing effect. 

I have recently purchased the ASI2600mc pro camera which came bundled with a ZWO filter drawer.

Last night was my first light with the camera and I have noticed a strange circular pattern in the image on the right side.

The image is a widefield M81. 

29 * 300 second exposures

Matching darks and flats

Setup

William Optics ZenithStar73 with flattener

AZ-EQ6 Pro

ASIAIR Pro

ZWO EAF

ZWO filter drawer 

Optolong L-Extreme filter

The back focus is set correctly. Camera, filter drawer, 16.5mm spacer, field flattener.

Camera is set to -10 and 100 gain. Focus is rough focused and then auto focus and refocused every 1 hour or 1 degree change.

I have used the same setup with my 2600mm pro and filter wheel but don't see this same pattern.

Only thing to try is remove the filter drawer but I can't see why that would cause this strange ring pattern?

Anyone any ideas what it could be?

Hello again,

Just wanted to say thanks for all the helpful advice I was given, I did give it a go last night but just couldn't focus to anything so decided this morning to follow the suggestion of attaching the cam to a 80mm refractor that I have. I have managed to capture (after some time focussing) the tree in my back garden.

Do people find that there is a large amount of travel in focus between eyepieces and the cam?

Hello, thank you for your replies.

I think I will just give it a try tonight and see what happens.

Hello all, I need some help.

A few years back I bought what I thought was a Philips spc900nc cam that I was going to do some planetary photography. Unfortunately I had some ill health so everything went into storage but I have got it all out today and I think what I actually have is a spc880 which has been flashed.

My question isn't about that. I have connected the cam to my laptop and installed SharpCap, but despite connecting to the camera, all I see is light and dark depending on where I point the camera, no image.

Is this correct? I don't have the original focuser as it came to me already modified with the eyepiece adapter.

I have added a picture which is suppose to be outside of my house.