EEVA Lots of questions

[Marvin Jenkins]

I have been following this sub forum on and off for a month or so and it has peaked my interest. I have been doing basic astronomy for nearly three years and hoovering up all the info I can.

At first amazed by everything, then anything. All the discoveries, Open Clusters, Globs, Galaxies, Plan nebs, NEBS. Still amazed but something happened...

I watched a YouTube vid of a guy in the US using a big Dob (ES 16 inch) but with night vision. I thought it was fascinating.

Recently I stumbled across a website called Mantrapskies.com which appears to be one mans attempt to record photographically the entire ARP list. Now I have to say that until looking in the EEVA forum I had no idea that the ARP catalogue existed.

Now I realise that the Mantrapskies site was not EEVA but the only place I had heard ARP targets were this forum and the above website.

Now I realise they are distant targets, but what is the general idea for minimum equipment needed for ARP hunting and in particular EEVA.

Marv

[Mike JW]

Hi Marv,

No simple answer to your question. Popular size scopes are 6 to 8 inch aperture but EEVA can be carried out with any scope. Shorter focal length scopes will give you a wider field of view and thus are good for large extended objects - nebulae. My particular interest is galaxies (Arps, VV, SHK groups, Hicksons......) and for that I prefer larger aperture and narrower field of view.

I note you have been observing for about three years. I observed visually for 20 years before I thought about going down the digital route. I still observe visually - double stars, lunar, planets, clusters, comets and the brighter Deep Sky Objects. Personally I still prefer visual observing with no electronic aids over EEVA . If I was in a very dark sky and had silly money to spare then I would love a 30" Dob for a life time of visual work.

I appreciate the wonder of EEVA because it has enabled me to "see" DSOs in more detail than I could when I owned a big Dob. To me doing direct visual astronomy first is a bit like doing an apprenticeship to learn the trade (in this case to learn and understand the heavens). 

So back to your question. Use your existing scope to build up your knowledge and buy a suitable camera to have a go at EEVA.

As to the Arps. I saw some with my large Dob but much of the time not much more than grey fuzz. A mate with his 24" sees much more but generally not as much as I (and others) see using the EEVA technique.  Hence I dream of the monster 30" Dob in very dark skies and at least 100 clear nights a year.....

There are all sorts of lists. I have lists for suitable double stars for 8" scopes, lists of suitable DSOs for 8" scopes, lists for the large Dob...........some off the internet, others made up over the years.

Forgive me for being direct at this point - "are you trying to run before you can walk"? I have hours of visual fun and fascination with my small 7" scope and sometimes much prefer to get this little scope out rather than use a bigger scope or camera set up. Astronomy is a life long pursuit (and expensive).

Have fun and enjoy the interest.

Other folk will express a different view to mine which is one of the joys of sharing the hobby.

Feel free to ask more questions and to get different answers.

Mike

[Martin Meredith]

Hi Marv

I have been using a Lodestar X2 mono + 8" f4 reflector (800mm FL), mounted in alt-az, without guiding and without cooling, to do EEVA-style observing for the last 5 years and haven't felt more than a passing temptation to upgrade any of these components. Such a setup can reach to mag 20 and fainter on good nights from my observing site which is about 11km from a city with a population of 230,000, with best SQM measurements of around 20.5 on moonless nights (more typically around 20). For the occasions when I want colour (mainly for globs and open clusters) I use the same setup along with a Starlight Xpress electronic filter wheel with Baader filters, combined live in software.

With a very similar FL of 750mm, your 150mm PDS would most likely show plenty of detail in the Arps. It is somewhat slower at f5, but still pretty fast and would be fine if paired with a sensitive sensor (i.e. with a high QE).

Regarding sensors, I may well be in the minority here, but I see very little to be gained if you are mainly interested in galaxies by using a sensor that produces a large FOV, and plenty of disadvantages in terms of processing time and storage (as well as initial cost).  My Lodestar coupled with the Quattro has a FOV of 0.44 x 0.35 degrees -- tiny by modern standards. Your 150mm scope would produce a slightly larger FOV of 0.47 x 0.37 degrees -- see https://astronomy.tools/calculators/field_of_view/ with the Lodestar or similar. What does this buy you in terms of visible DSOs? A surprising amount! Taking 20' as the maximum diameter of the DSO (i.e. leaving some space around it on the sensor), you get

100% of all quasars (million or so)
100% of the globulars (157)
100% of the Hicksons (100)
all but 1 (very faint) planetary nebulae (2390)
all but 4 galaxies (exceptions being M31, NGC 292, M33 and NGC 55, although I have managed decent images of M33 with my sensor)
99.8% of the VVs (2010)
99% of the Arps (335)
95% of the Abell galaxy clusters (though admittedly not the closer i.e. brighter ones)
86% of all open clusters (1847)
84% of reflection nebulae (134)
57% of dark nebulae (2850)
41% of bright nebulae (518)

There is a tendency nowadays to promote CMOS cameras with low read noise and there is nothing wrong with that, but I would say that at 750mm or so FL you can easily get 20-30s sub-exposures even in alt-az mode with no guiding, so the advantages of low read noise are somewhat diminished. I still prefer CCDs like the Lodestar because the gain is fixed so that is one less parameter to mess around with.

As a minimum for Arp hunting, I'd say you need a driven mount, a fast focal ratio scope, a modest pixel count but sensitive mono camera, a USB connection and a computer. And software of course, ideally capable of hot pixel removal as a minimum.

I can't lay my hands on it at the moment but I have some code that will compute the signal to noise ratio for a given scope/camera combination to be able to see a point source of a given magnitude. Later I will plug in the details for your scope and see what it comes up with. Meanwhile, if you look at this thread you can see a comparison of mono cameras for EEVA: 

 

 

HTH, and feel free to ask more questions! Lots of fun to try to answer them.

Martin

 

[Martin Meredith]

Just to add (I found the code). Suppose you are trying to detect a mag 20 point source (e.g. a very distant quasar) from skies of moderate quality (SQM 19, FWHM 3") using your existing scope and a Lodestar X2 mono. With 10 x 20s subs you obtain a signal-to-noise ratio of around 3.5, enough for detection. By comparison, my 8" f4 scope reaches that SNR in 6 x 20s subs. So in reality there is not that much difference, in the sense that by waiting a little longer you can obtain the same SNR. At the same time, an f5 scope is easier to keep in collimation and ought to produce better looking stars across the field.

I know quasars are not what you asked about, but this kind of comparison is likely to give an indication also for how long it will take to acquire faint details in the Arps, for instance.

Martin

[Marvin Jenkins]

3 hours ago, Mike JW said:

Hi Marv,

No simple answer to your question. Popular size scopes are 6 to 8 inch aperture but EEVA can be carried out with any scope. Shorter focal length scopes will give you a wider field of view and thus are good for large extended objects - nebulae. My particular interest is galaxies (Arps, VV, SHK groups, Hicksons......) and for that I prefer larger aperture and narrower field of view.

I note you have been observing for about three years. I observed visually for 20 years before I thought about going down the digital route. I still observe visually - double stars, lunar, planets, clusters, comets and the brighter Deep Sky Objects. Personally I still prefer visual observing with no electronic aids over EEVA . If I was in a very dark sky and had silly money to spare then I would love a 30" Dob for a life time of visual work.

I appreciate the wonder of EEVA because it has enabled me to "see" DSOs in more detail than I could when I owned a big Dob. To me doing direct visual astronomy first is a bit like doing an apprenticeship to learn the trade (in this case to learn and understand the heavens). 

So back to your question. Use your existing scope to build up your knowledge and buy a suitable camera to have a go at EEVA.

As to the Arps. I saw some with my large Dob but much of the time not much more than grey fuzz. A mate with his 24" sees much more but generally not as much as I (and others) see using the EEVA technique.  Hence I dream of the monster 30" Dob in very dark skies and at least 100 clear nights a year.....

There are all sorts of lists. I have lists for suitable double stars for 8" scopes, lists of suitable DSOs for 8" scopes, lists for the large Dob...........some off the internet, others made up over the years.

Forgive me for being direct at this point - "are you trying to run before you can walk"? I have hours of visual fun and fascination with my small 7" scope and sometimes much prefer to get this little scope out rather than use a bigger scope or camera set up. Astronomy is a life long pursuit (and expensive).

Have fun and enjoy the interest.

Other folk will express a different view to mine which is one of the joys of sharing the hobby.

Feel free to ask more questions and to get different answers.

Mike

Thanks Mike. I have no immediate need to go down the Eva route. Definitely run before walking territory, as you say I need to build up more experience.

Just stumbled onto the subject and seemed very interesting and new. Perhaps one day in the future, and I will keep following this forum out of interest.

Marv

[Marvin Jenkins]

1 hour ago, Martin Meredith said:

Just to add (I found the code). Suppose you are trying to detect a mag 20 point source (e.g. a very distant quasar) from skies of moderate quality (SQM 19, FWHM 3") using your existing scope and a Lodestar X2 mono. With 10 x 20s subs you obtain a signal-to-noise ratio of around 3.5, enough for detection. By comparison, my 8" f4 scope reaches that SNR in 6 x 20s subs. So in reality there is not that much difference, in the sense that by waiting a little longer you can obtain the same SNR. At the same time, an f5 scope is easier to keep in collimation and ought to produce better looking stars across the field.

I know quasars are not what you asked about, but this kind of comparison is likely to give an indication also for how long it will take to acquire faint details in the Arps, for instance.

Martin

Thank you so much for all the info. I will try to take it all in this weekend. I enjoy a learning curv no matter how steep.

Marv