FWHM qustions

[gonzostar]

Hi 

My set us is basically a 102mm APO refractor on a AVX mount

I now use a 70d Canon DSLR camera replacing the 450d. I use Background EOS tool for image capture frame and focus. But mainly focus by eyeball method

With the 450d I can get FWHM values down to say 3-4. However with the new camera my FWHM values have shot up to 5-6 when i stack the images 

The star on the movable screen looks sharp and round when magnified.

Is this due to the new IDAS-D2 filter

or

The pixels are smaller compared to the 450d, and there are more mega pixels. 

or something else, ie a better method of focussing or poor sky conditions

The stars on the background EOS previw look terrible specially when magnified, but look fine when processed? My held is spinning!

Any tips much appreciated.

Thankyou 

Dean

 

[newbie alert]

Bahtinov mask..

[gonzostar]

, Thanks Dont seem to understand few nights ago could get the 450d to focus fine with eyeball. However unsure why the 70d seems harder to focus. Is that due to smaller pixels, I have a different filter in imaging train or not so good atmospheric conditions or am just getting used to flip screen?

Maybe the mask is the answer. 

 

[newbie alert]

53 minutes ago, gonzostar said:

, Thanks Dont seem to understand few nights ago could get the 450d to focus fine with eyeball. However unsure why the 70d seems harder to focus. Is that due to smaller pixels, I have a different filter in imaging train or not so good atmospheric conditions or am just getting used to flip screen?

Maybe the mask is the answer. 

 

Atmospherics do play a part and different filters will require different levels of focus..HA especially...i don't use the FWHM method so maybe I'm missing something but as a test I focused by eye once and felt that it was the best I could get..put the mask on and was out by a fair bit so I always use a mask from now on..

[gonzostar]

Whilst i was figuring out focus and trying out new IDAS-D2 filter with canon 70d i took this image made up just 4*300s sub frames (with dark n bias only) 

Does this look way out of focus?

 

Cheers 

Dean

[newbie alert]

7 minutes ago, gonzostar said:

Whilst i was figuring out focus and trying out new IDAS-D2 filter with canon 70d i took this image made up just 4*300s sub frames (with dark n bias only) 

Does this look way out of focus?

 

Cheers 

Dean

Not out of focus but to me there seems that the stars to the left of the main one are elongated in the same direction..camera tilt maybe?

[gonzostar]

Quite possibly. I was aiming for the lagoon nebula so calibrated fot that. Low cloud came over in that direction. So quickly slewed to Sadr and pressed butten. So not calibrated to subject properly. At this stage just experimenting  

[david_taurus83]

All the stars around the edge look eggy so field curvature?

[gonzostar]

I agree. I dont have a field flattener. Also hadnt calibrated to the object. I was concentrating on focus, as i thought i was having issues focusing  ie eyeballing with new 70d compared to backgroun EOS

 

Dean