GazK

On 22/03/2022 at 16:13, alacant said:

Hi

Given the zoom lens' astigmatism and that you are not guiding, the processed image looks good.

If you want more good frames, the next step would be to dismantle clean, lubricate and adjust the mechanisms. It's quite simple.

HTH

Thanks, that's very reassuring. It's just annoying that I'm imaging for 2x the amount of data I get.

Thanks for the link, I'll work through it.

On 21/03/2022 at 20:05, happy-kat said:

With reference to my experience with an altaz mount imaging to the South and North in the NH is most demanding and star trails show quicker. Orion and family are very much in the South now, if you setup to image to the East with the same equipment would you get 1 minute exposures you were OK with?

I realise you are using an EQ mount but thought it might still be worth commenting.

thanks, that's a good point. Going to point it at Leo next chance I get, see how that goes.

10 minutes ago, Elp said:

Is the setup balanced, from the animation it looks like the mounts trying to move one way and something is counteracting the motion.

Yes it is balanced in both axes. I checked after moving the camera onto the target.

26 minutes ago, alacant said:

Hi

Assuming the drive is meshing correctly and you do not plan to employ autoguiding...

 What did the processed image look like? Not sure what you're expecting.

Guess: the stars remain in the same position from one frame to the next? You really don't want that. Do you have the mirror locked up? Unless you have a very solid mounting, at 200mm, the return of the reflex mirror with a cheepo lens on a DSLR is enough to shift a sa as your gif suggests. Free dither:) Otherwise, soft ground, wind, inadequate mounting, something loose, poor balance...

Maybe a photo of your setup along single acceptable and trailed frames would help us if you want to diagnose further.

Cheers

 

Thanks. I don't know what I was expecting really, I'm a n00b! I suppose I'm just surprised at a) the amount of field shift between subs and b) the ratio of sharp subs.

I'll set the rig up in the next couple of days and post a pic. Basically a Benro video tripod, fully extended, stock SA pro on top of that, standard SA Dec bracket with counterweight, camera mount as close as possible to RA axis without fouling the reticle illuminator, canon 80d and 70-300 mounted on a rack and pinion bracket to allow balance (this could be a weak point for one-ff shifts, the 1/4" fixing doesn't have as much grab as I'd like, but the lens doesn't have a tripod collar).

Example good and bad frames attached, also a very rough process of the final image (I wasn't aiming for an actual image, hence the trees!)

11 minutes ago, Elp said:

When I was using my modded dslr with my Z61 (f5.9) I found 2 mins was the absolute minimum on this target per sub at iso 1600 to resolve any form, 3 mins was better. This is from a bortle 7 zone. It's autoguiding territory unless you have a super quality unguided tracking mount. The longer your focal length the better the PA and guiding needs to be. I had an SA but would never use it with a scope.

Thanks, I get that. But right now I'm back at square one, trying to work out why I'm getting star trails in most of my images in 1 minute subs at half that focal length. See my last post.

Thanks all for responding.

I went out last night and pointed the DSLR with my 70-300 @ 200mm at Orion, purely to do a tracking test. The lens is mostly plastic, so pretty light; DSLR + lens is under 2kg. Polar alignment was pretty accurate I thought, rechecked after the load was added. Balance was also checked in both axes. Also there was no wind and I'm inside a walled garden.

The following gif is a crop into one section of the resulting 2 hours worth of 60 second subs. E-W is roughly in the Y axis. Ignore the stars moving through the tree line and clouds in the later images. You can clearly see a periodic shift in azimuth, which I don't understand at all. It is the same behaviour I've seen on previous shifts. I don't think bad polar alignment could explain this could it? If not, then what is going on?

I wouldn't mind if it was just shift between subs, but 2/3 of these subs were useless because of star trailing in the same axis. Surely a 2/3 rejection rate when the mount is within its load envelope isn't right?

Thanks to everyone who responded - no I'm not using a field flattener. About to hit "buy" on one to remove both the halo and the blurry stars.

Hi all, n00b here again with another starter question.

Flush from managing to get a result with M42, I decided last night to try to capture the horsehead and flame. Yes, I know, don't run before you can etc etc. It was clear, I got carried away, what can I say.

I pushed the sub time to 45s with my WO Z71 on the star adventurer and took 1.25 hours of data. I'm now sitting here mid-process, and while I do have a head and it is horse-shaped, its a lot fainter than I'd hoped for.

The first thing that becomes very apparent looking at my subs is that, while about 50% have acceptably round stars, the other 50% show minor or significant trailing when zoomed in - so I had to reject 40 mins of data. Additionally, the star field is moving around somewhat between frames, and not linearly. My last imaging session (same rig, 30sec sub) had a much lower discard rate and none of the wandering. There was no wind on either night, and while I don't think the seeing was very good - lots of twinkly stars - I'm not sure that would account for it.

Can anyone help me diagnose the problem?

4 hours ago, vlaiv said:

My guess would be that it is due to synthetic flats / software background removal.

First image was stacked in DSS, then followed one of Nico Carver's videos for processing in photoshop, admittedly that video was for an untracked DSLR stack. Second image was using Siril for stacking and most processing, using a different video tutorial.

I just assumed that the lack of colour was down to the limitation of 30 second subs, I had to work quite hard to get anything at all out of the lower portion. But I screwed up the flats and so used a different session's flats, that could be the problem. And yes I did use the Siril background removal tool.

I do have some 15sec subs from that session, so I'll try adding that as suggested for the core, might allow me to push the faint neb further in the 30sec stack.

16 hours ago, glafnazur said:

That looks loads better, great detail and it looks more natural, nice one 👍

thanks!

Taking advice from others on the forum, I'm starting to use Siril. 

When I first hit "autostretch" on my image I get this weird circular halo. It doesn't matter too much on this image as I'll crop in, but on others e.g. starfields, it will.

Optical train is WO Zenithstar 71 > 2" to 1.25" adapter > 1.25" T-adapter > Canon 80d

What could be causing this?

Taken on the feedback and processed in Siril, with just the lightest of touches at the end in PS. Feels a much more natural image to me, plus the background is a bit more under control. Could have gone brighter but then I lose the core. Comments welcome. 

On 27/02/2022 at 20:42, alacant said:

Hi

Lovely shot.

80D? So ISO 200 and lose the dark frames.

Cheers and HTH

 

thanks, it does.

1 hour ago, Elp said:

It's a good image. Orion nebula is so bright I think you can get away with a low iso, even short exposures of 2-4 seconds duration it captures decently without blowing the core out too much, 10 seconds even better. You need to find the balance based on what settings you're likely to use.

Thanks! The 80D has the advantage of being ISO-invariant, which I assume must have helped hold the core down despite 30 second subs.

16 minutes ago, glafnazur said:

It's a lovely shot, well done 👍

thank you!

I'm just getting into tracked DSO imaging and I'm very much using what I already have from visual observing and daytime photography at the moment. Which is, specifically, a Canon 80D (APS-C sensor) and a WO Zenithstar 71.

I had a 1.25" T-mount adapter lying around from moon imaging on my 5" mak, so I've been using that. But the WO scope has a 2" rear aperture (with a 1.25" adapter). If I swapped the 1.25" T-mount for a 2" one, would I get more photons to the sensor? Would my images be brighter / better?

3 hours ago, AstroMuni said:

Here is a screen shot of what it could look like. I have applied Photometric calibration in Siril to your uploaded image @GazK

Your shot is really good...And to be fair you have taken on one of the harder DSOs - its easy to capture but hard to process due to the extreme dark & bright shades on it.

Thanks! That's really helpful. Just lifting the exposure and moving the black point in the final image has brought me closer to your process.  I'm having a play with Siril now

8 hours ago, alacant said:

Hi

Lovely shot.

Minor improvements which are easy to do...

1. 80d: ISO 200. 100 may be even better. 

2. Use flat frames: Without removing the camera, set the 80d on Av and point the telescope at an evenly lit light source so as to give an exposure of around 2s. Use distance/paper/card/t-shirts to control the light. Switch back to M and set the same exposure. Take at least 15 frames. 

3. IIRC, to control the halos on a wo, focus on a white star using a bm. remove the latter then ease focus away from that point until the blue halo begins to turn red. Now compromise between those two focus positions. 

4. Use a field flattener

+1. 

Cheers and HTH

Thanks! Yes will drop to 200 now I know my effort won't be wasted. For some reason I'm struggling to get flats to work, will practise in the warm this cloudy weekend. 

And I'll give that focusing trick a go. In the medium term I want a FF, but its quite a lot of £££ when I'm still working out where I want to go with the hobby.

9 hours ago, Swillis said:

I think going up to the WO71 was a good idea, the star shapes look much better. Maybe it was your lens which was the problem with the star shapes previously. Zoom lenses are not great for AP, maybe there are some good ones out there but I have all sorts of weird star shapes with mine. 

I agree, I does look a bit blue.  What are you processing in?  In Siril you can do photometric colour calibration, which works brilliantly.

Great work 👍

Thanks very much! Yes, I'm still at the stage of using what I have from visual astro and normal photography, so the tele zoom is far from ideal. Don't get me started on the manual focuser (ugh) and tendency for the zoom to slide at high elevations. At some point I'll probably be dropping cash on a Rokinon.

Stacking was DSS, processing in photoshop. I'll have a play with Siril, thanks

Is it just me or does the colour temperature need warming up a little?

So, flushed with the relative success of my first tracked image, and amazed at more actual clear skies, I decided to go for broke and step up to my WO Zenithstar 71, still on the Star Adventurer. Took advice from here and dropped ISO to 400 - too scared of failure to go to 200! - and pushed subs up to 30 secs. 40 mins of data, no darks, no flats (because I'm an idiot who can't read a histogram!)

I mean I'm blown away at this image considering I did my first polar alignment a week ago, and before this month had never imaged a DSO, and this is close to the weight limit of the mount. But as always I'm keen to know what I can do to improve on this.

On 28/02/2022 at 17:02, dweller25 said:

That’s a great image 👍

Ta!

On 28/02/2022 at 17:00, AstroMuni said:

Nice shot. And an excellent one for a first attempt

The areas to improve over and above what has been said by others is the bottom half of your image has oblong stars, while top half is quite round. So thats one to get to the bottom of. Good luck

Thanks! Any ideas why that might happen?

On 28/02/2022 at 15:43, happy-kat said:

If using a canon if you have an Android phone then the app DSLR controller is great if your particular model is supported (assuming aren't already using a laptop) as get a bigger screen for liveview and controls.

A Lord Y mask is easy to create out of card and creates big spikes to help with focusing.

Thanks! Good point about the app, I use it a lot for normal photography but I forgot it also does live view.

Will look into the Y mask.

On 28/02/2022 at 15:04, Bluemoonjim said:

Congratulations, good shots.
I was using a Canon dslr and found getting the iso down as low as possible (around 200) combined with as many subs as possible was the way to go.
Focus assistant in BackYard EOS was also a game changer.

Cheers
Jack

Thanks! Yes, have dropped the ISO to very positive effect. Will look into backyard.