Poor focus, poor seeing, clouds, bad guiding ????????????????

[Skipper Billy]

Last night was only the second clear night since August so I was determined to 'have a go' with my 'new to me' camera !!!

After 5 hours in temps down to minus 10 I am bitterly disappointed ...............

I used to use a Canon DSLR on an ED80 unguided and got great results - I have bought a SXVF H9C OSC and added guiding and its all gone downhill !!!

This is from an SXVF H9C, ED80, guided with a ST80 and  QHY5 and PHD2 - imaging and focus controlled by APT. Mounted on a HEQ5/ASCOM/EQDIR.

Its the best 13 x 300 second subs stacked mildly stretched and edges cropped - nothing else.  I discarded more than half as there must have been cloud passing through.

I am not experienced enough to know whether this is straight forward out of focus (although the focus aid FWHM reported perfect focus) or some other cause like poor guiding????????? Its probably not dew as the heaters were on all the time and the optics were clear at the end of the session even though everything else was covered in haw frost.

Its a totally rubbish photo so don't hold back on critique - I need to know what I have got wrong - tonight looks clear as well !!!!!

There are also black dots in the nebula?????????????

Any help, comment or guidance (no pun intended) is very welcome.

[MiguelMJr]

I'm no expert but... maybe someone else will chime in.

To me it looks like your guiding is fine as the stars are all nice and round. Maybe it is focus as the stars look kind of big.

The black dots seem to be in focus which points to stuff on the glass covering the chip.

My calculations say.....

With a SW ED80 of 600mm focal length and a average seeing of 3 (middle of the road, better seeing would require smaller pixels) you should be shooting with a pixel size of 3.3um (ICX 834 has 3.1um pixel size) for correct sampling. Your camera has a pixel size of 6.45 so you are way undersampling which will cause a "soft focus" appearance. Whether this is the issue I really don't know. I am not sure how OSC affects this undersampling but I think that It is not in a positive direction. If you used a reducer then this would make the undersampling even worse.

Can you try the camera on your 200 PDS (or some other longer scope) without any "extra" glass like reducers or coma correctors? it has a slightly longer focal length so would have slightly better sampling.

That camera (in a mono version) should be used with a minimum focal length of 1450mm - 1500mm at a seeing of 3 or worse.

Like I said.... "My calculations"

http://www.astro-imaging.com/Tutorial/MatchingCCD.html

Miguel

[MiguelMJr]

Here are my calculations......

On the left are the scopes working focal lengths, at the top is the seeing and in the middle section is the calculated pixel size as per ... ((seeing in arcsec * focal length in mm)/206.3)/3.3

I made a slight mistake in the above post. A 3.3um pixel would be for a seeing of 2.5 arcsecs at 900mm focal length, not a seeing of 3 arcsec.

Hope I have my calculations correct!

Miguel

[Carina Lass]

If it isn't the above, it may possibly be the Seeing.

many pics have been ruined by upper atmosphere tricks.

[Skipper Billy]

Had another go this evening - I think part of the problem may have been ice in the slots of my Bahtinov mask !!!

The seeing was awful tonight - visible mist and a huge halo round the moon but my stars are visibly tighter. I think its just too low in the sky at the moment for where I am - I am shooting just over the top of snow fields which are also reflecting the moonlight back upwards.

This is just stacked and converted to JPEG - no processing at all.

Any ideas what the dark circle is - bottom left quarter of the image ??????

[Carina Lass]

Dark matter - on your sensor

[gnomus]

I'd be interested to know what these black dots/lines are all over the image.  Could this be a problem with the sensor?  The dark circle looks like a DSLR dust bunny to me.