SharpCap Forums

So - slightly ahead of the JWST - this large telescope is finally set up with electronic focuser and guide scope etc. 300 mm x 1200 mm - F 4.0 - and a total of about 21kg of weight rather dwarfing a mount designed for 31 kg max.

Does going quite so big make any sense for astrophotography ? Image scale of 0.8 arcsec/ pixel - so slight oversampling even when and if skies ever were to permit 2 arcsec resolution. Weight and focal length making guiding more difficult? Low F number making both focus and collimation difficult. No expection to see any 'deeper' since that is a function of (Bortle 6) sky brightness rather than aperture. But set against these considerations - shorter image acquisition times (which matters under typical UK sky conditions) and the potential for even very short -potentially sharper - subs versus brighter objects. - and still transportable (if not exactly 'portable')

Herewith a first try at capturing the detail within M94 - in comparison with a previous best image of the same compiled from subs using the same camera and a PDS200 F 5.0 Newtonian.

VX12 Orion Optics (UK) Newtonian (f = 1200mm, F4.0), SW parracor type coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm.

ZWO AS1294 MC OSC camera, 4.63 um pixels, 14 bit ADU. All frames taken under moonless Bortle 6 skies. All frames pre-selected for quality using the FWHM and brightness filter within Sharpcap, darks and grayscale master flats (no bias) prepared using Sharpcap. Preprocessing and processing in PixInsight.

M94. 138 x40s RGB frames, gain124. On 260222 conditions were good and even with the mount so heavily loaded PHD2 guiding was running at about 0.5 arcsec RMS. The seeing must also have been really pretty good because the PixInsight subframe selector estimate of the FWHM value of the linear debayered stacked image was 2.45.

To me the 138 frame VX12 image looks not only brighter (more so than expected purely on the basis of f ratio) but also more detailed than the earlier taken 190 frame PDS200 image. Generally - across a few other galaxy images - I got the impression of getting better colour - and on this occasion slightly better sharpness - more quickly. After figuring out its various foibles - the tube rings need to be surprisingly tight and a few screws in the mirror cell needed tightening - the VX12 seems to be working well.

Tim

Hi Tim,

Better quality in less time. Well worth the investment! Where do you get all the clear skies? I get nothing here.

Brian

Hi Tim

The 138 frame VX12 image is indeed way more defined. Seems indeed a good investment!

Menno

Thanks Brian, Menno

Yes clear skies - and especially night-time hours without the moon up have been at a real premium. Then about three came together. The night of 24/02 was clear but too windy. The night of 25/02 was also clear and the wind had dropped which was perfect - and so I spent about an hour or so on each of 4 galaxies. But at the moment I am still only learning how to really make best use of this big F4 scope - it requires careful adjustment. The nights of 26 and 27/02 were also not bad but by then I had tinkered too much trying to perfect the alignment and had only succeeded in messing things up- so no decent images. Finally got it right with a laser dot right in the centre of the primary mirror and laser and Cheshire collimation in agreement. But of course since then - no decent nights. But I have at least managed to get long enough to test optical performance with stars and was pleased to see good coma correction across the field and FWHM scores right down almost to 2 arcsec in some frames. The weightlifting aspect of lifting 44 lb straight, very carefully and away from the body at above head height is also proving challenging -- but haven't dropped it yet - so the investment is still intact at least.

Tim