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Lakeside focusing.. Help


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25 minutes ago, swag72 said:

Seriously when I have everything working I don't touch anything!! 

Ok, ok I believe you  :D you really could be my sister because I’m the same. Can’t really say the same about Ray because the inner engineer in him always wants to fiddle :D

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1 minute ago, souls33k3r said:

Ok, ok I believe you  :D you really could be my sister because I’m the same. Can’t really say the same about Ray because the inner engineer in him always wants to fiddle :D

It's the law ?

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This got me thinking last night. Say when i'm imaging more than one filter per night (which i normally do) and i write down the focuser position number (orientation of the camera and filter wheel are already marked) and pack my gear away, can i not bring out my focuser to those positions in doors and take flats?

Gradients is what's killing me most during processing and i would like to tackle them in a better way.

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15 minutes ago, souls33k3r said:

Gradients is what's killing me most during processing and i would like to tackle them in a better way.

Me too, it's the curse of living in / near London.

Dave

M101.png.1f1f8bbfcfdf0ecf625fb856d9f325e8.png

 

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2 minutes ago, Davey-T said:

Me too, it's the curse of living in / near London.

Dave

M101.png.1f1f8bbfcfdf0ecf625fb856d9f325e8.png

 

oh mate, i do feel your pain. Yours aren't too bad, mine are just having a dance party on a weekday. 

So do you think my way of dealing with flats would work?

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50 minutes ago, Davey-T said:

Are you leaving the camera on the scope ?

Dave

Yes mate I usually do. I mean the last time I took it off was about a year ago when I bought the Star 71. The whole unit goes in to a case with only FW moved to one side to that the scope sits in the case properly. 

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2 hours ago, souls33k3r said:

This got me thinking last night. Say when i'm imaging more than one filter per night (which i normally do) and i write down the focuser position number (orientation of the camera and filter wheel are already marked) and pack my gear away, can i not bring out my focuser to those positions in doors and take flats?

Gradients is what's killing me most during processing and i would like to tackle them in a better way.

No reason why you can't mate.  The only thing that you would need to be mindful of is dust moving around as you move the scope around.  I have done it this way many times (brought the kit indoors and then did flats) and never had an issue.

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7 minutes ago, RayD said:

No reason why you can't mate.  The only thing that you would need to be mindful of is dust moving around as you move the scope around.  I have done it this way many times (brought the kit indoors and then did flats) and never had an issue.

Ah cheers for the very quick response mate. 

My feeble mind keep is on extra time and thinks about new things and ways to improve my astro journey :D

I must admit, i really haven't noticed any dust on my image so far so i should be alright *runs to the nearest wood and touches it* :)

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Right so here I am with an update on a few things. 

Firstly, @RayD, that skin issue on PUB for the limit worked brilliantly. Cheers for that mate.

Secondly, again thanks to all for your help with this V-curve business. All I have to say "Sweet baby jesus!!!" it not only works but blimey my images are soooo sharp.

I absolutely agree with you Ray, I really don't know how I lived without one. 

Here's the V/U-curve... Should I leave it as it is or I should tinker with it? 

received_10160951898675571.jpeg.13d722a3d6a581d0f4e7fbf109678a58.jpeg

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4 minutes ago, Davey-T said:

HFR 0.88 should be good, I'd leave well alone :)

Dave

Manually I'd be lucky to get anything below 1.66. 0.8 is me dreaming seriously. 

Left well alone matey :) I'm quite surprised how simple this whole process is and yet it does so much of a better job than bahtinov mask. Crickey, I think I'm in love... Again?

 

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10 hours ago, souls33k3r said:

Right so here I am with an update on a few things. 

Firstly, @RayD, that skin issue on PUB for the limit worked brilliantly. Cheers for that mate.

Secondly, again thanks to all for your help with this V-curve business. All I have to say "Sweet baby jesus!!!" it not only works but blimey my images are soooo sharp.

I absolutely agree with you Ray, I really don't know how I lived without one. 

Here's the V/U-curve... Should I leave it as it is or I should tinker with it? 

Great stuff mate, really glad you're seeing the benefits of it.  It certainly makes quite a difference and, rather nicely, does it all again for you throughout the night to keep you in focus :thumbright:

HFR at 0.88 is very good, can't argue with that.  The only comment would be the top of the curve is a little low, and I would expect to see it somewhere over the 3 mark, so you may need to just double check your step sizes as it seems this may be a little low.  With this said, the final value speaks for itself, so may be worth seeing how it goes with this setting for now.

Now get imaging!!! ? 

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9 minutes ago, RayD said:

Great stuff mate, really glad you're seeing the benefits of it.  It certainly makes quite a difference and, rather nicely, does it all again for you throughout the night to keep you in focus :thumbright:

HFR at 0.88 is very good, can't argue with that.  The only comment would be the top of the curve is a little low, and I would expect to see it somewhere over the 3 mark, so you may need to just double check your step sizes as it seems this may be a little low.  With this said, the final value speaks for itself, so may be worth seeing how it goes with this setting for now.

Now get imaging!!! ? 

Hahahahaha imaging away my friend, love the fact that i don't have to get bit by mosquitoes any more :D

I've checked and double checked my steps size (thanks to your brilliant YouTube video which explains it in such great detail and in such simple way).

Mind you, my very first curve did start from 3+ mark when it was a bit out of focus. This is the second degree change of the night when i managed to take a screenshot. I thought that the reason why it did that was because i was already in focus and the curve started from just out of focus like it should do.

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32 minutes ago, souls33k3r said:

Hahahahaha imaging away my friend, love the fact that i don't have to get bit by mosquitoes any more :D

I've checked and double checked my steps size (thanks to your brilliant YouTube video which explains it in such great detail and in such simple way).

Mind you, my very first curve did start from 3+ mark when it was a bit out of focus. This is the second degree change of the night when i managed to take a screenshot. I thought that the reason why it did that was because i was already in focus and the curve started from just out of focus like it should do.

Yeah it is probably ok, mate.  With an in focus HFR of 0.8 I would be looking for an out of focus point about 3.2 (halfway between the suggested 3-5 times the in focus reading).  I suspect your average HFR would be around 1.2 (ish) so you may want to aim for a point around the 4.0 - 4.5 mark, which should work well in all cases?

As noted, if it's working, leave it, and only tickle it if it becomes necessary.

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Not touching it EVER again Sara :D i'm just glad i got it working with the help of everyone's brilliant advice. Something that should've been a pain was a breeze only because i had fantastic help at hand :)

Ray, does it actually matter where it should start or should it matter what HFR values i get as the end result?

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2 hours ago, souls33k3r said:

Not touching it EVER again Sara :D i'm just glad i got it working with the help of everyone's brilliant advice. Something that should've been a pain was a breeze only because i had fantastic help at hand :)

Ray, does it actually matter where it should start or should it matter what HFR values i get as the end result?

It only matters as the algorithm uses the entire range of change to calculate the best HFR value, but if you are achieving 0.8 as it is then leave it as it is clearly working.

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1 hour ago, RayD said:

It only matters as the algorithm uses the entire range of change to calculate the best HFR value, but if you are achieving 0.8 as it is then leave it as it is clearly working.

Nice one, cheers for that matey.

Can there ever be the case that the HFR ends up any where south of 1.5? If so, what should i look out for? hazy / clouded skies? If there is anything else, please do let me know before i start ripping off any hair that is left on my head :)

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1 hour ago, souls33k3r said:

Nice one, cheers for that matey.

Can there ever be the case that the HFR ends up any where south of 1.5? If so, what should i look out for? hazy / clouded skies? If there is anything else, please do let me know before i start ripping off any hair that is left on my head :)

You'll be fine. Yes the HFR will probably drift up from that, it is a pretty good value. If that happens see how it performs then, and if necessary have a little tweak, but in the meantime just enjoy the luxury it provides and spend the evening running a brush through your flowing locks ?

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15 hours ago, RayD said:

You'll be fine. Yes the HFR will probably drift up from that, it is a pretty good value. If that happens see how it performs then, and if necessary have a little tweak, but in the meantime just enjoy the luxury it provides and spend the evening running a brush through your flowing locks ?

I'm certainly no Rapunzel but i am most definitely enjoying the fact that all works well without me wasting any time :D

Now to work on the filter offsets and work out how to set these values.

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  • 2 weeks later...

Can I pick someone's brains if I may? When lakeside does it AF routine it find the best focus as say 0.88 HFR. The mean read out started with 1023. As the night progressed the mean read out become lower and lower but my HFR in the last two images has just increased (1.98 and then 2.87).The focus point is still at the same point where it was when I first focused. Surely something isn't right? 

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The mean focus point during autofocus will decrease as the temperature drops during the night. HFR getting worse could be caused by haze or thin high clouds. Also as the altitude of the target decreases 'the seeing' will get worse and make the HFR value increase. Did you notice the SNR of the guide star dropping during the last two images. This is normally a symptom of the sky quality decreasing.

Alan

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11 hours ago, symmetal said:

The mean focus point during autofocus will decrease as the temperature drops during the night. HFR getting worse could be caused by haze or thin high clouds. Also as the altitude of the target decreases 'the seeing' will get worse and make the HFR value increase. Did you notice the SNR of the guide star dropping during the last two images. This is normally a symptom of the sky quality decreasing.

Alan

Cheers for the input Alan. The temperature did not drop significantly. It mostly kept on lurking around 23.40 - 23.60 degrees. The focus happened at around 23.50 degrees. Thin high clouds could be the case but the mean readout in SGP got better and better throughout the night. The traget was still on the rise, i started imaging at around 70 - 80 degrees and ended after it crossed the zenith. I must admit, i did not pay much attention to the SNR of the guide star.

I do also want to find out why if the optimum focus was suggested to be was a 0.96 but then the very first image that got downloaded i noticed that the HFR was at 1.98 and the second image HRF went up?

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The HFR for your autofocus was done with an exposure of a few seconds. Your actual images had exposures that were a lot longer so tracking errors throughout the exposure of just an arcsecond or so will accumulate and make the final star image larger. Also the longer image exposure will make the stars 'bloat' more than an exposure of a few seconds. I assume SGP doesn't use excessively clipped stars in the HFR reading.  After autofocusing I just check the images for reasonably tight round stars and don't look at the HFR value.

If you wish take an imaging run with the same exposure as your autofocus and see if the HFR values are then very similar.

Alan

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