View Single Post
Old 29-06-2015, 02:54 PM
PRejto's Avatar
PRejto (Peter)
Registered User

PRejto is offline
Join Date: Jan 2011
Location: Sydney, Australia
Posts: 1,303
I took the liberty of writing directly to Roberto Abraham of the University of Toronto. He answered me immediately and coincidentally has just arrived in Melbourne for a few days of meetings! He indicated that he was a bit too busy to participate in this thread but he has given me permission to quote from our email exchanges. I hope you find it interesting. I really appreciate that he responded!

"Thanks for your email! I am pretty swamped at the moment so don't have time to participate on the Ice In Space thread, but I did read through the posts quickly and as far as I can tell the posters are making fair comments on the general pros and cons of the Dragonfly setup and I don't have a lot to add. Some of the points of discussion in the thread (focal ratio vs aperture etc) are gone over in our PASP paper describing Dragonfly. Here's a link:

Some of the issues being discussed in thread are gone over in the footnotes. When writing this we tried to make it accessible to a broad audience (including amateur astronomers) as we figured some of you folks might want to have a go at something similar. Hope we succeeded… if not we'll try to do better if we write a paper describing the upgraded telescope we're working on.

Canon's optical design for the lenses is proprietary but we're pretty sure only one element has the nanostructure coatings… they've clearly done a careful job of modelling ghosts though as remaining ghosts are at a really low level… we quantify it in the PASP paper. I think Canon's standard multi-coatings are really good too.

By the way, check out this nice paper that confirmed our identification of ultra-low surface brightness galaxies in Coma using the Subaru telescope:

What is really neat is that the authors of this paper (not) only confirmed the existence of the ultra-low surface brightness we detected, they found almost 10x more objects than we did! Subaru is an incredible telescope (the perfect combination of large aperture, amazing optics, wide-field capability and a great site) and its image is far superior to what we're able to do with Dragonfly in terms of resolution and depth on small scales. So why hadn't they identified ultra-diffuse galaxies before? Turns out the ultra-low surface brightness population had been missed in the past because this population was mistaken for compact galaxies (because the low-surface brightness envelopes were missed and they only found the cores) or by flat fielding errors, ghosts etc. Now that Dragonfly has shown that these ultra-diffuse things are real, the bigger telescopes will be able to optimize to detect them and clean up.

Anyway, when it comes to a few niche things like intracluster light and local galaxy envelopes (degree scale structures) I think Dragonfly will do better than Subaru, but in general for most things one wants to tackle in extragalactic astronomy (arcsecond to arcminute scale problems like the Coma objects) bigger telescopes on better sites are a bazillion times better than Dragonfly. Physics is physics! Of course a single night on a large telescope costs about $100K, which is basically what we spent on Dragonfly, so I really have been enjoying seeing how our work with these telephoto lenses has been inspiring this activity with Keck, Subaru, HST etc."

Posted with permission from Roberto Abraham

Reply With Quote