Lens performs very well.
It seems the external aperture improves the performance of all longer than 200mm lenses, not only Canon (and not only re spikes, CA is also reduced dramatically).
I was looking at this on my desktop and a thought struck me that it might work (the Omega) as a 3d cross eyed image thingy.
So I played around with the Omega side and came up with this cheap version, seems to work and gives you a 3D version (as pathetic as it is.) Just be sure to click on the "fit image to page compass looking button on the top right so you can see it all.
Hope you dont mind, if you do, I can remove it.
Just playing around with some quality data, had to save it down as a JPG, so its not as good as your original quality.
Cheers
Chris
Last edited by Screwdriverone; 26-03-2010 at 02:31 PM.
I was just taking a look at your image again and I noticed that it seems you have captured a Fourcade-Figureoa object as mentioned and pictured in AS&T May/June 2009 (page 66) in Les Dalrymple's Deep Sky Delights column - ESO 270-17! [Excellent column by the way, Les, alas my subscription has run out......hint hint..... ]
I have attached it to this post and circled in yellow where it is, certainly, if you click on your Hi Res link and zoom in, it compares EXACTLY to the pic in AS&T.
Just thought you would like to know and also to say that it is a mighty impressive pic to capture that as well and is even better captured (resolution and extent) than the NASA version in the mag (yes I know its only a small B&W photo - but still!)
Nicely done! Bravo!
Cheers
Chris
Last edited by Screwdriverone; 26-03-2010 at 07:59 PM.
Reason: Forgot to add the pic and the page number (DOH!)
Thanks for the comments. This is the sort of quality my mosaics done with this lens has.
I routinely upsize my images by a factor of 1.6 before stacking. The image of the two Centaurus objects above is the result of stacking four sets of twenty 192MB tiff images. These four exposure stacks are then used to produce the HDR image which is then finally tone mapped to an LDR image. That is why you can see the core of OC without it being blown out as well as the very faint galaxies.
The Vela SNR mosaic is 11800 x 11200 pixel sized image and 770MB Tiff. I had to reduce it to 6000 pixels wide as some of my 32 bit programs just cannot manipulate such large files due to memory limitations.
Below is a map showing the positions of many of the faint galaxies. Some of these are quite visible in the image.
Chris I would not put up high resolution images if I was worried about what people with do with them. The images I take are for all to see and use for their own enjoyment and education. The usual acknowledgement is all that is expected if reproduced somewhere else. If for profit, I will generally give written permission if asked.
The external aperture has two effects.
1. It only allows light actually contributing to the image to enter the lens. There is then almost no scatter of light (from the interior of the lens) not contributing to the image which reduces contrast or signal to noise. The lens hood extension also really helps here. This is the same effect that baffles have in a high quality refractor.
2. No difraction effects from the lens aperture blades. The lens aperture is left wide open at f/2.8. I cannot stand unavoidable diffraction artefacts.
If weather and time permits I am going to try an external aperture and lens hood extension to a 50mm or 85mm lens. I am sure it would increase contrast and definitely get rid of those pesky difraction spikes.
I had not considered an improvement of less CA Bojan apart from eliminating the lens outer edges where most of the CA is produced. It could be that the internal lens aperture does not eliminate all off axis not image contributing light.
I was just taking a look at your image again and I noticed that it seems you have captured a Fourcade-Figureoa object as mentioned and pictured in AS&T May/June 2009 (page 66) in Les Dalrymple's Deep Sky Delights column - ESO 270-17! [Excellent column by the way, Les, alas my subscription has run out......hint hint..... ]
Yep, it is ESO 270-17 without doubt. You have also captured the NGC 5090 group of galaxies. You can see them as one small, merged but slightly elongated blob at about the 2-o'clock position from NGC 5128 just beyond a 7th magnitude star.
BTW, the "NASA" image in the magazine is a digitised scan of the Schmidt survey plate (DSS) -- sometimes that's all that is available you know ...
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