Horsehead Comparison

[sdbodin]

Another comparison of imaging choices. This time the hydrogen alpha luminance in both the Rokinon 135mm telephoto and the BigDog 16 at 2600mm efl. Kind of fun seeing the difference in resolution. But the comparison is not one to one, different cameras and the IrfanView drop-and-paste pic maker rescales to fit.

Rokinon image at f2, 6/5min thru 12nm Ha filter to ASI1600MC-cool, BigDog 16 at f6.5 with Atik 460ex mono thru 6nm Ha filter and 2x2 binned also 6/5 min exposure.

Clear skies,
Steve

[STEVE333]

That Big-Dog really brings out the fine details. Thanks for sharing.

Steve

[messier 111]

both lead to something interesting.
thx.

[BigKahuna]

Both are really nice but the 16 inch picture is wonderful

[Greenman]

Well, one has field of view giving context, the 16inch has great detail. To me both are equally nice and valid.

[Jockinireland]

I have to agree with Tony, they are so different that it would be hard to judge between them. Its great to see the structure in the 16" version. But then seeing the context of the wider fov is also great.

[Roverich]

Another comparison of imaging choices. This time the hydrogen alpha luminance in both the Rokinon 135mm telephoto and the BigDog 16 at 2600mm efl. Kind of fun seeing the difference in resolution. But the comparison is not one to one, different cameras and the IrfanView drop-and-paste pic maker rescales to fit.



Rokinon image at f2, 6/5min thru 12nm Ha filter to ASI1600MC-cool, BigDog 16 at f6.5 with Atik 460ex mono thru 6nm Ha filter and 2x2 binned also 6/5 min exposure.

Clear skies,
Steve

WOW . Spectacular. Great images. Thanks for sharing these.

[SkyHiker]

I like seeing comparisons but this one's a bit hard. I have seen many horses from an 80 mm that show much more detail than your Rokinon 135 mm. Were they both autoguided? If not, your Rokinon is not nearly performing as well as a telescope, and the comparison is not one of aperture/Dawes limit based resolution. The 16" one looks super BTW.

[sdbodin]

I like seeing comparisons but this one's a bit hard. I have seen many horses from an 80 mm that show much more detail than your Rokinon 135 mm. Were they both autoguided? If not, your Rokinon is not nearly performing as well as a telescope, and the comparison is not one of aperture/Dawes limit based resolution. The 16" one looks super BTW.

Thanks for the feedback,
I have to agree that the Rokinon is not an 80 by any means, 67 actually, and the short focal length is the key to resolution short comings. At 135mm the pixel pitch is the main driver and the ASI1600 at 3.8 microns works out to 5.81 "/pixel, way short of the 1.63"/pixel that my 80 has with this camera and the 0.72"/pixel on the 16 at 2x2 binning with the Atik 460 at 4.54 microns. An old 80 crop attached, way better than the Rokinon, but 460mm efl is most of the difference in my opinion. Yes all were autoguided and all are 6/5min exposures.

Thanks again, always good to get a discussion going on imaging to the limit of the equipment and finding the hard-stop.
Steve

[SkyHiker]

I like seeing comparisons but this one's a bit hard. I have seen many horses from an 80 mm that show much more detail than your Rokinon 135 mm. Were they both autoguided? If not, your Rokinon is not nearly performing as well as a telescope, and the comparison is not one of aperture/Dawes limit based resolution. The 16" one looks super BTW.

Thanks for the feedback,
I have to agree that the Rokinon is not an 80 by any means, 67 actually, and the short focal length is the key to resolution short comings. At 135mm the pixel pitch is the main driver and the ASI1600 at 3.8 microns works out to 5.81 "/pixel, way short of the 1.63"/pixel that my 80 has with this camera and the 0.72"/pixel on the 16 at 2x2 binning with the Atik 460 at 4.54 microns. An old 80 crop attached, way better than the Rokinon, but 460mm efl is most of the difference in my opinion. Yes all were autoguided and all are 6/5min exposures.


Thanks again, always good to get a discussion going on imaging to the limit of the equipment and finding the hard-stop.
Steve

Ah of course, when talking about camera lenses the number is about the FL not diameter as opposed to telescopes. This is a zoom lens, right? Zoom lenses are always a compromise. Your numbers make sense, I wonder how the Dawes criterion works out for it, I don't have Scilab handy right now. But that 80 mm image rivals your 16" one!

[SkyHiker]

And here's a reason why the 80 mm performs almost as well as the 16", skip to the section with the HH pictures, https://www.cloudynights.com/articles/c ... rt-5-r2321 .

[sdbodin]

And here's a reason why the 80 mm performs almost as well as the 16", skip to the section with the HH pictures, https://www.cloudynights.com/articles/c ... rt-5-r2321 .

Great article,
Yes seeing is the key, 2" average limits what the 16 can do except that 'lucky-imaging' technique. I need to re-read that whole series on CN for a refresher. But, it seems to match my experience in imaging.

BTW that whole telephoto and telescope spec thing is a constant source of confusion. I should remember to be more specific. And that Rokinon is a fixed focus manual lens and this image was wide open at f2.0 and only about 10% crop of the full field and off-axis to boot. Part of this image:

Thanks again,
Steve

[BABOafrica]

Both are really nice but the 16 inch picture is wonderful

That's the one...

BABO

[jthommes]

Nice comparison. I guess it is kind of showing results that one would more or less expect, but it is nice to actually see the visual comparison.