parallaxerr

Got over 2hrs of good data on M33 last night. Total integration time now 4hrs 15mins.

Definitely more detail coming out but hard to balance detail and background noise.

Of course, no live view for you. Just slewed to Mirach and saw a tiny focus shift. Longest time then spent taking 30s exposures to ensure M33's centered.

Are triplets more prone to focus shift? I've heard of the pinched optics problem.

1 minute ago, Filroden said:

One think I'm noticing more tonight is how badly the focus drifts as the temperature drops. After only 15 frames I'm going to have to pause and tighten up the focus more.

Something I've not considered. I set the camera going on M33 an hour ago, better go check I suppose. Will have to goto a bright star which I'm reluctant to do because it's tracking so well, but no point tracking a blur!

I thought lowering the gain would free up more DR as with DSLRs?

24 minutes ago, The Admiral said:

Haven't we been down this avenue before? Your FITS shouldn't be that big. Have you got something switched on in DSS that shouldn't be, like drizzle or mosaic?

No drizzle, but, to be fair that was a mosaic. I wanted to see the extent of the field rotation and have as much area as possible to crop from.

EDIT: How strange, I just loaded a standard (not mosaic) stack of the same image, but X2 drizzle @ 1.08Gb into ST in just a few seconds?

19 minutes ago, The Admiral said:

Thanks Jon.

It's getting a bit frenetic on this thread, and what with sorting out my own images I'll have to catch up later!

Ian

Agreed, I for one am going to attempt to stop opening cans of worms and stick to posting my results, as per the original thread intent!

That looks great Ian. I can't comment on what should/shouldn't be there but the detail in the nebulosity is really fine

3 minutes ago, alacant said:

That's a really nice image crying out for the rather nice ST Life module. Worth a try?

Good shout. I'm going to re-run the manual dev as I prefer the result. I'll try the life module.

2 minutes ago, Nigel G said:

Have you tried binning 35% that can improve S/N ratio by a fair amount.

Yes, the whole image is binned 50%.

Wow these images look ropey on my mobile!!!

And here's the AutoDev'd version. Struggling with colour a bit and as you can see, there's more noise...

I think I prefer manual Dev, if only I could pull a bit more detail out. Maybe more subs will increase SNR and enable me to do so.

6 minutes ago, Filroden said:

Given your large field of view you could probably crop a little more and reduce file size/processing time.

It's only the loading time that's an issue Ken, once ST has it open, processing is quick enough. Strange.

What a difference a few degrees alt makes! OK, more like 35-40°. After imaging M33 between 60-70° last night I came down to take a quick peek at M42 @ approximately 30°, just look at the difference in LP! I know where I'll be imaging in future!

Had a super session last night. I ran with M33 for over 3hrs straight. Due to it being relatively small and having a good FOV with my setup, I allowed for a full 90° of field rotation as I can crop it out. I really wanted to see what a good amount of data could show, so far I've been processing mostly around one hours worth of data, but last night I gathered nearly 2hrs of subs.

Even better, due to the tweaks to my mount last week, tracking appeared to be vastly improved.  DSS only dropped 4 frames so I got 1hr54m out of a possible 1hr56m I plan to do exactly the same tonight, aiming for 4hrs of data on M33.

I've just run last nights data through ST to see what's there. I'm experimenting with the differences between AutoDev and manual Dev. AutoDev seems to bring out more data, but more noise along with it, whereas manual is cleaner but detail is subtler. Here's the result of a quick manual Dev, loading the FITS up again for AutoDev now, but it takes about an hour to load in ST @550mb

Final point to note - NO DARK FRAMES

I had to take a day off posting in the thread yesterday after my brain melt on Saturday night! The pace that this thread moves at can be really hard to keep up with at times, so thanks to those who commented on my rather long post, it'd be a mission to try to quote them all so I'll summarise my response.

It seems my conclusions attract mixed responses, as expected. One thing I note though is that the modus operandi of individuals seems based purely on preference, whether it be with regard to calibration frames or target selection or whatever. Everyone here is producing excellent results using some significantly different approaches and that makes me happy because it means I'm not doing anything hideously wrong!

I have gleaned further information from your responses which, whilst adding to the knowledge bank, also adds more...not confusion...but more to compute, perhaps.

One plus point that I'm really happy with is that Mr. Stark claims aperture is not all ruling in AP, so I don't have to fret any longer over 66mm apo or 120mm achro!

Hello, Alt/Az’ers, it’s nice to see some of you had a productive evening yesterday. For me, last night was a tale of two halves. I have nothing to show for my efforts, however, I believe I learnt a LOT about my set-up and the direction I need to go in. This may turn out to be a long post so apologies in advance as I’m finding it hard to get all these thoughts straight in my head, but I find sharing my findings here to be rewarding as someone always responds with a little nougat of previously unknown information!

So what went wrong?

Well....first off, due to it being the first clear night in a while, I thought I’d make the most of it and hit several targets one after another as Alt and/or FOV limits came in to play. First off was M31, then M33, then I decided to have a pop at the horse head. What this meant, was that I never really got enough subs on any of my targets to produce anything decent with.

Secondly, I decided to try a change of ISO, choosing 3200 because Sensorgen.info suggests than read noise for my camera drops off at higher ISO. But, and this is a BIG BUT...despite claiming files are recorded in RAW, Nikon apply an internal de-read noise to RAW files. In years past, this process was known as the “Nikon star eater” filter in the AP world, due to the de-noise process mistaking stars for hot-pixels. However, this is reported not to be the case with more recent Nikons.

Finally a flat battery! I have previously been impressed with the battery life of my Nikon, but last night it gave up half way through taking darks.

I came away with a load of subs on various targets but after inspection, many were binned due to thin cloud and satellite passes and ultimately I did not record enough darks.

Moving on.....The good news is that the tweaks I made to the mount and balancing of the OTA has done away with star trailing on the alt axis that I experienced during my last session. So, I decided to process a few images anyway, without flats/dark flats to see what I had and made some pretty important observations, I think.

What I learned...

ISO - Previous attempts at M31 have been at ISO 1600. On processing in ST, I struggled with a lot of background noise which I thought was LP. As such, I fitted my Baader semi-apo filter (an LPfilter + fringe killer) to try to combat it, however, I don’t think LP was the issue as I saw exactly the same when processing last nights data, in fact worse. As well as a decrease in read noise, higher ISO brings with it reduced saturation capacity and thus dynamic range – I “think” the noise I’m seeing is a result of the noise floor being too high, i.e. the dynamic range being too small. Histograms aren’t clipped but stretching the image brings out terrible grainy red background sky, which, I did not see when imaging M42 at ISO800 where I have a few more stops of DR to play with. So, whilst I’m not saturating the sensor, maybe I’m not allowing enough to capture the full DR of the target and the noise floor is being brought up in ST.

Semi-apo filter – If LP isn’t the cause of the background noise then this isn’t going to cure it. Proven last night. With such a small scope I also think cutting any light wavelengths out is counterproductive and the green tint it casts is a pest in colour processing.

Dark frames – I don’t think I need them! Darks frames are dark from my DSLR, as in completely black. No noise, not a jot. I have stacked last nights M31, with & without darks and the difference is ZERO. Recent Nikons are famed for very low read noise sensors and the in-built noise-reduction negates the need for me to take dark frames. (Note – there is an option to turn long exposure noise-reduction off, which I have done, but read noise reduction is still applied). There is a Nikon hack program available called “dark current enabler” which does away with the NR, I have tried it and got darks as we’re used to seeing with the purple/red noise, but it’s a PITA to use and requires a PC. But, if the in-built NR isn’t eating stars, then what’s the point anyway?

Aperture – I’m struggling with this. Having tried the ST120 a few weeks back, it’s clear it gathers photons far faster than the ZS66 – half the exposure time produced twice the detail on M33, notwithstanding some heavy CA. Exposure time vs CA? On a bit of a lose lose here as far as my available scopes are concerned, but I found the CA objectionable in the achromat – I wonder if reducing the ISO reduces blue bloat? Either way, not having the alt limit (once I get my new intervalometer cable) with the ZS66 is nice and I’ve ordered a second battery for the camera to allow longer sessions...If only the weather would allow. More data is always a plus, regardless of aperture, it’s just going to take me a little longer to gather the photons.

So, I feel like I have come to these conclusions (until I have another great learning experience):

·         Plan imaging sessions better – one target at a time.

·         Maximum ISO – 800.

·         Read noise for my camera is irrelevant.

·         Semi-apo filter is not required.

·         Don’t waste exposure time on darks.

For any of you that have read this far, I thankyou! Maybe this will give others something to think about and please feel free to correct me where I am mistaken, probably everywhere.

Jon

Clear as a bell but gusty here. 80 subs on M31 in the bag, this time at ISO 3200. Having learnt a little more about reading histograms etc, looks like the blue channel is being clipped at any lower ISO on the fuzzies, probably due to the semi-apo filter. Found out I do still have a slight alt limit in that the intervalometer plug connected to my Nikon contacts the mount, it bends out of the way but does offer some resistance so I've now re-targeted. 90° plug on order & M33 subs underway.

Loving No.4 Ken  

5 minutes ago, Filroden said:

I can set slew limits plus I use it manually as I have limited views. You can save your three manual areas as a user defined program so you can reuse it if you set up in the same spot each time.

its one downside is that you do lose alignment a little each time you remove it from the mount as you can't put it back in the view finder slot quite the same each time. But my target is still in the centre of the frame and a small manual slew gets it where I want it.

Like the sound of that Ken, especially the user defined areas. More functions than I realised. 

Dear Santa......

On 18/11/2016 at 18:14, Filroden said:

my StarSense fits my refractor after changing its mounting plate so all this time I've been fighting to do three star aligns and I could have been doing it automatically!

 

How does the starsense cope with an alt limitation? Despite getting good alignments, I've been fancying one for the plate solving, but I thought I may get a mount conflict if it's free to slew where it wants.

Made a few changes to my set up last night as a result of the discussion above. 

The WO OTA has an L bracket attached which has a vixen dovetail form. It's neat but doesn't allow me much adjustment. I dug out a 7" dovetail and eventually found some bolts to fit as the two required are different threads!!! One bolt goes through the dovetail and attaches to the L bracket photo tripod adapter which is 1/4-20UNC and the other goes through the dovetail and L bracket and screws into the OTA, think its a UNF thread.

I had to remove the plastic trim around the dovetail clamp as the focus knobs inerfered, but now I have full freedom to slide the scope fore and aft.

The result is that I'm now balanced slightly objective heavy. Hopefully this means the Alt gear is always under load and driving the scope up instead of allowing it up, as it was when tail heavy, if you see what I mean? Also, I now have no Alt restriction 

The clutch was also a tad loose. Whilst there was some friction between the plates, there was barely any torque on the nut so that's been tweaked up. Hopefully less binned subs next session.

2 hours ago, Nigel G said:

always do a sync encoder on one of the stars and go back to the object to start collecting data

I found this made my goto accuracy worse. For some reason, after syncing to a nearby star, the goto to the target object was not repeatable, neither was returning to the sync object? Auto two star works best for me, then straight to target, take one sub, adjust framing then start collecting.

1 hour ago, Filroden said:

You've all cursed me. Having not dropped a sub for tracking for I don't know how long...after 45 minutes tonight my tracking just stopped and I couldn't get it going again! I suspect battery issues but I need to investigate further.

I reported a judder in the alt axis to FLO just recently. Martin was quite explicit about using 13+ volts for a supply. Ensuring I have at least 12V reduces the effect but it still happens occasionally, so these mounts are obviously voltage sensitive. I guess you have little option with the Evo internal battery though. Can you use external power too?

1 hour ago, Nigel G said:

I think I might have and idea what's making mine play up, could be the altitude clutch, I won't know until the next time I use it as I have loosened it up when cleaning it a couple of days ago. 

Good shout Nige, I did the very same about  month ago after a re-grease to the main gear. Last night was by far the coldest I've imaged in so maybe a little contraction in the clutch let things slip. I just grabbed the OTA and it moved in Alt, not easily but readily so you may be on to something. My star trails were straight up, which agrees with this theory - where's that spanner...

5 minutes ago, Filroden said:

I used to get this but I increased the weight to the back and it stopped. Now I can image for hours and it keeps rock solid on the target. 

Interesting because my setup is already very tail heavy. So much so, I was thinking of getting an ADM dovetail bar to move it forward a little.

Fortunately the wetness was dew not rain, so no harm done.

Here's the result of last nights attempt, second go at M42. This time I gathered more subs, although only an extra 30mins or so despite being out for an extra 2hrs. I had some serious PE (I think - major star trailing on Alt axis for 4-5 frames each time) every 10mins or so, so lots of subs got binned. Also had about 15-20° field rotation at a guess, so lots of cropping was required.

WO ZS66SD unguided on Nexstar SE 6/8 Alt/Az, Nikon D3200 w/Baader Semi-Apo filter. 198x30s subs, 50 dark, 50 flat, 50 dark flat.

Well that was dumb!

Put the scope out a few hours ago to cool, not that a 66mm frac needs much cooling time. Did my alignment, hibernated the mount and turned everything off, including dew heat, awaiting the rise of M42.

Went back out to get started and everything's dripping wet, no drama. BUT, took the dew cap off and the objective was totally fogged over. Had to put an extra dew band on along with the normal one and put my hand warmer in the dew shield with cap back on for 20mins or so to clear the objective, not sure if that will cause imaging issues?

Well the weather didn't exactly play ball tonight but I got my experiment done and I'm really happy with the result. Had a window of about 1.5hrs to image and grabbed 59m30s of decent subs.

M42. WO ZS66SD, Baader MPCC & semi-apo filter and ISO800. 119 x30s subs, 50 dark, 50 flat, 50 dark flat.

Bashed this though startools as fast as I could - Autodev, wipe, autodev, crop, bin 50%, colour, de-noise. That's it, left most settings as standard then upped the brightness and contrast a touch in GIMP. There's a slight green to the stars, probably from the filter buy boy do I prefer an apo, bye bye CA! It's obvious I need more subs with the smaller scope but that's fine, I'll keep adding to them now. Much better FOV too, think my mind's made up on which scope I'll be sticking to imaging with and keeping the ST120 for DSO visual (if I ever look through it again!).

Only downside is a touch of coma top corners which the ST120 didn't suffer with, maybe there's a little tilt in the WO focuser?

P.S. Calibrated my monitor today, hopefully I'm now seeing the same images as you guys, the gamma was waaaaay off!