MarkS

We should do this, but I have no idea what is the best/easiest way to set up such a knowledge base. Do we have in our cohort anyone who can and is willing to do so? Or can we simply use this forum via some dedicated 'knowledge base threads'? Presumably ASA would not object to such an initiative. Mark

Hi all, Thanks for this discussion. What I understand from this is, with the ASA mounts, there is little difference between MLPT and guided performance provided that the system is well set up and aligned. There are reasons to expect that, if the MLPT track has been accurately determined, the very fast response of the mount/AS/ Sequence combination should give better tracking than guiding with its slow 'after the event' corrections.This is what I would expect but I have made no direct comparisons. I can vouch for the DDM's spectacular response to wind gusts - it is really interesting to see the short term current spikes as they happen. As Waldemar says, adaptive optics is perhaps the only path to improving star FWHM for a given seeing condition. Mark

Hi Max, I'm using the ASA10N, usually at f/3.6, but often at f/6.8 and sometimes at f/2.8. I have both a DDM85A and a DDM60. I have never tried to guide them. I always use Sequence and MLPT. With my usual seeing conditions of about 3" - very rarely 2" - I think star size is determined by seeing and focus variations, not inadequate tracking of the mount, but I've never tried to do a comparison between guided and unguided. Mark

Hi All, I notice that some of you are guiding the DDM85 mounts, whilst others do not. Has anyone done an in-depth comparison of guided performance vs. MLPT on a well set up system? My reason for asking is that I have seen claims that stars will always be smaller and sharper with guiding, no matter how good the mount is. I find this hard to understand if the unguided mount is tracking to sub-pixel accuracy over the time of each exposure, which my mobile set-up certainly does - in fact I've measured my DDM60 to track within 0.75 arcsec over an hour. I would dearly like to be enlightened on this issue. Mark

Hi Antonio, Very clean, very interesting image! And no, I'm not enjoying Southern winter. I have not had a really decent night since the end of May!!!!!! So I must content myself with looking at such nice images as this! Mark

Lukas, Interested in your comments on focus. I have found that the Sequence AF routine does not seem to be accurate enough at f/2.8 on the ASA10N/OK3. I am currently using manual focus, which, with a temperature drop of ~10C over 4 hours, needs no adjustment. As for trailing stars, I've never been keen on large pointing files. Sometimes I make a 10-15 star file if there is time available between PA and session start, but usually I just go with the last 3 star same DEC file obtained in the PA process, and use MLPT. I find this very reliable. Mark

Hi Dale, Chase them again, and copy the email to Dietmar Mark

Hi Christer, I went for the Class2. My sensor has one noticeable column defect at room temperature, which is almost invisible at -25C. As you say, this easily accounted for by calibration. I understand that the Onsemi processing is producing a high proportion of Class1 sensors, but they are still asking a high premium! Mark

I haven't found the limit yet, as it's winter here, but at 43C below ambient it is running at less than 70% power. Mark

Hi Christer, Good luck with that! I 'bit the bullet' and bought a set of 50mm filters. As you say, more expensive than the camera! Moravian were not enthusiastic about the use of 36mm, but with a good set of flats you might get away with it. Incidentally, I bought the EC (extended cooling) version, due to our summer night time temperatures. But I guess you don't have that problem. Mark

Hi Christer, With no guiding, there is no problem. I used the Moravian M48 nosepiece, and designed an adapter to fit between the ASA Wynne and the nosepiece. The front of the nose piece to sensor distance is 41mm. With 3mm filter thickness the adapter needs to be 17.6mm thick - or 17.3mm if there is no glass cover on the sensor. The final result is similar to the ASA style adapters. You need different thickness adapters for the reducer and barlow. If I was getting a second set made, I would possibly design for a larger aperture than M48 for the Wynne as there is a little vignetting in the corners. However, as you can see from the image, calibration deals with the vignetting well. For the reducer and barlow I wouldn't bother, because they both have image circles that do not cover the 16200 sensor - necessitating a crop to manage coma. Mark

Hi Lukas, I can't help with the backfocus, but I thought you might be interested in the enclosed image. I got a G3-16200 more than two months ago, but the weather here has been horrible! So last night I got it under the stars for the first time. Unfortunately I was in suburban Melbourne, and there was 25% Moon, so the SQL was 18.3. Narrow band was in order. In the event I got only one 10 minute sub in Ha that was not ruined by cloud.... So here it is: it has been very mimimally processed - just calibrated and given a very little clean-up with MLT, then stretched, in Pixinsight. The frame was prepared for the web in CS5, with a very low dose of sharpening to compensate for the file size reduction. I've shown the full frame so you can see how the ASA10N and Wynne Corrector handle the corners. ASA10N at f/3.6; DDM60; G3-16200; Astrodon 5nm Ha filter; 10minute exposure. Mark

Very clear and sharp image and very nice colours Mark

Very interesting - good to see, especially as it is too far north for me. Fine shot! Mark

Thanks Luis. A few hours at f/2.8 is worth a lot!

This image was shot from my Mt. Macedon site on 30th May. ASA10N at f/2.8, DDM85A, Moravian G2-8300 camera, Astrodon filters. Total exposure 4hours: 2 hours L, 2hours RGB. Not a particularly good night: SQL best 21.24, seeing ~3". Just managed to beat the dew as RH > 100% near the end of the run. As a sidebar to this, the original image exhibited two minor planet/asteroid tracks. The first was readily identified as 7 Iris, but the second took some tracking down with help from the people at Siding Spring. It was finally identified as 1109 Tata, a 66km diameter object with a 88 year orbital period and apparent magnitude 14 that night. Of course, both these left unsightly multicoloured tracks which I removed for this picture.

These distant galaxies can be tricky. You've caught the colour contrasts beautifully! BTW, the best SQL I've measured is at nature conservation property - unfortunately 700km from home - 21.78. The best I've obtained at my 'best within easy reach' site is 21.55, but this site seems to be gradually deteriorating as Melbourne grows - and the local councils don't give a damn about light pollution. However it still does better than 21.2 most nights. The best seeing I've experienced - as measured by CCDInspector - is 1.8". Mark

Hi Luis, Beautifully resolved image! Mark

I get essentially the same results with the DDM85 as the DDM60. Both will easily do 20 min subs. I ran a test last night with the f/2.75 set-up (1.6"/px) and on two consecutive 20 min subs there no detectable drag. When examined at 300% size, tiny faint stars showed seeing variations, but no systematic drift. PA was 1.7arcmin RA and 0.5 arcmin DE. Balance reasonably OK (maximum current draw shown by ammeter ~0.55A). 10 star config; MLPT used. (Accurate focus is the issue for me at f/2.75 - I went back to manual focussing, which remained accurate for > 4 hours including meridian flip and 12 degree C temperature change) Mark

Antonio and John, Thanks for looking and your comments.

Hi Denis, The tuning parameters depend on the telescope/camera combination, so it is difficult to comment on your numbers without knowing what the system is. Vibration during slewing is usually a sign that the fast tuning parameters need to be backed off a little. It can also be a sign that the tripod is not solid enough or well enough damped. Mark

Thanks Luis and George. George, best at my usual site is 21.59. Best I have measured - unfortunately not visited much because it is 700km away - was 21.78(!) Mark

NGC 4038 and 4039 are two interacting galaxies in Corvus, about 50 million light years away. They are currently in a starburst phase, and it is estimated that they started to interact about 900 milliom years ago and that the antennae formation started around 300 million years ago. The cores of the pair are about 4 arcminutes in diameter, and the antennae span about 20 arcminutes. The galaxies are listed as magnitude 11, but the antennae are very tenuous. This image was shot with the ASA10N in f/6.8 configuration with all subs binned x2, giving a plate scale of 1.3"/px and an effective focal ratio of about f/3.4. Total exposure 5 hours 20min LRGB. Camera Moravian G2-8300; DDM85A mount. SQL reading only fair at 21.2, and seeing also only fair, at ~3". Processed in Pixinsight and Photoshop. Mark

Impressive performance from the whole system! Splendid result. It would be nice to see an uncropped version at higher resolution! Mark

This edge-on spiral galaxy in Centaurus (Type SB(s)bc) is very dusty, with a super-energetic core thought to contain a large black hole. It is 11.7Mly distant, and about 65kly in diameter. ASA10N at f/3.6; Moravian G2-8300 camera with Astrodon filters; DDM85A mount. L 1hr; R,G,B 40min each. SQL 21.15; seeing ~3". the field of view is 36' x 25'. Processed in Pixinsight and PS CS5. Mark