Re: Used GM-8 Guiding Help
Nick..
?
If
you give me your address, you can borrow my extra brass worm to see if you want
to install one / if it helps solve the problem..
?
Then
you can either buy one from Losmandy and send mine back to me or pay me for
mine..
?
Email
me directly if you are interested..
?
Derek
?breit_ideas@...
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Re: Eastside Heavy Rule - How to Practically Apply Query
I
move the lower counterweight up or down the shaft depending on which side of
the mount things are.. *AND* I find where these points are ¨C before ever
turning on the mount ¨C during initial balancing..
?
Doesn¡¯t
take much offset from balanced, just ¡°some¡±..
?
With
the Gemini II, you also have a balance function that you might like more, but
since my configuration never changes, I just find where the weights go once and
just put the weights where they go when they need to go there..
?
Derek
?
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From: [email protected] [mailto:[email protected]] On Behalf Of Terry Pullen via groups.io
Sent: Thursday, January 28, 2021
5:11 AM
To: [email protected]
Subject: [Losmandy_users_io]
Eastside Heavy Rule - How to Practically Apply Query
?
Hello Group
Many times over the years I have seen and heard it mentioned that it is
beneficial to have a non-perfect mount balance such that the 'east side' of the
mount is biased to be slightly heavier when doing astrophotography. Am I
correct in thinking this is to do with reducing backlash when tracking or
guiding or both.
I was wondering if this 'rule' is true at all times irrespective of wthether
the scope or the counterweight shaft is actually on the east side?
How do those who use this approach manage to keep the east heavy rule applied
when imaging? Is it advisable to move the lower weight on the counterweight
shaft further down the shaft a little or have a separate, tempoary additional
'movable' weight that can be placed on either the shaft or the scope depending
which side of the meridian they are?
Just interested in what other imagers do - grateful for any insight. I saw on
this Group several weeks ago an ingenious solution using an automated method
which fasinated me and sparked my interest but is way beyond my mechanical
abilities. I am interested in a better understanding of the 'eastside heavy
rule' and any suggestions for a simpler method to apply the necessary bias.
With help from this Group I am slowly getting back into imaging with my 14 yr
old G11, Gemini-1 and my DSLR after several years away from the hobby.
Many thanks
Terry [uk]
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Re: Used GM-8 Guiding Help
Just a few further thoughts on periodic error. See graph below:?
If you start imaging at point B, then in half the worm period, you will get a shift in the image of 2P arc seconds. For your G8 data, P is about 20", and the worm period is 8 minutes. Therefore you will get a star moving by 40" in 4 mins (or 5" in 30 seconds). This is the worst case. If you start at point A, you will only get an image shift of P in half the worm period - for your case this would be 2.5" in 30 seconds. If you're imaging at a scale of 2" per pixel, you should be able to get unguided images OK for 15-30 seconds even with the mount as it is now.?
This is ignoring the use of PEC. If you use PEC, then the data in your first figure suggests that P is reduced to only 4 or 5". So with PEC enabled, you would get an image shift of only 1" per minute.?
I'm ignoring any high frequency features in the periodic error - if you can get rid of these you should be OK to do some unguided imaging.
You can check how long you can go before you get an unacceptable rate of bad frames.?
Then you would only need autoguiding if you want to go longer than this.
With some of the recent CMOS cameras that are available (like the ASI 071) there are many who are choosing to go to high gain/short exposure time (10-20 seconds) and simply collecting hundreds of frames, and if you choose to go this route you could potentially get rid of autoguiding altogether.?
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Re: Hello from a new user
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Re: Hello from a new user
To paraphrase an old jingle "You meet the nicest people on a Losmandy."? Welcome back Brian!? -- Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
?
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Re: Making the most of cloudy winter nights with a new mount and scope
I¡¯ll also add, that my routine for using the AAP with the Gemini 1 is as follows, which might help?
- Power up AAP
- Power on Gemini
- Focus using AAP (I also have an EAF)
- Cold start Gemini (I set up each night)
- set location from stored location if cold start lat long incorrect (check mount time is correct UTC no DST)
- restart Gemini 1 (if changed location)
- connect to mount is AAP
- Undertake PA process in AAP and mount bolts
- Slew to target with AAP
- take preview picture (5 secs)
- plate solve and Centre in AAP (just to ensure the target is centred)
- start looping and guide process in AAP (I always calibrate every time as I setup each time)
- check mount tracking is on (should be automatic)
- Start imaging using auto run in AAP.
- sit in the warm house and monitor on your phone or tablet!
Hope this helps. Took me a while to get a routine that consistently worked with the ASP and Gemini 1. I suspect Gemini 2 isn¡¯t too different.
Bryn
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Re: Making the most of cloudy winter nights with a new mount and scope
Join the ASIAIR and ASIAIR Pro user groups on Facebook. Lots of excellent help and assistance. The AAP has really been a game changer for me, getting me imaging whenever the weather allows.
Make sure the epoch on the mount is set to ¡°current¡± not J2000. Took me weeks to figure this out after my AAP would never properly plate solve and Centre targets! The AAP uses know (current) Epoch.
Start with Dec and RA aggressiveness of +45 and calibration figures of 500, 300 and 300 for guiding the HM-8 with the AAP, this should give you a reasonable starting point (again, this took me a while to sort and lots of forum surfing!)
Back up the AAP SD card immediately. If it corrupts without backup, it¡¯s a bit of a pain to sort out with ZWO by all accounts.
I can¡¯t really help with other stuff, but I have been using the AAP with Gemini 1 for 5-6 months now so have experience. There do not seem to be many ASP and Gemini users around?
Bryn
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Re: Hello from a new user
Hi Brian,
Welcome back to astronomy...we've missed you. But seriously...do have fun!!!
Jamey
Hi all. My wife and I got into this hobby in the mid-80s with a classic orange C8. After getting a ton of use out if it, both visually and a bit of film-based AP, a new?10¡± LX50 followed in the late 90s. But life intrudes, and the past two decades in Dallas and LA put the kebosh on stargazing, for both time and sky quality reasons. We¡¯ve finally gotten back into it after a move to Utah and subsequent retirement.?
Three months ago I suddenly discovered that I¡¯m 24 years older than when we bought the 65-pound Meade contraption, that the assembly and tear down was, well, tearing me down, and it was time for something more portable. We researched the crap out of the mount market. Long story short, we bought a new G11G with the RA extension and two great carrying cases from Scott and company in the late fall, de-forked the ¡®ol LX50 OTA and started anew. More or less.?
Three things - first, dealing with the people in Burbank was a true pleasure, and I can¡¯t say enough positive things about them. Second, the quality and functionality of the G11G is far beyond our expectations. Third, we¡¯re thrilled by the advancements in observing and AP tech over the years and look forward to getting back into it in a big way. We¡¯re confident that our new mount and old scope will give us a great start.?
Very happy to join this group, as well as the Gemini group. Good to ¡°meet¡± you all.
Brian
?
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Eastside Heavy Rule - How to Practically Apply Query
Hello Group
Many times over the years I have seen and heard it mentioned that it is beneficial to have a non-perfect mount balance such that the 'east side' of the mount is biased to be slightly heavier when doing astrophotography. Am I correct in thinking this is to do with reducing backlash when tracking or guiding or both.
I was wondering if this 'rule' is true at all times irrespective of wthether the scope or the counterweight shaft is actually on the east side?
How do those who use this approach manage to keep the east heavy rule applied when imaging? Is it advisable to move the lower weight on the counterweight shaft further down the shaft a little or have a separate, tempoary additional 'movable' weight that can be placed on either the shaft or the scope depending which side of the meridian they are?
Just interested in what other imagers do - grateful for any insight. I saw on this Group several weeks ago an ingenious solution using an automated method which fasinated me and sparked my interest but is way beyond my mechanical abilities. I am interested in a better understanding of the 'eastside heavy rule' and any suggestions for a simpler method to apply the necessary bias.
With help from this Group I am slowly getting back into imaging with my 14 yr old G11, Gemini-1 and my DSLR after several years away from the hobby.
Many thanks
Terry [uk]
|
Re: Used GM-8 Guiding Help
Hello Nick - it looks like you got a lot of data there!?
The first image shows PE of about +/-20". I have heard before that people say that the PE of a G8 mount is double that of a G11, so that would equate to around +/-10" for a G11, which is quite high, but believable (with the old worm).?
However you also need to take account of the fact that the worm period is twice that of the G11. I think the issue with your curve is that there are some PE components with much shorter wavelengths than the worm period.?
The second image also shows around +/-20" but there is a long wavelength sinusoidal component (the green curve) which PECPrep has not accounted for in the numbers in the second figure.?
I have started taking the output from PECPrep and analysing them in Excel, so I can remove longer wavelength components (using Excel's trendline tool) - think PECPrep only removes a linear trend (not anything that is sinusoidal or other type of variation) -? I have also seen a long wavelength sinusoidal component superimposed on the periodic error - I think this can only come from small variations in radius of the large gear wheel (which would explain why people find "high" spots).?
The figure below shows a comparison of my G11 with the old worm and before I regreased and realigned everything and installed a new high precision worm (I also changed the bearings in the RA worm block and put a Belleville washer in). This was with quite a small telescope (around 6 kg) and I'm going to repeat the PE measurement with a larger telescope (since when I did that with the old worm fitted, the PE seemed much smoother). I would definitely recommend putting a high precision worm in the RA axis (but you probably don't need one for DEC). With the older worm I was getting approx +/-10", and once I had put in the new worm, and regreased and realigned everything it came down to about +/-5".
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Re: Useful tip for G11 Digital Drive owners: https://nova.astrometry.net/
Hello Paul - yes I check that the main and finder scope are aligned and centred, but I usually do this visually, and the issue is the focus point for the eyepiece for the finder and main scope is different from that of the cameras, so once I have found a bright star whose position I know, you then have to refocus the cameras.?
What I am suggesting is that you can bypass the visual step by just pointing the main telescope, with camera focussed, on a random bit of sky somewhere in the region of the DSO, upload the photo to the??website, and after a couple of minutes that will tell you the exact RA and DEC position of the centre of the photo, which you then set on your setting circles, and then you can move to the coordinates of the DSO for the photo session.
Incidentally, I have recently got a new ASI 071 MC Pro Cooled camera, and am seriously considering ditching autoguiding altogether, for simply taking short exposures of 10-20 seconds, and stacking hundreds of images (with the gain set to 200 and offset to 60). If this works it will mean I don't need to autoguide at all. For the image scale I have and the periodic error of my mount, 10 or 20 seconds should be OK for tracking.?
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Hi all. My wife and I got into this hobby in the mid-80s with a classic orange C8. After getting a ton of use out if it, both visually and a bit of film-based AP, a new?10¡± LX50 followed in the late 90s. But life intrudes, and the past two decades in Dallas and LA put the kebosh on stargazing, for both time and sky quality reasons. We¡¯ve finally gotten back into it after a move to Utah and subsequent retirement.?
Three months ago I suddenly discovered that I¡¯m 24 years older than when we bought the 65-pound Meade contraption, that the assembly and tear down was, well, tearing me down, and it was time for something more portable. We researched the crap out of the mount market. Long story short, we bought a new G11G with the RA extension and two great carrying cases from Scott and company in the late fall, de-forked the ¡®ol LX50 OTA and started anew. More or less.?
Three things - first, dealing with the people in Burbank was a true pleasure, and I can¡¯t say enough positive things about them. Second, the quality and functionality of the G11G is far beyond our expectations. Third, we¡¯re thrilled by the advancements in observing and AP tech over the years and look forward to getting back into it in a big way. We¡¯re confident that our new mount and old scope will give us a great start.?
Very happy to join this group, as well as the Gemini group. Good to ¡°meet¡± you all.
Brian
?
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Re: Useful tip for G11 Digital Drive owners: https://nova.astrometry.net/
Robert,
There are two things I don¡¯t understand about what you say.
1) Do you align the main and finder scope before doing this? Is so, then once an object is centred in the finder it should be centred in the main scope as well.
2) Why do you have to refocus after adjusting the setting circles?
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Hello - I do astrophotography on a Digital Drive G11 - one problem I have had in the past is that if I use the finderscope of my telescope to find a bright star, then centre it in my main telescope, set the setting circles to the star's coordinates, I then have to refocus the main and guider camera, before moving to the position of the object I want to photograph.?
Maybe it is obvious to others but I have now started to use??- you simply point your main telescope in roughly the right direction of the DSO, and take a photograph. Then you upload the photo to??which after a minute or so tells you the exact RA and DEC coordinates of the middle of the photo. You can then set the setting circles to these values and can then quickly move to the DSO coordinates.?
This does depend on you having internet access on your computer when you are observing, but is a neat trick for those G11 owners that don't have Goto.?
My main telescope has a focal length of around 700 mm (or 500 mm with a focal reducer) and when coupled with a ZWO ASI 071 camera, the field of view is about 2 degrees by 1 degree, so the above method should enable you to get the DSO in the field of view of the camera, and you can then use the hand controller to centre it.?
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Re: Making the most of cloudy winter nights with a new mount and scope
Geoff,
So many things to suggest here for AP:
-Go to the??website and read as much as possible to get acquainted with the mount controller
-Go to the Losmandy channel on YouTube and watch all the videos, especially how to create a star model and sync for accuracy.
-Get a good AP book such as The Deep Sky Imaging Primer by Charles Bracken. He will show you all the steps from capture to final processing
-Learn all about PHD2 and how to connect to mount and guide scope
-Decide on your capture software. I am a fan of Sequence Generator Pro but NINA is a pretty good free one
-Cloudy nights are a good time to collect your bias and dark frames and start building a Library of files. They should be taken at the same temperature as when you collect the light frames.
-Learn about collecting flat frames after your imaging session to remove dust motes, vignetting and other optical defects from your lights. I never got anything good with sky flats and use a light tracing panel covered with a sheet of translucent white acrylic sheet.
-If you go to the Astro Imaging Channel on YouTube, there are hundred of videos on AP and related topics
-Think about the processing software you want to use. PixInsight is very popular, also Photoshop and some others
-You may want to get a dedicated astro camera or astro-modify you DSLR (but voids warrantee!)
Get ready to go down the rabbit hole.
Best of luck,
John
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Re: Used GM-8 Guiding Help
Nice testing work, Nick.
If you turn your mount head upside down, you will find it's serial number stamped there. The Losmandy company can tell you when it was produced.
As you have the original steel worms, and two separate worm blocks, your GM8 system is of the original design.??
Your PE test shows a lot of fast oscillations within a GM8 worm period.? There is a known plastic gearbox first to second gear ratio reduction of 7.5:1 of a G11 period.? So it might be that the "fast" oscillation is from that plastic gearbox.? When you changed the RA with DEC gearbox that oscillation character changed...so it could support the idea it comes from the gearbox.? A new gearbox may also help you clean up the PE.?
The bearings are another question and your changing them will help reduce the PE.? Eventually getting the precision brass worm will help a lot too.? Chip mentioned that change could cut your PE to half.? ?
So keep going and let us know how it goes.
Best of luck, Michael
Thanks for the input! Luckily I had clear skies last night and tonight so I will give an update on where I at.
Last night:
I had 3 separate unguided runs using PHD2's guiding assistant which I was able to trim to the usable data in the middle of the guiding (toward the end I was losing stars due to trees in the way). The first run I didn't get much data, the second run I had good data but realized my polar alignment was significantly off, and the third run I fixed the polar alignment to be very good and had usable data. I analyzed the third most viable run in PECPrep with help from Michael Herman and found a horrible periodic error with almost every harmonic and also the gearbox bringing in an error at 32sec. See pictures 001 and 002 for last nights graphs from PECPrep. This was done at focal length 200mm with the ASI120mm
Today:
After noticing such large errors and gearbox issues last night my first test was to swap RA and DEC worms and gearboxes. While the mount was apart I also noticed the bearings on the Dec axis seemed to move more smoothly (still a little jittery), so I also swapped RA and Dec worm blocks. I did notice the RA gearbox had a sticky point, and after playing with it had a faint "click" and it was smooth again, I believe I may have misaligned something the last time I had the mount apart (last week) for greasing and when putting the motor back on I admittedly put a little force on the motor when the gears were not meshing correctly. For now it seems okay but may order a new gearbox if data shows its shot. I did slightly grease the oldham coupler for good measure also.?
Tonight:
I was able to get more unguided data tonight from PHD2 guiding assistant and made sure to have a good polar alignment. I also did an east biased balance (new larger heavier scope is not in the cards right now unfortunately). I did the same process of trimming any ends of data that were corrupted due to obstructions or settling time, then ran through PECPrep for analysis. It may be worth noting tonight I used a focal length of 344 instead of 200 used last night. The peaks appear to be worse, however the gearbox error seems to have been removed mostly. See pictures 003 and 004 for tonights graphs/analysis
Future:
I may try swapping worms again but keep the gearbox configuration. I need to do adjustments anyways as I was getting RA motor lags warnings again on certain high points of the worm wheel (no lag errors during the unguided data though, the high points were not in that area). I ended up purchasing (4) new abec 7 bearings as well as the belleville washers and plan to do the upgrade this weekend (choosing best 2 bearings for RA). It's looking like a HP worm is desperately needed, but I will first see what I can get done with these modest mods. I noticed the current bearings are a little "jittery" when rotated, so I'm hoping a more buttery smooth bearing will help out. In regards to adjustments in a warm house, luckily I'm in sunny south florida where the temperature is warmer outside if anything! As for guiding rates etc, the errors are so bad that guiding wont even provide enough correction at 100 aggressiveness on the RA but I will focus on dialing in guiding when the time comes. I'm not sure how old this mount is but I would guess early 2000s, I may have gotten somewhat of a lemon, but hoping to get it running nicely again upgrade by upgrade, and try to take it slow and enjoy the process! Thanks everyone for your help, and I'm open to any additional input!
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Re: Used GM-8 Guiding Help
Thanks for the input! Luckily I had clear skies last night and tonight so I will give an update on where I at.
Last night:
I had 3 separate unguided runs using PHD2's guiding assistant which I was able to trim to the usable data in the middle of the guiding (toward the end I was losing stars due to trees in the way). The first run I didn't get much data, the second run I had good data but realized my polar alignment was significantly off, and the third run I fixed the polar alignment to be very good and had usable data. I analyzed the third most viable run in PECPrep with help from Michael Herman and found a horrible periodic error with almost every harmonic and also the gearbox bringing in an error at 32sec. See pictures 001 and 002 for last nights graphs from PECPrep. This was done at focal length 200mm with the ASI120mm
Today:
After noticing such large errors and gearbox issues last night my first test was to swap RA and DEC worms and gearboxes. While the mount was apart I also noticed the bearings on the Dec axis seemed to move more smoothly (still a little jittery), so I also swapped RA and Dec worm blocks. I did notice the RA gearbox had a sticky point, and after playing with it had a faint "click" and it was smooth again, I believe I may have misaligned something the last time I had the mount apart (last week) for greasing and when putting the motor back on I admittedly put a little force on the motor when the gears were not meshing correctly. For now it seems okay but may order a new gearbox if data shows its shot. I did slightly grease the oldham coupler for good measure also.?
Tonight:
I was able to get more unguided data tonight from PHD2 guiding assistant and made sure to have a good polar alignment. I also did an east biased balance (new larger heavier scope is not in the cards right now unfortunately). I did the same process of trimming any ends of data that were corrupted due to obstructions or settling time, then ran through PECPrep for analysis. It may be worth noting tonight I used a focal length of 344 instead of 200 used last night. The peaks appear to be worse, however the gearbox error seems to have been removed mostly. See pictures 003 and 004 for tonights graphs/analysis
Future:
I may try swapping worms again but keep the gearbox configuration. I need to do adjustments anyways as I was getting RA motor lags warnings again on certain high points of the worm wheel (no lag errors during the unguided data though, the high points were not in that area). I ended up purchasing (4) new abec 7 bearings as well as the belleville washers and plan to do the upgrade this weekend (choosing best 2 bearings for RA). It's looking like a HP worm is desperately needed, but I will first see what I can get done with these modest mods. I noticed the current bearings are a little "jittery" when rotated, so I'm hoping a more buttery smooth bearing will help out. In regards to adjustments in a warm house, luckily I'm in sunny south florida where the temperature is warmer outside if anything! As for guiding rates etc, the errors are so bad that guiding wont even provide enough correction at 100 aggressiveness on the RA but I will focus on dialing in guiding when the time comes. I'm not sure how old this mount is but I would guess early 2000s, I may have gotten somewhat of a lemon, but hoping to get it running nicely again upgrade by upgrade, and try to take it slow and enjoy the process! Thanks everyone for your help, and I'm open to any additional input!
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Re: Used GM-8 Guiding Help
Hi Nick,? One of the better qualities of SuperLube is the low viscosity even when extremely cold, additionally it won't run all over when hot and get on your clutch discs. This helps with smaller payloads in the saddle of Losmandy mounts which as Robert mentioned tends to prefer heavier payloads than lighter payloads due to the Losmandy mount design's relatively low sensitivity to imbalance even when well lubed and adjusted. This is often interpreted as stiction but is designed in, caused by the friction of the large disc surface area used in the Porter slip clutches. Being a visual observer I'd take the imbalance insensitivity to have the Porter slip clutches and finger tip PUSH-TO operation. The best solution is to buy a bigger scope, but you could also just leave some imbalance in the mount to load it by keeping the worm pushing on the worm gear moving it uphill and not bouncing from one worm/worm gear face to the other worm/worm gear face. These mounts also do much better with less aggressive correction factors in PHD2, 0.5 guide rate and longer 2 second exposures slow the complete system's reactions to seeing so the mount does not cause a looping hysteresis problem by chasing the seeing trying to compensate dozens of times repeatedly when in the real world virtually no correction is needed.? Fresh ABEC 5 or better bearings will improve your mount if they have never been changed, do not be tempted to lube them in anyway. The Belleville discs resolve a smaller issue by preloading the bearings and forcing the balls to move with the worm and they help with setting backlash by forcing the worm to remove axial worm backlash between the bearing blocks. Regarding the Oldham coupler, if you can replace it completely with a new one or the plastic center coupler part if you can find the right one (they wear out) any looseness is bad in this part, a drop of SuperLube won't hurt here either but only a tiny drop.? A couple of other notes: you could swap the steel worm from the DEC to RA and see if that makes a difference but in my experience with the steel worms the fastest way to finding good PE performance on a classic Losmandy mount is to buy a new HP worm and install it in your RA. The HP worms typically reduce PE error by half of a steel worm on the same mount. I suggest ordering the HP worm now, do not change the bearings and add the Belleville discs until you have the HP worm to install on at least the RA axis before running your baseline tests. Do not adjust the mount in a warm house, leave the mount out in the cold several hours and only after the mount has fully cold acclimated do a worm backlash adjustment. These mounts when cold acclimated shrink a LOT and you can get lagging and stalls due to the loss of adequate backlash. In a warm room you will be temped to readjust out the now excessive amount of backlash - DON'T DO IT!?? Yes, find the baseline and use it to improve on. Make notes and if things go crazy go back to that setup and verify it works as you think it should before messing with it some more.? Hope this helps! -- Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
?
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Making the most of cloudy winter nights with a new mount and scope
With my new GM811G, I have been working through setup details. When the scope came, we had three clear nights and I was able to be out, getting familiar with the new mount.?I love it!!
?
My experience and equipment: I¡¯m still pretty new at visual work and brand new at AP.??I am on my second scope and mount, having swapped out a TV 100 ED doublet for an ES 127 triplet 2 months ago, and an ieq30 for a GM811G two weeks ago. Lots to learn on the new scope and mount. Then my ASIAIR Pro (AAP) and my ASI290mm-mini and my?ZWO 30mm mini Guide Scope all arrived, and I¡¯ve been working on connecting them?to my Gemini 2 and a GL-iNet Mango mini router.?I think it works. Whew!
?
What I would love to do is practice, practice, practice. But the skies are likely to stay cloudy for more weeks, maybe all next month.?
?
Q: Let¡¯s say I have more weeks of cloudy weather, and I want to hit the ground running when the skies clear. What can I do now that will make both viewing and beginning AP easier then?
?
My goals by summer:?
¡¤??????Continue visual observing. Been using ¡°left Turn¡¡± and SkySafari+ to get around with my goto. I want to learn the constellations and the sky much better.
¡¤??????Learn my setup routine both local (often) and remote (occasional).??The GM811G seems miles deep in its competencies, and there is a lot to explore
¡¤??????Learn to PA and guide with the ASIair Pro, camera and scope.?
¡¤??????Learn how to use my Fuji XT3 on my mount for both widefield (with fuji lenses) and deep sky (through my scope). I have attachments.
I know that processing is a whole other area that lies in the future, but I¡¯d rather leave it alone for now and develop some competence with what I have.?
What can I practice with my scope and mount setup now that can get me ready for clear skies when they come? What do you all do on cloudy weeks when you want to do something to build your skills???Any advice would be welcome!!
Geoff Chapman
?
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Re: Useful tip for G11 Digital Drive owners: https://nova.astrometry.net/
Robert,
Nice tip. I'll bookmark the site for use at home - I can't use it in the field but it is nice to have the option at home.
The way I have gotten around this problem is to use a flip mirror on my finder/guider and then at the start of the evening (I have to set up and tear down every night) verify that the imaging scope and the guider are co-boresighted so the finder/guider is always pointed at the same spot in the sky as the imaging scope (usually 1100mm with an APS-C sized CCD chip so my FOV is roughly the same as yours). I slip-focus the eyepiece (if used) in the imaging scope when I do this so I don't have to touch the focus knob on the imaging scope. That way I don't have to radically re-focus the imaging scope after installing the camera for the evening - I do a one-time focus tweak of the camera each evening or between shots, if required. Such is the price of working from the trunk of car.
The guider is set up so the guide camera and the eyepiece of the flip mirror on the finder/guider have a common (para-) focus. Doing this requires enough in-focus of the guide scope but the 80X500 short tubes commonly used have a lot of that.
When imaging at shorter focal lengths (under 700mm or so) I just use a modified 8X50 finder. There I had to hacksaw off about an inch from the tube to get the required in-focus. See:
I also built a slightly bigger (and marginally more expensive) version from one objective cone of a 15X70mm Celestron Skymaster bino and a Vixen flip mirror, using the other objective cone to make a wide-field scope.? I bought the binos decades ago (when the price was $58) and didn't use them much. Re-used both eyepieces as well.
Regards,
Mark Christensen
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Re: RA Divisor on Gemini 2 G811 mount.
Eric - Many thanks for this. A nice addition to my small, but growing trove of useful Gemini documents!
Ed
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Chip Louie
Michael Herman