MG01

Hi Derek, not sure if you'll remember me but we met a few times at Kielder...the last of which was probably was back in 2012/13 when we had our youngest son with us. He was a toddler back then but is now 10 and has his own scope! Anyway, we're back to astronomy after an almost 10yr break...still have the FLT132 and are thinking about a trip up to Galloway as the revised dates fit in with half term so we can make the journey worthwhile with a full week break. What are the options for accommodation? Is it just tents or are there any huts/statics available? Jen and our youngest Calvin will be joinjng us but I'm a little worried about them camping early February in scotland!! Anyway, hope you're well! Clear Skies Michael

Love this...one day my prin(ce)ter will come!

Thanks for the feedback. I also wish it was the mono....I think you saw my face palm thread when I realised why I'd managed to pick up such a 'bargain'! 😆🤣 But that's okay. I'm happy taking baby steps for the time being.

Thanks Sam that makes sense...I know I need a long total integration time and am aiming for at least 20 subs to get the most out of stacking so now I can not worry too much about pushing past 10min subs. I just hope the bloody snows gone before I head up on Sunday!

Thanks Olly. My biggest problem is that at the moment I don't have many opportunities for imaging outside of the few weeks I can spend at kielder each year. So I've not had the chance to tweak and fiddle and test...only to read, tweak and fiddle. So I'm trying to get as much knowledge about the kit I have so that when I do get out I'm making the most of my time. I've been going through my software using ascom simulators to test my understanding of my processes and I've had a short test of everything so that I know my hardware is working. So that's why I'm now focusing on making sure the data I get is the best it can be. I can delve deep into my processing for the next six months between sessions, when I'm sure you'll see me post about affinity2 or if I take the plunge, pixinsight. Interestingly though I suspect you unwittingly answered my question with your quip about old ccds needing 30min subs. I am using an old atik383 OSC so I'm guessing yes, aim for as long as I can reliably guide for. Right?

I've just finished watching the excellent talk given by Dr Robin Glover at the 2019 Practical Astronomy Show, which is available on YouTube here if you haven't seen it. It's a very well set out presentation and I can highly recommend it for those who like myself are delving into the subject a little beyond some of the classic rules of thumb. However it did leave me with a few questions that I hope some of the knowledgeable membership here might be able to help me with. Those in the know will recognise that I'm talking about the following equation: R = Camera Read Noise P = Sky Electron Rate (Calculated from http://tools.sharpcap.co.uk/) E = Acceptable % increase in Noise above minimum When I work this through I get the following exposure times...which seem, well a little long! * calculated for Atik 383L+ OSC (QE of 57% Pix Size 5.4μm) at f7 with site SQM of 21.89 mag/arc sec2 (e.g. Kielder Star Camp) I could probably manage 735 sec, but does this mean I'll be getting significant noise which I'll then I'll still need multiple hours of exposures in order to stack enough images to benefit from the noise reduction? What I'm curious to find out is if there is a way to work out how many images you need to stack to get the same benefit in noise reduction in relation to the minimum noise threshold as a long exposure. Exposures of 20min plus seem extremely risky. I'd appreciate some thoughts on this. I was initially just going to try and knock out as many 5min subs as possible on each target (ideally 30-50 weather permitting) but now I'm a little unsure. They do say a little knowledge is dangerous! 😛

I'm pretty certain I've sorted this now and so thought I'd share the final combinations just in case anyone else finds themselves in the same situation. I'm still slightly concerned that I'm going to get vignetting and/or OAG shadows, but won't know that until I can get it all assembled. Option A uses the TMB flattener with the M42 back shown in the William Optics drawing, but with the filterwheel and OAG the backfocus is about 4mm longer than the 113.31mm I'm aiming for from the WO spec, and there's not really anywhere to lose it. Option B uses the Flattener with the optional SCT back. I've used a this Astro Essentials Low Profile SCT / 2" to M48 Adapter with TS M48 Variable Adaptor with M63 which allows me to get a pretty bang on spacing for the field flattener. Again I'm a little worried that the light cone is getting truncated here but it seems the best option for attaching the Atik in this train. Option C is how I'd plan to attach my DSLR. Surprisingly it's only a fraction off the Flattener backfocus so should give a pretty good result. This uses the following ultra short EF adaptor with an M48 extension tube. So if anyone has any comments, particularly on how you might trace light paths to work out if there will be any problems before I get all the bits, I'd love to hear them. Cheers

Lol, sorry Michael...I should have said 'if ikea made flats panels....!' Oops!

Thought I'd share my recently completed flats panel with you all. It was super cheap, using a number 10p off-cuts from my local hardware store for the timber plus a rummage in the scraps bin for the hardwood to make the lid locator. I already had the magnets that hold it together, but again these are cheaply purchased online. The cheap A4 tracing panel was £16 from Amazon and I used a little spare draft sealing tape around the inside of the opening so it will friction fit to the dewshield. I added a panel of frosted perspex to increase diffusion a little too. Unfortunately the light panel leaked loads of light from the back that creaped out of the thin edges, so I ended up sealing it all in with some aluminium tape left over from our renovations. Won't be able to test properly until I'm up at Kielder next week, but the brightness is adjustable and I always have the option of adding in some sheets of paper. Bit of an overkill I know, but hope you like this crossover with my other hobby of making things out of wood. Mike

@Yoddha Hi Ivo, apologies for cross posting from the APT Forum, but I couldn't attach my diagram (in post #1) to the thread over there! I'm still struggling to understand how backlash can be cumulative, which is why I tried to draw it out. When using the APT backlash aid I'm getting vastly different results depending upon the number of iterations. I would have thought that any inward move that is greater than the backlash will effectively cancel out the backlash of that move. Obviously I'm missing something here as you and the team are the experts, but I'm really keen to understand better and hope you don't mind helping when you get the time....no rush though as I know you're always super busy on the next release! Many thanks! Michael

In APT there's a setting to make a final inward move. If the focuser is moved outward by you or the auto routine, it will always move out the additional number of steps specified before returning in by the same number of steps. I'm assuming NINA has something similar.

That makes sense starflyer.

Love it....a low tech solution to calibrating our high tech gear! I still think it's incredible how tiny the focuser steps are...we're super lucky to be using such precision equipment, even if it doesn't feel like it some nights!

I don't think the focuser saying it is at a focus point suggests anything, but how do you assess image quality? I would have thought HFR or FWHM analysis of an image is a pretty good indicator and certainly to my eye seems to be repeatable and more precise than I've managed with just a bahtinov mask.

I've not tried NINA yet properly as I've been spending my time getting to grips with APT. I've generally used a bahtinov mask for focusing, but more recently have been using whole image HFR making use of ASTAP. This led me down the path of auto-focus and then I started looking at the settings and the various options for backlash compensation and measurement and my head started to hurt so I had to try and work things out so I could understand it. As far as I could tell APT uses a similar process to NINA and SGP for auto-focus in that it analyses the image and plots HFR or FWHM against focuser position to generate a v-curve to which an algorithm is applied to find a best fit and establish the focus point. But so that these focuser positions are correct it requires some form of backlash compensation to be applied. I've gone down the road of applying a final inward move rather than a specific backlash compensation because I'm not convinced that backlash remains the same at all positions due to minor manufacturing differences in gear train components and shifts in system weight etc. I agree tha filter and temp offsets also feel unreliable and would much rather just set to auto focus after a filterchange and on temperature change....to what degree of temperature change I'm not yet experienced to know what works best as I'm still dabbling. I'm assuming you couldn't find any glaring errors in my assumptions regarding what backlash is and how backlash affects things? I got myself so tangled in understanded the autofocus routines that I started to question if I'd even got these basics correct!! At one point I was even questioning the significance of backlash when we're aiming for a critical focus zone that's 50+ steps wide....but I guess every little helps

I've been trying to get my head around focuser backlash, why it's a problem and what to do about it. I'm still a little confused an so I decided to draw up my understanding of the problem and ask you all for your input. As far as I understand, the problem is that (using the example above) movements OUT will always result in B having an undetermined exact position where after A has finished moving, B could move further (creep) over time up to the amount of the backlash (10 steps in this case). Movements IN that are smaller than the backlash would also potentially be subject to similar creep. The amount of creep would be dependant upon numerous factors, e.g. the friction in the system, weight of imaging kit attached (wheels, cameras OAG etc) and the angle of scope...and as such is difficult to measure precisely. But the maximum creep would be equal to the backlash. Obviously the solution would be to always make a final move inward that is greater than the backlash. But how do you accurately measure the backlash? As far as I can tell from reading a number of other posts and videos it's not possible to get an exact number but you can get pretty close and then apply the good old engineering safety factor of x1.5 to give a number of steps to make your final inward move. My focuser has a maximum extension of 42000 steps and I normally get focus around 26400. So this is what I did: First I established the amount of focuser travel per step Go OUT max position at 42,000, then return IN to position 40,000. This should ensure gears engaged. Measure focuser extension with digital calliper (A=105.66mm) Move IN 30,000 steps to position 10,000. Measure extension again (B=26.41mm) We now know that 30,000 steps equals Measurement A - Measurement B. (105.66-26.41=79.25mm) So focuser travel per step = 79.25mm/30,000 = 0.0026416667mm or 2.642um per step Then to approximate backlash Go OUT halfway to position 21,000, then return IN to position 10,000. Gears should be engaged. Measure focuser extension with digital callipers (C=26.42mm) notice slight difference caused by inaccuracies of measurements. NOTE: Calliper accuracy of +/-0.01mm equates to approx. 4 steps of focuser, so chasing perfection is going to be very difficult!! Move OUT 1000 steps to position 11,000. We should now have moved 1000 steps minus the backlash. Measure extension again (D=28.96mm) Measurement D - Measurement C gives us the Measured travel for 1000 steps. (28.96-26.42=2.54mm) Calculated 1000 steps should be 1000 x travel per step calculated above = 2.642mm Backlash equals 2.642-2.54mm = 0.102mm which when divided by travel per step gives backlash of 38.6 or approximately 39 steps SO if I set a final inward travel of 1.5x39 = 58.5, lets say 60 steps I should have eliminated backlash right? Apologies if this ended up a bit of a brain dump...but hopefully that makes sense and if I'm way off the mark then someone will be able help set me back on course. Cheers!

Tell me, if I'm using software to adjust focus every few degrees of temperature change, do I need to retake flats everytime I shift focus and then stack seperately for each change in focus? Also, what sort of temperature change might I expect to cause noticeable focus change? My setup is a 925mm f7 scope with atik 383 osc so at least I don't have to multiple the extra work by 3 or 4! 😁

Thanks again everyone...I'm slowly getting the rig together again. Just wish I had more chances to play with it.

This makes me wonder if I'm going to need to dim my flat panel to get decent flats? Didn't have a problem with my dslr, but that also shot daylight. 😀

Those look good. Hopefully it's a buy once last for many years so not too worried if they're a bit more expensive so long as they are flexible and don't coil too much and snag.

The shortest exposure seems to be 0.2s and still completely blown out. I think you're right. Very sensitive sensor, which I suppose is what I want really...just frustrating I can't sort out some of these little setup tasks during the day. Once I have it setup I'll whip out some tape to mark the focus points so that setup is a little quicker next time.

Made me laugh...😆 I've used Canford cables before and they are nice...Just a pity they have a £35 ex vat min order and then a minimum £8 delivery charge..

I've recently picked up an Atik 383 OSC and I wanted to get my focus and OAG aligned during the day. But I can't seem to take anything but complete white frames, even at the shortest exposure. I don't know if there's a setting somewhere I've not found but if anyone has any ideas I'd appreciate it.

Good plan. I was slightly concerned about them getting mucky as this is for my main mount PC connection so it drags on the ground a bit. But I don't think a little mud is too bad.

Yes, I think the higher spec has a 4-way spliter that runs the length of the cable to separate the twisted pairs and this makes them super stiff. I've bought nice cable from Canford before and made my own, but I only need the one 2-3m length this time.