Focusing, Bhatinov Mask Help

[loopy]

Hi all.  A bit of background;  I have a Celestron Nextar 130 SLT which I have been enjoying on and off for a while using just my eyes.  I use the standard 25mm and 9mm eyepieces and also a 5mm eyepiece and have a 2x Barlow and I interchange these for different viewing.

Recently I started trying astrophotography using a Canon 650d and using BackyardEOS.  I have pretty happy with the set up and guess as a beginner I still have experience to build up but, hopefully this forum can fast track me a little.  Just to get an idea of what I have been doing, the first two images attached were taken on 12th September and the last two were taken on 13th September 2020.  I did take some of Mars but, I was not happy with the results at all so will try that another night (I think my batteries were going and the tracking on the telescope was aweful).

So, I realise that the planets in my part of the UK are a bit low for good seeing, less than 20 degrees above the horizon and also I have some light pollution here but that aside, I still think there is room for improvement.

I got a Bhatinov Mask to help me get focus and this is something I am not sure of right now.

My telescope is unmodified so to reach focus I have to use the Barlow to extend the focal length.

When I put the Bhatinov Mask on and track on say, Arcturus using just the 2x  Barlow, I get diffraction spikes on the screen but, they are not as defined as I thought they should be.  I use the camera/BackyardEOS to zoom and also increase the ISO and eposure which helps a little but not great.  The result is, I "think" my focus is good but, I cannot absolutely tell.  Add to this the "shake" from the telescope it's difficult to make fine adjustments so, having clear diffraction spikes will really help.

Tonight, I added the 25mm eyepiece to the Barlow to get a bit more magnification.  I realise this is trickier to get centred and tracked as the field of view is reduced when adding magnification but, I need to learn and get practice.  The problem with this is worse though because, the diffraction spikes nearly are not there at all when adding the 25mm eyepiece so, my focus was there are there about but, I can't say it's spot on.  The idea of a Bhatinov Mask is to get the best focus with easy effort but, if I can't see the diffraction spikes very well then, well, it's not helping.

Basically, any ideas how I can get nice bright clear diffraction spikes with this set up?

[Pryce]

I haven't gotten my Bhatinov's yet, but isn't the point of those to do test exposures and then look at the defraction spikes so you don't have to use a EP and focus that way?

Anyways, you're using a scope 130mm with 650mm focal length and a barlow.  Take that into account I'd say your second set of images are pretty good compared to others with similar scopes I've seen!

Edited September 14, 2020 by Pryce

[loopy]

Ah you know what, it could be schoolboy error I have made.  I have been using the "live view" on both the camera and BackyardEOS.  I'll have another night and take actual pictures at different exposures and see if that makes a difference.

[alacant]

On 14/09/2020 at 01:05, loopy said:

nice bright clear diffraction spikes

Hi. The planets look great.

I don't think you're gonna get enough light for live view but try a higher ISO anyway.

If you want to get good spikes, don't use a planet and take a sequence loop of say, 2s exposures, refocus between each frame. Blue stars work best. Vega is good ATM.

HTH

[rickwayne]

You may find that e.g. Vega is good to get roughed in, but that dimmer stars will allow you to better discern small focusing errors. Use ISO eleventy-million for the shortest exposure times possible, and definitely use magnification of the live view to really peer at the details.