bomberbaz

On 21/05/2022 at 12:23, vlaiv said:

Bias as such is not needed in calibration workflow because it cancels out. Let me show you (and explain why that is).

Workflow involving bias goes like this:

You create master bias by stacking bias subs - let's call that MB

You create master dark by stacking (D - MB) subs - or in words - you take each dark and remove bias by subtracting master bias from it and then stack those - lets call that MD

You calibrate each light sub by

1) removing bias

2) removing dark

3) doing flat calibration (this step is not important for this so I won't bother with it)

calibrated light = light - MB - MD

Right? But let's just expand that expression a bit

calibrated light = light - MB - average(D - MB)

If you have a constant in average, you can pull that constant out as average(D-MB) is just (D1-MB) + (D2-MB) + (D3-MB) + .... + (DN-MB) all divided with N or number of subs. If we rearrange brackets we end up with D1+D2+D3+ ... + DN - MB -MB -MB (this repeats N times) all divided with N

That is further (D1+D2+...+DN - N * MB)/N

And from this you can see that you can pull MB out of that as N/N is 1

so above expression

calibrated light = light - MB - average(D - MB)

transforms into

calibrated light = light - MB - (average(D) - MB) = light - MB + MB - average(D) = light - average(D)

There we go

calibrated light = light - average(D)

No need to use bias to get calibrated light.

Why is bias then used in some cases?

Two reasons really. Sometimes bias is used instead of flat dark. This is strictly speaking wrong - but in many cases, flat exposure is short and dark current is low - it can work, or rather error will be too small to notice.

Second reason is if you plan to scale darks or use dark optimization (which is really the same thing except computer trying to figure out proper scale factor).

Sometimes you build dark library of say 10 minute exposures, but for some reason use 5 minute exposures when shooting target - you can still calibrate your light subs with mismatched darks if you scale them.

Dark current signal builds up linearly with time - which means that in 10 minutes it will be twice as strong as in 5 minute exposure, or 5 times as strong as in 2 minute dark exposure.

We can exploit this fact if our camera behaves properly (CCDs tend to behave good for this and CMOS cameras behave poorly - so I would say that this is mostly available for CCDs).

Dark subs contain dark current signal and bias signal. If we remove bias signal we can then multiply dark current signal (bias does not depend on time so we must not multiply it - we must first subtract it).

This is the reason why there is bias subtraction in above expression - but it is only needed if you plan to scale your dark current. If you plan to scale dark current - you can no longer take bias in front of the brackets and it won't cancel out. It is needed for whole thing,

Makes sense?

Thanks @vlaiv for the above explanation, I get it all until the last (underlined) equation. However rather than mash my brain trying to really get my head around it, I will accept that you are right and they are not really needed.

However I am one of these people who will go out now and run comparisons because I want to see for myself. I guess that is the scientist part in me. I can accept what someone tells me is right but I won't fully believe it until I prove it right. 

On 21/05/2022 at 19:16, Anthonyexmouth said:

I recently watched this by Adam Block when i was looking into using WBPP for PI, but it actually gives quite a good and understandable explanation of calibration frames. Something that i'd never actually seen in such a simple way before. 

 

Anthony, now I know what WBPP is (google is ace), I shall watch this as I really do want to get my head around calibration frames fully. As above vlaiv's explanation is very detailed but lost me at the last minute.  Maybe this video will help a few pennies drop.

Cheers guys.

Steve

22 minutes ago, AstroNebulee said:

Ahh I see, I had to have the mount slide switch off to change it to ethernet. I'll attach a screenshot of mine for you. Seems its the same as yours Steve. 

I always have serial showing as connected and didn't know about the ethernet setting. Not sure what difference it makes, so I'll keep mine in serial and baud rate 9600.

Cheers 

Lee 

cheers Lee, that's bang on pal 👌

@AstroNebulee just click next to the serial by baud and it changed over mine, funny setting and needs a little work by development imho

Question. Can someone go into their IP and port settings in the app and tell me what ethernet address is and port number plus either TCP or UDP please.

Mine is at IP 10.0.0.1, PORT 4030 and TCP.

I have read it should be 10.0.0.10 and UDP but would like to see if mine is the only one defaulting to this.

cheers

steve

Hi guys.

Ok so I was getting a preview from the guide but here's where the problem may lie and only a live test will tell. 

The tracking button just above the 3 buttons for sidereal, solar and lunar was not ticked. I thought it defaulted to sidereal if left unticked but maybe not.

Anyway, I shall give it a bash either tonight but doubtful due to cloud, or more likely tomorrow as it is more likely.

Cheers

Steve

1 hour ago, AstroNebulee said:

Hi Steve 

I set my baud rate to 9600 and choose eq mod mount with my eq dir cable from my az gti to my AAP and tracking to sidereal. 

So my cabling for AAP is storage key in USB 3, 294mc pro usb3 cable to USB 3 port, 120mc-s guide camera usb3 cable to USB 2 port, eq dir cable from az gti to USB 2 port. 

Your setup worked fine when you had your 50ed on it didn't it, so strange how the tracking has changed. 

Will rack my brains more to help

Cheers 

Lee 

You got it spot on there Lee.

I am wondering if anything has changed that I didn't notice. I shall go back through settings later and see if anything changed during the re-wire boggle when I changed scopes. 

tried doiing a test run last night, everything worked fine until tracking, not tracking at all.

I tried swapping cable around, changing the baud rate but nope, anyone got any tips or a method of checking the cables?

5 minutes ago, Priesters said:

It was from AliExpress.  Ordered 28/4 and arrived yesterday - £44 with shipping so not cheap.  I tried the StarAdventurer counterweight kit but it didn’t seem heavy enough.  I considered getting an additional SA counterweight which I’ve seen a few people do but I went for this bar as it’s designed specifically for the AZ GTi and is a bit longer I think (in case I want to really overload the mount in the future 😂).  The counterweight is a Bresser 2kg which I bought from Amazon - £32.  If there’s a way of doing something more expensively, I’ll find it 🙄.

My bar could do with extending if I am honest, thats why I noticed yours.

I was thinking about buying a new one as it is ever so slightly unbalanced.

Think I might just try a small bolt into the bottom of the bar, some tape and a large washer, will be cheaper and hidden anyway. 🤔 

At home stellarium, sky safari both on the pc and occasionally cambridge star atlas desktop version. 

In the field almost always sky Safari 6 plus subscribed version but sometimes stellarium, both on a smart phone. 

Tablets are just a little clunky for my liking.

I hope we are not going to descend into an argument about how electronic sky atlases in astronomy takes away from it's appeal, or is cheating, or isn't proper astronomy, or you don't learn the sky the same! 

Remember goto ? 🤣

Sorry, (not sorry).

Steve

21 hours ago, Priesters said:

Ta dah - and for once, no additional purchases necessary.  Bolt attaching mount to dovetail (and serving as a safety bolt) has been pinched from the tripod extension that I’m not using.  The green dovetail came with the Evoguide and the silver dovetail with my WO GT81 and I’ve already upgraded that to Losmandy so it was spare.  Using a short 1/4 - 20 bolt that I had in stock for the safety on the green dovetail.  You can probably tell I’m quite pleased with tonight’s efforts.  Thanks for the advice all 👍

Looks ace that, the evoguide setup is such a nice rig

Where did you get the bar and c/weight??

For polaris there is SynscanInit on android. It gives you your coords and also a virtual position of polaris.

I only use it for coords though.

You may need a signal for it to work, not sure. 

On 27/02/2021 at 13:28, Jonny_H said:

I use the Lynx Astro psu to power my asiair pro with no issues. 

https://www.firstlightoptics.com/batteries-powerpacks/lynx-astro-12v-dc-5amp-low-noise-mains-power-supply.html

The only thing I will say is that the psu to DC jack end of the cable is very short. To overcome this I purchased the Baader male to female extension cable (below).

https://www.firstlightoptics.com/astronomy-cables-leads-accessories/baader-2m-extension-cable-for-12v-cable-with-baader-outdoor-telescope-power-supply.html

 

Clear skies.

Jonny

Just bought the ext cable, thanks for link. Been meaning to look for one for ages. 

1 minute ago, faulksy said:

just looking on light pollution map. to the west nearest town is 90 km and south is 80 km which is brecon 🤣

just waiting for solicitors to pull there fingers out

4 km from the house is 21.82

Have you taken tgese readi gs from a lp map, cos they are not most accurate. However if you can get 21.82, that is black, milky way casting a shadow dark!

On 26/04/2022 at 16:16, vlaiv said:

I use a lot of subs.

There is no rule of thumb really - same thing applies to darks and bias as it does to lights - noise goes down by square root of stacked subs.

You inject back this noise into every light you calibrate so it is worth spending some more time to minimize this noise you put back in.

Good thing is that you don't have to shoot all your subs at one time.

You can start one day and do 4h of darks. You can add next batch of darks in few days when you have the time. I usually just leave it in basement where temperature is lower so it is easier to get to target temperature for 4h at a time while I'm doing something else.

I've used up to 256 of subs in my stacks (256 is "default" for flats and flat darks). I start with 64 dark subs and build from there.

By the way, if you don't scale darks and don't optimize them - then bias are really waste of time. You only need flats, flat darks and darks for complete / proper calibration.

Forgot to ask about this, what is meant by scaling darks and why are bias not reallyneeded.

I ask because ASI air, SIRIL, DSS etc all ask for them as part of their programme/

23 minutes ago, faulksy said:

im moving soon to a near bortle 3 area measures with my sqm 21.68 should be ace 😆 this is uk, spain fell through. 8 weeks left untill we move to mid wales

Horsehead skies them mate, m33 easy naked eye. Not a lot out of amateur visual range tbf. Not one bit jealous though 🙄

20 minutes ago, alacant said:

No. 

Learn it manually simply means do this. 

After working through that, you'll not only understand why you're calibrating and stacking but could be left wondering why you'd need anything automated in the first place.

You'll also be in a much better position to troubleshoot what went wrong and what you missed out on doing when it did. You need only look at the posts concerning processing e.g. flat frames on this very forum to realise the frustration and time wasted not knowing!

Cheers and good luck.

Thank you very much, just found it on the tutorial menu page Siril - Tutorials (along with many others), it's amazing what you can see when you look 🙄

I note it is listed as a 2 out of 5 for difficulty! Challenge accepted 😉

cheers

steve

2 hours ago, alacant said:

Hi

If you like modern clean screen apps, you'll get on well with it. If you're expecting conventional menus-along-the-top with windows everywhere, less so.

To begin, we'd recommend learning it manually; put yourself in charge.

Cheers, HTH and good luck.

is this Siril - Full image processing (pre-processed with scripts) something that should be read then? 

I don't want to sound negative but just stating "learn it manually" doesn't tell me a lot to be fair!

I am reasonably computer literate but by no means a wizard.

cheers

steve

Much obliged. I shall have a good read and see what's what. 

12 minutes ago, AstroMuni said:

I have tried Pyastro and didnt find it that useful. I tend to use GMIC which is not astro specific but certainly helps. I do my initial processing in SIRIL and its only the final polishing that gets done in Gimp

Ah now this is interesting, I have SIRIL installed but not had a go with it yet.

How do you find it for user friendliness?

9 hours ago, vlaiv said:

It doubles the number of used pixels, but those pixels won't include new / valuable information.

It is really like visual astronomy. You can always add a barlow to scope / eyepiece combination - but if you already have short focal length eyepiece - you will get larger darker image without additional detail.

This is the same thing - you already have very small pixels compared to what scope can deliver (it's like using 2mm eyepiece) and you want to add barlow to that.

I get it now, I was looking at this from wrong angle entirely.

It is what goes in at the front that counts, you can mess around all you like at the other end but that fundamental factor remains unchanged. 

Thanks @vlaiv, you help is greatly appreciated. 

Thank you @vlaiv for your detailed explanation. That is much clearer to me now but still something is missing in my mind.

I am still not 100% on the physics side of it as in why the barlow at x2 doesn't double the pixels because the way my mind thinks, I am thinking you are doubling the image size on the sensor. Or perhaps I am mixing up different aspects of the image process. 

I will re-read this tomorrow after a good nights sleep.

Thanks again

Steve

15 minutes ago, AstroNebulee said:

I seen thread this earlier Steve, not reading material but may have some good nuggets of help for you. 

Cheers 

Lee 

Just realised it is nearly 2 hours so hopefully quite a bit of good info in there. 

6 minutes ago, AstroNebulee said:

I seen thread this earlier Steve, not reading material but may have some good nuggets of help for you. 

Cheers 

Lee 

Thanks Lee, I shall bookmark it for tomorrow. Bit late just now. 

Hello all.

Recently I am finding myself with a lot of questions in my head regarding imaging covering many different aspects of it. Not the actual setting up so much as more methodology and such. Things such as binning, over sampling, use of ancillary extras such as filters or barlows/reducers and so on.

So rather than keep asking questions, which I know people are happy to answer normally I think it might be better if I started researching for myself.

I have placed a wanted advert for "every photon counts" but just wondered if anyone has any other suggestions for resource that gives you a start up tutorial. I mean from the beginning too, I know I am already doing a little already but I can bet there are many useful tips I could pick up from some beginner type guides.

I have already done some google searches but the trouble is so much comes up and much of it is not really what I am after. 

Not bothered what type the resource is. Web page, book, you tube or whatever although I do like my you tube stuff if I am honest. 

Any help gratefully received.

Steve

10 minutes ago, vlaiv said:

There is only so much resolution that you can achieve with 60mm scope and you are already over sampling with 2.4um pixel size (probably even when using super pixel mode).

No benefit what so ever in using barlow lens - effect will be the same as when you take regular image without barlow and enlarge it by factor of x2 or whatever barlow you were planning on using.

 

Thanks @vlaiv, one other query, will binning not help with the over sampling or am I getting it wrong?