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Lambda Cygni and my LX 70 8R


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#1 MistrBadgr

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Posted 31 August 2015 - 07:09 PM

I have been slowly working with my new LX 70 eight inch f/5 reflector to see what its limits are. One of the tests I am performing is to see what it can do with double stars. I did not really buy the scope for double star splitting, but I wanted to try and see just how close it could come to the Dawes Limit. I have always been told that a scope with as fast of a focal ratio would most likely not get there, simply because its tolerance to miscollimation is too small. This tolerance decreases proportional to the square of the focal ratio. An f/7 scope will have about twice the tolerance of an f/5.

Looking at some star maps, Sissy Haas' book on double stars for small telescopes, and a few other books, I decided to use Lambda Cygni. It is currently located high in the sky and is relatively easy to find. It has a separation of 0.9 arc seconds. An eight inch scope is supposed to be able to split two equal magnitude stars around mag 6 with a split of 0.6 arc seconds. With the uneven magnitudes of something around 4.5 and 6, the 1.5 magnitude difference is supposed to take that achievable split to 0.9, which is what this star has.

With the scope, I have been using my HD 60 eyepieces and a Meade #140 2X Barlow. I have been having trouble with turbulence in the air, but I have still been working on splitting this double star and getting the collimation better as I go along. Tonight, I worked my way all the way to the Barlow and the 4.5 mm eyepiece. This is a magnification of 444X. The sky was better tonight, but was not really still, so it was a bit of a bumpy ride. I do not think I could have stayed with the star at all if I did not have the little motor drive system that I bought as an accessory. With a little better weather and a better (but not completely perfect) collimation, I could tell that there were two stars of differing color. At times, they seemed to be kissing, while at other times the second star seemed to be swallowed up with the first diffraction ring of the primary. The primary seemed to have a slightly orange cast, while the secondary star seemed to look a bit bluish grey in comparison.

I turned off the drive momentarily to find exactly where west was and (zip!)I found out quickly at that magnification. With that piece of information, the secondary seemed to have a PA almost due North. The books say it is a tiny bit east of due North, but I will take that as confirmation I had the right star.

I will keep working on the collimation, find out where that tiny error is at high magnification, and see if I can make a correction and make a better split. This double star is definitely tough for an eight inch f/5 scope.

With all that said, I believe the 8 inch reflector is a good scope. I will talk about it more in other posts, but thought I would put this in the visual section where it belongs.

Bill Steen
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#2 Mark Sibole

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Posted 31 August 2015 - 07:21 PM

you have a imager where is the picture???


Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#3 MistrBadgr

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Posted 01 September 2015 - 02:58 PM

I haven't gotten that far yet. I am a slow poke! :)

If I took a picture, I would have had to post in a different section and not under visual astronomy!
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#4 Mark Sibole

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Posted 02 September 2015 - 08:20 AM

Ahhhh you could still post it.I wont tell    lol a picture with a nice explination goes a long way my friend. I finally got out to the OBS to repair storm damage and replace a dead PC last week and took my first image in 2 years.Between health issues and pc failiers it has been a while since i was able to image.But the smoke from out west has made it here to michigan and skies are a mess. but I did manage 100 minutes on NGC 6888 the Crescent Nebula area. 

c4nim.jpg


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Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#5 MistrBadgr

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Posted 02 September 2015 - 07:01 PM

That is cool! I like the Crescent. It is a favorite with my 100 f/8 as a challenge object from my back yard. I have seen indications of nebulosity all the way around it at times, but thought it was my imagination.

I did finally get figured out there were instructions for setting up the polar scope, which I did this evening. With that done, I think I got a better polar alignment. With that, the little tracking motors seemed to do a better job.

Last night I got a reasonable look at Lambda Cygni, even though things were weaving in and out pretty bad. I used a 4X Barlow I have with a self centering tightening device and the HD 60 eyepieces, just to make sure my collimation problem was not in the 2X I was using that has a single retaining screw. It might have been better, but not a lot. I did, however, take the scope all the way to 888X with the 4X Barlow and the 4.5 mm HD 60. It was messy, but fun. I did see the two disks somewhere between a figure 8 and kissing.

I still have a collimation problem with the scope. I can get a laser to center on the primary and bounce back into the center of the angle screen just fine. The image I see on the Primary mirror is not round. With the angle of the axis being somewhat odd, I am thinking I have a problem with the secondary not being positioned quite right in both axial and rotational position. It is close enough that I am making up for it with the collimation screws, but that is not good enough. It may be the focuser's collimation and this focuser does have collimation screws on it.

The skies are getting a bit quieter, but the humidity has increased, along with the mosquito population. I have them fooled though. They land but do not like it and leave....both deet and laundry softener sheets.

Take care, Mark, and do some more imaging! :)

Bill
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#6 MistrBadgr

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Posted 04 September 2015 - 08:57 PM

Well, I finally made enough small adjustments with collimation, then still not where I want it, to get the job done. The weather helped by calming down enough to give me non-wiggly air. Using a 4X centering Barlow and my HD 60 eyepieces, I finally got a good split on Lambda Cygni. The secondary star sits right on the first defraction ring of the primary, so technically it might need to be a little farther apart to meet some people's standards, but I did have black space between the two stars. With the 9mm eyepiece in place, I would occasionally get a split second clear image of the two disks with the secondary one being more orange than the primary. The position angle was a touch east of due North, which matches the 5 to 7 degrees I find listed in several catalogs. The clearest spread between the two stars was with the 6.5 mm. With the 4.5 mm, the secondary seemed to be spreading out a bit with the primary star's first defraction ring. Using the 9 mm eyepiece and the 4X Barlow, the magnification was 444X. With the 6.5, it was 615X, and with the 4.5, it was 889X. With the 4.5 things were really getting pretty wiggly, but it was possible to see something....just not optimum.

For the beginner, the magnification of 444X with the 9 mm eyepiece and Barlow is about the highest I would ever expect to use effectively, except maybe on the Moon in really still air. The only reason the higher magnifications can mean anything is because I was looking at behavior characteristics of light coming from two infinitesimal but very bright sources of light. There was no real object to view. For most objects, much lower powers are better. For large dim objects, I am normally trying to get as low of a power with as wide of a field as I can get to see the whole object.

I will add more later as I try the scope on different things. I am finding I can have some fun splitting double stars, even though a reflector with this fast of an f-ratio (f/5 or 1000 mm focal length divided by the 200 mm mirror diameter)is really not considered effective enough for that type of observing. Being successful with this kind of observing with this scope requires a lot of care and patience when collimating. A scope like this has very little tolerance for errors if you want to get that last little bit of resolution. For viewing lower magnifications for nebula, star clusters....things like that, for which a scope like this is generally intended, the collimation is not as critical.

Bill
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#7 MistrBadgr

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Posted 07 September 2015 - 02:58 PM

Last night, I once again split Lambda Cygni, just for a repeat. The sky was not quite as nice, being just average, but I did manage.

I went on to Saturn, which is a bit low for me to get the kind of view I like. However, it is what I have. The good views will have to come with future years, which Saturn make a path farther North in my sky. I had no problem with seeing the Cassini Division. There seemed to be a couple of bands on the planet it self that were evident to me. I know there was at least one and do not think the second one was my imagination. It was not as evident as the first. I am getting enough brightening around the planet, due to a little fog behind the new lenses in my eyes, that it makes it a little difficult to see the smaller moons when they appear close in. I finally did see, I think, all three if the normal ones, with two of them using averted vision.

I went to M-22, a globular cluster, and was able to resolve a couple or three dozen stars with the rest showing up as more of a mottled fog.

The Great Hercules Cluster, M-13, was really nice in this scope. There were too many stars resolved to get a good estimate, but there were still regions that looked more like a fog. With the 12 inch Lightbridge, everything seems to be resolved.

The star cluster in the Lagoon Nebula was nice. I could see some of the nebula itself, but the weather was just enough off and the light pollution in that direction was enough to diminish what I could see. I will try again with a light pollution filter the next time I am out.

I then put in the adapter for 2 inch eyepieces and starting using my Meade 5000 series ultra wide angle eyepieces. I wanted to see what the image looked like with those eyepieces in this scope. With the 30 mm, the first thing I noticed was I had to tighten down the locks on both axis in order to hold the scope. Normally, the scope is very well balanced with the HD 60 eyepieces, which all weigh about the same. The 30 mm UWA is a different thing again with weight. I really did not want to re-balance the scope for that particular eyepiece, so I just watched things a bit closer. The pupil size with this scope and that eyepiece is 6 mm, which is what my pupil measures at the eye doctor's office with their eye drops in my eyes, but that is larger than what I experience in my back yard with the light pollution. The center two thirds of the field was trying to darken, but there really were no other antics going on. The view itself was good. I normally see spikes on bright stars with just my eyes looking at the sky. With this eyepiece, the spikes appeared to be a little closer to what I see with just my eyes. All of the spikes rotated as I rotated my head, which I am sure would look somewhat strange to my neighbors if they saw me! With higher powered eyepieces, the spikes appear finer with more of them, but they all rotate with my head. I am sure they are from my eyes and not the scope or eyepiece. With the 30 mm UWA in place, the stars looked good all the way to the edge with no changes in their characteristics or the spikes I was seeing. Though I cannot be totally for sure, I believe the stars in the view were pretty much pinpoint. Any coma was less than what I normally see, which makes it outside my ability to detect.

I want to talk about other characteristics of this scope, but I am not sure where to put those comments. I will think about it some more and may include those comments on this string, simply because it is going. I really do not have another place to put them, since there is no LX 70 section yet. These were be more physical considerations of the scope and the way it works mechanically.

Bill Steen
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma




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