Icesheet

As Vlaiv stated, astrophotography bears little resemblance to day photography. For example you mention conversions of focal length to full frame equivalent. The focal length is the focal length and that’s what will test the precision and accuracy of the mount you choose not the size of the sensor. Of course you should consider sensor size, FOV and pixel scale when considering the framing of your object but there is no crop factor as you commonly hear in landscape type photography. Also, it’s unlikely you will be shooting anywhere near ISO65. I’m not familiar with the PhaseOne’s but it’s unlikely to be under ISO800. 
 

It’s not clear to me exactly what you would plan to shoot. Is it landscape milkyway type photography or, do you plan to do deep sky astrophotography? You mentioned a 240mm lens with 2x tele-convertor. If you really plan to shoot at 480mm then one of the strainwave mounts mentioned would probably be your best bet as you would have to guide anyway. As an aside I wouldn’t use that lens with the tele-convertor as f9 would be slower than you want for night sky photography.
 

If it’s more widefield work then there are a plethora of sky trackers that would work for you. The Fornax Lighttrak ii is probably the most accurate on the market and will handle the 240mm lens without guiding. It lacks GoTo though. The Star Adventurer GTi has Go To and seems to be popular. Or you could consider the Benro Polaris if you will only shoot at shorter focal lengths as it negates the need for polar alignment and you can shoot fully automated panoramas which may be of interest to you.

There’s likely to be some great advice on this thread but also use YouTube as a resource as there are plenty of content creators doing a wide range of astro work. 
 

Edit: Apologies, re-reading, I see you mention deep sky. Then, I would not recommend the Benro Polaris for that. Probably a strainwave mount would be best but factor in what else you need for guiding and polar alignment. I would also look for another option other than using the 2x convertor with the 240mm lens. 

13 hours ago, ollypenrice said:

This may come as a surprise, but I have never dithered.

Caveats:

I've only ever used cooled cameras.

I've never bust a gut to finesse polar alignment, though, in the CCD days, it needed to support 30 minute subs.  Now it only needs to support 3 minute subs.

Given the short exposures needed by CMOS, and their tiny pixels and low read noise, won't a small polar alignment error provide any dither that your system actually needs? If it really needs any at all?

I would forget the clamour of the orthodoxy and received wisdom and just try not dithering and getting more good subs.

Olly

You know, I actually haven’t even compared to see if dithering has made a difference in my images. In the main I’m dithering for drizzle integration in PixInsight but I haven’t checked the difference between a drizzled and non drizzled. I really should but just accepted the general consensus that it was worth it. 

I think a small polar alignment error may not provide enough random movement to replicate a true dither but I’m no expert either. May be time to make a comparison of what I have!

On 22/11/2023 at 11:43, fireballxl5 said:

 

I've had my RST-135E for 2 years now and although I've never dithered with this mount (at least during an imaging run🙃), I have found that this mount needs:

1) a good stable power supply,  >12V. I usually dedicate a small Tracer LiFePO4 battery just for the mount

2) a rock steady base if imaging at high ish resolution,  say <1.5"/pix. I've found that light-weight, collapsible ali tripods aren't solid enough if the mount is carrying 8-9kg of imaging gear (without a CW of course😉) and there is some movement.  These are the kind of tripods I've taken abroad for less demanding imaging. For my RC6/ASI533 combo I now use a re-purposed AstroTrac pier that has very little movement as the scope tracks across the sky. It would be nice to have a more manageable carbon fibre tripod if I could be sure it was sufficiently stable. 

HTH,  Andy

I imaging at 1.94”/px with <5kg on the Sightron carbon fibre tripod so I don’t think tripod stability is the issue here. At least it shouldn’t be. I do have a Berlebach uni tripod I could test. The power supply is something that keeps coming up so I should definitely check that out I think. How is your guiding with the RC6?

16 hours ago, Elp said:

Something I haven't suggested, which might be the culprit which I've mentioned a number of times in other threads, late last year, early this year I updated to the 2.0 asiair app version and it contains the appropriate firmware updates to the airs. My once workmanlike asiair pro suddenly became as useful to AP as a brick, I also had issues with my mini. I wasted so many sessions trying to find out the issue as it would usually be something different every time causing an end to the session but the often ones were it'd fail plate solving after the second iteration try then slew the telescope in a kamikaze dive towards the ground and the tripod, sometimes stopping responding to commands full stop, turning sidereal tracking off by itself mid plan, and the one similar to yours, after dithering it'd kamikaze again and the next two to three subs would be star trailed before it decided to recentre and star again, then do it again after the next dither and so on. It was related to the sidereal turning itself off as far as I know so obviously you'd lose your guidestars.

Solution? Well I was lucky enough to have an old beta asiair app version on an old phone, this is important because when you roll back the airs firmware, connecting back to them with the old app doesn't force update a firmware installation because it doesn't have one. So I'm using the factory firmwares on all my airs. Haven't had a single problem since.

 

Thanks, I don’t think I have any back up software and I haven’t experienced any of the other issues you mentioned but I’ll keep an eye on it. 

15 hours ago, ONIKKINEN said:

You can safely drop the dithering rate to something like once every 20 minutes if you have one of the newer cooled Sony sensor cameras (not sure about others). You will want to calibrate with a bad pixel map in that case, as hot pixels could otherwise remain in the stacked image. Think i recall reading that some imx571 users here dont dither at all and with a BPM it still works out.

I also have/had dither settle issues in my AZ-EQ6 because its a little bit stiff, and the solution was to just not dither as much.

I use the IMX571 so I’ll look into that. If I can limit the dithering it’s going to make a huge difference. Thanks!

I’m going to look into the power supply issue with the RST135 to see if that may be contributing. 

3 hours ago, Elp said:

What are your sub lengths? Initially I'd suggest dither less frequently depending if your dither to sub frequency is something like after every 5 to 10 minutes imaging time, also 5 pixels I'd say is too small a number for dithering (in relation to the quality of your final image, I used to use a small number but now always use 30).

I'm surprised your mount takes so long, I was going to say a HD mount settles very quickly, my hem15 is typically reimaging within 10-15s after dithering compared to the 30 odd seconds of my gem.

If your guiding is erratic after a dither are there any sources of vibration, wind, what's the tripod like?

Not sure but maybe try increasing the settling time, it might be at 5s your setup may not be dampening down.

For RGB it’s 120-180s and for narrowband it’s 300s. I did change to every two and I suppose I could go to every three frames for RGB exposures. Ok, interesting to know that 5 pixels was not enough. So, going to 30 you noticed a difference in the final image?

I haven’t spent much time analysing the mount to be honest but I am aware that sometimes it doesn’t play well with a 12v power supply and that’s what I’ve been using, so I may have to look into that as a potential source. I use the Sightron carbon fibre tripod and I don’t think wind is a factor here. It’s pretty stable when just guiding normally. Just seems to go haywire after a dither. Would dithering induce vibrations?

I’ve recently noticed that my imaging efficiency is low. Basically, I need up to 1.4 hours for each hour of actual gathered data, depending on exposure length. I think I’ve narrowed it down to dithering and in particular the time to settle. What I’m not sure is if this is down to the settings I have chosen or the ASI air and/or mount itself. 
 

Here’s a screenshot of my current settings in the ASI air 

On my latter part of my last run I changed to dithering every 2nd frame and that helped a little. Still, it seems it’s the settling that’s causing most of the issue. After a dither the guiding is quite erratic and frequently a new exposure starts after a 60s timeout. 

For info the mount is a Rainbow Astro 135. Guiding maybe hasn’t been as good as I would necessarily want but it’s under 1”RMS in general and given I’m imaging at 2”/px I’ve not spent anytime trying to optimise. 
 

Anyone had a similar experience and can suggest a good way to approach this so I don’t waste even more imaging time?

Looking at this again it seems like I still had a slight gradient. This a new version with an ABE. Think this is better?

First time capturing and processing a dark nebula. I had aimed for 7-8hrs integration but only ended up with 5.5 then had to throw away another hour. So, with 4.5hrs I was worried I wouldn’t have enough to work to work with. 
 

In the end I’m happy with the result considering but I did have to push quite a bit and I think that shows when you look closely. Will definitely get more integration time here and would love to eventually incorporate the squid and fireworks galaxy in a mosaic. 
 

Seen some great dark nebula work here so hoping for some constructive input on processing. 
 

Askar FRA400 and ASI2600MC

140x120s

30x dark, bias and flats

Processed in PixInsight  

Nice image! Definitely invest in a wedge and convert the AzGti to EQ mode. This will make a world of difference! As mentioned, as much integration time as possible 

Thanks, I’ll look into the GAME script too. Actually, made some progress last night so hoping I can get a satisfactory result. 

7 minutes ago, The Lazy Astronomer said:

Using GHS for stretching, applying RGB colour to Ha stars, and using Starnet to allow a seperate gentler stretch on the stars worked well enough for me I think.

Another great image! How are you adding RGB colour to the Ha stars? 
 

I did use star removal and I can keep it small enough it’s really the halo that I’m struggling with. You don’t seem to have any here which I’m jealous of!

7 hours ago, Fegato said:

It's hard to manage a very bright star like that, and Alnitak is a favourite bugbear! Even starless processing generally leaves stuff behind which only grows with the stretches. I must admit with mine, I just decided it was part of the glory of the image and let it shine forth! I much prefer a big bright star than any obvious artifacts.

 

Fantastic image and I would happily take your Altinak in all its glory! Yes, StarNet and StarXterminator can’t remove everything and that doesn’t help matters. 
 

6 hours ago, TerryMcK said:

Try shooting shorter subs. That way the sensor will not become oversaturated. It will still pick up the wispy stuff and when stacked the image will be great and you will see Alnitak’s companion star. If I remember correctly I shot 120 second subs in Ha and S2 on this one below. There were a lot of subs and it takes some time to stack but I ended up with a good image not dominated by the star.

Most bright objects can be done this way and modern CMOS sensors work well with this method.

Another great image and it’s very well controlled here. I did think at the time that I should have taken some shorter exposures! I’ll try that next time I have a clear night. My dual narrowband subs have tighter stars as expected but I really don’t like the stars from the L-extreme filter. 
 

I've collected some dual narrowband and RGB data on the horsehead but I'm really struggling to control Alnitak in what is an image I'm otherwise delighted with.

I've attached a screenshot of the STF of the RGB stack and the best draft I have come up with so far. To me it really distracts from the final image. I've tried masking while stretching with/ without stars. Clone stamping, star reduction. Nothing seems to control it or I'm left with a ugly artifact. Anyone out there with any Alnitak magic bullet?!

One of the best I've seen 👏

Thanks @vlaiv. So presumably I can do this with existing exposures I have that have tracked across the different Bortle zones in my area on the same night? Now that I think about it I have noticed a trend from the PixInsight subframe selector that my exposures seem to get poorer as the night progresses. I wonder if that correlates with moving to a more light polluted part of the sky. 

7 hours ago, Trippelforge said:

Someone shared a few charts with me showing the various differences in exposure times, and you are right. It's pretty mind blowing how quickly it rockets upward. 

 

Does anyone know the background of this table, how it is measured and how reliable it is? I was obviously aware of the hugely detrimental effect of light pollution but hadn’t really seen it set out numerically like this. That’s mind blowing to me and potentially hugely significant. According to light pollution maps I image from just inside a Bortle 4 zone. However, depending on the direction I image it can be towards B2/3 or B5/6. Given the significance of the apparent jump from 4-5, I wonder if my imaging time is better spent solely towards Bortle 4 and under. Could anyone suggest what I could do to test this?

Edit: Apologies, I see this is in an Observing forum. I can start a new topic in an Imaging forum if it’s preferable. 

1 hour ago, ollypenrice said:

I like them all.

BTW, cropping, of itself, has no effect on resolution. In daytime photography there is a careless tendency to confuse pixel count with resolution but they are not at all the same thing.

Olly

Thanks ☺️ 

Yeah, I did actually know this. The word ‘apparent’ was my lazy attempt at acknowledging it. Funny you should mention daytime photography. I just watched a video where a very popular landscape photographer discussed resolution in this context and it annoyed me enough to comment on his video. I’ll need to be clearer next time!

Here's the widefield for reference...

Another target I haven't paid much attention to previously. Clear skies with a nearly full moon turned my attention to the Veil nebula for the first time. I imaged it for 3.5hrs with the Askar FRA400 and ASI2600MC but I didn't think the widefield image was so appealing, so I cropped to the West and East side of the Veil despite losing some apparent resolution. I found it hard not to push the saturation too much on these. I still think I've maybe gone too far, what do you think?

Yeah I did use BXT, SXT and NXT. I’ve only recently got the FRA 400 and I’ve been very happy with it. It has been hassle free and has given me round stars into the corners. I think the trade off is it’s maybe not as sharp as other scopes but processing techniques  help there. 

Yeah it’s HOO data. Maybe, it’s better described as pseudo Hubble palette? I used one of these narrowband scripts in PI to map it.

I shoot from Bortle 4 according to the light pollution maps. Depending on target that can be towards B3 or B5.  

Surprisingly, this is a target I have not shown much interest in. However, I had unexpected clear skies and no time to search for something else and this fitted perfectly in my FOV. Actually very happy with the final outcome for ~4hrs of integration   

Askar FRA400 with ASI2600MC

40x300s with l-extreme 

10x120 for RGB stars. 

Processed in PixInsight 

Congrats! Well deserved 👏🏻 

Yeah, good idea. I’ll test with and without a mask. Will help with some selective colour saturation too. 

I thought running SCNR might actually remove some of the OIII signal. I’ll definitely give that a go when I try again. Will also see what I can do in photoshop although I haven’t used that in ages. Thanks 😊