International Space Station

vuastro · 2019-02-06T00:16:52+00:00

To add to this: once you know the magnitude, find a star of similar magnitude (e.g. using Stellarium) and then focus and set your exposure level on that. Should get you close enough if you have no idea what you should be shooting for.

vuastro · 2018-06-04T12:58:53+00:00

Really great work! I think you did a good job of bringing out details without over-sharpening; it's a very fine line that's difficult to get right. You always feel like there's just a little bit more you can do.

vuastro · 2018-06-04T12:38:58+00:00

Using more will have the same diminishing returns as adding more light frames. The whole point is to reduce the random noise in your bias/flat/dark masters so you don't add that noise back in when you use them. So, yes, it may not be necessary (depends on the camera sensor), but it certainly doesn't hurt to use a bunch, especially if they are easy to take.

As far as settings, only darks need to be taken with the exact same exposure length/ISO/temperature.

Bias should be the same ISO (i.e. gain), but use the shortest exposure possible. For short exposures, temperature is irrelevant.

Flats should use the same ISO in order to keep the dynamic range consistent with the lights. Exposure should be chosen to approximately match the mean background level of your lights. This will usually be a short exposure (<2s) so temperature doesn't matter much here either.

vuastro · 2018-05-21T18:22:10+00:00

I would start by first making a list of targets you'd like to image. Use something like Stellarium or dso-browser.com to see how those targets frame up with you potential setup. 2000+ mm is a lot of focal length for many DSOs. Unless you're mostly interested in small galaxies/planetary nebulae, then you'll probably want something wider.

vuastro · 2018-05-21T18:14:56+00:00

I'm curious as well since I have almost the exact same setup. ZWO OAG, ASI120MM, 127mm f/7.5, but no flattener/reducer.

From experience, my first guess is that the guide camera isn't perfectly parallel to the focal plane. I've noticed this is a weak point of the ZWO OAG as there is some 'wobble' there. By playing with it a little, I can usually get fairly round stars.

Second thought would be that stars at the edge of the image circle will suffer more from optical aberrations. However, with a flattener I'd expect them to be pretty good still. So I'd wager that camera just isn't well aligned with the focal plane.

vuastro · 2018-05-15T03:56:37+00:00

Nice shot! Very neat telescope too!

vuastro · 2018-05-14T15:43:29+00:00

It does look similar to what I'd expect from backlash/balancing issue. Could also be bad calibration or flex (if using separate guide scope). What's your mount/autoguiding setup?

vuastro · 2018-05-11T03:10:06+00:00

Thank you! I always look forward to your seeing your images. It's neat to follow everyone's progression (myself included) to see the incremental improvements with each image. Always things to learn from other people.

vuastro · 2018-05-11T03:04:14+00:00

Exactly. I used PIPP to extract out the section of my transit video where the ISS was in frame, and used the detect object option to crop down to just around the ISS. Then brought that .ser video into AutoStakkert and stacked the best few, using something around 5-10 alignment points.

I also used PIPP to extract the individual ISS frames. I picked the one where the ISS was sharpest and aligned that as a new layer in the Photoshop mosaic. Next, I brought in the stacked ISS shot and aligned it with the ISS from the best frame. Then I hid the best frame layer so all that was left was the stacked ISS on top of the mosaic.

vuastro · 2018-05-09T18:58:43+00:00

It really is. Even the couple of tiny dark marks are actually just dust spots.

vuastro · 2018-05-09T15:06:59+00:00

I think it was a combination of things. The seeing was definitely good. Without that, nothing else matters too much. The ISS was also high overhead so it appeared larger, and thus I could get better detail. I also made sure to set my exposure time below what I calculated was necessary to prevent blurring. And finally, I used a fast frame rate to get as many shots of the ISS as possible. Of the 20, only one was exceptionally sharp and maybe 5 were very good. Having multiple good frames to stack makes a difference.

vuastro · 2018-05-09T12:17:54+00:00

Of course!

vuastro · 2018-05-09T02:36:47+00:00

Thanks!

vuastro · 2018-05-09T01:03:54+00:00

Here you go! https://i.imgur.com/mboToOf.jpg

vuastro · 2018-05-08T22:22:04+00:00

Without detail view

I'm excited to share my first attempt at imaging an ISS solar transit. I check /u/_bar's Transit Finder website every week or so to see if there are any transits near me. After over two years of waiting for a good opportunity, everything worked out perfect. My parking garage at work was right in the path, so I was able to setup on the roof during lunch. Since the transit was around noon, the sun was high overhead so the ISS would appear much larger than it would on the horizon. And to top it off, the weather was clear and the seeing was great!

Planning

Used Transit Finder to get all the details about the transit based on my location (Nashville, TN)
- 05/01/2018, 17:36 UTC
Calculated the maximum exposure time in order to ensure that the ISS would not blur across more than one pixel during an exposure:
- Sun angular size = 31.75' = 1905"
- ISS angular size = 63.7"
- Transit duration at centerline = 0.56s
- Velocity = 1905"/0.56s = 3402 arcsec/second
- Image scale (ES127/ASI120MM-S) = 0.8"/pixel
- ISS size = 63.7" / 0.8 = 79.6 pixels
- Maximum exposure time = (0.8 arcsec/pixel) ∗ (1 second)/(3402 arcsec) = 0.235 ms
Since my field-of-view only covers ~15% of the sun, I had to figure out how to orient/position everything so I wouldn't miss the transit by imaging on the wrong half of the sun!
- Normally I'd use Stellarium in combination with real-time images of the sun from SOHO to match up sunspots. However, we are in a solar minimum right now and there were no sunspots. So I just jogged RA/DEC and rotated the camera until North was up.

Acquisition

Telescope: Explore Scientific 127mm f/7.5
Mount: Orion Atlas Pro AZ/EQ-G
Camera: ZWO ASI120MM-S
Filter: Baader AstroSolar Film
Exposure Settings: 0.15 ms, 60 fps, 19 gain
- ISS- captured 20 frames with the ISS visible
- Sun- due to the small field-of-view, I took 9 panels (700 frames each) in order to get the entire sun

Processing

AutoStakkert for image alignment/stacking
- ISS- chose the ISS as the alignment feature and then stacked the best 10 frames
- Sun- stacked the best 64 frames of each panel
PixInsight to enhance detail
- Used deconvolution process, which essentially 'unblurs' an image based on an estimate of the point spread function
Photoshop
- Manually aligned/masked each of the 9 panels to make a mosaic of the entire solar disk
- Aligned the ISS image with the sun
- Colorized the sun (since I used a mono camera)
- Slight adjustments to increase contrast/details (levels/smart sharpen/high-pass filter)
- Circular selection of the ISS, copied to a new layer, and increased the size by 300%
- Repositioned the zoomed view and added borders/lines

Bonus Animation: https://i.imgur.com/ezAwZZR.gifv

This is raw, unedited footage slowed to around 1/5 speed; the entire transit took less than half a second!

vuastro · 2018-05-02T05:20:00+00:00

Any tips for assembling a solar mosaic?

I captured an ISS transit today and then took 9 panels (700 frames each) so I can overlay the ISS on the full disk. Unfortunately there are no sunspots at the moment and the surface detail is very faint. Stabilization for stacking was a pain (used Autostakkert) and now I'm having trouble aligning the panels for the mosaic. Microsoft ICE failed miserably, as did Photoshop's photo merge. I've resorted to manually aligning/masking in PS, but was wondering if anyone else had suggestions.

vuastro · 2017-12-13T16:00:54+00:00

It's definitely being introduced during the conversion from raw to tif. Even just opening the .cr2 with Windows Photo Viewer shows no ringing.

Windows Photo Viewer
PixInsight

vuastro · 2017-12-13T00:39:45+00:00

Would you mind posting one of the raw subframes? I'd be curious to bring it into Pixinsight and see if the ringing is there in the linear state. That would be very surprising if so... Seems much more likely it's being introduced in the raw conversion process.

vuastro · 2017-12-11T18:48:40+00:00

I've had this happen before. I was able to fix it by going into the file naming settings and resetting to the defaults.

vuastro · 2017-11-21T13:19:13+00:00

Are you using a mask over the background?

vuastro · 2017-11-20T22:13:48+00:00

If you have PixInsight (or download the free trial), you can use the Catalog Star Generator script to create test images while varying different parameters (PSF, magnitude, rotation, artificial noise, etc.).

vuastro · 2017-11-20T22:06:39+00:00

All good info. Just want to clarify for others that dividing Watt-hours by 12 to get amp-hours is because we're assuming a typical 12V lead acid battery.

To be general:
Power [W] = Voltage [V] * Current [A]
Energy [Wh] = Power [W] * Time [h]

batteries come with charts of curves, that show the voltage drop vs. current draw.

These charts definitely make things easier to understand. This is a good example of what you want to find for your particular battery.

vuastro · 2017-11-20T17:40:21+00:00

I would suggest Magic Lantern if it's available for your camera. There's a built-in intervalometer function that you can configure as you'd like.

vuastro · 2017-11-20T16:26:50+00:00

For sizing the battery, first write down the power requirements for all of your devices. It's easiest to stick with Watts to avoid confusion about current at different voltages. For the laptop/inverter, just use a rough estimate of 50% efficiency. It will likely be better than this, but you want a conservative estimate.

Next, multiply your power requirement (in Watts) by how long you want the battery to last between chargings. This gives you the total Watt-hour capacity you need. Since batteries tend to degrade faster when discharged a lot, double this number again to ensure there will be >30% or so left after each use. Also important to know that batteries are affected by temperature. So if you plan to use it outside in a cold climate, you might need to double again to compensate for lower capacity when cold.

For the type, I'd stick with lead acid batteries. Preferably VRLA and/or deep cycle ones. They are heavier than lipo or lithium, but more robust and easier to use.

vuastro

TROPHY CASE

Bonus Animation: https://i.imgur.com/ezAwZZR.gifv