widefield astronomy

[Ivor]

Hi,

On holiday at last and I have time to try the night sky again. I've escaped to the French alps for a couple of weeks and I've brought along my QHY8L with a 50mm f1.8 lens and I'm struggling to get the focus sharp enough. This is a 20s image with roughly centered on M20:




I'm using EZCAP but I just can't seem to get a nice focus, I've selected a star and used the focus function and the best FWHM I can get is 7, am I approaching this imaging technique complete wrong?

I'd be grateful for some suggestions on how to get a sharper image?

Thanks

Ivor

[JohnP]

Never used that software - Duncan can probs advise. My only comment would be to perfect your focus technique during the day to save wasting those nice dark skies... Cant you focus on a distant object on horizon or something & lock or mark position on lens?  John

[Carole]

I found EZcap really bizarre, the cooling seemed to work when it felt like it, switched on when you hadn't asked it to, and was very wayward.  As for capture it's not at all user logical.  I managed to use it once successfully the whole time I used my QHY8L.  Never tried to focus with a lens so can't help there, but focussing on a land object might be your best bet. 

Zakalwe on SGL seems to be experienced with this software, though I think he hasn't used it for a while, but I am sure he could help.

You probably don't have your processing software with you, but it looks much better for a colour balance.

Carole

[Ivor]

Never used that software - Duncan can probs advise. My only comment would be to perfect your focus technique during the day to save wasting those nice dark skies... Cant you focus on a distant object on horizon or something & lock or mark position on lens?  John

I started the focus approach on the mountains an hour before dust, any earlier and the 1ms  minimum exposure time saturates the image. However the stars aren't sharp.

I found EZcap really bizarre, the cooling seemed to work when it felt like it, switched on when you hadn't asked it to, and was very wayward.  As for capture it's not at all user logical.  I managed to use it once successfully the whole time I used my QHY8L.  Never tried to focus with a lens so can't help there, but focussing on a land object might be your best bet. 

Zakalwe on SGL seems to be experienced with this software, though I think he hasn't used it for a while, but I am sure he could help.

You probably don't have your processing software with you, but it looks much better for a colour balance.

Carole

I have Astroart 5 and PixInsight with me as well, so I can try AA5 as well it just isn't as smooth with the QHY8L. I'd not tried rebalancing the image as i wanted to get the focus right first, I'll try AA5 tomorrow night.

[JohnP]

Any chance of using moon...

[Carole]

To be honest I found focussing with a telescope a nightmare with QHY8L, I could not see even the brightest stars with looping at all and had to keep taking quick shots with a Bahtinov mask to achieve focus, so I would have thought trying to focus using a camera lens even worse. 

Carole

[The Thing]

What is the lens? I've had a Nikon lens that produced rubbish stars and a 9euro one (Pentax zoom) that is pin sharp. Wide open at f1.8 is unlikely to be sharp unless you paid a lot of money for it. Stopping the lens down really helps with all lens issues, start there.

[Ivor]

IThanks for the advise, it was the 50mm Canon lens circa £70 so not super expensive. Before I second my daughter's telephoto lens is there some software that would let me change f number as I don't think I can do it with AstroArt or EZCAP? maybe APT?

[MarkS]

IThanks for the advise, it was the 50mm Canon lens circa £70 so not super expensive. Before I second my daughter's telephoto lens is there some software that would let me change f number as I don't think I can do it with AstroArt or EZCAP? maybe APT?

I bought a standard Canon 50mm F1.8 lens (brand new) and it was terrible for astro - really severe aberrations.  I then got a second-hand Nikon 50mm F1.8 really cheaply off eBay and this was only bad i.e. much better than the Canon.  I have to use it stopped down at F5.6 or F8 if I want stars that are not triangular.

Mark

[The Thing]

IThanks for the advise, it was the 50mm Canon lens circa £70 so not super expensive. Before I second my daughter's telephoto lens is there some software that would let me change f number as I don't think I can do it with AstroArt or EZCAP? maybe APT?

As the lens is not on the manufacturers camera you can't change the aperture unless it has the appropriate f stop ring. If it was on a Canon you could control everything, even autofocus.