Friday, July 15, 2011

f-ratio myth - indeed

After reading of Stan Moore's "f-ratio myth"*, I decided to test the concept. And, I agree with him (that it is a myth). Afterall, when you adjust the f-ratio on a camera, all you're really doing is stopping down the lens - i.e., reducing the aperture. Makes sense - and I think this test supports his contention. 

Both images below were taken with an SBIG ST-8300M (monochrome CCD camera) on an 11 inch Celestron EdgeHD SCT using 10 minute exposure times. (The images were taken as part of testing the Optec Lepus focal reducer and the f/10 was a baseline.)

See individual images at: http://www.pbase.com/wjshaheen/fratio_myth__indeed

If f-ratio determined "brightness", then the f/7 image should be twice as bright as the f/10. As it is, the difference is simply in the scale (and resolution) of the two images.

*( See http://www.stanmooreastro.com/f_ratio_myth.htm )

Wednesday, May 18, 2011

Horizontal blooming in the Kodak KAF8300 sensor, when binned

Referring to the image here: http://www.pbase.com/wjshaheen/image/134819312/large
it turns out that what was suspected to be tracking errors, resulting in the "protrusion", or bulging to the right in star images, is actually caused by a characteristic inherent in the Kodak KAF8300 sensor known as "horizontal blooming", when binned. See discussion in the QSI support group here: http://tech.groups.yahoo.com/group/QSI-ccd/message/8682

In the process of centering an object the other evening, I was taking 0.5 sec binned images and noticed that even that short of an exposure exhibited the smearing I've been wrestling with for several months now. See the examples in this album:
http://www.pbase.com/wjshaheen/horizontal_blooming_in_the_kaf8300_ccd

Note the 2x, 3x, and 4x images exhibit progressively larger "bleeding" to the right, whereas the 1x1 example show no anomolies, other than a misshapen star due to atmospheric turbulence.

To attempt to isolate the cause and rule out tracking errors, I devised a simple test:
I rotated the camera approximately 45 degrees. (I normally image with the camera x-axis aligned to the RA axis.) The resulting binned image still showed the blooming directly and solely in the horizontal axis.

I then took similar images using Nebulosity2 instead of ImagesPlus - same result. The next morning, I reviewed past images taken with the SBIG ST-8300M - same result. Here is an example showing both tracking error as well as horizontal blooming:
http://www.pbase.com/wjshaheen/image/134819488/original
Note the distinct oval shape more characteristic of tracking errors (in both axes) versus the bleeding into adjacent pixels caused by horizontal blooming.

After trying a different USB port and eventually a different computer, and still seeing the same, consistent results, I browsed the QSI support group and found this is a known and common problem.

The good news, however, is that the fine detail strucure in an image would not be affectd by this issue (I had been wondering why there was no noticeable "smearing" in my M42 and M16 images, when tracking went well). And, some have suggested this could be addressed in post-processing.

But, as the saying goes, "the proof is in the pudding". So, here's a sample unbinned 10 minute image, dust mote notwithstanding:
http://www.pbase.com/wjshaheen/image/134819756/large

The area is in the neighborhood of PGC54526, RA 15h 17m, DEC 07d 00m, just north of M5.

With the Optc Lepus 0.62x reducer due to arrive any day, I will be able to image unbinned, albeit at a less comfortable 0.58 arc-sec scale. But, I'm very pleased that I've finally gotten to the bottom of a long-standing issue.

Regards,

Bill

Friday, April 1, 2011

Testing the Optec Lepus 0.62x Focal Reducer

Testing the Optec Lepus 0.62x Focal Reducer with the 11" Celestron EdgeHD telescope and the SBIG ST-8300M (monochrome) CCD camera. The telescope's stock rear adapter (with SCT threads) was replaced with an Astro-Physics 2" Visual Back (AP part # ADASCTLC) in order to install the focal reducer as close as possible to the OTA, as recommended by Optec.

I'm pleased to report that, overall, I found the reducer to produce very satisfying images, resulting in a reduction factor of 0.69x. See http://www.pbase.com/wjshaheen/optec_lepus_062x_focal_reducer_testing for full scale test images as well as an f/10 baseline image.

Update 24-Apr-2011: I resumed testing after resolving several issues having to do with the baseline - i.e., SCT collimation, guide-camera flexure and focuser flexure (yes, the Feather Touch focuser resulted in a slight drift, which was not mirror shift).

Visit http://www.pbase.com/wjshaheen/optec_lepus_062x_focal_reducer_testing and see the 4 images of M57 (Ring Nebula) taken this date - on the bottom row.

Some coma is noticeable in the lower left corner only and may be due to a tilted plane, which itself may be the result of, again, the leading edge of the reducer stopping at the edge of the internal field flattener. This is being researched with the vendor.

On another note, I have a professional source whose contact at Celestron indicates they will be releasing a reducer this summer. It will have a respectable back-focus (90 to 110 mm) but may not have the coverage originally desired. It will however cover an APS size chip and certainly the 8300.

Update 11-May-2011:
Update on the question of the reducer possibly not seating squarely (the leading edge of the reducer stopping at the edge of the internal field flattener), I just received word from Optec that they "have developed a different mounting configuration for the Edge HD scopes. For the C11 HD and C9.25 HD scopes a spacer is required to keep the lens housing from touching the Edge HD retaining ring." . (At the time I ordered mine from OPT, they had the former version in stock.)

Optec is sending me the new lens and housing gratis and I will be testing it in about a week.
(Thanks, Jeff!)

As an aside, I've replaced the ST-8300M with a QSI-583wsg - solves a host of flexure issues up and down the imaging train as well as with any mirror flop or guidescope flexure. The Starlight Xpress Lodestar connects easily to the QSI's guideport, given the standard C-mount adapter) and so far I've had no problem locating a guidestar.

It pays to collimate your optics

I have to admit I've frequently given collimation (aligning the optics of a telescope) the short-shrift in my haste to produce an image. But, after examining the NGC3628 photos taken lately and some visual viewing the other night, I took another set of images after doing a "proper" collimation.*

Here's the image from 3/28/2011 (prior to collimating):
http://www.pbase.com/wjshaheen/image/133518647/large

This is from last night (after collimating):
http://www.pbase.com/wjshaheen/image/133590305/large

(Feel free to explore the Original sizes.)

And, here is the side-by-side comparison:
http://www.pbase.com/wjshaheen/image/133590304/original

Further, here's an excellent paper on how to collimate:
http://legault.perso.sfr.fr/collim.html

I for one will never sell collimation short again.

Bill

Sunday, March 20, 2011

The Moon Illusion

What causes the "Moon Illusion"?  Is a full moon near the horizon really larger than when it's over head?

Well, let's first look at the evidence - http://www.pbase.com/wjshaheen/project_moon_illusion shown below.



As you can see, the recorded images are the same size. And, if anything, the moon should be larger since it is 4,000 miles closer to the observer. I've also read that the atmosphere's refraction should actually make the moon appear smaller.

So, why the illusion?
The theory that the illusion is due to foreground objects (trees, etc.) is contradicted by the fact that pilots frequently observe the same phenomonon.  (See, "Airline pilots flying at very high altitudes sometimes experience the Moon Illusion without any objects in the foreground." in http://science.nasa.gov/science-news/science-at-nasa/2005/20jun_moonillusion/ )

What causes the illusion?
The cause of the illusion has been debated for centuries but the more recent explanation is that it is due to the Ponzo illusion. (Thank goodness his name wasn't Ponzi, but that's another story.)

It turns out that we tend to see the sky, and the world around us for that matter, as being flat. We see objects in the sky (clouds, airplanes) as getting smaller with distance.  So, we think of the sky above us as a flat plane.  Whereas, the moon's orbit, and the sky in general, is a globe, or dome, over our heads.  As a result, we "expect" to see the rising moon to be smaller.

But, no matter how you look at it, it's still a beautiful site.

Here are some references that explain the effect much better than I:
http://en.wikipedia.org/wiki/Moon_illusion - See "Apparent distance hypothesis".
http://www.lhup.edu/~dsimanek/3d/moonillu.htm - Also shown in today's APOD.

William Shaheen
Superstition Mountain Astronomical League
Gold Canyon, AZ

Friday, February 25, 2011

NGC3190 - galaxy in the Hickson 44 Group

It's a little early for "galaxy season" but this target was well placed last
evening:


For larger versions, see here: http://www.pbase.com/wjshaheen/image/132775848/large

Hickson 44 is an exquisite group of galaxies. The original image was cropped
down to this view, which is 11.1 arc-mins across (approx. 1/3rd the width of a
full moon).

This really needs about 3 hours of exposure, and much more aperture. :O)

Bill

Thursday, February 10, 2011

For users of the Celestron NexStar system

Several members of our august group have Celestron telescopes which use the
popular NexStar system. (Note that NexStar has been used as both a telescope
model and also as the name of the software that controls a variety of Celestron
models.)

I'd like to refer those members to some terrific resources that are available
that go beyond the typical user manual.

First is the Yahoo group devoted to the NexStar system (software) itself:
http://tech.groups.yahoo.com/group/nexstar/
(Since you are already a Yahoo user, it will be easy to "Join This Group".)

Another is the Yahoo group that covers the NexStar 8 telescopes:
http://tech.groups.yahoo.com/group/NexStar_8i_Users/
Notice that it also covers the 8SE telescopes and I'm sure most of this is true
for the 6SE, and others.

But probably the most comprehensive resource available for NexStar users of all
varieties is the NexStar Resource Site, produced by Michael Swanson:
http://www.nexstarsite.com/index.html

It has links to everything related to the NexStar system, including the user
manuals - http://www.nexstarsite.com/Manuals.htm as well as links to Celestron
for downloading firmware updates.

If you own a NexStar telescope of any type, these resources are invaluable. Let
me know how these work out for you.

We can also review these on-line in the next meeting if anyone wishes, maybe in
the 3pm telescope clinic session.

Thanks and take care,

Bill Shaheen

Tuesday, February 8, 2011

Into the heart of Orion - M42 with 5 second exposures

Occasionally, while framing and focusing an object it helps to use short exposures (a few seconds) to expedite the process.  In doing so, bright objects such as M42, the Orion Nebula, show far greater detail since the starlight does not overwhelm the surrounding nebulosity.
In this example which combines 13 - 5 second images:


the 4 stars in the "Trapezium" are clearly resolved (discernable).

Also, notice the 2 or 3 stars to the lower left of the Trapezium. The image actually recorded the cones, depicting stellar material being blown away from the nascent stars - more commonly known for their appearance in the "Cone Nebula" (NGC2264) seen here: http://www.pbase.com/wjshaheen/image/121942660/large .

Interestingly, in the M42 image, the cones do not point directly away from the Trapezium. Is there possibly an even larger brighter star, or stars, hidden behind the dust to the left of the Trapezium?

Bill Shaheen
Superstition Mountain Astronomical League
Gold Canyon, AZ
USA

Update: 23-Feb-2011

I am pleased to report that I have resolved the question of what appeared (to me at least) to be light cones in the heart of the Orion Nebula.

Last evening, I imaged the area under investigation using a hydrogen alpha filter and without binning, i.e., higher resolution. It is much more apparent to me now after reducing the star halo that what appeared to be the right side of a cone is afterall a separate feature.

Here is the original image that prompted my question:
http://www.pbase.com/wjshaheen/image/132414886/large

Here is the Ha image from last night:
http://www.pbase.com/wjshaheen/image/132743306/large

And here is a side-by-side comparison with the area highlighted:
http://www.pbase.com/wjshaheen/image/132743747/large

It seems rather obvious now that what looked to me to be the illuminated right side of a light cone is actually a separate feature, and may in fact reside in the foreground.

This demonstrates the advantage of using higher resolution imaging and the use of narrow-band filtering to reveal the true detail.  And, of course, that appearance can indeed be deceiving.

Thanks for looking,

Bill Shaheen
Superstition Mountain Astronomical League
Gold Canyon, AZ
USA

Friday, February 4, 2011

Meteor caught on video

This happens every so often. While the autoguide camera is guiding on a star, a
meteor comes along. Well, this time I was ready for it and had the recorder
queued up with my finger over the record button.

http://www.youtube.com/watch?v=06swEgTd8R8
(Happens in the last couple seconds.)

I've even had geosynchronous satellites drift by. Well, actually, the satellite
is stationary but since the telescope is tracking the stars, they appear to
drift by. I'm actually trying to locate a geo satellite and test using it as a
collimation star.

Brings to mind another idea - have recording software running on a loop that
keeps just the previous 15 minutes or so in order to not miss the beginning of the meteor's appearance.

Tuesday, January 11, 2011

Canon T2i (550D) First Light

After agonizing for several days over the Canon 60D vs. the 550D (T2i), I decided on the latter. Here's a first light image:
http://www.pbase.com/wjshaheen/image/131753708/large

I think it's a terrific camera.

Bill Shaheen
Gold Canyon, AZ
USA

Tuesday, January 4, 2011

The Horsehead and Conventional Wisdom

Conventional wisdom says that when shooting flat frames one should
not rotate the camera or in any way change the optics. I certainly
wouldn't argue with that but as an unexpected opportunity to image
the Horsehead came up the other night I just had to capture it in
all its glory. And, even though I had just put together a master flat
of 32 frames the previous morning, the one flaw I saw seemed to be on
the camera's filter. So, I took a shot and here's the result of 12 -
12 min. subs:

http://www.pbase.com/wjshaheen/image/107633162/large

Now, I'm not advocating this as a matter of practice. But, consider
that since I'm using a refractor and did not have a focal reducer in
the light path, the nearest optic after the camera and filter is the
telescope's objective, which is 3 ft. away.

At any rate, I think it turned out pretty well. Of course, the darks,
bias frames and chilly temperature (for me) didn't hurt.

Adaptive Richardson-Lucy deconvolution demonstration

I've never been a big fan of altering images with photo-shopping techniques, other than an occasional mild sharpening and maybe contrast enhancement with a curve adjustment.

But there is one with a good deal of legitimacy - the Richardson-Lucy deconvolution algorithm -  a software method of enhancing images that was developed to correct the Hubble telescope's originally flawed optics. 

Here is a flashing comparison of an image taken last night before and after applying the algorithm (using ImagesPlus v3.82) -
http://www.pbase.com/wjshaheen/image/124134321/original

Here is a still of the finished product:
http://www.pbase.com/wjshaheen/image/124175541/large

Note that this is also the product of a nearly 2 year effort to image at close to 1 arc-second/pixel resolution (versus previous 1.4 as/p).

Jupiter in HD

Up to now I've been using the venerable Philips SPC900NC webcam for imaging planets. At 640x480, it produces reasonably good images.

This video, however,  http://www.youtube.com/watch?v=Z0CXFbIKbKU   was taken with the next generation of webcam - Logitech Webcam Pro9000, at 1200x1600. Although it has been downsampled to a more common 720p (1280x720) format, it's still not too shabby.

The imaging train consisted of a Televue 4x Powermate and an Orion Sirius 17mm Plossl eyepiece.

As a side note, I'm very impressed with the performance of the Celestron EdgeHD 9.25" and its ability to support insane magnifications. Earlier one morning, I observed Jupiter with the 4x Powermate and a 13mm EP for a mag of 552x and the image was excellent. This compares very favorably with a high-end APO refractor I once had.

Attaching a video camera to a telescope

Being duly impressed with my new Sony video camera (HDR-CX150), I just had to
try it out at the telescope. Hand-holding the camera up to the eyepiece showed
possiblities so I immediately thought about how to attach the camera in a solid
fashion. After some research to determine the specs of the threaded front
(30mm), I shopped around for a step-up ring to mate to a standard 42mm T-ring.
When I couldn't locate one, Jim Henson at ScopeStuff suggested he could assemble
one.

Here is a picture of the set-up:
http://www.pbase.com/wjshaheen/image/129357993/large
The eyepiece projection adapter houses a 17mm eyepiece.

And here is a brief clip to show the results:
http://www.youtube.com/watch?v=5WNtOGyxAd0

Of course the quality of the video is mainly determined by a number of factors
other than the means of connection (image quality, optics, procesing skills).
And the same could be achieved using a DSLR with live view. But, this new
adapter provides a solid, secure way to connect any T-thread device to an HD
video camera.

The product code at ScopeStuff is TTSH.

Comet 103P - Hartley2

Details and link to video here:
http://www.pbase.com/wjshaheen/image/129411756/large

The field of view is approx. 26.4 arc-minutes. So, this puppy was moving pretty
quickly - timespan was 1.5 hours.

By the way, with the new autoguiding set-up (Lodestar/Stellarvue 50mm Barlowed),
I'm getting an RMS of 0.42 arc-seconds. Compared to the Q-Guide (QHY5), the
Lodestar is *much* more sensitive, presents cleaner images and downloads a lot
faster, which seems to improve the responsiveness of sending corrections to the
mount. With the previous QHY5, PHD would exhibit delays.

The power of resolving power (aperture rules - again)

It broke my heart to sell my TEC-APO140 (a premium 5.5 inch apochromatic refractor).  And I still recall a fellow amateur astronomer saying, "I'd take that scope to the grave".  (I nearly did when I told my wife I wanted anther telescope.)  But, numbers don't lie and I was after improved resolution and contrast in my deep sky images.  So, I decided I wanted the increased resolving power of the larger aperture 9.25 inch SCT over the 5.5 inch refractor.  Besides, the new Celestron EdgeHD series promised sharp stars across the entire field-of-view (FOV). And they delivered.

So, bracing myself for a complex conversion (new accessories, focuser, etc.),  I sold the TEC APO-140. The new owner says it provides better views of planets than his 12 inch Meade SCT. 

While imaging last night, it occured to me I could perform the below comparison, using an image taken of the Horsehead with the previous scope back in January.  Here is a side-by-side:
http://www.pbase.com/wjshaheen/tecapo140_to_edgehd925_comparison

Here is the work to date using the new telescope:
http://www.pbase.com/wjshaheen/gallery/celestron_edgehd_925_and_the_sbig_st8300m

I feel the changeover was worth it.