DDM60 workflow question for a portable setup

[AnakChan]

Hi All,

Owning my DDM60 for a year now I'm still learning about it (not used it for any imaging yet, but just doing lots of "tests"). I don't have an observatory and use it as a portable setup in my backyard. Currently my setup time from carrying my gear out to my lawn, balancing, PA'ing, syncing, and all-sky modelling takes me approx 2 hrs at best. Furthermore as my OTA is a Takahashi µ250CRS and I image at native 2500mm FL with an ASI6200MM (therefore imaging at 0.31"/px unpinned or 0.62"/px binned), I'll have to use MLPT too.

I came across @ChristerS presentation in TAIC he made 5 yrs back and according to that, I could actually skip the sky AutoPoint (which would save me about 1 hr for 100 point model), and just go straight into MLPT. But according to documentation, the recommendation is to do MLPT on top of AutoPoint.

1) Can anyone please recommend a workflow for my setup?
2) Also, for a situation where I do leave my setup outside for the next evening, I do the home find position but I take it I don't have to find a star to sync (and set new homefind position)? I made a mistake of doing a star sync and I think I had to redo my entire AutoPoint model again for the 2nd night

Cheers for any advice you're able to offer,
Sean

[MarkS]

Hi Sean,

I don't have an observatory, so I have all my gear set up on a rollabout (see picture). This saves a lot of time (and my back which needs special care!). I strongly recommend you consider doing this - I have built two of them, one for the DDM60/ASA10N, and one for my DDM85/OS RiDK setup which is far too heavy to assemble for each imaging session.

All I do is roll the set-up out of the house onto a concrete platform, align it to true north/south, and jack it off the wheels so it is firmly fixed and levelled. This takes about 5 minutes.

Then  synchronising,focusing, and polar alignment take another 15-20 min. This can be done while the camera is cooling. Once I have PA within 2 arcmin on both axes, I use that 3-star config and proceed straight to Sequence Run with MLPT incorporated. This procedure is fast, and pointing is not always super accurate, but it's always OK if I allow for a little cropping of the images. If you prefer to make a multi-star pointing model each night, don't waste time on a 100-star model - around 10 stars will suffice if you always use MLPT. However, I never bother, unless I find I have time to kill before Astronomical twilight ends. Note that you can start on synchronising etc well before it gets truly dark, so you don't need to waste precious imaging time on setting up.

At the end of a session, the rollabout can be inside within 5 minutes, but I always take longer because the camera warm-up should not be hurried.

[AnakChan]

Hi Mark,

Thank you for the very good tips! I've always wondered about those trolleys as I wonder how stable from movement during imaging, etc. Mine's done on my lawn. I'll dig into the trolleys approach a little more.

That's great to know that I don't need a 100 point model if I'm using MLPT - ok so I'll still do an all sky but just 10 would be sufficient, then MLPT for my particular target Dec. That will save me a lot of time.

I"ve been using N.I.N.A. for polar alignment (then switch back to AutoSlew/Sequence), I've not tried AutoSlew's 3 star PA routine yet but will give that a shot. Thank you for sharing your workflow! Helps me understand which areas I need to focus on and where I'm overkilling it.

Cheers,

Sean

[MarkS]

Hi Sean,

I forgot to mention that I think you should use X2 binning  - there is no point in running 0.31arcsec resolution in Australia!

Cheers,

Mark

[AnakChan]

Hi Mark,

Actually been thinking about that 'cos usually binning would make sense esp for CCD but since I'm on a CMOS sensor I don't think I'd reap in the usual CCD benefits of binning. Probably the only benefit is the smaller file sizes for file transfer for CMOS?

Cheers,

Sean

[MarkS]

If you bin using averaging, you do get an improvement  - the read noise of the combined pixels will halve. That is, for a gain of 0, the effective read noise will be 1.75 eRMS, not 3.5.

At 0.62"/px the resolution is very unlikely to ever result in undersampling of your images - unless you pick a great night in the Atacama! On the other hand, excessive oversampling does not make for better images.

My Moravian camera using the same sensor as yours has hardware binning available. I am going to use it on my 2400mm focal length set-up. If I get any decent weather in the next dark cycle, I will be able to compare how the system performs.

Cheers,

Mark

PS: MLPT is an absolute cornerstone of the ASA unguided tracking performance. Always use it!!!!!

[ColinR]

I've been a set up every night kinda DDM60 user for 5 years now, we've spoken in the past Sean over Facebook and IIS.

I've been doing the same as Mark for a long time. Not the roll out idea, that's great but not possible in my backyard. I've got small dug in pavers for the tripod so I know where to put the legs. It's level when it goes down. Balancing is what takes the longest and is most stressful for me! I use the 3 star alignment in Dec for PA. It's quick and pretty accurate for getting your PA low. You quickly learn to see the numbers and know how much to turn the knobs without using the actual PA routine which is a bit of a nightmare at longer focal lengths. Having used the DDM60 and Mewlon 250 setup for a few years I'd never do more than 5-10 stars on each side purely for pointing and then use MLPT for actual imaging. I'd sometimes do a 30-40  point model just to waste some time before astronomical darkness sets in.

With my new setup I've just started doing 100 point models (takes 30 minutes) and I'm currently testing to see how long I can image for without needing to do MLPT. Currently doing 120s narrowband images with FWHM down around 1.4"-1.7" with a 10" F/5.8 CDK and QHY600. Going to try some 300s tonight if the seeing is okay.

[AnakChan]

Colin, cheers for your advice. Actually I did a 32 point model (I counted 32 on the screen, but the actual number of subs it plate solved was like 47?) yesterday. I decided to do short 60 min Lum subs with my 250CRS (2500mm FL native) and didn't need any MLPT at all. I left my scope outside and continued this evening using the same model and acquired another target of diff dec/ra. Using the same 60 sec subs, I didn't need MLPT for this other target either.

If I had to shoot 600sec subs with narrowband, then MLPT is likely to be more a necessity at that same 2500mm FL.

Edited February 25, 2023 by AnakChan