diffraction spike difference between images

[smr]

Hi all,

Currently imaging M42 to add to the data from a couple of nights ago, but just reviewing some of the images from tonight's session as it progresses and I notice that there are diffraction spikes in my images from tonight, but there were none from the other night. Why is this? 

Tonight I took longer than usual focusing (still waiting for RVO to send my bahitnov mask) and used 10x zoom and focused until I thought it was good.

Tonight's images have diffraction spikes but the subs from the other night do not.. see pics. 

Did I then, have better focus the other night? Or is tonight's focus better? 

 

[steppenwolf]

Overhead cable in the way? A tree branch? Spider's web?

[smr]

53 minutes ago, steppenwolf said:

Overhead cable in the way? A tree branch? Spider's web?

Thanks. I think it must have been a tree and its twigs in the next garden. I set about imaging earlier than I have before and I thought M42 had cleared the tree but it must not have at that time. No diffraction spikes now.

[steppenwolf]

Excellent! ?

[smr]

49 minutes ago, steppenwolf said:

Excellent! ?

Steve just wondered if you could advise me please, will be changing target soon, should I take flat frames before slewing to a different target or should I just take them at the end of the night after imaging both targets?

[vlaiv]

32 minutes ago, smr said:

Steve just wondered if you could advise me please, will be changing target soon, should I take flat frames before slewing to a different target or should I just take them at the end of the night after imaging both targets?

If you don't change anything in your optical train - just slew to other target and use same filter and everything - one set of flats is enough. You can do it mid session or at the end - which ever is more suitable. I sometimes park scope on meridian flip and do flats while I wait for target to cross it.

[steppenwolf]

10 hours ago, vlaiv said:

If you don't change anything in your optical train - just slew to other target and use same filter and everything - one set of flats is enough. You can do it mid session or at the end - which ever is more suitable. I sometimes park scope on meridian flip and do flats while I wait for target to cross it.

As above but very importantly, don't move the focus position.