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Sunday, September 20, 2009

Messier 103

All right, back in the game! With cooler nights and cleaner workflow, its getting better. Here's a nice take of M103, the last I-am-not-a-comet object recorded by Charles Messier. Some 8,000 light years distant, Charles apparently never observed this open cluster. It was included in his work based on a report received by Pierre Mechain in 1781 of whom he became friends with in 1774.

Looks like it is time to collimate this RC scope, coma is apparent in the left and upper left bounds of the image. Gasp!

Thursday, September 17, 2009

Messier 76, Little Dumbbell Nebula

One of the faintest Messier Objects, a planetary nebula discovered in 1780 near the 4th magnitude star 51 Andromedae. 243 x 15 sec. JPEG frames at 1600 ISO, noise reduction, unguided, bias/flat calibrated.

Started taking this a little too early, as neighbor's outdoor lights came on and off a few times before going to bed. Some remnant remains. Shouldn't try starting before 9 or 10pm.

Wednesday, September 16, 2009

Messier 29, the "less impressive" cluster

As quoted by the SEDS organization on its Messier Catalog site, "Messier 29 is a rather coarse and less impressive cluster."


Kind of took that as a challenge, so I captured what I think is pleasing view of this simple open galactic cluster of blue giants, 7,200 light years distant. Charles thought enough of it in 1764 to write it down.

250 x 15 sec. JPEG frames at 1600 ISO, unguided. 250 bias, 173 flat calibration frames.

This image taken without field flattener and only flat/bias calibration. Rather than post-process dark frame calibration, the camera's built-in noise reduction (dark frame subtraction) was applied to each exposure, shortening the post-process time.

Creating a new master flat

New camera, new master flat.

After crawling numerous blog and forum postings regarding flats, I never came across anything that really explained how simple creating a master flat calibration frame can be. After some personal research coupled with trial and error, I eventually understood the purpose of and how the calculation works. In addition, it became exceedingly clear to me that a common recommendation to point the telescope at various regions of the blue sky before twilight is collectively bad advice.

I want to correct this now!

What you want is a calibration image that will scale your pixels consistently to normalize individual pixel intensity - removing the variation in detected energy due to curved optical plane, the effect referred to as vignetting. Key phrase here, "scale your pixels consistently."

What does that mean? It means record a neutral image of your optical curvature. What does neutral mean in this context? It means without preference to any color channel (i.e., grayscale, folks). If you still don't get it, find a new hobby or just follow the instructions below and don't worry about it.

So, here's a simple recipe for creating flat calibration frames for DSLR prime focus astrophotography:

1) On a bright, sunny afternoon bring out your telescope and attach the camera exactly as you would for shooting
2) Ensure the camera is "focused", this will require some thinking on your part (suggestion: lock the focuser down from a prior night's shooting when the camera was focused on a star)
3) Tape a white sheet of paper without wrinkles across the opening of the telescope (see picture above)
4) Set the camera to aperture-priority mode and ISO 100 (best dynamic range/low noise), this will record our "white" light in the median range of the combined color channels - forming our grayscale image. Afterwards, look at the histogram readings from the images and you'll see what I mean.
5) Take as many shots as you can, I strongly recommend over 100 to get good saturation and signal coverage. This shoot I'm taking 250 as I tend to go for 200+ image frames on any good outing.
6) Once you've collected them, use your favorite stacking program to apply a standard distribution.

You'll also want to adjust the RGB channel offsets, so they are right on top of each other (this is a one-click operation in Nebulosity called Adjust Color Background). This will account for the slight fluctuations of the channels we recorded and then you'll have your wonderfully neutral master flat!

Good luck!

Thursday, September 10, 2009

Canon T1i mod gone bad...

Well, attempted to mod the T1i by removing the IR cut filter. Got into the point of removing the sensor plate, only to discover some special torque screws (for which I have nothing to get them out). Put it back together, apparently a little too quickly, only to discover that it will no longer take a picture - "temperature too high." Great. Something is shorted...could be one of a hundred contacts that were involved in various ribbon cables or even the aluminum shield plate.

When I have more time, and patience, I'll look into trying to bring it back. For now, I've decided to continue the DSLR path and when convenient, pay someone to do the mod. A new Rebel XSi has arrived, a couple hundred cheaper than the T1i, lighter and less noise (see previous post).


Tuesday, September 1, 2009

Noise and more noise

After a few months of taking additional photos with the new Rebel T1i (500D) DSLR camera at various high speed settings, there really has not been any improvement in eliminating high end noise as compared to the early generation Canon Rebel XT. In fact, after some comparative study of detailed reviews carried out by professional camera webzines, the T1i fares slightly worse than the model its intended to replace, the Rebel XS (450D). And my test photos support this, too.

The good news is that noise reduction modes at ISO 1600 perform comparably with the 450D.

It is not a complete loss. Where the Rebel XT was an 8 mega-pixel camera, the T1i is 15!! Longer battery life, and more importantly no battery amp glow!! There is still much I would like to accomplish with DSLR astrophotography. In the near term, I am looking forward to eventually replacing the IR cut filter with a wider band version designed for deeper reds and extended UV.