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Arran townsend

Where Did This Star Come From?

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On 09/07/2019 at 13:17, The Admiral said:

I have no idea what might have caused it, but surely this wouldn't necessarily be true if the star(s) are bright enough to saturate the sensor?

I rather prefer the explanation being a transient movement of the mount. Is it a manually operated barn door tracker? Then again, it's suprising that there is no star streaking, which would mean it would have to move between exposures? Hmm!

Ian

It is a arduino driven barn door tracker

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On 09/07/2019 at 13:34, vlaiv said:

After some thought we need to check if it is actually possible that said satellite could possibly caused such "flare". I have certain reservations about it so it is best to do "sanity check".

We would need to calculate angular speed of said satellite - we have basic info on that:

Orbital period: 124.3 minutes (semi major axis - 8252 km)

We would also need resolution of above shots in arc seconds per pixel. We can conclude that flaring object did not move more than one pixels for duration of flare. This will give us maximum total flare time. Next we need to calculate amount of reflected solar photons from flat surface of certain size (we can just make approximate there based on Sun magnitude in Earth orbit and some surface area of reflection common for satellites, or even find exact size of solar panels for that particular satellite). We can model reflection to be 100% without much impact on result.

Then we need to see how much photons will reach aperture on earth (given the distance and aperture size) and integrate for max duration of flare.

I have a feeling it will not be enough to saturate sensor for that brief moment - but it might be.

Hi Vlaiv, judging from my unfiltered photos, do you think that using a light pollution filter would benifit me?, I live in a bortal 7 area, but I can't see any light pollution in my images, perhaps I don't know what it looks like...

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9 hours ago, Arran townsend said:

Hi Vlaiv, judging from my unfiltered photos, do you think that using a light pollution filter would benifit me?, I live in a bortal 7 area, but I can't see any light pollution in my images, perhaps I don't know what it looks like...

Not sure if you are going to see much LP in short exposures such as 15s - but that does not mean that there is none - it just does not build up too much. It's going to be easiest to spot when you do a stack of subs and look at final result - there will almost certainly be some gradients in the background.

I think that decent LP filter is going to help a bit. Maybe best effect will be seen from UHC type filter - that is not general purpose LP filter and it is mostly suitable to emission nebulae. Other than that, you need to figure out type of LP (at least dominant type - if your sky at night looks orange - or has such hue that is good in terms of LP suppression - as it can be filtered, but neutral gray/bluish is worse - it usually means there are plenty of LED lighting around - that is harder to filter out).

Good LP filter for general purpose (galaxies and such) is not going to be cheap, so it depends on your budget. Given that you are using barn door tracker, maybe it would be better to invest that kind of money into small ap mount like star advanturer or AZ-GTI (with accessories to go EQ mode), unless of course using of one's own DIY tracking device is part of the fun in this hobby.

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Posted (edited)
10 hours ago, Arran townsend said:

Hi Vlaiv, judging from my unfiltered photos, do you think that using a light pollution filter would benifit me?, I live in a bortal 7 area, but I can't see any light pollution in my images, perhaps I don't know what it looks like...

Hi Aaran,
I will agree with Vlaiv,

In your case even 15sec exposures have star trails @ 300mm FL. And light pollution has the minor impact... Star trails is the main battle you should fight. 
To get nice images, you will need to reduce your exposures drastically or upgrade tracker.

In the first case, @F7 and short exposures, - you will not get much data to produce nice images... Or it will take quite a few sessions... But, as I understand, you are limited to one target per session, as to re-target next night is quite difficult task with your set-up.

If you do not want to go small EQ tracker way, - reduce FL to 135 or 200mm and try imaging closer to F4 and with shorter exposures.

Once you get a nice round stars in the center of the images (you will have some coma/"egg shaped" stars in the corners, - you will not avoid it probably), try to get longer exposures by improving your barn door tracker..

And once you will notice, you reached the exposure time then images become too bright (or Histogram Peak falls into the right side), - you may start thinking about filters.

The image below, is only the example what you may get without filters, - it was done from London Bortle 8/9, ISO100, no filters, but @F2 135mm and 30sec exposures (45sec exposures, were too bright at F2..., 60sec almost white).

This one is not even close to the perfect image, just a usual not experienced image using EQ mount, - but I would start thinking about filters after I get result like this or even better one.

 

M42_Samyang_TEST

 

Edited by RolandKol

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2 hours ago, RolandKol said:

Hi Aaran,
I will agree with Vlaiv,

In your case even 15sec exposures have star trails @ 300mm FL. And light pollution has the minor impact... Star trails is the main battle you should fight. 
To get nice images, you will need to reduce your exposures drastically or upgrade tracker.

In the first case, @F7 and short exposures, - you will not get much data to produce nice images... Or it will take quite a few sessions... But, as I understand, you are limited to one target per session, as to re-target next night is quite difficult task with your set-up.

If you do not want to go small EQ tracker way, - reduce FL to 135 or 200mm and try imaging closer to F4 and with shorter exposures.

Once you get a nice round stars in the center of the images (you will have some coma/"egg shaped" stars in the corners, - you will not avoid it probably), try to get longer exposures by improving your barn door tracker..

And once you will notice, you reached the exposure time then images become too bright (or Histogram Peak falls into the right side), - you may start thinking about filters.

The image below, is only the example what you may get without filters, - it was done from London Bortle 8/9, ISO100, no filters, but @F2 135mm and 30sec exposures (45sec exposures, were too bright at F2..., 60sec almost white).

This one is not even close to the perfect image, just a usual not experienced image using EQ mount, - but I would start thinking about filters after I get result like this or even better one.

 

M42_Samyang_TEST

 

Hi, I agree with the fact about countering star trails, those 15 second shots were not very good due to poor judgment with polar alignment, I have fashioned together a polar scope using an old finderscope I had, using a calculator and some wire to make a polar scope, when I tested this I had good star tracking at 300seconds which dropped my jaw!

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Just now, Arran townsend said:

Hi, I agree with the fact about countering star trails, those 15 second shots were not very good due to poor judgment with polar alignment, I have fashioned together a polar scope using an old finderscope I had, using a calculator and some wire to make a polar scope, when I tested this I had good star tracking at 300seconds which dropped my jaw!

Which do you think I should get, a light pollution filter or a genuine polar scope?

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Posted (edited)
21 hours ago, Arran townsend said:

Which do you think I should get, a light pollution filter or a genuine polar scope?

First of all! - 300sec with a barn door tracker - SUPER! :) Very good job done! :)


As to the rest: I cannot give you a proper advise as there are some variables: 

1) How fast and how repeatable your good PA can be achieved?
300sec means, - you are in the game even without a proper Polar Scope... However, if the current set up makes it very difficult to re-align and get to 5min exposures, means you will not be able to repeat it each session, or you will lose lots of the dark time by setting it up...

PA is essential... You know it better than me... Bad PA=Bad Tracking... If you have Bad tracking, - LP filter is useless as you have no result anyway! :)

2) And if, lets say, PA does not take much time to get to 300sec and it can be repeated easily, 
I would go for LP filter only if images at 300sec are getting too bright, OR even better,
Would check how to advance re-targeting procedures for the next night session, as I guess... You end up missing the target all the time and end up cropping quite a lot at the end. Finder scope, which you modded to Polar Scope, would help in this step.

If you get 300secs with Histogram Peak at Left or Close to Center, - LP filter will help, but not too much, you simply need more data on the same target. It means, more sessions, - good PA and good re-targeting first.

On another hand, there are CLS clipIn filters for around £80, - not so expensive... Plus, you may probably try finding the second hand ones for half a price.

As I understand, you use Canon 1200D, which is the entry level cam... I would also consider to check for the second hand AstroModified camera on the astrobuysell and eBay auctions, - or...

you know what I mean! :) 

get your hands dirty and mod 1200D yourself :)

but I am not sure if 1200D worth time, I never had it.

P.S. "Mein Kampf" against the Light Polution ended up in Mono imaging... Probably everyone can assure you, there is no better way as a narrow band imaging from the city...  Some people do use DSLRs and Narrow Band filters, -  investigate this area also.  5min exposures probably will be enough for H-Alpha 12nm.

P.P.S.

Focusing, - get bahtinov mask for your lens, or make one.. And the easy "Y focusing mask" works well also :)

 

 

Edited by RolandKol

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