vlaiv

I'm somewhat confused by all of this.

Does "traditional EAA", either in form of video astronomy (old video cams at eyepiece) or live stacking type fall under EEVA definition?

Also, @GavStar and @alanjgreen, this is a genuine question, not trying to provoke an argument or mock subject or whatever - Why do you feel that NV is more visual astronomy then for example live stacking?

If I understand things correctly, both NV and Live stacking - use light sensing device, a form of amplification of signal and light emitting device to enable observer to look at object with their own eyes. Granted, NV device is self contained / compact one, while camera / cable / laptop with screen is not as compact, but both systems in essence provide the same thing. Also, experience will differ, but does the principle of operation outlined above differ as well?

4 hours ago, Starwiz said:

If all goes to plan I'll be starting imaging with an ASI1600mm-Pro next month.  The exposure times seem incredibly short compared to the 10 - 15 minutes I was doing with my modded Canon 1200d.  Is that because the sensor is much more sensitive on the ASI?

BTW, I've just emigrated to Malta, so looking forward to the cloudless skies.  Light pollution where I am is slightly worse than my UK location (Bortle 5 compared to Bortle 4), but I'll also be doing narrow-band as well as LRGB.

No, sensitivity does not play a part in that. Here we are talking about splitting one very large exposure into smaller ones. You can look at it that way - instead of doing 1 grand exposure lasting multiple hours, you break it into shorter ones and add up those shorter ones. All things that are important to final result add up with time - signal adds up, more you image more there is of it. Light pollution behaves the same - longer exposure you accumulate more light pollution. Thermal noise is also the same - more you image, more it builds up. Everything except the read noise - it is the same regardless of exposure length. 10 minute sub will have same read noise as 1 minute sub.

And that is the difference - more subs you take, more times you add read noise. Level of read noise determines how much it will impact final result - lower the read noise, less impact it will have compared to other sources. Most often read noise is compared to LP noise - look above at triangle explanation, but other noise sources also participate. With narrowband imaging you eliminate most of LP - this is why you need to go longer in NB - read noise becomes important factor.

ASI1600 has very low read noise compared to other sensors. Most CCDs and DSLRs have it at about 7-9e range, some low read noise models have it at 4-5e, but that is still x3 compared to ASI1600 (and other CMOS models). With DSLRs it's often recommended to go for ISO800 or similar instead of ISO100 - this is because CMOS sensors tend to have lower read noise at higher gain settings.

1 minute ago, eshy76 said:

The 20 x read noise can also be 3 x read noise squared or 10 x read noise squared....there's some discussion about that. 

There is no definite value that one should use here. It comes down to when you can consider read noise contribution too small to matter. Best way to "visualize" this is by right angle triangle. If one side is much smaller than other - longer side approaches hypotenuse in length. Total noise is hypotenuse and read noise and LP shot noise are sides of right angle triangle. When LP shot noise "side" becomes much larger than read noise "side" - total noise (hypotenuse) comes close to that LP shot noise "side".

a = b implies c>b

O<<A implies H and A almost equal in length (O here being read noise almost has no impact on total noise - it's dominated by LP noise - here A)

30 minutes ago, simmo39 said:

BTW, I think the SQM value here is: 20.4–21.3

If it's 21.3 - that would be considered fairly dark sky in terms of imaging. You would benefit from longer exposures then.

1 minute ago, Adam J said:

Not sure about very long focal length unless that is also implying very slow F-ratio in which case longer exposures will be required.

Indeed, that is what I meant

5 minutes ago, Adam J said:

The longest Luminance sub I have ever felt the need to do from my 5/6 location is 30 seconds. Higher than that then I would think 15 seconds is not a bad idea. All this talk of 3 or 4 min exposures only makes sense in a very dark site.

Or when one is using very long focal length, high resolution (and maybe binning afterwards in software). Even in red bordering with white zone, I benefit from couple of minutes subs at 0.5"/px (this gets binned afterwards as it is oversampling). Skyglow also gets "diluted" over large number of pixels and LP noise is smaller in given time when imaging at high resolution.

2 minutes ago, simmo39 said:

Hi Vlaiv. Thanks for the reply. I'm going to be using my new SW 72ED. Think it's about F5. Comparing to my SW 130 PDS is F4.8 I think. I have been using 240s subs for narrow band with that and was hoping that 240s for NB would be good for the 72ED.  As for the RGB I was thinking about 120s, do you think that would be a good starting point or should I see if I can push it to 240s?

What is your light pollution like? Do you know average SQM reading for your site? (or maybe data from lightpollution.info)?

I think numbers that you mention are good for average to strong LP (120s). Only if you have very dark skies it makes sense to go longer.

That really depends on various factors. For any given setup and conditions, longer subs will always produce better results, but relationship is not straight forward. What happens is: going from 1m to 2m will have significant impact, going from 2m to 3m is going to have noticeable impact, going from 3m to 4m will be barely noticeable and going from 4m to 5m is not going to produce any perceivable difference.

Above numbers are arbitrary and serve just to show you that there is no linear dependence between sub length and improvement - at some point improvement starts to rapidly fall of until it reaches undetectable levels (meaning you can't tell difference to SNR by eye alone and it has virtually 0 impact on image quality as perceived by human eye).

Thing is - above numbers depend on many factors - focal length of scope, aperture, light pollution levels, etc ... With higher sampling resolution (less "/px) - increase sub length. With darker skies - increase sub length. With larger aperture increase sub length. When you have combination of those factors then it's not easy to say without calculations (like using lower sampling rate while moving to darker skies, or other combinations).

As for lum vs RGB, that one is even harder to tell. I usually do it equally for each filter - meaning same time for L, R, G and B. Some people do it like equal time for L as for R, G and B combined and they split R, G and B equally. In theory, given limited time budget there is optimum split - but it is way hard to calculate and one would need much more information than is available prior to imaging (like target brightness in each band - you don't know that until you image target).

One thing that can be useful is: don't be afraid of long exposures if your mount/scope system supports them (guiding and tracking are up to task). You can always get few short exposures at the end to blend in what ever you saturated in long exposures.

Check if ND3 filter is properly installed in wedge before you use it.

Easiest way to do it is to look down the wedge without it being attached to scope - point it to bright daylight and it should be very very dark.

CPL or linear polarizer should be placed at eyepiece. Light from wedge is polarized and addition of another polarizing filter lets you adjust amount of light reaching your eye by rotating eyepiece. So if you screw CPL filter into eyepiece that you are going to use to observe the sun and put that eyepiece in wedge - by unclamping it and rotating it you can adjust brightness of your view for best contrast, then tighten EP clamp again and continue to observe.

1 minute ago, Gina said:

The possible problem with water cooling is that the waterblock is going to be the highest part of the system and could suffer from an airlock unless the pump is powerful enough to flush the air out.  I think I shall have to do some experiments.

I think that can be easily solved with submerged pump - no way to get air in once you flush all air from tubing.

52 minutes ago, Gina said:

Yes, water cooling is one of the ideas mentioned above but is not so easy with the waterblock so high up.  I have used water cooling in the past for camera cooling and use it currently in one of my 3D printers.  I am well familiar with it.

I obviously did not read your post careful enough - you mentioned water cooling indeed.

Most of camera coolers use very smooth running - electronics cooling fans, like ones for computers. This is because of noise and shake - as they are mounted on cameras.

There are industrial grade fans that are designed to be resilient - for example ones used in kitchen extractor fans and such - can operate under steam and higher temperatures (but I'm sure you can find ones that work in lower temperatures as well).

These usually have higher level of vibration and noise due to slack - design decision to prevent them from seizing in higher temps. Maybe you can use one of those - but it would involve quite a bit of DIY.

There is also option to go for heat pipes - you can source them from aftermarket CPU coolers - can be used for both air and water cooling based solution.

I have an idea how to handle cooling in adverse atmospheric conditions if you feel that you need it.

It will involve a bit of DIY but it should work without fans that would be susceptible to moisture or seizing up in cold weather.

Liquid cooling. You'll need a pump, reservoir, some tubing and cooling block. All of this can be purchased. Pumps are used for fish tanks and cooling blocks are used by overclockers to cool computer components. With enough tank capacity you won't need to dissipate temperature actively - tank will help cool liquid to ambient (liquid is just distilled water with addition of antifreeze). Just use metal tank holding couple of liters of liquid. You can mount aluminum finned radiator to side of tank to help dissipate heat from tank.

What are you trying to measure / record with ASC?

I can't really tell the difference between all of these frames - different scale / presence of moon, etc ...

I would first start by assessing actual need for active cooling?

What sort of exposures are we talking here? I think that for anything 10s or less, for ASC you don't really active cooling. ASC by design uses short focal length lens that is fast (F/1.4-F/2). Let's say that doubling temperature is 6C.

If we assume something like 0.05e/s/pix at 0C of dark current (ASI1600 has ~0.03e/s/pix at 0C), for sensor temperature of 24C we can expect 16 times larger dark current. At 24C that is 0.8e/s/pix, hence for exposures up to 10s you will have something like 8e of dark current - or less than 3e dark current noise per pixel - that is comparable to read noise of camera, and probably less than LP noise with fast lens.

Btw, we can see what sort of LP noise we can expect in very dark skies in 10s exposure. In 21.5 Mag skies, with F/2 18mm lens, with 50% QE camera having 3.75um pixels, one will get ~1.24e/s or 12.4s sky brightness. That gives us 3.5e LP shot noise from sky alone - more than dark current noise.

Is it really worth having actively cooled camera under these circumstances?

How about one of these two?

https://www.firstlightoptics.com/zwo-accessories/zwo-replacement-150-degree-wide-angle-lens-for-zwo-asi-cameras.html

https://www.firstlightoptics.com/zwo-accessories/zwo-cs-lens-2-8mm-12mm-f1-4.html

Or this one:

https://www.teleskop-express.de/shop/product_info.php/info/p10246_ZWO-CCTV-Lens-2-5mm-170-Degree---for-ASI-Cameras-without-cooling.html

1 hour ago, parallaxerr said:

Right, that's it, I've washed my hands of it. Have raised a claim and Paypal are investigating. I may have let myself in for a longer wait but I just can't put up with TS's ridiculously slow response times and poor service.

Will you still do a star test? I was hoping to read your first impressions ...

1 minute ago, parallaxerr said:

I have no issue changing a focuser, done it plenty of times. It's the faint chance of causing more damage which I would be liable for that is the issue.

However, I am now considering something similar to what Fabio says. Star test the scope tonight and if it's OK, send the focuser back for repair. It is definitely not my preferred outcome but probably the quickest way to resolve the issue.

It did not occur to me that you can do that with faulty focuser - its not that faulty that you can't reach focus with it - but you certainly can although movement is rough due to bent shaft. Star testing it as is - is very good idea.

Just to add, I don't think changing focuser is a big deal, but I might not be aware of some issues with that.

I've done it on one of my scopes - ordered "aftermarket" upgrade unit and fitted it without any issues - just unscrewed original and screwed in replacement.

Many people upgraded their focuser also. I don't think they worried too much of what could go wrong with that.

There is issue with lens being knocked out of collimation or something, but as far as I know - refractors are pretty resilient to this. On one occasion, while ordering the scope from above supplier, due to mix up in the post, my scope ended up being sent to completely different country It was in transit almost 3 weeks - being sent to Romania first, then returned to Germany, then again sent to me. I was really worried that scope will arrive in bad shape due to that much time spent in rough handling - but to my relief - it was in perfect shape.

I think that you should definitively consider what is the best option for you - what will bring you resolution in easiest way. If you think said scope has potential to serve you well and you don't think it will be too complicated to change focuser - do that, but ask for a guarantee for prompt resolution in case something else is wrong with the scope. If you don't want to bother with it all - go for refund.

Here is how would I do it, but do take into account that I've never done it

You need a good star mask.

For recommended exposure - go for one that will not saturate stars, even brightest ones. For number of exposures - same thing holds as always when imaging - as much as you can afford within your imaging budget.

Stack everything into corresponding stacks, make sure it's properly aligned to same reference frame.

Do your NB composure / channel mixing and stretch. Do the same with RGB - compose image, stretch and do color balance. Don't worry about star bloat in RGB or if you stretched to far (visible noise next to stars is not important), only thing that you need to worry is star color at this point - make it properly balanced and "rich" (to your liking).

Next steps I can't explain in terms of PS steps, but I'll list them in general - each processing software will have its own way of doing it.

Make a copy of NB image and split it into LAB components. Save L component of split (as mono image), or just keep it open - that is what we are going to need.

Take RGB image and do the same - split into LAB components, but keep A and B, discard L from this one.

Recompose RGB image from LAB by using L component saved from NB image and AB components from your RGB image.

Use star mask to blend this recomposed RGB in with original NB image.

4 minutes ago, parallaxerr said:

I have not set an ultimate deadline. I will raise it as a claim with PP come Friday, which will be 7 days.

What is aggravating me the most is the ridiculous notion of inspecting the goods and packaging before aportioning blame, I assume so that TS can claim their costs back from UPS (who I don't believe are at fault) before progressing. This should be done by TS after satisfying the customer and should not delay a replacement or refund, imo.

In my view, main culprit is lack of protective packing. It could well be that scope got damaged in transport although there are no marks on the outside of the box. Box might have been just shoved against flat wall or any other surface and scope slammed to the side due to inertia bending focuser shaft and cracking focuser cap. That just means OTA was not properly secured in the box.

In any case - you are right, it has nothing to do with you and their priority should be towards you.

8 minutes ago, parallaxerr said:

Thanks Mike and you're right, not an exciting or enjoyable experience at all. I keep wondering if I'm being too sensetive or expecting too much but the messages I've received have felt quite dismissive.

From my experience, their e-mails seem to be lacking in both words, and sometimes sense . I completely feel for you, and I would also be extremely annoyed by the state of the scope and also way it's been handled.

However, I don't think couple of days should be considered "ultimate deadline" for dealing with this. I would personally start to get deeply annoyed after a week maybe?

Beautiful image indeed!

1 minute ago, Anthonyexmouth said:

Is that likely to be caused by my blundering around with the worm gear tension? or maybe tight belts?

I don't think tight belts will cause this - I have mine really tight. When I first did my mod, I thought I had them tight, but it turned out that I need them like really, really tight - so now they are as tight as they can be - motor can't move any further.

But worm gear tension can be issue, and also I would look into end float. The graph shown in EQMod window represents one revolution of worm gear - that means big gear that belt is put on and one that you adjust end floats for (from the link I posted). Above graph shows two tight spots - exactly half way around - I would say that end float is to blame.

Did you check all your gears by hand? By actually turning gears with your fingers you can sense a lot of issues with it - just do it slowly and feel their motion under your fingers.

Yes that would be perfect example of "sticky" graph - mount nearly stops (slope goes almost vertical) - and then it continues "like nothing happened" at perfect speed - slope horizontal.

2 minutes ago, michael8554 said:

Doesn't the "High-frequency Star Motion in GA tell you the seeing conditions ?

Michael

I guess it would for very short guide exposure, but not for something like 2.5s. With such exposures FWHM is better measure.

High frequency star motion can be susceptible to all kinds of other factors than seeing alone - wind shake, roughness of mount, ...