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DSLR DSO Astro - testing/planning advice


Alex_

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Hi everyone,

After my initial foray into DSO astrophotography with very poor results in terms of actual data in the images, I am about to embark on some trial and error. From all the reading I am doing and have done, I think I am using the wrong object to start (M31) and therefore I am making other mistakes along the road without really understanding where the flaws are in my plans.

I am doing my best to work with what I have, and not spending more money without good, well thought out reason, since I only received the telescope in December and am new to both observing and astrophotography. Again trying to heed advice I've read, even though I realise there are much better ways of doing this :D.

HW I have available as follows:

  • Nextstar 8SE with the supplied Alt/Az mount
  • Celestron Plössl 25mm
  • Canon 60D
  • Celestron piggy back mount
  • Celestron T-adapter to mount camera straight to telescope (currently used successfully for moonscapes)
  • 50mm f1.8 Canon Prime lens
  • 70-300mm Tamron f4-5.6 (non-prime)
  • 105mm Sigma f2.8 EX DG OS HSM
  • intervalometer for taking subs

Plan is to use the available tracking the Alt/Az mount gives me.

Location is our back garden bortle 6 with approx 10 degrees of obstruction from 0 in all directions.

The real questions behind all of this are:

  1. What setup should I start with to learn this trade (OTA or Piggyback with lens)
  2. What DSO would you recommend for that setup?

My goal is to hone my skills on a target that I can find easily with the go to alignment/tracking and then have a clear plan to test a pre-planned list of exposure times to better learn where the limits of trailing etc happens with my setup. I am hoping this will avoid me wasting more nights shooting 100+ subs that are mostly black and when stacked show very little.

In terms of future investment thoughts if I use the OTA:

  • bhatinov mask
  • Focal reducer f6.3
  • Astronomik CLS Clip in filter 

I've tried to be as thorough and as clear as possible, and I'm sure there will be many follow up questions, or pointers to gaps in my thinking and resources I have yet to find. Appreciate any and all support.

Edited by Alex_
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My opinion: attempting AP as an absolute beginner with the over 2000mm of focal length offered by the 8SE is a fools errand. In fact, the 8SE is not particularly well suited to DSO imaging altogether (great for planets and moon though), so stick to the lenses for now.

The shorter the lens, the easier it should be in terms of tracking errors, so start short. An example target for a 50mm lens: everyone's favourite, Orion. - pretty much the whole constellation will fit in the frame, and there are a LOT of nebulous regions in here. Granted most will be faint, and may not show up well on your camera (unless it's astro modified??). 

Screenshot_20220224-124253.jpg.624585726c22b767697d2b48f12a6cf4.jpg

Only real issue is it's getting a bit late in the season for Orion now.

Piggybacking will probably be fine to start out with, but the alt az nature of the mount will limit you somewhat (not to say that great things can't be done with alt az - check out the no EQ DSO imaging thread), so maybe consider your next purchase to be a star tracker of some sorts (or maybe, dare l suggest it, an HEQ5 😁).

A cursory look on Google tells me your camera has a pixel size of about 4.3um, read noise of about 3e- at ISO1600, and a QE of around 40% (important note: I did not read further to verify this), so subs of as short as ~5s would be adequately exposed with the 50mm lens for your skies.

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Thanks for the response. I am definitely feeling your point on the focal length. I really am resisting the urge to get another OTA just for DSO so want to learn first ;)

I'll be sure to check the thread you mention. I did try Orion Nebula the other night and tracking was an issue with the nebula slipping out of frame after 30 minutes. I'm sure I'll find more there. Stop trying to tempt me with the HEQ5 ;) 

I did more detailed research on the 50mm with the camera (not modified) a few weeks ago and and got 6s as the sweet spot, so will give that a go tonight.

Edited by Alex_
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When using a altaz mount in the northern hemisphere then the best direction to aim is East or West below 60 degrees. Unfortunately Orion is now more southerly so will show star trailing quite quickly. You can get red dot finder to mount in the flash hot shoe should you mount your camera on a dove bar and remove the OTA from the mount.

The bee hive cluster is placed well you could use your 100mm.

Stopping down might be needed to improve star shapes across the frame.

Focus where a third intersects can even out focus.

16457334598843.jpg.59f334c491594bb97b137312a951f6d0.jpg

And being a canon if you don't have a laptop but do have an android phone see if your camera is supported by DSLR Controller, need an OTG cable. Great for focusing great for camera control.

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Have to concur -- 2000mm on that mount would really be Crazy Town for deep-sky objects. I would counsel that you start with the 50, and teach yourself imaging and processing (including shooting and using calibration frames -- flats, flat darks or bias, and darks, if they're appropriate for your camera. Do it right from the get-go, is my advice.

M31 is actually quite a large object, so you can frame it well with surprisingly short focal lengths, especially if you're willing to do a bit of cropping.

Two great free tools for figuring these issues out are the Telescope Simulator in telescopius.com, and a desktop planetarium app like KStars or Stellarium (and there are other good ones too).

And one terrific non-free tool: If you haven't already, invest in a book like Steve Richards' Making Every Photon Count or Charles Brackens' The Deep-Sky Imaging Primer. You will learn a TON about how this stuff works and that will enable you to avoid many of the classic beginner mistakes.

BTW you can print a Bahtinov mask on paper, cardboard, or thin plastic and cut one out for yourself. Although a nice 3D-printed one that fits over your optics like a lens cap is a real convenience. There are so many details in this hobby, so much to keep track of and so much to do just right, that little conveniences turn out to be important.

Welcome, and enjoy the journey.

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7 minutes ago, happy-kat said:

When using a altaz mount in the northern hemisphere then the best direction to aim is East or West below 60 degrees. Unfortunately Orion is now more southerly so will show star trailing quite quickly. You can get red dot finder to mount in the flash hot shoe should you mount your camera on a dove bar and remove the OTA from the mount.

The bee hive cluster is placed well you could use your 100mm.

Stopping down might be needed to improve star shapes across the frame.

Focus where a third intersects can even out focus.

16457334598843.jpg.59f334c491594bb97b137312a951f6d0.jpg

And being a canon if you don't have a laptop but do have an android phone see if your camera is supported by DSLR Controller, need an OTG cable. Great for focusing great for camera control.

Thanks for the tips. I do have a laptop. I think that's my next step to plan all that out.

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6 minutes ago, rickwayne said:

Have to concur -- 2000mm on that mount would really be Crazy Town for deep-sky objects. I would counsel that you start with the 50, and teach yourself imaging and processing (including shooting and using calibration frames -- flats, flat darks or bias, and darks, if they're appropriate for your camera. Do it right from the get-go, is my advice.

M31 is actually quite a large object, so you can frame it well with surprisingly short focal lengths, especially if you're willing to do a bit of cropping.

Two great free tools for figuring these issues out are the Telescope Simulator in telescopius.com, and a desktop planetarium app like KStars or Stellarium (and there are other good ones too).

And one terrific non-free tool: If you haven't already, invest in a book like Steve Richards' Making Every Photon Count or Charles Brackens' The Deep-Sky Imaging Primer. You will learn a TON about how this stuff works and that will enable you to avoid many of the classic beginner mistakes.

BTW you can print a Bahtinov mask on paper, cardboard, or thin plastic and cut one out for yourself. Although a nice 3D-printed one that fits over your optics like a lens cap is a real convenience. There are so many details in this hobby, so much to keep track of and so much to do just right, that little conveniences turn out to be important.

Welcome, and enjoy the journey.

Ah yes, thanks for the book tips. I've seen them before and hadn't remembered to order at least one. As I own a Mac laptop, I've started using Stellarium which has been super helpful so far. I haven't plugged in the 50mm yet though, so that will help greatly!

Just having written this all out has helped me calm down and enjoy things more!

Very much enjoying the journey :D

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I make mine out of cardboard and a Lord Y mask, very easy to make. There are set  measurements to follow.

16405238906822.jpg

Also I use a flocked flowerpot to stop dew forming on the lens.

This is slightly off fucus, the middle line needs to be in the middle.

IMG_6619-1-1.jpg.3e93c27a23ed9dc549f966075f8f1a9e.jpg

Edited by happy-kat
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