Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

iksose7

Pleiades Star Cluster @ 200mm

Recommended Posts

Hi all, heres my attempt at M45 this year. 

Exposure details: 

60x210 seconds, f2.8, ISO 800, calibration frames, 200mm

With just under 3 hours 30 minutes this has fallen far from how i wanted it to be. I planned on getting 10 hours! But with cloud forecast all week i'll settle with this till later in the year. 

I shot using the lens wide open and using the 3rd point focusing method, hoping to have enough light grasp to pick up some of that faint dust in the area. I picked up 7 hours over 2 nights and thats when problems started.

My first imaging session was the first time i used my new dew heater, i focused and then turned the heater on which shifted the focus i think, leaving me with over 3 hours of un-stackable data! This image is made up of data from the second session, you can see that the stars appear to trail and i wanted to ask if anyone using this focusing method has ever been left with stars like those in the image? They appear to streak a little bit and look as if they are rotating around a center point. I have spoken to one other person who has experienced this. 

Because i have recently started using Backyard EOS, im not aware how to set up the live view so you have the 4 intersecting lines (if its even possible) so when focusing i roughly guessed where the intersecting lines would be. If i didnt have the star in the right place, could it have caused the stars to appear the way they do?

Anyway, heres the image.

gallery_26473_2818_44225.jpg

Clear skies!

Edited by iksose7
  • Like 6

Share this post


Link to post
Share on other sites

Nice work Callum, you have picked up quite a bit of the low intensity nebulosity there.

I'd try to get longer exposures instead of more of the same if you can, that way you can get more of the low intensity nebulosity and blend it with this image. Taking many hours of the same exposure length will only increase the S/N ratio, it won't make it brighter (though it will allow you to stretch it further with less noise, but if you haven't captured the signal, you can't increase its intensity).

Regarding focus, I always check it every other frame. A lens' focal point changes slightly with temperature, the dew heater is only heating the front element, not the entire lens so it will change during an imaging session. I have heard of the intersection at 1/3 point focus but never use it. I always find some star somewhere in the field and focus on that (easy with this target), many times per session. I don't know what I would do if I couldn't find a star...I'd have to slew to somewhere there is one, refocus then slew back. No Bahtoniv mask, no FWHM, I just eyeball it at 10x magnification on the LCD. Works for me though your mileage may vary...

Share this post


Link to post
Share on other sites

Thanks Stuart!

Yes, longer exposures are needed desperately! The first time i tested out my NEQ6, after a long time tweaking polar alignment i was managing 5 minute subs. But now thats it freezing at night, i dont have the patience to get PA spot on so i settle for anything over 3 minutes. Next payday will go towards a guiding set up!

I am still in the middle of my Backyard EOS trial and i absolutely love the FHWM function for focusing. Combined with my micro-focuser you can get focus spot on. But like you said, the dew heater may change that over the night. Will have to start checking focus every half hour or so. I dont usually use the 3rd points technique but did for this as i wanted to use the lens wide open to avoid star spikes. I prefer shooting at f4 and probably will do from now on, its a much simpler process!

Share this post


Link to post
Share on other sites

The rotation looks like polar alignment more than focusing problems

  • Like 1

Share this post


Link to post
Share on other sites

Trailing aside nice shot caught plenty of nebulosity.I use a bahtinov mask and a program called bahtinov grabber(free) to focus.However I am with Francis on this one it looks more like PA  

Share this post


Link to post
Share on other sites

I love the blue nebulosity in your picture of Pleiades, I can never make it out when I'm observing it though. :sad: Would a filter help?

Share this post


Link to post
Share on other sites

I love the blue nebulosity in your picture of Pleiades, I can never make it out when I'm observing it though. :sad: Would a filter help?

Thanks Daz!

To be honest i'm not an observer other than through binos so couldnt tell you! I'm guessing the more aperture you have the more of the blue nebulosity you would see?

Share this post


Link to post
Share on other sites

F2.8 is a very fast focal ratio - I use it all the time with a DSLR ;-)  

You certainly won't be needing longer exposures at that fast focal ratio - not unless you have extremely black sky.

You already have over 3 hours of data and you are showing plenty of faint wispy bits - I think the key is in further stretching the data you already have and taking even more similar exposures.

I also think it is worth taking a few shorter exposures (which don't saturate the bright stars so much) to combine with the existing data.  You can create an HDR image or perform some kind of layering to combine them.

Mark

Share this post


Link to post
Share on other sites

Nice capture. I agree that the main problem seems polar alignment, not focus.

I love the blue nebulosity in your picture of Pleiades, I can never make it out when I'm observing it though. :sad: Would a filter help?

Reflection nebulae like these are not helped by UHC filters, although wide-band LPR filters can help a bit. I have seen the nebulosity around the Pleiades, but only from very dark sites (in the Alps in particular). The nebulae do not need much aperture (my 80mm was fine) but they do need very dark and transparent skies, and you need good optics with little glare or internal reflections.

Share this post


Link to post
Share on other sites

PA for me, too. We see rotation. Are individual subs like this? Or does it build up in the stack?

Psychobilly managed to get perfect stars wide open using the thirds method. He sent me some test shots which were great.

A big issue is focusing physically and at F2.8 I'd say fingers were out. Telescope Service do these devices which I'd consider a must. 

IMG_1193-M.jpg

Olly

By the way, there are faint reds in there as well which might be worth hunting for in the data.

Edited by ollypenrice

Share this post


Link to post
Share on other sites

Telescope Service do these devices which I'd consider a must. 

IMG_1193-M.jpg

I'm intrigued Olly.

What are these devices and how do they help?

Share this post


Link to post
Share on other sites

No, all my subs were like that Olly. Upon closer inspection of the single subs, it shows that the stars do trail (from 10 o'clock to 4 o'clock). But i dont think that explains the larger odd shaped stars. On a single unstretched sub its is apparent that the bigger stars are diamond shaped and do indeed appear to rotate around a centre point (as if i were imaging Polaris).

Imho, i'd say its something to do with focus. But i dont know too much! Not to say i've been put off by Pshycobillys technique, i'm sure i have messed up somewhere along the way and will definitely use this technique again, just be more careful and make sure stars are spot on next time!

Oh and i already have the TS Microfocuser ;) hated it at first but couldn't do without now!

What do you mean by hunting for faint reds?? A colour boost?

Share this post


Link to post
Share on other sites

If you have problems at 10 and 4 (directly opposite each other on the clock face) then you could have astigmatism in the system. Likely if you get good focus at 10 and 4 then 7 and 1 will show the same problem at right angles to 10/4...

Edited by fwm891

Share this post


Link to post
Share on other sites

Looking at the full size image on Flickr, I think the weird star shapes near the corners are probably caused by lens aberrations.  Unfortunately you would need to stop down the lens to cure this, which means less light getting to the sensor.  To confirm or refute this, try taking some pictures of a point source of light in the middle and corners of your image frame (it doesn't need to be a star).  You can then determine which F-ratio gives good enough results.

Mark

Share this post


Link to post
Share on other sites

Hi Francis,

The 10 and 4 o'clock is the direction of star trailing, not the location of star trails. The trailing appears all over the image, not a lot but noticeable when zoomed in. The strange shaped (diamond shaped) stars trail at right angles to the ones i just mentioned which makes me think its not a PA issue but rather a focus, although clearly PA was off a bit.

I dont think i am explaining it very well so i drew a quick pic. 

This is exaggerated obviously. The lack streaks being the normal star trailing as expected if PA is off a bit, traveling from 10 to 4 o'clock. The Blue streaks would be the diamond stars which dont run at the same angle as the normal stars and appear to rotate round an imaginary center point

gallery_26473_2703_20519.jpg

Not to say astigmatism is not the problem! I will be having a look into that after work :)

Share this post


Link to post
Share on other sites

Thanks twin!

Yes mark, i usually shoot at f4 and find it pretty much perfect but didnt want star spikes on the cluster! Think i'll have to make some aperture masks at some point. 

Share this post


Link to post
Share on other sites

Yes mark, i usually shoot at f4 and find it pretty much perfect but didnt want star spikes on the cluster! Think i'll have to make some aperture masks at some point. 

That makes sense. The diaphragm blades would give you some very serious looking diffraction spikes on the Pleiades!

Mark

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By grievous
      Hello! I have a question on how can I mount my camera to my Sky-Watcher Starquest 130P telescope? I’ve watched so many videos about it and there’s so many different answers on what I need to do that. At the moment, I have 2x Barlow lens and a DSLR. I know that a T-ring is also necessary but is there anything more? Any help is highly appreciated, thanks! (I’m really new to telescopes and astrophotography in general so I hope I don’t say anything dumb)
    • By Ken Mitchell
      Hi all,
      For a long time I wanted to shoot this frame, probably from the early days of my astrophotography adventure.
      Finally after all these years I managed to get a decent result of the 'stuff' between these two beautiful nebulae. Fairly happy with the image but always looking for improvement.
      I hope one day to redo this all with a mono camera and filters. 
      Apart from NGC1499 , M45 and the Baby Eagle Nebula no idea what else is in the picture. If you happen to have an idea feel free to educate me.
       
      Some info on image and capturing:
      Widefield Pleiades to California.
      Taken over 2 nights with a total of 11hrs 25min integration.  
      With a stock Nikon d610 and Nikkor 85mm 1.8 objective.
      Tracking was done with the Skywatcher Star Adventurer.
      Lights and all calibrations frames were stacked in DSS.
      Processing was done in Adobe Photoshop CC using Adobe Raw, GradientXterminator plugin, HLVG plugin, Nik software plugins and Photokemi action set.
       
      Ken

       
    • By Bigdaddyjeff
      Please find for sale my SkyWatcher 250 Reflector and NEQ6 SynScan mount. 
       
      The reflector has of course been used and shows sign of use on the outside of the tube but the mirrors show little sign of wear or tear apart from a few dust specks. As you can see from the photos the Scope is in very good condition and all viewings are welcome.
       
      The NEQ6 mount powers up but refuses to move. This may be just an update to the handset or maybe the gears need a touch of TLC due to itself being sat doing nothing for so long. The tripod is missing the locking pin that pulls the plate up against the legs but this will be reflected in the price. 
       
      i would like to offer this to the SGL community as I know it will go to someone who will appreciate the kit and do so much more with it than I’ve been able to. 
       
      Given the fact I haven’t used this kit for a few years now and I’m also moving house, I know longer have the time or room for it so this is the only reason for sale. 

      *** Update 26/1/2020
      I have purchased a new support shaft for the tripod and I have also got the NEQ6 moving so the motors seem to be absolutely fine, please see latest video attached of the NEQ6 powered up and moving. 
      Skywatcher 250 - £200 
      NEQ6 - £450 
      Collection only from Walsall/West Midlands 
      Please don’t hesitate to contact me if you have any questions and I will do my best to answer them. 
      Wishing you all clear skies wherever you are
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
       
      IMG_2242.MOV
    • By beka
      Hi All,
      Having had to move to an apartment where I could not use my CPC 1100, I decided that I have to see what I could do with my NexStar SLT 102 (alt-az achromatic 102mm f6.47 refractor). Setting up on my narrow balcony was challenging and the altitude bearing was so loose that it almost moved from the weight of the Canon 700D. I could not see M31 in the estimated 3.5 magnitude sky so I did a two star alignment and used the live-view to focus on a bright star. I then took a 15 second exposure after slewing to M31 which allowed me to see that I had it in the field of view. After a few more 15 second exposures and playing with the motion controls I managed to get it centered. The resulting picture is from 39 subs of 30 seconds at ISO 1600, 9 flats. The images were stacked and stretched with Siril and then I played with the curves on Gimp, cropped and scaled. Not too unhappy.
       

    • By astrosathya
      Just thought i'll bring this up as a point of discussion. Today, cooled CMOS Astro Cameras are available in plenty. QHY, ZWO and other variants of the same camera are selling for very reasonable prices. However, there was a point of time when astrophotographers used to cool down their DSLR's as a cheap OSC alternative to CCD cameras. Give a choice, I would've purchased a dedicated CMOS OSC which can cool to 40 C below ambient, but since I had a Canon 500D which I had self modded, I requested a friend Kaustav Chatterjee (an avid model railroader) to cold mod my 500D (he had cold modded his 1000D long back). This newly modded camera has a TEC12703 single peltier and cools to approximately 20 below ambient.What do you guys think?




×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.