Jump to content

Banner2.jpg.35fd74882a15b2b8a1b4142f7dcc8bed.jpg

Newbie's first go at Pleiades


imakebeer
 Share

Recommended Posts

I managed to get out in the garden the other night and had my first proper go at photographing the Pleiades. At the moment I'm working with a very basic setup so bear with me - simply a Nikon D5500 + Nikkor 18-300mm lens on a very basic lightweight Alt-Az tripod. That said, any tips, advice or suggestions on any aspect of photographing DSOs will be most welcome! (In the last couple of days I've acquired a tracking mount and bigger scope so hopefully that will help a lot!)

I got about 40 light frames (plus 5 dark) at 5s exposure and ISO 1000, f/6.3 is as wide open as this lens goes at this FL. Stacked in Sequator where I played with the settings a bit, then tinkered with some more (and cropped) in GIMP, for which I watched a video on YouTube but beyond that I'm still very much figuring out what I'm doing. I have a couple of images to compare:

There is some star trailing but I like this first one, the way the stars are very bright against a dark background. But I know I've lost a lot of the background detail in post-processing (looks better on a smaller screen though!)

Pleiades_01_2022_11_21.thumb.jpg.be6d885263ba4268bbe4d354cc8fa807.jpg

 

But then when I Googled imaged of the Pleiades I noticed some nebulosity (?) which I'd noticed but dismissed in the original stacked image. So I went back through GIMP and took more care not to lose so much background detail - this image is noisier but around Merope in particular am I picking up a bit of nebulosity there, or just some artefact or something I'm imagining/wishful thinking???

Pleiades_01b_2022_11_21.thumb.jpg.7809c4d539f09317239c3126dd5a0ce4.jpg

  • Like 4
Link to comment
Share on other sites

It's a good start and there's nebulosity in there. 👍

Things which may help for the next session:

  • Increase your ISO to 1600 or even try 3200. This may increase the noise but it will also increase the amount of data collected.
  • Experiment with the exposure timing and see at what point the stars start to trail, then reduce the exposure until they don't trail and stick with that.
  • Take lots of exposures - if they're short, like 5-10 seconds, then take a couple of hundred and stack them all together. More exposures = more data = better images.
  • I wouldn't bother with Dark calibration frames, you would be better off with Bias and Flats with a DSLR.

Keep going, you'll be surprised what you can get. ;) 

Edited by Budgie1
  • Thanks 1
Link to comment
Share on other sites

Not familiar with the lens but if you reduce the focal length does the focal ratio go down? A faster f stop will help greatly as long as the chromatic aberration doesn't get affected massively, and the shorter focal length will reduce the effect of star trailing. 5s exposures you'd need to take a few hundred/thousand photos so pair with an intervelometer to take care of the image acquisition and maybe put a slight delay between photos to reduce risk of shutter shadow. 

You can also image Orion Nebula and Andromeda galaxy with these short exposures, maybe up to 10s per image.

Edited by Elp
Link to comment
Share on other sites

@Budgie1 thanks for the tips. I assume that's a typo and you mean bias frames, not bios right? By dark frames I mean I just took pictures with the same settings with the lens cap on - I need to read up exactly what a bias frame is. And if I recall, flats are where you put a white T-shirt over the lens (to take care of vignetting???)

@Elp Oh OK, I see what you're getting at - yeah, the lens goes from f/3.5 at 18mm FL to f/6.3 at 300mm. So yeah, if I back off to 200mm FL then the aperture should be a little bigger, so yeah this might allow me to reduce star trailing. I can see what you mean, there are tunes I can play here. The camera has a built in timer so it's easy to set it and forget it to take loads of frames. Oh, and the lens is made of ED glass I think so hopefully CA shouldn't be an issue 🤞

Good point about the Orion Nebula and Andromeda - I've actually already been having a go at the latter here. In fact, while I was playing in GIMP processing these Pleiades shots I had another go at processing my previous Andromeda M31 shot - good practice but not sure I got anything conclusively better.

Question for you folks: I've actually just taken delivery of a new SW Explorer 150PDS, plus an HEQ5 mount + ZWO ASI 120MC-S I bought from another forum member. Haven't set it up or used it in anger yet, but am I right in thinking the ZWO can be used for DSO as well as planetary? I'm interested to experiment and see how the ZWO compares with the Nikon D5500, plus I also have a used Canon 450D I can also try. I'd also like to try the Nikon on the HEQ5 (piggy back maybe?) and see what it can produce on a tracking mount.

Edited by imakebeer
Added a point
Link to comment
Share on other sites

The f stop decrease is more to do with light gathering capability, more light entering the lens so you might pick up on the nebulosity a bit more once you've stacked.

No harm in trying the 120 for DSO, I found my 224 limited to around 30s before the sensor became swamped with read noise, my uncooled 485 however I can do 120s, maybe a minute more at a push.

Link to comment
Share on other sites

4 minutes ago, imakebeer said:

 

Question for you folks: I've actually just taken delivery of a new SW Explorer 150PDS, plus an HEQ5 mount + ZWO ASI 120MC-S I bought from another forum member. Haven't set it up or used it in anger yet, but am I right in thinking the ZWO can be used for DSO as well as planetary? I'm interested to experiment and see how the ZWO compares with the Nikon D5500, plus I also have a used Canon 450D I can also try. I'd also like to try the Nikon on the HEQ5 (piggy back maybe?) and see what it can produce on a tracking mount.

You will have a great setup now.  I wouldnt bother using the 120MC for any deep sky work personally, really small sensor/FOV and noisy. 

Link to comment
Share on other sites

36 minutes ago, imakebeer said:

@Budgie1 thanks for the tips. I assume that's a typo and you mean bias frames, not bios right? By dark frames I mean I just took pictures with the same settings with the lens cap on - I need to read up exactly what a bias frame is. And if I recall, flats are where you put a white T-shirt over the lens (to take care of vignetting???)

Oops :o, yes I meant Bias (now corrected). 

Here's one explanation of the different calibration frames and how they're captured: http://deepskystacker.free.fr/english/faq.htm 

As said above, the ASI120 MC is more of a planetary or guide camera, because of the small sensor. I would stick with using the Nikon or 450D for DSO's, you'll get much better images. ;) 

  • Thanks 1
Link to comment
Share on other sites

59 minutes ago, Elp said:

The f stop decrease is more to do with light gathering capability, more light entering the lens so you might pick up on the nebulosity a bit more once you've stacked.

Sure - I get exactly what you mean, even if I can't quite express it in words! 😁

 

54 minutes ago, tooth_dr said:

You will have a great setup now.  I wouldnt bother using the 120MC for any deep sky work personally, really small sensor/FOV and noisy. 

 

16 minutes ago, Budgie1 said:

Here's one explanation of the different calibration frames and how they're captured: http://deepskystacker.free.fr/english/faq.htm 

As said above, the ASI120 MC is more of a planetary or guide camera, because of the small sensor. I would stick with using the Nikon or 450D for DSO's, you'll get much better images. ;) 

Thanks, I'll check out that link. And good to know about the 120MC vs. DSLR.

I'm really interested to see how the ZWO compares to what I've manged so far on Jupiter and Mars (looks like Saturn has gone for me now though - boo!) with my DSLRs, but useful advice regarding DSOs. I'm too new to be firmly entrenched either way, except to say that I really like BackyardEOS/Nikon whereas my very brief look so far at Sharpcap and Firecapture suggests more homework will be needed! 😂

Link to comment
Share on other sites

The 120 will be better for planetary than your DSLR as it's framerate will be faster so you can capture more frames over time, hence when you stack you'll have more data which is likely to have frozen the seeing.

  • Thanks 1
Link to comment
Share on other sites

1 minute ago, Elp said:

The 120 will be better for planetary than your DSLR as it's framerate will be faster so you can capture more frames over time, hence when you stack you'll have more data which is likely to have frozen the seeing.

And I suspect its read noise will be lower too as compared to DSLR.

  • Thanks 1
Link to comment
Share on other sites

17 minutes ago, imakebeer said:

@Elp Yeah, I see what you mean now about FOV for DSLR vs. ZWO - no comparison is there! 🤣

It was a good tip already, but the illustrations from the FOV calculator really drive it home ("words fail, see sketch") 👍

I’ll take some credit for it too 😂

  • Haha 2
Link to comment
Share on other sites

Here's a few thoughts I have. 

1. It doesn't matter what lens you have, no manufacture can remove all CA from a wide zoom like an 18-300.  I'm guessing your lens has a variable wide aperture like f4 at 18mm and f6.3 at 300mm?  So I would suggest increasing your ISO to 1600 and stopping down to f8.  Exposure wise it will be about the same as what you are getting now.

2. Increase the total # of exposures.  40 might sound like alot but not really. Try to shoot 100 exposures. Then, shoot at least 20-25 darks with the cap on at the same settings. Bias frames are like dark frames except at the fastest shutter speed your camera is capable of, say 1/4000 or 1/8000 sec. Shoot the same number as you do for darks.  Flats can be done with the t-Shirt and dim light. You want the histogram to be in the middle of just slightly to the left of center.

3. This might be the best bit of advice I can give you. Much of your blur may be coming from mirror slap. If your camera has a mirror-lockup feature, use it.  Also, hopefully you are using a wired or wireless cable release to trigger the shutter. This will greatly assist in eliminating blur and shake.  Mirror lockup is key though.

Edited by SiriusDoggy
  • Thanks 1
Link to comment
Share on other sites

5 minutes ago, SiriusDoggy said:

Also, hopefully you are using a wired or wireless cable release to trigger the shutter.

Thanks for these helpful suggestions. Good point about mirror lockup, I'll investigate (I have a feeling it might as I was looking at this the other day after I saw it mentioned).

Regarding a remote shutter release - is your point that I don't want to be physically touching the camera myself as this will make it wobble? I'm using the built in timer so I can set it up to do 100s of frames with whatever delay between them I set (also useful for doing startrails as I've discovered).

Hopefully this will work in function with mirror lock up if my camera does it 👍

Link to comment
Share on other sites

1 hour ago, imakebeer said:

Regarding a remote shutter release - is your point that I don't want to be physically touching the camera myself as this will make it wobble? I'm using the built in timer so I can set it up to do 100s of frames with whatever delay between them I set (also useful for doing startrails as I've discovered).

 

Yes. But since you are using the timer to take multiple images, touching the camera to strt it will mean just throwing away the first image that will surely have some camera shake in it.

I'm not sure if the timer feature will work while using the mirror lockup feature. I know from my old Canon days, it didn't. But newer models might. Ideally you want the mirror to lock up, then delay for at least 2 seconds before opening the shutter.

  • Like 1
Link to comment
Share on other sites

Regarding m45 try not to make the background sky jet black as you will undoubtedly lose data in the nebulosity ( called black clipping)

The heq5 will open up a whole new avenue and allow you to capture far longer subs, you can use the 120 to guide.. good luck ... It's exciting...

  • Like 1
Link to comment
Share on other sites

+1 for the HEQ5, it's a very solid tracking mount for astrophotography. The 150PDS is also a great scope - great value for money, good-sized aperture, easy to use, good quality optics. It will give you years of enjoyment. Not perfect though, and you will find info on the web about some simple mods that make a big difference. The main issue that I had when I started with mine was that they leak light through the focuser and from behind the primary mirror. A black swimming cap is recommended over the back-end,  and I use some tin-foil wrapped around the focuser draw-tube. Looks very low-tech but it works for me (although I use a woolly hat because I didn't have a swimming cap! 🙂  )!

If you enjoy tinkering, there's no end of fun to be had with a HEQ5 and a 150PDS.

As mentioned above, the ZWO camera will work well for planetary, using Firecapture or Sharpcap. Stick with the DSLR for DSO until you can afford a cooled ZWO, and use BackyardEOS or Astrophotography Toolkit (APT) for DSO capture. Take a look at APT, it's very good. NINA is great for DSO capture, but last I looked it didn't support DSLRs. (afterthought: the latest version of Sharpcap has greatly upgraded its DSO capture capability but as I'm firmly in the NINA camp by now, I haven't looked at it).

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.