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Andromeda galaxy

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Posted By stephp [Profile] [Gallery] Original Filesize 1.19 MB
Category PentaxForums Exclusive Gallery Original Dimensions 1800 x 1192
Date Posted 12-20-2012 Number Of Views 5,823
Average Rating 3.63, 8 votes Number Of Comments 9
Title Andromeda galaxy
Description The O-GPS1 unit is really efficient
Combined with the DA*200 lens I've got some very good results.
This picture is the result of 8 stacked (DeepSkyStacker) images. 30 seconds exposure time @1600 ISO for each raw picture.

My astrophotography album
Camera K-5
Lens DA*200
Location ~50 km south of Paris
EXIF Information:
File Name Andromeda_galaxy.jpg File Size 1247121 Bytes
File Date 2012:12:20 15:59:04 Camera Make PENTAX
Camera Model PENTAX K-5 Date/Time 2011:09:03 03:41:33
Resolution 1800 x 1192 Flash Used No
Focal Length 200.0mm (35mm Equivalent: 300mm) Exposure Time 30.000 s
Aperture f/2.8 ISO Equivalent 1600
White Balance Auto Metering Mode pattern
Exposure Manual Exposure Mode Manual
GPS Latitude N 48d 22.7118m 0s GPS Longitude E 2d 17.627m 0s
GPS Altitude 118.90m    
Links to Photo:

Comments
#1
12-26-2012
stephp
Junior Member




Andromeda galaxy

How I got this image !

Getting ready
===========

- Apart the GPS unit and the camera you need a (solid) tripod and a remote control.
- Prepare the camera: mount a lens, switch to RAW mode (mandatory), choose 1600 ISO (800 if sky conditions are very good, you will benefit from a higher dynamic) and the maximum lens aperture or step down 1 speed depending of the lens quality (but remember that stepping down one speed means doubling the total exposure time to obtain the same result).
- Put the gps unit on the camera with full charged batteries. One GPS battery capacity is about 4 hours, you will have to change it before the K-5 battery.
- After switched on the gps, you wait less than 1 minute the gps receives signal from satellites
- Perform a precise calibration (it take more or less one minute, retry if it failed)
- Switch to 'M' shooting mode, take aim at a bright star, and perform precise focus using the liveview at x10
- Switch to 'B' (bulb) mode
- Choose the 3s with remote control triggering mode

The maximum exposure time depends of the lens you use:
From my experience you can expect up to 1 minute with a 200mm lens for the best case (close to the north pole), 30 seconds for the worst (near zenith or near the celestial equator).
With a 50mm lens you can expect up to 5 minutes exposures.

The most interesting part: shooting !!
=============================

In order to improve the S/N ratio and because of the limited exposure time, It's necessary to perform more than one single shoot (8 for this image). The S/N ratio progresses with the root square of the shoots number (it's multiplied by 2 with 4 shoots) you will take more than. It's important to notice that you have to adjust field every 2 to 3 shots (with 200mm lens).

Dark frames:
Usually dark frames are necessary to get the read-out signal and subtracting it from the images. But thanks to the Exmor sensor the read-out signal is very low and dark frames may be avoided when shooting (relatively) bright objects

Processing:
=========

Pre-processing:

I used Lightroom for the demosaizing process and applied the lens corrections. It 's very important to obtain a uniform background because the subject's dynamic may be less than the background variations, so thanks to Lightroom to offer vary fine corrections for the DA*200. Otherwise you need to add your own flat field images in the pp.

Reject images where stars are notably stretched.

So just perform less corrections in Lightroom and export images in 16-bits TIFF format.

Stacking:

I use DeepSkyStacker. It's a freeware very easy to use. It can load 16-bits TIFF or even RAW format data. It will also automatically align the images.

Save the stacked images in 16-bits TIFF format

Post-processing:

Import the TIFF image into Lightroom and adjust the levels using (mainly) the tonal curve tool.

Enjoy https://www.pentaxforums.com/gallery/images/smilies/smile.png
stephp is offline
#2
01-01-2013
Ash
Community Manager




Andromeda galaxy

Brilliant.
Wonderful image. Excellent, clinical technique.
Well done and congrats.
Ash is offline
#3
01-18-2013
bossa
Veteran Member




Andromeda galaxy

Thanks for the detailed explanation. I'll be buying a O-GPS1 ASAP and putting my DA*200 to good use.
bossa is offline
#4
01-20-2013
david94903
Site Supporter




Andromeda galaxy

Wow! Great shot, great write up. I've been thinking about getting a O-GPS1, and now I'm thinking that I will sooner rather than later.
david94903 is offline
#5
01-24-2013
bezuidar
Site Supporter




Andromeda galaxy

Very good image!
bezuidar is offline




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