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On occasion a question is asked about the suitability of a particular DSC for a specific application. Answers come back like "The DSC should be adequate or the DSC places the object square in the middle of the field" or a host of othe vague comments. I would like to describe a more general and rigorous method of evaluation of the DSC for a specific application. The readability of Losmandy's DSC is 1 min. (time) in RA and 0.1 arcdeg on Dec. A little consideration shows that a reading difference on the meter can actuall be as large as 1.8 units. Coverting RA from time to arcangle is 1.8x15 arcmin and Dec. is 1.8x6 arcmin. This means that the window for placing an object has the dimentions of of 27 arcmin in RA and 10.8 in Dec. directions. Given this information, a quantitative decision can be made for a specific application. For example, consider a scope with a 3000 mm FL with a 12 mm ep. The field of view is 40 arcmin. The object will be some where in the FOV but not necessarily in the center. If one uses a 1000 mm scope and an ep of 32 mm the FOV will be 3000 mm. In this case the object will appear to be (smack) in the center. For the case of CCD cameras, with either scope, one will have to estimate the (considerably reduced) FOV for the specific application. In general, the rectangle with the above dimentions is ideal because it assumes no experimental errors such as poor polar alignment. I made an attempt to measure the size of my experimental window using a 12 in SCT (FL=3030 mm). I determined the positions of 10 stars whose coordinates were available from SKYChart III and found the dimensions of the box to be 30 by 8 arcmins. This gives me the confidence that my polar alignment procedure, choice of Deneb as the calibration star and the instrument is comperable to the specification of the DSC. In other words there is no experimental reason to choose a more southerly star or be more finicky about my alingment proceedure. Any comments are welcomed.

suscribir

I forgot while writing my last post, I still haven't been able to find the lock-screw that is used to lock the mechanical declination circle in place once it's calibrated. Were there some modes of G-11 that were made without that screw (i.e., with no way to lock down the declination circle)? Thanks, **** Ray Porter lrporter@... dragon@... ray_porter@... Home Page: http://www.unc.edu/~dragon/ "Meddle not in the affairs of dragons for thou art crunchy and taste good with ketchup"

Thanks again to everyone who has responded to my questions so far. The weather forecast for tomorrow calls for clearing so maybe I'll actually be able to get this thing out under the stars tomorrow evening. Gregory, I suspect that our polar scopes are the same, or at least very close. I checked the retaining ring closely this afternoon and there is a hole in the ring for the set screw you mentioned. It appears that the set screw has been lost though. I'll ask the mount's current owner but I suspect he will have not idea about where it's at. He usually preferred to drift, even when only observing visually. Consequently he pretty much never used the polar scope and was unlikely to have noticed when the screw was lost. What do I need to look for as a replacement? I set everything up in the living room this afternoon, with the scope mounted, just as I would start a visual observing session. I wanted to see how things looked and moved with a load on the mount. I also wanted to go through the little DSC walkthrough in section 6 of the manual. I noticed that the RA motor ticks quite loudly. Is this normal or am I likely to encounter the vibration that I've seen mentioned in this forum several times? Everything was balanced and there was a working load of about 20 pounds on the mount (not counting counterweights). Thanks, **** Ray Porter lrporter@... dragon@... ray_porter@... Home Page: http://www.unc.edu/~dragon/ "Meddle not in the affairs of dragons for thou art crunchy and taste good with ketchup" **** Ray Porter lrporter@... dragon@... ray_porter@... Home Page: http://www.unc.edu/~dragon/ "Meddle not in the affairs of dragons for thou art crunchy and taste good with ketchup"

Hi everyone, I am in the process of purchasing a used G-11 with Losmandy digital setting circles and polar alignment scope from a fellow club member. After years of using fork mounts, I'm still getting used to using German mounts and I have a few questions that don't seem to be really covered in the manuals, mostly about the DSCs. Fortunately, the current owner is allowing me to borrow the mount before actually purchasing it so I can "kick the tires" and get any questions answered up front. 1) The manual states that the polar bore scope should rotate freely when inserted in the RA housing. However, after tightening the retaining ring, the finder won't budge. Is it normal to have to loosen the retaining ring slightly to rotate the polar finder? 2) Will the DSCs in alt-az mode with the G-11? 3) Will the polar scope give me a sufficiently close alignment that the DSCs will work with a 1-star alignment? 4) Appendix A in the DSC manual describes a process for determining the +90 degree position for the telescope/mount that is necessary for a 2-star alignment with a GEM. Shimming the mount may be all fine and dandy if you have a permanent installation, but it sounds impractical if you have to setup and take down the scope and mount for every viewing session. How accurate does this process have to be? Will centering Polaris and setting the mechanical declination circle get me close enough? 5) The illuminator and battery pack for the polar bore scope seems a little cumbersome. Is there an illuminator available with a self-contained battery? I'm sure I'll have other questions as I start using the mount. Thanks, ================================================ Ray Porter Applications Analyst Programmer Administrative Information Services, UNC-CH Phone: 966-5878 email: ray_porter@... dragon@... Home Page: http://www.unc.edu/~dragon/ "Meddle not in the affairs of dragons, for thou art crunchy and taste good with ketchup."

The battery pack that I use claims that a radio or TV can be operated for 20 hrs. On several occassions, by freshly charged battery went dead driving the G-11 with DSC. I couldn't understand this at first, and later concluded that a fine layer of bubbles formed over the battery plates made it appear dead. So when it happened again, I simpley shook the battery as hard as I could but to no avail. Any comments, or does the G-11 draw about 5 times the current of a radio or TV

Hi Everyone, Just received my new GM-8 yesterday and my initial impressions are very positive. I had never seen one before and purchased it on its reputation. I think I've made a good choice. I'm sure I'll have some questions for the group as I become more familiar with it and already have one question regarding the hand controller. Looking at the hand controller with the RA and DEC reverse switches at the top, there is a diamond shape arrangement of four buttons. My assumption was that the buttons opposite each other would control the motion of the same axis. However, on this particular controller, the TOP and LEFT buttons seem to work on one axis while the RIGHT and BOTTOM buttons control the other axis. I've found it very frustrating as it is not intuitive at all. Is this the normal operation for the GM-8 hand controller or is my specific example "wired wrong" ?? Thanks for the help, Tony

I am going to purchase an SCT but am undecided on a GEM or a fork mount. Under consideration are: C8 Deluxe, LX 200, U2K and C 9.25 on a GM 8. Any information you could offer on the following would be appreciated: 1) Advantages / disadvantages of a SCT-GM8 combination compared to a fork mounted SCT. 2) Portability of GM 8 compared to forks. 3) Experience of anyone using a C 9.25 with a GM 8. 4) Is a GM 8 enough mount for the C 9.25 or is a G 11 more appropriate. This will be a significant investment for me so any information you can provide would be appreciated. George Smith

OK...where can I find one of these suckers??? I've tried a couple of local places with no success. Bill

Hi all, Well, I'm reasonably pleased with the improvement that I have been able to achieve in my G11's tracking and periodic error. Take a look at http://www.barry.net/Astro/losmandy_g11_ra_pe.html to see the results. I am curious how the PE shown on the web page above compares to other G11 mounts out there. I still am not sure if the problems with the mount I received are typical or a fluke. I have made the fix permanent since my original post back on 8/13, but I did risk damaging the mount in the process. Specifically, I pressed in a new needle bearing with .002" stainless steel shim stock wrapped around the OUTSIDE of the bearing (I know, I was against it in an earlier post ;-) I do not recommend this! You can easily damage your mount unless you are VERY careful. Five things can go wrong. 1. The needles in the bearing can seize. 2. The bearing can easily distort due to the amount of force require to press it in. 3. The fit can bee too good, and the shaft will bind due to the relative misalignment of all three needle bearings. 4. You can permanently knock the RA wheel gear bearing sleeve off axis or bend it. 5. You can expand the OD of the RA wheel gear bearing sleeve so that the wheel gear will no longer fit. However, this strategy did cause the ID of the needle bearing to shrink (exactly the amount needed in my particular case) and I now have a very nice on-axis fit with no measurable slop. The OD of the RA wheel gear sleeve bearing did expand slightly (approx .0002") and I needed to lap it a bit to ensure that it would not bind over an appreciable operating temperature range. Anyway, now that the RA shaft was not flopping around, I was finally able to see how well the mount would track. Now I had a fairly regular PE of about 11-12 arc seconds. After lapping the RA worm and wheel gear it dropped to under 10 and became even more regular. After training the SkyWalker II PEC, it tracks within 2 arc seconds. Not too shabby given where this all started. Neal

I have a GM-8/Gemini on order and one question that I have has to do with some Losmandy owners having to redo the grease on their G11/GM-8 mounts. Does Losmandy use a special shipping grease? Has anyone asked Losmandy why the sticky grease is even being used? This group has been helpful in answering just about all the other questions I had (just be searching by keyword), and I have found the procedures to redo the grease. Thanks. Reid Williams

Hi everyone, I'm confused as to where we stand on the undersized shaft issue. In summary: 1. Is it beneficial to insert a third bearing in the RA axis up near the pressure plate? 2. Is it relatively easy to insert? 3. Will Scott sell us an additional bearing, and if so, at what cost? Thanks, Steve

What's the proper way to use the vernier markings on the manual setting circles?? I understand that it is to interpolate between hash marks, but it doesn't seem to work the same as my vernier calipers. Bill

Thanks Brian. This group has really taken off a big way which confirms that it's been long overdue! It's clearly a great learning tool for inexperienced users like myself but I'm glad to see that the group is helping to bring out into the open problems that experienced amateurs are facing. Hopefully through the innovation of many of this groups members, including Scott himself (many thanks for participating Scott), these problems can be overcome. I look forward to getting great images using my forthcoming G-11 and eagerly await the new GoTo - should be fun! Thanks to everyone so far for making this group work so well. Clear skies, Ian. ndy_users@..., "Brian Kennedy" <draco61@f...> wrote: > I just wanted to say hi and thank Ian for starting this group. I just > purchasd a GM8 any will no doubt have many questions. In reading the > previous posts, I see we are well represented by many knowledgeable > people. > > Brian

Excuse me if I missed this earlier. What exactly is "stiction"? I just received my GM8 and am wondering if this is a real concern and something I should worry about. Thanks, Brian

Hello Paul! I think you are right. Scott is sending me a new worm bearing block that will allow more movement. This will help to correct problem #1, but I am afraid that the major issue is #2. Do you have any suggestion to solve such a problem? I understand from the list that the fix is not so easy. So, I am thinking of asking my dealer (as soon as he is back from his vacation) for replacing the whole dec assembly (the mount is only a few weeks old). Maybe this will take some time, but at the moment I don't see any other solution. What do you think? Regards, Girolamo ----- Original Message ----- From: Paul Sterngold <psterngold@...> To: <Losmandy_users@...> Sent: Tuesday, August 15, 2000 4:55 PM Subject: Re: [Losmandy_users] G11 Declination problem > Welcome, Girolamo! > > I suspect the play in your DEC shaft, and its inconsistency, is caused by > two things: > > 1) A small amount of play between the worm and the worm wheel (gear); and > > 2) A small amount of play between the DEC shaft and the shaft bearings. > > #2 permits the shaft to be slightly off-center with regards to the axis. > Therefore, #1 can come and go as the worm wheel pushes more or less against > the worm itself. > > This is speculation, but there's been a lot of discussion recently on the > list regarding #2. > > An alternative possibility, and one that I read about on the > Astrophotography Mail List (APML) about three years ago, is that the hold > in the center of the worm wheel itself is slightly larger than the shaft, > and therefore the worm wheel can be "locked" (via the clutch knob) in a > slightly eccentric position relative to the shaft. > > I hope this helps. > > Paul Sterngold >

I have a question about the vernier scale on my G-11. All the verviers that I have used have one scale up against another so that a choce can be made which two lines are aligned. In my G-11 there is a gap of about 1/32 in making it difficult to use the vernier. Do I have a problem or is this the way it is. Thanks for any response.

This is about my fifth attempt at posting. I hope this works

Hello all. Good idea starting this group. Brian

To those that might be in the know: One of the applications I hope to achieve with the goto system would be 'remote' imaging (remote in the sense of 30' to 100' away in a nice warm room.) One of the issues that I need to contend with is centering up or otherwise framing objects in the CCD's field of view. Since it probably won't be likely that the pointing accuracy will be such that the object will be exactly centered (or not, depending on what you're after), it requires the ability to move the scope in small increments at a reasonable rate of speed (like around 4X or so.) It seems that there will at least be a slewing speed (~800+X) available through planetarium programs (I have Guide 7.0) and a guiding speed (~.2 - .8X) available through the CCD camera control (as in MaxIm). Question I have is will there be a centering speed available remotely (i.e. one around 4X) or will I be limited to the 2 speeds above? Also, is there any way possible for the information stored in the controller box to be sent to a separate program on a remote computer such that you would have access to all the functions on the controller? Or is this something planned for future software upgrades? Thanks in advance for any info you might have. -- Jim Girard http://www.teleport.com/~argo