Skies Over Picketpost Mountain

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Rusty Mountain Observatory development

The development of Rusty Mountain Observatory is well underway and at this point I'm just waiting for the new mount (Software Bisque's Paramount MX) - hopefully early April. (Hopefully sooner.)

The photo to the left shows the permanent pier, sold by the same company, bolted to a concrete foundation.


See the continuing storyboard for ongoing developements and details: http://www.pbase.com/wjshaheen/rusty_mountain_observatory

Rusty Mountain Observatory development

Construction is underway with the pouring of a pier foundation for Rusty Mountain Observatory in Gold Canyon, AZ.  Visit http://www.pbase.com/wjshaheen/rusty_mountain_observatory for monitoring progress.

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 )

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

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