meade dsi: deep sky astrophotos “your first night out”?meade dsi: deep sky astrophotos “your...

Meade DSI: Deep Sky Astrophotos “Your First Night Out”?by Suk Lee

An imaging revolution from Meade?

“Take Pictures Just Like These Your First Night Out” proclaims Meade’s beautiful full-page color adsfor their new Deep Sky Imager (DSI) CCD camera. The ads show impressive pictures of M20, M51,NGC891, etc, all for the VERY tempting price of only $299. The fine print below the pictures says “Allimages were taken with a Meade 8” LX200 GPS using Meade’s Deep Sky Imager.”

How capable is the camera and can you really accomplish picture like those the first night out? I’ll cutthe suspense – the answer is definitely “yes”, but there’s a little fine print of my own. Read on…

Copyright (C) 2004 Cloudy Nights Telescope Reviews

What's in the box?

The DSI comes with (clockwise from top left):- DSI camera body- RJ to DB9 adapter- eyepiece parfocalizing ring- Autostar Suite CDROM- Quickstart instructions- 4 wire RJ cable- 6 wire RJ cable- USB cable

Everything you need to use the DSI is supplied in thebox, including a built-in IR filter. The camera body is anicely machined block of metal with a standard 1.25”nosepiece, threaded for 1.25” filters.

The nosepiece unscrews to reveal the unusual IRfilter sitting below the nosepiece. Unlike a regular1.25” or 2” filter, it’s a flat disk of glass with arectangular IR block area that fits over the CCDsensor. The quickstart instructions warn to removethe nosepiece carefully, as the filter is loose. If youplan on taking the filter in and out a lot, you mightwant to invest in a regular 1.25” screw-in filter for thefront of the nosepiece.

The specifications say that the sensor is a “HighSensitivity Sony Super HAD Color CCD”, andspecifies the pixels as 9.6x7.5 microns, in an array of510 x 492 pixels. The use of the HAD CCD is goodnews as they are known to have good sensitivity with low dark current (thermal noise). The pixel sizeis larger than the ones in the ubiquitous Philips TouCam Pro, so it’s not the same sensor, althoughfrom the same family of sensors.

Exposure time capability is listed as being from 1/10,000s to 1 hour.

One of the benefits of the Meade ground-up design, rather than modifying an existing webcam, is thatlong-exposure control does not necessitate a separate parallel cable – everything is controlledthrough one convenient USB cable.


Autostar Suite Overview

The Autostar Suite software package that comes with the DSI is a combinationPlanetarium/Telescope Control/Imaging Acquisition/Image Processing system. As I do not have aMeade telescope, I only evaluated Autostar Suite's image acquisition and processing capabilities.

Software installation is straightforward. Pay attention to the numerous warnings not to re-boot yourcomputer until the very end of the installation. Also noted in various on-line forums was somedifficulties with USB ports, etc. Immediately after installing the software (Dec 2004) I installed thelatest patch from Meade, obtained from their website, and experienced no problems.

After installation of the software you attach the camera to your USB port with the supplied cable(which is a little on the short side) to complete the hardware driver install process. Launching thesoftware brings up the following screen:


Clicking on Image -> DSI Imaging brings up the image acquisition window:

Going clockwise from upper left the major functional areas are:- camera controls for exposure and gain control- image acquisition control area controlling how pictures are acquired and initially processed- image preview/viewing screen- Magic Eye Focus assist window- image contrast/brightness & histogram window

Autostar Suite - Capturing your first terrestrial image

Acquainting yourself with the DSI and Autostar Suite is easiest in the daytime where you have abright stationary object. Select a terrestrial object far away enough from your scope that you canreach focus and select an object that has a bright glint on it. A reflection off of a street lamp, forexample, is perfect. Focus with your eyepiece then remove the eyepiece and insert the DSI. Theylikely will not be parfocal so expect to have to refocus. The purpose of selecting an object with abright glint is to be able to see something to focus on.


Make sure "LIVE" and “Terrestrial” areselected and click on "Auto Adj" to get thecamera rolling. Autostar Suite will set theexposure to 1 millisecond then graduallyincrease exposure until you have areasonable image and then stop. This cantake a little time so be patient

Ignore the "Magic Eye" at this point andmanually focus until you have a crisp image. Ifound the default image a little dim andmanually increased the exposure time until Igot a brighter picture. I also reduced the gainso that the brighter areas of the picture didn’tburn out.

At this point you’re set to head out under the night sky and focus on a star.


Autostar Suite Magic Eye focus assist

In my review of the Meade LPI, I covered the Magic Eye focus assist and didn’t find it to be useful,recommending instead a Hartmann mask. Here’s the section on using a Hartmann mask from thatreview. Note that the screen shots are slightly different because they’re showing the LPI window, butthe principles are the same.

Make aHartmannmask,basicallyanaperturecover withtwo holescut in it.As youcan seefrom thepicture itdoesn'thave to beparticularlyprecise orpretty. Formy largertelescopesI’ve madepermanentmasks outoffoamcore.


Start upAutostarSuite andget closeto focusand thenput themask onyourtelescope.Instead ofone staryou nowhave two.As you getcloser tofocus theimageswillapproacheachother.

As you getcloser tofocus theimageswill alsogetbrighter,making ithard tojudgeexactlywhen theyoverlap.


Manuallyreduceexposureto reducethebrightnesso f t h eimagesand thenbring themintooverlap.You are infocus.

Once you've achieve critical focus on a star you can swing over to your object of interest.


First Light – M1 with Mewlon 250 and 0.375x reducer

As the MSI is advertised as being suitable for an 8” SCT, I used a configuration which would give asimilar focal length. I selected M1 as a reasonable first small DSO. I used a Mewlon 250 (3000mmprime focal length) and 0.375x reducer, the SBIG FR237. The FR237 is a 1.25” filter thread lenswhich conveniently screws into the nosepiece of the DSI. Equivalent reducers designed specificallyfor webcams are available from various manufacturers. The combination leads to a focal length of1100mm, which is similar in focal length and therefore field-of-view to an 8” SCT with a 0.63x reducer.

Compare FOV with and without the reducer:


Step 1: Focus

I selected Capella as a nice bright star and focused. Note that the LIVE window is all that wasnecessary with an exposure of 1 second, making it very easy to locate and focus on the star:

Step 2: Take dark frames

Every CCD camera generates spurious electrical signal due to heat in the CCD. Fortunately, theaccumulation of signal is very predictable, so it’s possible to take a set of “dark frames” (with thetelescope capped) which are just the spurious signal and then subtract the spurious signal out of yourimages. In order for this process to work precisely, the CCD must be temperature controlled. The DSIis not, however if the ambient temperature is fairly constant, then a good approximation can be madeby turning on the camera, letting it equalize to ambient temperature, then taking a set of dark framesjust before image acquisition.


In Autostar Suite select “Take Darks” under the “Image Process” pulldown:

The window to the right will change to show the range of darks that will be taken by Autostar Suiteand the total time, 8.5 minutes in this case. I left it to the defaults it came up with, and clicked on“Start”.

The software then thoughtfully reminds you to cap your telescope and click “OK” before really startingthe sequence. Go have a cup of coffee…

When you come back, you’ll find that the “Dark Subtract” checkbox is now checked, and the programis reminding you to uncap your telescope. You’re set up to take long exposure pictures with automaticdark frame subtraction now:


Step 3: Frame M1 and set up a guidestar

Finding M1 will be the first real challenge for that “First Night Out”. Even with a 1 minute exposure,M1 is essentially invisible. Plus, the field of view at this focal length is so small that star-hopping withthe camera will be very difficult. This is where GOTO becomes a real life-saver. Focusing on thatbright star also serves as a reference point for your GOTO telescope. I centered Capella as above,then instructed my mount to swing to M1. I set an exposure of 1 minute and clicked on “Long exp”and “Preview”. The Count Down window shows the time left in the exposure:

As you can see in the picture above, M1 is virtually invisible, but I’m trusting that it’s in theresomewhere. So, we’ll get ready to take a bunch of exposures and accumulate them.

Autostar Suite has a feature which they calling “Tracking” and which other manufacturers often call“Track-and-accumulate”. In this mode a succession of pictures are taken, aligned in realtime, andthen summed in realtime. This feature allows you to take a set of pictures with the effective exposureof one long exposure, but without autoguiding. If you telescope is accurately polar aligned, then shortexposures without autoguiding will be sharp enough to allow you to stack a bunch to increase theoverall effective exposure. In order to align the pictures, you have to identify a star that Autostar willuse to align successive pictures. Pick a bright star without any nearby neighbors to confuse theprogram (easy in this case!) and draw a box around it with the mouse as shown above. Autostar Suitewill now use this star to align and accumulate frames.


Step 4: Start taking long exposures

OK, I’ll admit something, I cheated a little. I used an autoguider setup since I wanted to take longexposures of M1 (5 min) and I had a feeling that my mount wouldn’t track accurately at 1100mm for 5minutes. However, the test of Autostar Suite’s Track mode was still valid because there was stillsome frame drift because I wasn’t autoguiding on a star very near M1. In other words, Autostar Suitestill had to align frames before accumulating them.

Here’s the setup I used:

1) Set up for 5 minute exposures2) Make sure “Dark Subtract” is checked3) Set up “Image Process” to “Deep Sky”4) Set “Min Quality” to 0 to force Autostar Suite to select and stack every exposure5) Set “Evaluation Count” to 1 for the same reason and make sure “Combine” is checked6) Put in the object name7) Click on “Save Proc…” to bring up the popup and8) Set up to “Save Every Composite Image”

In normal operation, Autostar Suite will just save one composite image. However, since there are a lotof airplanes in my area, I didn’t want to chance having an airplane fly through the frame and have itstrail saved into the image. When “Save Every Composite Image” mode is set, every successive


composite (e.g. 1, 1+2, 1+2+3, 1+2+3+4, etc) is saved, so at least I have the previous images if aplane flies through the field-of-view.

Here’s the result after clicking on “Start”:

Note that M1 is now visible (GOTO rules!) and that Autostar Suite has drawn green crosshairsmarking the position of the guidestar.


Here’s the result of 13 exposures, 65 minutes of total exposure, straight out of Autostar Suite:

And here’s the result after some histogram tweaking, color adjust and slight color boost in Photoshop:

Pretty impressive for a $299 camera and with most of the work done by Autostar Suite!


Second Light – M42 with Megrez 80 and 0.63 focal reducer

At this time of the year, M42 is a great DSO object for initial imaging because it’s bright, large, easy tofind, and spectacular to image. Because the DSI has a small imaging chip, a short focal length wouldbe needed to get a decent field-of-view on M42. Doing the calculations indicated a desired focallength of around 300mm. That’s a LOT shorter than an 8” SCT focal length of 2000mm, and shorterthan what can be achieved with an 8” SCT and 0.33x focal reducer (660mm). Fortunately, I had aMegrez80 achro refractor and Celestron 0.63x reducer on hand, which gives almost exactly 300mm.

While the 0.63x isn’t designed for refractor applications, because it’s also designed to correct for thefield curvature of an SCT which is different than a short focal length refractor, the small image sensormeans it will work well.

I also had the “variable T to SCT adapter” from the Meade 0.33x focal reducer handy, which isneeded to get approximately the right spacing between the 0.63x reducer and the DSI. I Put it alltogether, slap onto the Megrez80, focus on a bright star, then swing over to M42 and compose.

Again, a guidestar was selected and a series of pictures taken. Because the dynamic range of M42 isso great , I took a series of photos of 30 seconds, 2 minutes, and 5 minutes exposure, planning oncompositing them together later.

Here are the results, straight out of Autostar Suite:


16 x 30seconds:

4 x 2 min:


4 x 5min:

As exposure time increases, more of the surrounding nebulosity is captured, but the central area isburned out because it’s so much brighter than the surrounding areas that it saturates the CCD. In the4 x 120s and 4 x 300s images, the burned out regions aren’t just white, they have an unpleasantmottled green appearance.

To get a nice picture of M42, compressing the dynamic range of the image, I stacked the threepictures. On top, was the 4 x 300s image, with the burned out regions masked out so that theunderlying image could show through. Underneath was the 4 x 120s image, again with the burned outregions masked out, and finally on the bottom was the 16 x 30s image. Each image was black pointadjusted and curved to match the previous layer.


It’s easier to explain with a picture:


The resulting image was then composited together, slightly histogram adjusted further in Photoshopand then “Despeckled” and “Dust and Scratch Filtered” and finally gently unsharp masked:

A very nice image.

Summary

At the beginning of the review I said you could get deep sky pictures “out of the box” in one evening. Icertainly did. However, there are some caveats:

- my telescope was very well polar aligned- I had a bunch of telescopes and reducers available to get different fields-of-view- for some of the images I used a $3k autoguiding system (including scope)- I have a lot of experience with astrophotography

I think, realistically, if you have never done ANY imaging, you won’t be able to get comparableimages your first night out. It’s no fault of the DSI, it’s that there’s just too much stuff to learn, polaraligning, just getting focus (which can take HOURS the first time you try it), and image postprocessing.

However, for the price, this is the easiest “introductory” camera I have used, and is definitely capableof imaging virtually all of the Messier catalog with an impressive effort-and-cost-to-results ratio.


DSI likes:

- everything you need is “in the box”- one USB cable control is MUCH simpler than competing “parallel port assisted” designs- Autostar Suite track-and-accumulate works well- decent sensitivity and noise immunity- automatic dark frame mode

DSI dislikes:

- odd IR filter easy to damage – standard 1.25” thread-on filter would have been better- CCD isn’t temperature controlled, but hey, it’s only $299- no obvious ways to automatically do flat frames

Bottom line – Meade has set an impressive, new, low price point for entry level color DSO imaging. Ifyou want to dabble, this is a great way to start.

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meade dsi: deep sky astrophotos “your first night out”?meade dsi: deep sky astrophotos “your...

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