Are Baader filters Parfocal?

At a recent star party I made an offhand statement that I doubted that my narrowband filters were parfocal. That set me wondering if I was correct and how would I go about determining this for all my filters. So I did a little experimenting one night by imaging Betelgeuse through all my filters.

I decided to set focus with the luminosity filter in place, and then cycle through all my filters seeing if the focus changed. Sorry, but I don't have a focuser with a digital readout. To get some sense of any focal shift I put a Bahtinov mask on my scope and imaged the results. I used three stars of different spectral types (O, A, and M), just in case the results would be influenced by wavelength. (I was imaging through my TV-102, so I didn't expect to see any significant wavelength dependence.) Here is a test strip for Betelgeuse (click to see full scale image):

Betelgeuse imaged through various filter configurations with no adjustment of focus

I used 5 and 25 s exposures for the broadband and narrowband filters, respectively, and processed only using ImagesPlus digital development. It looks like the central spike produced by the mask moves little if at all as the filter is changed. As expected, the focus shifts significantly when changing to no filter in use. So how much shift is significant? Here is an image resulting from 1/12th turn of my fine-focus knob away from focus:

Appearance when defocused by about 0.3mm

This is approximately an adjustment of 0.3 mm in focus and the central Bahtinov spike has shifted quite a bit. From past imaging experience, I think my final focusing "tweaks" are about 1/5 of this in magnitude.

So are the filters (Baader LRGB and 7 to 8.5 nm Ha/S-II/O-III) parfocal? They look close to being so. To my surprise, the broadband and narrowband filter sets seem to be almost, but not quite, parfocal with each other. The results were the same for the other two stars, Sirius and Altinak. But I'll probably still refocus every time I change filters in the future, particularly when using anything less than an apochromatic telescope or there's been a change in temperature.

Photoshop Actions

I spent a little (emphasis on little) of my holiday money on the purchase of two Photoshop action packages for astrophotography. My simple goal for today was using the packages to reprocess one of my old images. Here's my original take on NGC 6781, a small planetary in Aquila. This was shot in June 2012 using H alpha and OIII narrowband filters with my ST8300M CCD and C925. This was my original "final" image:

Original Processing

I used the OIII data for both the blue and green channels, which produced a washed-out cyan in the nebula's interior. Other defects in this image include some uncorrected mild vignetting, a noisy background and almost colorless stars. Using the actions it was an easy task to generate a synthetic green channel, clean up the background, give the stars some color and pretty much obliterate the vignetting (without any flats). Wow! That's not bad for a day's work with new software. Here's the result:

Processed using actions

Not that it's perfect by any means. I think the background is too black and I've lost a lot of the dimmer stars. I'll take it as good enough for the first day of using the actions.

The two packages are Astronomy Tools ($21) and Annie's Astro Actions ($15).  There's some overlap between the packages, but they're so inexpensive that you can get both!

No More Mills Fleet Farm

Let's keep this simple.

• I want hunters to keep their hunting rifles.
• I want homeowners to keep their handguns intended for self defense. Even if it means that statistically they are more likely to be involved in handgun accidents involving their own children. They have a right to weigh the risk/benefit involved for themselves.

I see no legitimate reason for anyone not in law enforcement or the military to possess, much less use tactical weapons (semi-automatic rifles, or any weapon that allows a large number of rounds to be fired without reloading). Count in that any sort of armor-piercing or rounds designed to maximize damage to a person's body (such as soft- or hollow-point bullets). No reason at all. Personal gratification is not a legitimate reason.

Guns and Mills Fleet Farm

I love MFF. For those of you not in the Midwest area of the USA, it's a giant general store of sorts. Lots of good things at great prices. Tools, yard supplies, sporting goods, automotive items. Helpful, friendly staff. I buy my deep cycle batteries there that I use to power my Astronomy gear. Yes, we've even bought a gun case there.

Unfortunately they also sell semi-automatic rifles, tactical rifles and magazines, which is their right under the current laws. And because of that MFF and I am parting ways. I'll be shopping elsewhere until they stop selling these things. Menards and other stores will do quite well at replacing MFF. I've written MFF about this; I don't anticpate a reply.

Guns and John Kline

John Kline is a Republican and the Congressional Representative of District 2 in Minnesota. He has an "A" rating from the NRA. I've never voted for him, and quite possibly never will. I'd like to think that he's a rational man, navigating the messy world of politics by the use of his own moral compass,  and not simply beholden to the NRA and the gun culture. He will probably soon have a chance to participate in discussions about how to move away from the violent use of guns in mass murders. Independents like me will be watching closely to see what he says and does about this problem.

If you're from District 2, write to him; tell him what you think. You have the power, through him, to salvage some shred of good from the evil visited upon the children and people of Sandy Hook.

Guns and Acts of Terror

I doubt the shooters in the many recent multiple homicides see themselves as terrorists, but that is exactly what they are. After the terror attack on 911 people were afraid fly, now they are afraid to send their children to school. At what point do we draw the line against this? Are we so engrossed in our own selfishness that we can't look out for our fellow citizens? Are we so weak that a group of people (the NRA, gun manufacturers, and gun merchants) can pervert the second amendment in the name of their own greed and threaten the safety of all of us?

Many Americans fear for their own lives and the lives of their loved ones because of the profusion of weapons no one legitimately needs. That the NRA supports the distribution of these weapons in our society makes them no better than terrorists.

I thought there was a war on terror. Please don't let the terrorists win.

Afterword:

Poor Fleet Farm! They get it from both sides. I came across a gun advocate forum that was ripping FF for not letting customers carry unconcealed guns through their stores. One person was upset because he couldn't carry his rifle into and through the store to the gun counter for service. The fact that if he had done that he might be taken as an armed robber didn't seem to register with him.

On politics...

I'm going to momentarily step out of the role of amateur astronomer and comment on the election of a couple of days ago. In my state of Minnesota the Republicans got a severe thrashing, losing both houses of state government and seeing two amendments they promoted be denied. A very conservative house member was voted out after his first term, and the radical Michelle Bachmann barely won reelection to another term.

The Republican error--and a common one made by most of us these days--was inflating their own sense of moral and practical rightness. They gained control of the legislature only two years ago, selling themselves broadly as the party of jobs, and to a narrower constituency as the party of morality. The honeymoon was brief. Many of the new members were inexperienced at participating in government at a high level, and they quickly found themselves being outmaneuvered by the Democratic Governor. A sexual scandal erupted that became messy because of legal fees.
Failure to work with the Governor led to a shutdown of state government. The state Republican party outspent their resources and hardly looked like the party of fiscal responsibility. Republicans then dithered on a contentious stadium-building issue (managing to look both obstructionist and disorganized).

Republicans sealed their fate with two state constitutional amendments. The marriage = one man + one woman amendment was a slap at GLBT families, liberals, and libertarians, the latter being a significant portion of the Republican base. The voter ID amendment addressed a non problem and was perceived as oppressive and self-serving.

Republicans apparently judged themselves so popular and their mandate so large that they thought their base would carry them to any victory they sought. It worked out otherwise.

Democrats would do well to remember this lesson as they sweep back into power, lest they repeat mistakes they've made in the past. I consider myself an independent, and I hope that the Republicans can regroup around a more moderate base and continue to advance the ideals of conservatives.

HOASP, CCD Returns

It's back, and it works. SBIG contacted me after about three weeks that the problem had been diagnosed. The news was not good: both circuit boards were fried and would have to be replaced. The cost would be $695.

Ouch!

I told them to go ahead and do the repairs. My options were limited. The filter wheel and 36mm filters I use are tied to the ST-8300 and can't be easily adapted to another camera. While $700 could probably buy a used CCD, but it wouldn't be as good a camera as the 8300--and I would have to add the cost of a new filter wheel and filters to that.

A week later the 8300 came back, and it works like new so far as I can tell. The fan runs and the filter wheel aligns itself when powered up, the shutter clatters when initialized, and the cooling system cools. It's been cloudy here since the camera was returned, so all I've been able to do so far is shoot dark frames.

Two questions I asked SBIG that you may be interested in if you are an ST-8300 owner:

Q. How did the breakdown happen, and how can it be prevented in the future?

A. The camera apparently much prefers to be powered up first; always connect the 12V power before plugging the USB connection into your laptop.


Q. Even though the sensor was not replaced, do the new boards mean that I need to shoot new dark frames?

A. Probably not, but it would be a good idea to shoot some test dark frames that match the exposure time and temperature of old dark frames. If they compare well, then my flat library doesn't need to be rebuilt.

So I'm back in business, once the skies finally clear. While I'm waiting, I'm going to make myself a poor man's camera case using a Plano #761 toolbox, some foam from a craft store, a twin-blade electric carving knife and a hot glue gun. It won't be a Pelican, but it will cost about 1/4 as much. I'll post more about this micro-project when I'm finished.

The Heart of America Star Party was a viewing and imaging bust, but I had a good time, as did most of the attendees. All three nights were cloudy, and it rained pretty much from the second night through all of the third day, with a lot of lightning the second night. Severe weather was forecast for the third night so I folded my tent and stayed at the Days Inn in Butler. Fortunately the severe weather bypassed the observing area.

HOASP featured an abundance of knowledgeable and friendly people, excellent talks, great food (assembled if not made on the premises) and nightly movies to help people cope with the clouds. One vendor (Bushnell) was on site, the daily door prizes were decent (I won none). One word of advice: If you decide to play bingo, take several cards. It's a cutthroat game, bingo.

I'll definitely want to return.

Waiting Time

One week since I sent in my CCD to SBIG, and one week to go to the Heart of America Star Party 2012. I didn't expect to hear anything from SBIG this week; my impression is that the repair queue is about two weeks long. After that--in a few short days--you hear from them, they do the repair, and it's on its way back to you. So I'm guessing that I'll get it back sometime around the last week of October.

On the HOASP front, there's good and bad news. A friend who also owns an ST-8300M has agreed to loan me his for the trip. CCD imaging is back on the menu. I'm still waffling about which scope to bring, the TV102 or C925. Today, I'm favoring the TV102. Stand by.

Bad news is the weather forecast. At this time it has all three days of HOASP as showers and thunderstorms, so the whole CCD issue may very well end up moot. I've picked three targets as if there will be three nights of clear sky. The helix nebula (NGC 7293), The sculptor galaxy (NGC 253), and The foxface nebula (NGC 1788, a reflection and dark nebulae in Orion) Will any get imaged? Or will I come home having collected only mildew?

CCD Camera Goes in for Repairs

My ST-8300M began acting erratic at a star party a couple of weeks ago. I was able to pull a couple of dark frames off it when it lost contact with my laptop. Subsequent tries to reconnect all failed. Either the camera couldn't be found by the camera control software, or Windows was declaring it an unidentified USB device.

Cable swapping and driver reinstallation ensued to no good effect. It was time to consult a higher source.

I contacted SBIG and they suggested trying to use another computer. I loaded the drivers onto my desktop computer and got the same results. SBIG suggested sending in the camera for diagnosis and repair.

Two days ago I mailed it to them. I expect to hear back in a couple of weeks, and then perhaps another two weeks for repair and the return trip. Which means I'll miss the best part of autumn, and imaging from the Heart of America Star Party. Bummer.

The fallback is to rely on my DSLR for some dark-sky imaging at HOASP. I think it would be nice to do some reflection nebula imaging, perhaps the Iris?