Olympus 200mm Lens for Astrophotography

If you'd like to do some wide-field astronomy with a SLR lens and don't have a DSLR, it's possible to mount the lens on your CCD. The particulars of mounting vary from camera to camera. Some of the adapters can be relatively expensive, but adequate lenses are well within the reach of the low-budget imager.

In my case I have an SBIG ST-8300M camera with a filter wheel. SBIG sells a Canon lens adapter for about $300 that mounts on the filter wheel (a spacer is needed if you don't have the wheel). This opens up the possibility of imaging with any other lens that can be used with canon EOS cameras.One such lens is the Olympus OM lens type. An adapter is needed to mate an OM lens with the SBIG canon adapter. (Yes, two adapters are needed between the lens and filter wheel.)

I've already imaged with an old 135mm Tamron lens that lived its previous life on my OM-1 SLR. Given the good images that lens produced I shopped around for a fixed 200mm lens.

What I found was a used Olympus AUTO-T E-Zuiko f/4 200mm lens at a local camera shop. These sell on eBay for about $50.

Olympus E-Zuiko AUTO-T 200mm f/4.0 with lens shade retracted. Image by Jone Quinn

Technical information about this lens can be found here. Why 200mm? It plugs a focal length hole between my 135mm lens and AT65 (422mm). Yes, I'm actually buying telescopes and lenses partly on the basis of their fit to a trend line. See how neatly the 200mm fits in in the chart below?

Everyone uses a semi-log chart for choosing imaging telescopes, right?

This lens is semi-automatic; it is wide open until the shutter opens and the camera tells it to stop down. There's no way to handle this with the CCD, so I inserted a plastic wedge into the lens base to keep the iris stopped down to the dial setting.

Last night I took a few images just to see how it well it would serve for astrophotography. My concerns were if it could focus infinity properly (which isn't a given thanks to those adapters) and how far itwould need to be stopped down to get reasonable stars across the field.

It reaches focus if you put the "3" of the 30m mark over the left index line for f/16. In other words, infinite focus is at about 35m.

And field flatness? It's very good for a $50 price point. Here's a full-frame bias-calibrated and stretched luminance images from last night, first at f/5.6:

f 5.6

and next at f/4 (same exposure and processing):

f/4

Vignetting can be handled with flat frames, and the stars are decent at f/5.6, a little less so at f/4 (although some of this is probably star bloat from processing). This shouldn't be a surprise as this is a fixed focal length lens designed to illuminate 35mm format cameras. The KAF-8300 sensor size is about half that, so it avoids the worst of the off-axis distortions.

For ALBN imaging f/4 is perfectly adequate. For "pretty pictures" I'll probably used f/5.6.

When used with the ST-8300, the 200mm lens gives a 3.9 x 5.1 degree FOV, a nice size for some remaining ALBN objects, either singly or in combination. (My last post lists my planned targets for this lens.)

Map To 100 ALBNs

It's time to plan out the rest of the imaging needed to complete the ALBN. At this point it's looking quite likely that I'll be able to finish my 100 objects this year, thanks mainly to March cooperating and allowing eight objects to be completed.

The table below suggests there are 19 reasonably accessible objects to be had between now and September. Thanks to using short focal lengths they can be all be captured in 13 images. The two camera lenses will acount for nine objects in five images, with the remainder split between the AT65 and TV102.

If I finish or be close to it by mid-July I'll be free to use a possible trip to the Nebraska Star Party for creating pretty LRGB images instead of going after one of the faint ALBNs.

April (4 / 91)
Object	LBN brightness	Imager
LBN 1088	5	200mm
LBN 1089 LBN 1090	5 5	135mm
Sh 2-210	5	TV102
May-June (9 / 100)
Object	LBN brightness	Imager
LBN 11 LBN 10 LBN 8 LBN 1122	5 6 6 4	135mm
Sh 2-13 Sh 2-12	4? 4	200mm
NGC 6357	4?	AT65 or TV102
LBN 20 LBN 22	4 5	TV102 or AT65
June-July (5 / 105)
Object	LBN brightness	Imager
LBN 70	6	200mm
IC 4701 LBN 52	4 2	AT65
IC 4812 NGC 6729	? ?	AT65
August-September (2 / 107)
Object	LBN brightness	Imager
LBN 140	6	AT65
LBN 434	6	AT65

We've finally gotten some snow and the ground is again white. This means that Cherry Grove is not really suitable for use for a while. The snow needs to melt and the field needs some time to dry; it will probably be ready again around Easter. Until then I'll be working from my back yard and will be limited to narrowband.

Tonight is forecast to be clear, so I'll be able to test the 200mm at long last.

If you have the feeling I want to be done with the ALBN, you are correct.

EDIT: Looking for a backyard target on 3/29 I discovered that SkyTools3 has incorrect coordinates for LBN 10. This object is actually part of the LBN 8/11/1122 area. All four objects are a slightly better fit in the 135mm field oriented N-S, so I've changed the table to show this. I'm going to check the coordinates of all the table's objects against the SIMBAD database.

Messier Marathon Night

The MM was something of a bust this year. Instead of bitter wind chills or an observing field buried under a foot of snow, conditions were actually quite pleasant. But there were those clouds. Patches of opaque clouds gave way shortly after nightfall to a succession of semitransparent bands that simply wouldn't stop obscuring large chunks of the sky. For the most part I could shoot through the clouds, but visual observers were shut out of all but open clusters and the brightest nebulae and galaxies. 

Seeing was suggested to be poor, too. And then there was the wind. Southerly and modest at first, as a cold front passes they turned and gusted to almost 30 miles per hour. My autoguider struggled but held its own against this for the most part--a few frames had to be dropped because of poor tracking. 

I started the evening with thoughts of doing some MM work myself, but conditions ended that possibility. Instead I concentrated on imaging the brighter winter objects of the ALBN. 

The updated winter list (earlier images in green, MM night objects in red):

January: IC 2169, LBN 943, Sh 2-280, NGC 2296, IC 468, NGC 2359
February:
November: IC 360, NGC 1555, NGC 1579
December: LBN 945, NGC 1931, Sh 2-264, NGC 1999, Sh 2-240, LBN 962, NGC 2149, NGC 2174, IC 2162

This is the end of any chance to get more winter objects unless the skies clear quickly. Still, this winter netted eleven objects, leaving me at an ALBN list count of 87 done, 13 to go. Next up are some large LBNs that will test my still unused 200mm Olympus lens. LBN 1088 (200mm); a combo shot of LBN 1089 and 1090 (135mm), then another 200mm combo of LBNs 89 and 90.

From MM night, all taken using a TV-102, ST-8300M camera shooting luminance frames:

A combo image, the Cone and Hubble's Variable Nebula--

Cone and Hubble's Variable Nebulae

The effect of clouds is evident around 15 Mon (the bright star at top of image). Despite that the cone and Hubble are evident. Next is the Monkey Head--

NGC 2174 (Monkey Head)

Can't see the "Monkey?" It's more evident when shown south-upward instead of north-up as in this image. Some clouds here, too; the glow around 68 Ori (at lower left) is theirs.

Last, NGC 1931 (which is nameless, so far as I know)--

NGC 1931

Still some cloud effects. This deserved a longer focal length, but I wasn't about to swap telescopes at midnight at a remote site. An eventual overcast forced me to stop this sooner than I wanted.

I packed up and left the field at 1:23. I was the last to leave, which tells you what sort of MM it was. A nice get-together, a good no-pressure night for some of the club's beginners, some so-so imaging, and a spectacular fireball that lit up the sky. All of which were better than a -25F wind chill.

Imaging a Dwarf Planet

Did you know that many of the dwarf planets are bright enough to image? Here are some current magnitudes (and distances from the Sun in AU):

• Pluto: 14.2 (33.2)
• Makemake: 16.9 (51.5)
• Haumea: 17.2 (49.9)
• Eris: 18.7 (97.2)
• Quaoar: 18.9 (43.0)
• Orcus: 19.1 (47.1)
• (120178) 2003 OP32: 20.0 (42.9)
• (84922) 2003 VS2: 20.0 (36.7)

There are more, but they grow progressively dimmer. 

From my red zone skies I can get down to about 20th magnitude with an hour's total luminance exposure through my C 925 and ST-8300M. Doubtless you can do better if your skies are darker or your scope is larger.

I became interested in these thanks to the AL Bright Nebula list. The list has seasonal dead spots when combined with my tree-infested back yard.Right now I can catch a few of the lingering winter objects but there's a wait for summer's objects; after 11 here there's almost nothing to image until dawn. I noticed that Makemake fits nicely into that gap so I went after it. I captured it on the 10th and again on the 13th:

At magnitude 16.9 it shows up easily in the stacked frames (each of the images represent about an hour's worth of 2-minute luminance exposures.) The lighter background on the second image comes from clouds that night. It was a good thing I got that image when I did--clouds have been the rule since then.

Imaging objects like this tests your skill. You may need to shoot test frames to reveal very dim field stars in order to confirm that you have the right area. Even if you have great confidence in your go-to I suggest that you shoot some test frames and compare what you get with computer charts to be sure you're on target. In the test frames i relied on 12th magnitude stars that showed up in 10-second exposures.

Remember that if you want to confirm that you're looking at a Solar System body you'll have to image it twice. Consecutive nights are best, but we all know about the weather. I was lucky to get two clear nights in close proximity.

Haumea is next for me--it's a spring object. Then Quaoar during the summer and Eris in the late fall.

Three Months Later: Winter Imaging

At the end of November I listed the targets that might get me to the goal of 100 ALBN images. These were mainly the brightest objects that remained on the list. Quite a few were during the winter months, and I despaired that a bad winter would prolong this project. In the winter of 2013-2014 I did no imaging at all. I really needed to get at least seven objects off the list or face another winter of ALBN imaging. So how did things turn out?

Here's the list I drew up, with newly acquired objects in bold green:

January: IC 2169, LBN 943, Sh 2-280, NGC 2296, IC 468, NGC 2359
February:
November: IC 360, NGC 1555, NGC 1579
December: LBN 945, NGC 1931, Sh 2-264, NGC 1999, Sh 2-240, LBN 962, NGC 2149, NGC 2174, IC 2162

Sometimes all it takes is a good night once in a while. One night in January produced three objects (LBN 962, NGC 1999, Sh 2-240); a night in February gave Sh 2-264, and this week a couple of nights have given NGC 2359, IC 468, and IC 2162. Add one more object that was found on an existing image of the Rosette Nebula. That's eight winter objects. (Updated 3/14: IC 2169 makes it nine.)

There's something of a gap now between the fading objects in the winter Milky Way and those of the summer. If I can get a couple of clear nights between now and the first quarter moon I can probably pick up a few more before they're lost to the brightness of dusk.

Next time: Imaging a dwarf planet!

Global Warming

No, I'm not putting that title on this entry just to garner some hits. I'm writing this because of a fine interview article that appeared today in a local online news source, MinnPost. The interview was with Paul Douglas, a nationally known entrepreneur, weather expert, broadcast meteorologist--and conservative.

For years I taught an intro meteorology class at a local college, and my message to the students was always much the same as Douglas's: AGW is real and represents both challenges and rewards to those savvy enough to help society cope with the coming changes. Both sides of the political debate have stepped away from reality; some conservatives continue to deny and denigrate the science, while some liberals refuse to accept possible solutions.

Both sides strut their ignorance (feigned or real) by using weather events to deny or confirm their beliefs. For some trolls every cold snap is an opportunity to scoff at the reality of AGW, while for others every heat wave or drought is an excuse to trumpet what they see as the impending "heat death" of the planet.

The reality is both simpler and more complex at the same time.

In the no-brainer category: Significant atmospheric warming, sea level rise, and oceanic PH change are all happening now. Very likely on the way are shifts in local climate causing changes in rainfall, growing seasons, and availability of water. Things that are not so clear: Stronger storms, hurricanes, droughts, floods, heat waves. A great deal of work remains to be done to understand some of the side effects of AGW.

Back in the mid 1990's I told my classes that AGW wouldn't be accepted by the American public until around 2030. The current dysfunctional political climate leads me to think that statement remains about right.

I have no ax to grind on this issue. I no longer teach, so I'm not under any pressure to promote the company line. (I never was, actually.) I have no children or grandchildren who may be impacted by AGW. My days of chasing atmospheric science research funding from the National Science Foundation and NASA are far in the past. I don't sell educational, weather-related software any more, so I have no customers to keep happy.

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Back to the usual stuff: Astronomy! Tonight looks like it might be the last below-zero night of the winter. After this the forecast is for a run of days warming to almost 50 next week! What little snow we have on the ground (and it's not much) will disappear in the next 10 days, well in advance of the Messier Marathon. With a little luck (and I've used that phrase too many times lately) I may be able to pick up some straggler winter Bright Nebulae images. If that happens I have a real chance of completing the 100 this year (I'm currently at 79). Last time I mentioned a good night was about to happen. It did, and I got #79:

Sh 2-264

This is the big Sharpless object at the head of Orion. I only got two hours of Ha under red zone + first quarter moon skies, so it's kind of ratty. I love the big field of the 135mm Tamron lens, almost 5.7 by 7.6 degrees in this image!

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I'm now working on a gradient removal program that makes use of some of the meteorological code I created for some of the educational software mentioned above. (In some ways vignetting and light pollution gradients resemble atmospheric pressure fields.) This program is still in its infancy, so there's nothing to show at this point.