Dew controller and image noise

Well over a year ago I began noticing bands of noise on my images. Here's an example:

Stretched Light Frame showing noise band

And here's a patch of it at full scale (look just below the nebulosity). The appearance of the band will vary from frame to frame, but it's always a horizontal strip of hash. Longer exposures have more bands. Here's what it looks like at full scale:

Noise band at full scale

When that band covers your target, it overlays a great deal of noise that is difficult to remove. ImagesPlus noise removal reduces it, but you can be left with a light band.

I could not figure out what the source was. At first I thought it might be AC line noise (I was running using AC power). Moving to battery power didn't get rid of it. Bad cables to the CCD were suggested by others, but lots of cable swapping didn't fix it. Maybe it was the CCD camera itself? Online searches didn't suggest the camera had any problems like that. I did see some implications of interference from other devices being powered by shared batteries, so I isolated the CCD. The noise remained.

This was an intermittent problem, however. I didn't tumble to the cause until last week at Jeffers, while I was imaging M20/21. Almost every frame was noisy. For some reason I turned off the dew controller, and like magic the noise was gone. I imaged M17 the next night with no dew control (it wasn't needed) and every frame was free of the noise.

A more directed online search led me to a comment about the controller I use, the Model VI:

The Culprit: Kendrick Model VI

I immediately launched into more research and was happy to learn that Kendrick made an RFI-free controller that was in my budget range, the Standard Dual-Channel Controller (SDCC). $114 and shipped free from Astronomics.

The Solution: Kendrick Standard Dual-Channel Controller

A night of imaging with the SDCC keeping everything dry produced images that were all RFI noise-free.

If you're imaging and seeing a lot of horizontal noise bands, it may be your dew controller.

Two images from last weekend: M17, M20/21; Processing workflow.

I'm REALLY pleased with how this image of M17 came out:

Messier 17 (Omega or Swan Nebula), click for full size

The previous night's image was not quite as successful--M20 and 21. More about why in the next blog entry.

M20 (Triffid) and M21

Both images are full-frame. For all the gory details of acquisition, look at my gallery on AstroBin. By way of a quick summary, both are LRGB images made with an SBIG ST8300M CCD, TeleVue 102 apo and autoguided CGEM mount under mag 6+ skies. Dark and bias frames only, no flats.

Imaging is SO much faster doing LRGB in the dark than it is to use narrowband filters under light-polluted skies. 

I realize that the colors in the M17 image may look a little muted to you, but I kind of like them this way. What's particularly pleasing about the image from my standpoint is three-fold: The stars are nice and round right out to the edge of the field, meaning that my field flattener is doing its job perfectly; The merging of the LRGB channels seems to be spot-on. And finally, guiding with the Orion mini-guider works great at the 700mm focal length of the TV102 to correct mount errors. I'll eventually try out the mini on my C925.

My processing workflow continues to evolve. These two images were made by ping-ponging back and forth between Images Plus and Photoshop:

• Calibrate, align and stack using IP
• Stretch using PS
• Noise cleanup and star size reduction in IP
• LRGB combine in PS using Annie's Actions
• Color balance in IP
• Masked sharpening in PS

Yes, I know that's a mess, and some will say that all can be done in IP or PS or Maxim or whatever. Good for you if you can function with only one software package, but at this point I can't. I'm using IP 4.5, so probably some of the changes that have gone into later versions would make it a better processing tool. 

Seeing and Saturn

The environment really makes a difference when it comes to planetary imaging. Here are two images of Saturn; the first from a windy night with poor seeing, the second from last night--calm and good seeing.

Windy, Poor Seeing

Calm, Good Seeing

The differences are dramatic. With better conditions the artifacts at the ring-tips are gone, there's more ring structure, Saturn's limb and cloud belts are better defined, and the polar vortex can be seen. Contrast is higher, too. (Differences in color balance are due to processing, not the conditions.)

Now imagine if the seeing had been excellent. Maybe some day I'll have a third image that illustrates that.

(Both images were created using a Point Grey Chameleon, Celestron C925 XLT, and TeleVue 2X Barlow, FireCapture and Registax 6.)

Clouds, WOW, Focal Reducer

The abysmal spring of 2013 continues with clouds, clouds and more clouds. My plan to attend the Wisconsin Observers Weekend this weekend has fallen through because of weather. The first night is being clouded out as I type this, Tomorrow night is forecast to be partly cloudy (at best) and Saturday night is forecast to be rainy (50% chance) and cloudy.

Worst. Spring. Ever.

But anyway, I did manage last week to shoot some test images with my .63 Celestron Focal Reducer.  I fiddle with my adapters until I got a spacing of about 104mm (I think), and here's what I got:

Flat Field test

This is taken using a Celestron 925 XLT and Celestron 0.63 Focal Reducer/Flattener. The camera is an SBIG-ST8300M with filter wheel (total back focus 38mm). Spacing was provided by a Celestron SCT-to-T adapter #93633-A (about 58mm).

The above full-field image is six 10 second exposures (2x2 binned) aligned and stacked, then given a stretch by Images Plus. The scope was not even roughly polar aligned and was unguided. I was also shooting through overhead power lines. Yechh.

I think it's fairly flat, at least flat enough to make me happy. Some vignetting is present, but it's about the same as found when imaging without the FR. I will probably tinker with the spacing in the future.

What's nice is that this setup gives a much more solid connection between the scope and camera. I look forward to using it SHOULD THE FREAKING SKY EVER CLEAR. Really, no, I'm okay, but thanks for asking.

Messier 3 from April

One advantage of long periods of cloudy weather is the time it gives you to catch up on processing. I've had a shot of M3 sitting around for almost a month. I never processed it because it was an "end of the evening" afterthought. Low priority compared to getting my new planetary imager. Now that that's settled I took a look at it today. My first pass at processing it left it too yellow, and my in my second attempt I may have overcompensated.

Messier 3. Click image for full size.

Image details are here. 

The way things are going in terms of the weather I may not be able to resume my imaging Messier marathon project until the Wisconsin Observer's Weekend in early June.

Third Light with PGR Chameleon: Saturn

First light (5/12): I was using FlyCapture software distributed by Point Grey. The software behaved terribly, crashing repeatedly, but PG support was great in helping me to get the camera online. No .avi files were worth keeping.

Second light (5/13): Now using FireCapture software, which took some work to get going. The creator of the software is an active member of the FireCapture Yahoo group, and he responded to a question I posted almost immediately. Amazing support from both PG and FireCapture. Unfortunately, the night was really windy and the seeing was terrible. No .avi files worth keeping.

Third light (5/14--yes, three semi-clear nights in a row!): Everything was rolling, and the night was a little less windy. Seeing was still not at all good, but I did take some videos. Here's the "first light" f/20 image with my C925:

Saturn, the planet with those big bright rings

Awfully fuzzy, isn't it. And those rings look pretty shabby. Oh well, I'll blame the seeing.

And so another learning curve begins. I have a lot to learn about using FireCapture to optimize my imaging. So far Firecapture is far better than FlyCapture, Both in terms of stability and utility.

Point Grey Chameleon ready for action (clear skies?)

A long time between updates, but the weather has been incredibly awful. Clouds, Clouds, snow, Clouds.

But it was good for indoor activities like learning how to sell on eBay. My comic book sold for $300, and that along with other sales got me up to what I needed to get the Chameleon, a GSO Crayford focuser for my C925, and a nosepiece so that the Chameleon could use the focuser.

Getting the new camera to work was a brief bit of effort. The camera works well with FlyCapture software, also available from Point Grey. I made a mistake of downloading the latest beta of FlyCap, and it acted like a beta version: no video. As soon as I replaced that with the latest stable version everything worked great. The Crayford will give me zero image shift as I focus. Shift was obviously going to be a problem; the few times I tried video at f/20 it was hard to keep the target in the field of view.

Everything about Point Grey was superb. The camera was shipped via Fed Ex box in box in box; it works great, and when I wrote them asking for advice about the missing video their response was fast and professional.

Last night was the first one with the Chameleon under the stars. FlyCapture software is less than adequate, as it crashed repeatedly, and the GUI is clunky (in my opinion). I'm going to start searching for alternatives.