The Pleiades

[JohnSadlerAstro]

Hi,

Taken on the 21st September, around 2 hours total of 200sec exposures, ISO 1600 with an EOS 1000d.

Guided with ZWO ASI webcam and 50mm finder.

130P-DS on EQ5.

The finished result came out a bit noisy, but overall I'm very happy with the nebulosity that the longer exposures captured.

John

[tooth_dr]

Very nice John.  I have the same camera, and have been advised by those who know best, to use ISO 800!

[michael.h.f.wilkinson]

Very nice indeed. Lots of nebulosity captured

[newbie alert]

1 hour ago, tooth_dr said:

Very nice John.  I have the same camera, and have been advised by those who know best, to use ISO 800!

I like using iso 400-800..if you're doing long exposure on a higher iso then you just introduce more noise and potentially overexpose ...shorter subs you're looking to capture more signal so a higher iso could be beneficial ..depends on the target too..if it's bright you don't want to over expose

[tooth_dr]

52 minutes ago, newbie alert said:

I like using iso 400-800..if you're doing long exposure on a higher iso then you just introduce more noise and potentially overexpose ...shorter subs you're looking to capture more signal so a higher iso could be beneficial ..depends on the target too..if it's bright you don't want to over expose

Avoid ISO1600 on a 1000d is the message here!  But not to take away from the image posted which is doesnt seem to have suffered from the high ISO!

[newbie alert]

I think once the temps plummet you can get away with higher iso too

[John78]

Well the 1000D read noise is lowest at 1600iso but I believe 800iso is the optimum...

http://www.sensorgen.info/CanonEOS-1000D.html

All of this guys 1000d pictures are 800iso

http://www.astrobin.com/users/galaad16/

Good effort though - I haven't seen a star for ages.

[bobro]

Lovely colour, nebulosity and focus. Dithering should help eliminate the noise.

[Starwiz]

Very nice image.

John

[JohnSadlerAstro]

Thanks for the advice, folks, I'll try doubling the exposure length and going to ISO 800, that shouldn't be an issue as I am autoguiding.
I am planning to take as much of the setup as I can on our holiday to north Norfolk, a place in a village amongst the sea mashes where there's no not much light pollution; I think I will use the opportunity to image the Andromeda Galaxy.

I forgot to mention, I was using a LP filter, the £30 skywatcher one (which doubles my maximum exposure length)

John

[Gerry Casa Christiana]

I haven't done that image since before I was aitoguiding so it's something I have to try again. Very nice shot it's a fascinating group of young stars. They say the gravity that holds them together is quite astounding. They are literally tied together. 

Gerry

[bobro]

2 hours ago, JohnSadlerAstro said:

I'll try doubling the exposure length and going to ISO 800

The ISO setting makes no difference to the image captured by the sensor. It controls the 'amplification' used when the image is read from the sensor. So there is no need to double the exposure time when ISO is reduced. Image processing software is used to set the final brightness.

As @John78 points out, read noise is lower at ISO1600 for a 1000D, though dynamic range is better at ISO800.

Noise in your image is due to sensor pixel variation. This is best reduced using dithering - trying looking up 'Walking Noise'.

HTH

[Leonid]

Great picture! 

[MARS1960]

4 hours ago, bobro said:

The ISO setting makes no difference to the image captured by the sensor. It controls the 'amplification' used when the image is read from the sensor. So there is no need to double the exposure time when ISO is reduced. Image processing software is used to set the final brightness.

 

I'm pretty new to AP but, ISO must make a difference and you may well need to increase the exposure time. 

What if at ISO1600 at a certain exposure your histogram was just breaking away but at ISO800 it was slam up against it, how could you then stretch the histogram without clipping the black point? You only have exposure and ISO, it's not like you can alter the aperture so you must alter either exposure or ISO no?

Nice image OP. I would stick with ISO800 when possible but use an exposure time that gets your histogram about a 1/3 > 1/4 in from the left. 

[bobro]

1 hour ago, MARS1960 said:

What if at ISO1600 at a certain exposure your histogram was just breaking away but at ISO800 it was slam up against it, how could you then stretch the histogram without clipping the black point? You only have exposure and ISO, it's not like you can alter the aperture so you must alter either exposure or ISO no?

Stretching an image in software is basically doing the same thing as increasing the camera's ISO - amplifying the image. So, ignoring effects such as read noise and dynamic range, changing ISO / stretching in software  do basically the same thing. So you have more than just exposure time and ISO - stretching amount is another variable under control.

Stretching a histogram cannot clip the black point as stretching applies amplification (like increasing ISO), making image points brighter.

As you say, ISO800 is a good compromise setting for a 1000D.

[MARS1960]

6 minutes ago, bobro said:

Stretching an image in software is basically doing the same thing as increasing the camera's ISO - amplifying the image. So, ignoring effects such as read noise and dynamic range, changing ISO / stretching in software  do basically the same thing. So you have more than just exposure time and ISO - stretching amount is another variable under control.

Stretching a histogram cannot clip the black point as stretching applies amplification (like increasing ISO), making image points brighter.

As you say, ISO800 is a good compromise setting for a 1000D.

I don't think i made myself clear, during image capture you have exposure and ISO control,  if you want to add PP stretching as a variable then you may as well add all other instances that have a profound effect but i feel that image acquisition and post processing are two completely different things.

But thanks, i didn't realise you could stretch a histogram in any beneficial way if it was attached at the left hand side, and i mean't having to clip the back point deliberately to achieve any beneficial stretch if it was attached.

 

[JohnSadlerAstro]

 Ok, so:

So long as the left hand foot of the histogram peak has cleared the left hand edge, I'm good? And pushing the peak along to the right after that is essentially unnecessary because I can do that in processing.

And I can get more brightness levels by using ISO 800.

Is that correct?

John

[celestron8g8]

Very nice M45 . Did you by chance get a WF shot ? I seen an image the other day that shows two comets real close to M45 .

[Galen Gilmore]

Hey thats a very nice image! I really need to commit to getting a total integration of over an hour.

[JohnSadlerAstro]

Just now, celestron8g8 said:

Very nice M45 . Did you by chance get a WF shot ? I seen an image the other day that shows two comets real close to M45 .

Thanks

As far as I know, there was nothing abnormal, (for once) as Pleiades was lower than the America to Heathrow flight path.

The image data is almost 2 weeks old, though.

John

[JohnSadlerAstro]

1 minute ago, Galen Gilmore said:

Hey thats a very nice image! I really need to commit to getting a total integration of over an hour.

This is my first image which broke the one hour barrier, as far as I know. As I cant really start imaging until midnight when the council helpfully turns out the lights, I am a bit limited in time, but autoguiding makes for far more time-efficient frame capturing.

John

[Galen Gilmore]

Just now, JohnSadlerAstro said:

This is my first image which broke the one hour barrier, as far as I know. As I cant really start imaging until midnight when the council helpfully turns out the lights, I am a bit limited in time, but autoguiding makes for far more time-efficient frame capturing.

John

I have the same setup as you but without auto guiding that limits me to how long I can expose for.

Auto guiding would cost me nearly $700 at this point in time (including the cost for the go-to), too much for me unless I find a cheaper option. This is not including the cost of a laptop either, I have a laptop but it's too slow to run any programs.

What did you do for auto guiding?

[John78]

20 minutes ago, Galen Gilmore said:

I have the same setup as you but without auto guiding that limits me to how long I can expose for.

Auto guiding would cost me nearly $700 at this point in time (including the cost for the go-to), too much for me unless I find a cheaper option. This is not including the cost of a laptop either, I have a laptop but it's too slow to run any programs.

What did you do for auto guiding?

$700 thats more than I've spent on everything I own  ...

Assuming you have a EQ5 then you need an AstroEQ...  That gets you an EQmod goto scope for $100 - $150...

https://www.astroeq.co.uk/tutorials.php

Then you can use a Linx windows tablet which are about $100, that controls the scope and runs the guiding.

Then you need a QHY5 ($100) or ASI120M ($120) (the colour version of either of these is fine for guiding) and a adapter to put it in your 9x50 guide scope ($50 if you don't have one already)

 

So worst case buying everything turn key, motors, brackets, cameras tablets,  all ready to go is like $420, if you're partial to some DIY'ing or your EQ5 has the old motors which are slow to slew and you don't mind you can be running for $300, the slew speed isn't a massive issue if you can plate solve as you can point near your target and blind solve to it without waiting all night for the mount to move across the sky.  If its a synscan its the $300 ballpark also - it has fast slews compared to the old EQ5.

[JohnSadlerAstro]

36 minutes ago, Galen Gilmore said:

What did you do for auto guiding?

Although the Pros may frown  my system is all to simple.

So I have a basic, mechanical EQ5, NOT the GoTo one. I have the latest motor set and handset which includes an ST4 socket. I then use a Skywatcher 50mm finder with a cheap ASI ZWO webcam screwed into it. A USB cable goes from the webcam to the laptop and an ST4 goes from the cam to the mount, then I open up PHD guiding (free) and guide away!  altogether auto-guiding upgrades cost £150.

John

[Galen Gilmore]

10 minutes ago, JohnSadlerAstro said:

Although the Pros may frown  my system is all to simple.

So I have a basic, mechanical EQ5, NOT the GoTo one. I have the latest motor set and handset which includes an ST4 socket. I then use a Skywatcher 50mm finder with a cheap ASI ZWO webcam screwed into it. A USB cable goes from the webcam to the laptop and an ST4 goes from the cam to the mount, then I open up PHD guiding (free) and guide away!  altogether auto-guiding upgrades cost £150.

John

Ahhhhhhh, thats where I was going wrong. I was assuming that only the go-to version had the guiding port. It seems that I don't need to spend a fortune on go-to!

Everything else seems simple enough.