Ist widefield image with DSLR

[Carole]

As stated in other posts I have never had any success in imaging with the camera only, mainly due to not being able to focus properly.  However Mark suggested I got a lens without a zoom on it which might be easier. 

I had my first outing last night, it's somewhat of a new experience, and being wide field trees kept getting into the images, so I was having to change targets.

This is the first of the 3 images I did, and I do believe I might have finally got it in focus.  How I will cope with just using an LCD and no laptop to magnify things is another matter and another hurdle to overcome, but one step at a time.

I was messing around with the iso and F numbers as I didn't really have much of a clue what was best, as images were coming out far too light, this is what I ended up with.

This is 8 x 5mins 400iso @ F6.3
Modified Canon 450D (forgot that the clip in CLS filter would fit with an EF lens, so didn't use it).

The mess at the bottom left (near Saiph) is trees, I cropped most of the rest out as they looked pretty horrid.  Shame I didn't get Betelgeuse in the FOV. 

[MarkS]

That's an excellent result.  The focus looks spot on and the stars in the corners look free from aberrations.  You've managed to capture the Orion Nebula, Flame Nebula and even the Horsehead.  If you can mark the focus position or tape it down then it will work perfectly well next time as well.

If you are trying to get focus but don't have a laptop screen then use the following trick.  Display your image on the rear LCD of the camera and zoom right into the centre, corner or elsewhere using the "+" magnifier and "arrows".  Now, with the zoomed image still on the display, the knurled knob at the front will take you backwards and forwards through the images on the card showing exactly the same crop of each image at exactly the same magnification.  So, if you put the camera on a tripod and take a sequence of images, changing the focus very slightly between each one, then you can afterwards step through the magnified images with the knurled knob and determine which one is in focus.  It doesn't even matter if the stars begin to trail - it is still obvious which image is in focus.

Practice this technique in the daytime in the garden or even inside the house - you'll be pleasantly surprised how easy it is.

Mark

Mark

[Carole]

Thanks Mark, what did you think of my settings 8 x 5mins 400iso @ F6.3, should I do something different and what did you use to get Barnard's loop?

The flats didn't work very well on the dust I had to do a fair amount of touching up. 

Carole

[Kenny]

Lovely image Carole. Shows me what is possible! How did you get such long exposures? Was this using a tracking mount? I presume you got so much colour as your camera is astro modded?

[Carole]

Hi Kenny, Yes it's a tracking mount, the big brother of your (well the society's) HEQ5. 

I have only just realised I was doing 5 minutes unguided. 

Also yes my camera is Astro modded and same as yours I think, a 450D.

Carole

[MarkS]

Hi Carole,

You can see the settings I used here: http://www.markshelley.co.uk/Astronomy/2011/orion.html

I did 5 minute exposures at f/4.  You want as fast an f-ratio as possible but this will be limited by the amount of aberration you are prepared to accept in the corners of the image.  For 5 minute exposures, ISO 400 or 800 is fine.  Short exposures would need a higher ISO to keep the read noise manageable but at 5 minutes read noise will not be the limiting factor.

For calibration flats I used a LCD monitor displaying a white screen. 

Mark

[Carole]

Thanks Mark, I found the images were very light at F4, so thought they might being overexposed.  I'll give these settings a try next time.

Looking at your image also done with a DSLR and camera lens, any idea why I got diffraction spikes on mine?

Carole

[Fay]

I dont remember seeing that image before Mark, very nice

[MarkS]

Looking at your image also done with a DSLR and camera lens, any idea why I got diffraction spikes on mine?

Yes - it's the aperture blades within the lens.  Mine are curved and yours are straight edged.  A straight edge interrupting the light path (e.g. spider or aperture blade) will always create a diffraction spike.  If you find it objectionable, you can put a circular mask in front of the lens instead of stopping the lens down.

By comparison, this earlier image of Orion with a 50mm lens does have diffraction spikes:  http://www.markshelley.co.uk/Astronomy/2009/orion2009.html

If you find it too bright at f/4 then drop the ISO.

Mark

[Carole]

Thanks Mark.

Carole