wemartin

Hi Max, I might be interested in your repaired DDM85. Mine has broken again and I am tired of repairing it. Please use my email address below to let me know what model and how old it is as well as what fault is being repaired. Kind regards Bill william.e.martin@ntlworld.com

I just noticed the OK3 series focusers don't appear on the website any more. Does this mean they are no longer a product for sale? My OK3Z is getting very tired and I was thinking of buying a new one....

Hi Marcus, I suspect you will have to sync your mount/scope to a bright star again before you do the three to five star pointing file for polar alignment if you have deleted the old configuration. Bill

Hi Prefetch, I sent you a reply to your pm a couple of weeks ago. Apparently you didn't receive it. Here's the public version: I have had no issues of pointing stability or polar alignment with my PierTech 3 pier mounted on a 2m reinforced concrete column. The polar alignment is stable for many weeks at the level of repeatability of the Autoslew alignment procedure, about 0.2 arc min. There might be long term variability but this could very well be due to the column moving with temperature. One thing I do as a precaution is stop the pier raising to the very top limit of travel on the basis that the two columns of the PT3 may not be perfectly aligned. The sacrifice of a centimetre or so of height is a bit of insurance. So, basically you are more likely to change the polar alignment by changes to the OTA than I observe arising from the PT3. Of course if you crash into the mount all the extra mechanical interfaces mean you are more likely to shift something than with a solid pier. Bill

Hi Lukas, The latest version of Autoslew, v 5.2.0.7 from Philipp Keller has solved the AtPark problem with ACP, at least in the limited testing I have done on it. There may be some corners of the performance space that I have not explored yet, however. This version also has a workaround for the SideOfPier issues with ACP and the ASCOM standard definitions. Contact Philipp for the link. Kind regards Bill

Hi Waldemar, I agree with Gerald and will try one of these units. I have been fighting connection problems for months! Kind regards Bill

I have a distance of five metres between the mount and the control pc and I currently use high quality USB extension cables. The USB hubs in the mount are almost robust enough for this but I have had a lot of problems with USB connections to the mount and to the focuser and camera through the hub connection. Weird mount behaviour happens occasionally which, if everything is freshly rebooted, goes away for a while. I have tried active extenders which add another hub to the chain and a CYB Ethernet/USB extender. The latter won't work with the nested hubs in the mount for the focuser and camera but runs the mount just fine. Does anyone have any recommendations of USB cable extensions that work reliably? Bill

Hi Lukas, I have a 3" Wynn corrector from ASA. It's an excellent optical design but the internal masking for the polished edge on one of the lenses was not done properly. I had to take the corrector apart and cover this edge in order to get rid of some ghosts and to get good flat fields. If you take some images with and without the corrector (balance problem...) you should be able to isolate this. The pure Cassegrain images will also give you an idea of how much the corrector is doing for you at the FLI ccd edge. You say Cassegrain-Newton...does this mean the primary does not have a hole and you have two secondary mirrors? Baffling a fast configuration like this would be a real challenge and light diffracting around the Cassegrain secondary could be a problem with small misalignments. All well-known and ray-traceable.. Bill

Hi Lukas, Suggestion: Find a very bright star and centre it in your field of view, take the camera off and look through aperture and/or simply allow the light to fall on a white screen. You should be able to see if there are stray reflections from baffles or screws or whatever. By slewing the OTA you may be able to make these bad enough to find what's causing it and remove or mask these. You should be able to use the diffraction spikes from the secondary mirror to fine adjust the collimation and centering also (I am somewhat surprised these are not stronger on the brightest stars). The 'rings' look like they have stars in them which means a stray reflection is ending up in the focal plane. Have a close look at your corrector for polished edges on the optics which have not been masked. I would be surprised by a baffle reflection ending up focused. Usually these problems show up as poor contrast or 'blobs' in parts of the image. Good hunting. Bill

Hi Lukas, Looks like you have a collimation problem, could be primary or secondary. The focus is difficult to find when the collimation is off. Do you have a field flattener? Bill

And back again to Autoslew. It seems this problem is a DestinationSideOfPier issue not a SideOfPier issue. If Autoslew says it can report both SideOfPier and DestinationSideOfPier then ACP uses these for the time to flip calculation. Apparently the standard and the industry practice on how DestinationSideOfPier is determined can lead to differences which result in bad things about pier flipping times. These are not likely to arise frequently in normal operation but sadly the survey I am doing ends up with this issue almost every night since I am doing a long series of short exposures around the Pole. Messy, fixable but only within Autoslew if operation with ACP/Scheduler is expected to go smoothly. Bill

My apologies to all and especially Philipp Keller. I now know more than I ever wanted to know about German equatorial mounts and SideOfPier considerations. Finally reading and testing Autoslew and the mount against the ASCOM V2/V3 standard shows that the mount is reporting exactly what it should. There is no SideOfPier reporting problem. If you wish to check this yourself and find the very arcane definition that is the SideOfPier property and how it is not the same as the physical side of pier, I attach a short Visual Basic program that runs under ACP scripting that slews in a loop around the Meridian through the zenith and Pole. This has not solved my 17000sec wait for flipping the mount that ACP is generating but, AutoSlew reports correctly when slewing near the Pole in so far as I have been able to test it. Back to ACP then. Bill PierSide3.txt

Hi to All, If there is sufficient interest in doing 'real' science with ASA equipment then there are a very large number of projects that can take advantage of the singular attributes of small, dedicated telescopes. You should be aware that doing science with a small telescope will require a degree of commitment and dedication that may come as a bit of a shock. I am part of a survey team doing follow-up photometry on a large group of type M Dwarf stars using small telescopes. We are using 3-4 40cm telescopes in the really very bad conditions of the UK to do absolute and differential photometry on about 500 Northern stars ( Southern stars...w0mbat??) in a new database. It will take the best part of a year to complete this and it may not be successful if we cannot produce high quality data. The latter is not so much equipment dependent as it is on having good photometric conditions...a real problem here. The kind of experience one needs to do this particular study could be gained from successfully capturing exoplanet transits. One of the things I am responsible for at the University of Hertfordshire is encouraging non-professional astronomers to join in projects like the above. We have a large number of projects that are simply too long for students to undertake that could be done with small telescopes but, be aware that many of the projects involve 'staring' at an object for long periods, i.e. taking a series of exposures over days to months...this is where small telescopes can go that large telescopes cannot (economically). From my own experience I would recommend very strongly that your equipment should be capable of nearly autonomous operation...you will need to sleep once in a while. Exoplanet transits are a good training exercise. If you don't have the patience for these then you may wish ponder how much time more challenging targets may take. Free advice, it's worth the price... Bill

Oops. Should say 03h RA, 64deg DEC. Must be early onset Alzheimer's. Bill

This is actually a SideOfPier property reporting fault in AutoSlew. I have confirmed this several ways but the most obvious was today in some slewing tests in daylight. At 15:30 LST slew to 13h RA, 64deg DEC. AutoSlew (and ACP) report pier side is west and the mount is in the west position (counterweight shaft pointing west). Slew to 30h RA, 64deg DEC. AutoSlew (and ACP) report pier side is west but the mount is physically in the EAST position with the counterweight shaft pointing East. So there is a bug in the pier side reporting when the position is North of the Celestial Pole. Bill

I have the same configuration; roll off roof needing a Park setting very low. I set Autoslew to -1deg and this allows me to park the scope correctly but I set the observatory control s/w to +20deg above the horizon to keep the scope above the side walls when doing exposures. I use ACP but the horizon limits can also be set in most planetarium programs and in some of the camera programs that can control the observatory like Maxim. Issuing a Park command to Autoslew will override the observatory horizon limit and park the scope correctly. Bill

Hi Ralph, If you are still interested, the 31mm filters, a good collimation, and the vignetting is not detectable apart from a slight (~5%) roll-off at the edges in a QSI flat field frame. This is entirely corrected by the flat field process to less than +-1% over the whole frame. I've done this with both sky flats and with a EL panel with no surprises. Bill

Hi Clemens. I am running Starry Night Pro Plus with Autoslew and ACP. Are you still having problems? Bill

I have read all the explanations, done the tests, tried many combinations but have failed to find the right settings that minimise the waiting time in ACP when the object I am imaging crosses the Meridian. I am part of a survey consortium looking at particular stars for up to four hours per night total time using a repeating sequence that takes up to five minutes to cycle through. No individual exposure is longer than 2 minutes. Needless to say it's very difficult to avoid going through the Meridian with such a long dwell time on a single target. The minimum delay time ACP inserts is about 40minutes when crossing the Meridian and no exposures are done during this time. I have set the ACP flip points at zero (flip at the Meridian) and the Track Past at 50min with a 5min assurance time. I know from testing that the DDM85 will slew to 200min past the Meridian without flipping but I cannot use this as the OTA hits the pier in some configurations. So, I obviously have failed to grasp what ACP, AutoSlew, and the DDM85 are doing at the Meridian with my repeated exposure configuration. Can someone suggest a set of parameters that will reduce the waiting time? And why these work? Bill

Hector, I have a DDM85 with a ASA16N astrograph. It is mounted on a Pier Tech raising pier in a roll-off roof observatory. When the pier is up the telescope is fully exposed to the prevailing wind. The principal issue is how gusty the wind is rather than strictly wind speed. At my semi-urban site we can get gusts of 2-3x the average wind speed. I find that winds of less than about 6kph have little effect on star fwhm in a 120sec exposure. With gusts of 10kph the stars are trailed in the wind direction to about 2x the fwhm. Above 10kph constant speed I don't even try imaging but webcam 'lucky imaging' is possible if you are patient. I have set the limits in the weather sensor to 5kph and have had good success in automated photometric observations(so far...). Regards Bill

I have one of the Foster Systems optical sensors on my DDM85 since I use a PierTech PT3 to raise the mount for my roll-off roof. I thought the optical system would save me some messy wiring rather than using reed switches on a moving pier. It's ok but, it's not as sensitive to angular displacement as I had hoped. My roof is a very tight fit and it is possible to bump the telescope enough that it can hit the roof or intrude into the roof sensor beam and still appear to be parked on the sensor. It has to indicate parked at the top and bottom of the pier travel so I may be asking too much. More tweaking may permit better performance. Bill

Bob Denny and I went around this problem with ACP and Autoslew a couple of months ago. The work-around solution is to activate ACP's UserActions.wsc facility. For more information, look at the UserActions.wsc file itself with Notepad. The attached file has the shutdown logic. You will have to rename UserActions.wsc and register it as outlined in ACP Help. Oops, the site is not permitting me to upload the file as a .wsc, here's a text version. Have a look at the original and this version in the Shutdown logic. Bill UserActionsAutoSlewPark.txt

Hi Luke, Yes, the ACP workaround works ok and I have not been able to reproduce the Park 1, Park 2 issue. This may have been finger trouble on my part but my mount is at ASA for a USB hub upgrade so I am not able to check this at the present time. Bill

Gerhard, Doug A 4mm thickness of glass with n=1.5 is the equivalent of 6mm=4x1.5 of air so the delta thickness of the path in air is 2mm, not 1.32mm. Bill

Hi Ralph, I've just changed the filters to the 31mm versions but my mount is being upgraded so I can't tell you how they work. From the 1.25" filters it looks as if the CCD chip may be slightly off centre from the mechanical/optical centre of the 16N Wynne corrector. This could be a simple external misalignment problem from my initial collimation attempts but I won't be able to confirm this for a while. I have confirmed the corrector problem with flats and discussions are under way. Kind regards Bill