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3 Attempts, Not much to show. Where am I going wrong?


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Gear:
- Canon 70d (unmodified)
- Tokina 11-20mm f/2.8 lens
- Cannon 50mm f1.8 lens
- Asahi Pentax SMC 135mm/f2.5 lens
- Asahi Pentax SMC 200mm/f4 lens
- EQ3-2 mount
- Intervalometer
- Raspberry Pi with Astroberry.

I'm photographing unguided and untracked for now.
I do have an EQ6 that I'm rebuilding and will use that for tracking and will add a guider later as my results improve.

Attempt 1:
I struggled to find a decent target to image with my setup - my garden faces East/South-East.
I tried imaging Ursa Major, using my intervalometer.

- 11mm f/2.8, 50 x 1 sec lights at ISO 128000. No darks (because I only took one set - doh!)
- 50mm f/1.8 50 x 1/15 sec lights at ISO 1600. 20 darks,

What I learned:
- ISO 12800 is very noisy
- 1 sec was too short of an exposure, I could have got away with longer without trailing
- ISO1600 with 1/15 sec exposures captured practically nothing
- I need to take darks after each set of lights

Attempt 2:
I tried M81 - not a great choice I know.
This time, I used Ekos with the Cannon DSLR driver.

50 lights at 200mm/f4, ISO 1600, 0.25 sec exposure. 20 darks.

What I learned:
- 0.25 sec was too short
- Using Ekos was a learning curve and cost me a lot of imaging time messing with formats, transfer settings etc...
- The delay between subs was long. I think this delay is caused by sending image from camera -> pi, writing to disk etc.. but it feels like 10-20 seconds (i haven't timed it).

Attempt 3:
M42. Better target.
Still using Ekos... but I didn't get out until later than planned and was thwarted as Orion went behind my house!
This was compounded by the delay between subs mentioned earlier so I got only 1 or two useable frames.

50 lights at 200mm/f4, ISO 6400, 0.5 sec exposure, 20 darks.

What I learned:
- 0.5 sec is still too short
- I need to plan better

Overall

I'm probably doing a lot wrong, but learning as I go, so please feel free to point me in the right direction.
Before I head out again (tonight?) to try M42 I could do with some help:

1. To try and get Ekos to take quicker subs OR find another capture program OR revert back to intervalometer.
2. Reviewing the last set of Subs in DSS and they look almost black, barely any stars are visible. This makes me wonder whether I'm using the right setting on the camera? My plan is to keep everything the same but take 1 sec subs which at 200mm is apparently a fraction too long. When I ran the numbers it suggested 0.92s. Should I consider bumping the ISO higher at the expense of more noise?
 

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Basically : far too short exposures.

1/ use longer "subs" luke ! ISO between 800 and 3200 (varies with camera models, I'm not a specialist of Canons), and longest duration you can with no or moderate trailing (do some test shots)... This depends on focal length (lens) and pixel size (camera) : the longer focal, the shorter possible duration => start with a wide field, such as your Tokina, and 5-15s subs, to get something at least (take many subs and stack them !). Then move on progressively to a longer focal and shorter subs until you don't get enough signal to stack any more => that will be your untracked limit.

2/ for a starter until you know better, use a remote in continuous shooting mode (an intervalometer will also do it usually, but is not required)

Edited by rotatux
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Yep, longer exposures are needed.

With the camera mounted on the EQ3-2 (polar & star aligned) when it's tracking then you should be good for 30 seconds to a minute exposure with a 50mm at ISO 1600.

You want to take test shots and increase the exposure until you start to see the stars trailing, then knock the exposure time back until they stop trailing. That's your sweet spot and it will be different if you change ISO.

The Canons are good for ISO 800 - 3200, after that you start seeing too much noise. I tended to stick to ISO 800 or 1600.

Once you find that sweet spot with the exposure time, then take as many images of your target as time will allow. You will be tempted to fire off 20 images of one target then move to a new one, try not to do this and stick with one target per night, you end up with much better images in the long run. Then do your calibration frames (darks, flats, dark-flats & bias). I found with my Canon EOS 2000D & modded EOS 1300D that using darks didn't make any difference to the quality of the stacked image, so I stopped using them and only use flats, dark-flat & bias for calibration. But try both with & without darks and see what works best for your camera. ;)

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I would say to generally go for shorter focal length which then means longer exposures are possible. When I started with just a tripod it took a me quite a few tries before I learned what worked. Use the 500 rule together with the crop factor of your camera. So divide 300 with your focal length and you'll get a reasonable idea of what length exposure you can take. Experiment to find what works, that includes the ISO which can safely be kept at 800 or 1600 I would guess. Then start collecting lights, keep making sure your target is in the frame and focus is good and just get as many lights as you can.

Also remember to select targets appropriate for your camera if it's unmodified. Keep reasonable expectations.

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Posted (edited)

All good advice thanks. I think I'll look for a target with the 50mm lens,  ISO 1600 and subs of however long I can get without trails. I'll also leave the Pi indoors.

I was thinking about using the Tokina but I find I get a lot of the houses, neighbors tree etc... at the edge of frame 😆

 

Edited by dave_tucker
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Twenty seconds is a LONG time for Ekos to download an  image. The Capture module should list the download times for you. That's something you can play around with in daylight, no need to waste dark-sky  time. 

Especially with very short exposures, your sub-exposures will indeed look all dark. Check the histogram, though.  So long as you're not up against the left edge, how each subexposure looks doesn't matter a bit.  (If there are data right at the left edge, that strongly  implies that there were dimmer pixels in the scene too.)  Ideally the biggest peak -- the background or "skyfog" value, since dark sky is the commonest thing in astrophotos -- would be at about  1/3 of the  range. But  you haven't the margin for that kind  of nicety.

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Grab a couple of apps to help, I use these all the time (noob myself)...

Photopils - will tell you based on your camera and lens what exposure you can use without any trailing or barely noticeable trailing. It does a lot more besides.

SkyView - To plan what will be where in the sky and it’s track across the sky.

Not used Ekos, I use APT, but clunky but gives the control I want. Or Backyard EOS but you need to pay for that.

keep going...

 

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You've got good directions to face, East is your best bet on a static mount keeping below 60°.

I would use the 50mm at f4 (slight stopping down can help improve star shape quality). 

400/50 gives a start of 8 seconds to try them work shorter is needed. ISO 1600, raw. All in camera noise reduction turned off. Lights, flats and dark flats. Find a star where a third intersects to focus on, this spreads focus across the lens. If going for m42 try to get it in the middle of the frame to allow for cropping the edges away as they'll show field rotation. I use an intervalometre or dslr controller (Android app great on a mobile and really helps with focus if don't have a laptop). Hope it goes well. I've a red dot finder in the camera flash hot shoe great for aiming.

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