Ultimate Lens Test, ...... and the OM 50/1.4

[3dpan]

For me, the ultimate test of a lens imaging quality is its performance photographing stars, (the ones in the night sky). Any shortcomings in coma or chromatic aberration, or just resolution become immediately obvious.

So, about a year ago, after reading rave reviews about the OM 50mm f/1.4 lens (with serial numbers > 1,100,000), I bought one thinking it would be great as a short tele for astro pix.
Well, when I tried it, at f/1.4, there was so much coma and chromatic aberration that I put the lens away in disgust. (I had just bought the ZD 11-22mm and that kept me happy instead).

Anyway, last night, with a gap in the clouds, I relented and tried the OM 50/1.4 again but this time compared f/1.4, f/2.0, and f/2.8.

Well, f/1.4 was still c..p, f/2.0 was an improvement, but f/2.8 was outstanding. Surprise,surprise !!
Here's the result at f/2.8, 400 ISO, 1 minute, on my E-500. Just tracking, not guided.

Attachment 5605

Just for interest, the pink blob towards top right is the Lagoon Nebula, the even smaller pink blob lower and to the right of that is the Trifid Nebula, The dark blob in the centre is the Pipe Nebula, because it resembles the bowl of a pipe, with the stem pointing lower left. In the southern hemisphere this is also called the head of the kiwi, with the body of the kiwi being the brighter area to the right. And just to confuse things, the pipe/kiwi head along with the other dark areas to the right are also known as the horse nebula.

Enjoy, comments welcome,
Alec

[tspore]

Wow really neat. At some point I would love to see a whole portfolio, and also how you do it. I really know nothing about shooting the stars.
Maybe a full on article?

[jebir]

That looks great Alec!

It is a bit hard to see the true qualities of the lens at this limited size image though. However, it appars as there is no point in paying a premium to get f/1.4 since you most likely will get a similar result with a late ("made in japan") OMZ 50/1.8 stopped down to f/2.8. (Have you tried that lens for stars?)

Cheers, Jens.

PS. Thanks for the guided tour of the southern night sky. I'm surprised the you see so much at only 1 minutes exposure.

[Den]

There was a bizarrre competition for fastest lenses back in those days: with enthusiasts shelling out so much money for f1.4/f1.2 in the same way they'd pay a premium on any camera that could accept a motordrive, even if they never bought one...

I've got a Nikon 50mm f1.4, but only because it was £10 more than the f1.8 I wanted. The extra fraction of a stop is worth something in some of the low-light concerts I go to, but I'd never pay serious money for it.

[PeterMG]

Wow really neat. At some point I would love to see a whole portfolio, and also how you do it. I really know nothing about shooting the stars.
Maybe a full on article?

Being in the southern hemisphere is the first step. Having been born in New Zealand and living there until moving to the UK as an adult I'm still even now amazed at how many more stars are visible in the south on a clear moonless night whenever I visit "home".

[Rick_D]

Sorry, dumb question: What's the difference between tracking and guided?

Lovely picture, whether tracked or guided.

--Rick

p.s. to Den, reasons to prefer fast lenses, along with the ability to handhold in low light situations and isolate through shallow DOF, are their ability to brighten up an SLR's viewscreen and help enable very precise focus. I have only zooms for my E-510, and dream of the day I first put on a 1.4 prime!

[3dpan]

Thanks to all for your comments,

Tony, there is a Yahoo Group called Olympus Digital SLR Astrophotography, though there are times when there is not much traffic on it. I have a photo folder there under 3Dpan,
http://tech.ph.groups.yahoo.com/grou...os/browse/8562
(but I don't know if the link will work if you're not a member).
It could be just as useful if I, or anyone else, post the occasional photo here and answer any questions that it generates.

Jens, the most important reason for choosing f/1.4 (or even f/1.2) is to get enough light for focusing. I only just manage to focus on Jupiter at f/1.4, and f/1.8 would be even more difficult. Which brings up another advantage of Live View, focussing for astro pics.
So that's why I never considered the 50/1.8, and it didn't rate as highly in the published tests that I read either.

PeterMG, I didn't appreciate the number of stars in the sky until I moved to a dark sky site, albeit fighting with fog and cloud now.

Rick, "tracking" means just having a motorised tripod head which tracks across the sky at the same speed as the stars.
"Guiding" means superimposing a system of locking onto a star and making any corrections to the basic tracking, so the star stays precisely in the same place in the viewfinder. Essential at longer focal lengths/longer exposures for photography.
There is Manual Guiding where you glue your eye to an eyepiece on a separate telescope and use manual adjustments to keep a star centred in crosshairs, while the camera is making an exposure.
And there is Auto-Guiding where a separate camera (like a webcam) takes a stream of pictures through a separate lens/telescope and feeds them to a computer program, which then analyses any drift in the guide star and issues correction commands to the tracking mount motors. Can be tricky to set up but worth its weight in gold.
With auto-guiding working correctly I can set the imaging camera (E-500 etc) to an 8 min exposure + noise reduction, and go back inside for a quarter hour to warm up/watch tele/wash dishes/etc.

Cheers,
Alec

[PeterMG]

Thanks to all for your comments,


PeterMG, I didn't appreciate the number of stars in the sky until I moved to a dark sky site, albeit fighting with fog and cloud now.


Cheers,
Alec

Alec I grew up on the eastern side of Rotorua in the 60s and 70s. I can still remember them putting up the street lighting and spoiling the view, but up to that point it was very dark, especially with no moon.

For anyone that is remotely interested in the stars and lives in the North and visits the south it seems like there are a thousand times as many stars as up here. And the predominantly pollution free air help with low horizon views. I particularly like The Large Magellanic Cloud and was once lucky enough to look at through a telescope. I must say though that the photos that are obtained with digital are way beyond anything I can recall from 30 years ago.

[3dpan]

Just some miscellaneous information about the number of stars out there.

It is calculated that in the known Universe there are about ten stars for each grain of sand on the earth's beaches.
Refer,
http://answers.google.com/answers/threadview?id=539329

Cheers,
Alec

[jebir]

It is calculated that in the known Universe there are about ten stars for each grain of sand on the earth's beaches.

How large fraction of them are located on the southern sky then?

No, seriously: are there really more stars visible on the sky of the southern than the northern hemisphere? Or ist it just a matter of different amounts of urban areas creating air and light pollution?

Cheers, Jens.

[acme]

No, seriously: are there really more stars visible on the sky of the southern than the northern hemisphere? Or ist it just a matter of different amounts of urban areas creating air and light pollution?

Cheers, Jens.

The bulk of the core of the milky way, our local galaxy, as well as the magellanic clouds, dwarf galaxies that are nearly merged with it, are, at present, located in the southern celestial hemisphere (as viewed from Earth), and therefore the densest, brightest starfields are best viewed from locations south of the equator. The most impressive globular cluster and nebulae also remain well below the horizon for most northern stargazers. OTOH, there is no bright southern star so conveniently located as Polaris is in the north, so it's likely that early southern navigators had to pay more attention to the yearly constellations than northerners did.

Here's a link to Axel Mellinger's great and early all sky mosaic, and a hotlink to its product, which so starkly shows the difference. HTH!

[3dpan]

Jens,

As acme pointed out, the Milky Way represents the centre of our galaxy. Or, another way, when we look at the Milky Way, we are looking at the densest distribution of stars. And my image, above, is near the core of our galaxy. The reason there don't seem to be so many stars is that they are partly obscured by the dark dust clouds.

If at some time of the year you can see the Milky Way, then you are looking at the densest area of stars.
Currently, the core of the Milky Way is overhead for me.

I would say pollution will be limiting your view of the stars, whether light pollution or atmospheric pollution, (dust etc).

See this map for an idea of global light pollution,

Attachment 5613

Cheers,
Alec

[3dpan]

acme, that's a neat mosaic from Axel Mellinger. On the left edge of the right hand circle you can pick out my image (above), although upside-down.

And Rick, if you didn't already find it, see my earlier post about the difference between tracking and guiding.

Cheers,
Alec

[jebir]

Hi Alec,

I can esily see the milky way in the winter. What I didn't realize immediately was that we, in the north, are looking out towards our galaxie's 'perimeter' while you have the benefit of looking across its center.

Cheers, Jens.

[3dpan]

Sorry Jens,

I can't be sure about that, maybe someone with more global wisdom can confirm or otherwise, but I suspect at some time of the year you would be looking at the galaxy core, maybe just not now.
I don't get the same view of the Milky Way all year round.

Cheers,
Alec

[marcof]

I love those wide-field astro photos.
I've recently picked up the hobby again, after 5+ years of inactivity. Apart from my eyepieces and camera adaptors I have to re-purchase everything... (on the bright side.. technology has improved and become cheaper as well).

I was so bold to ask olympus europa of the possibility of "built to order" E410 cameras for astrophotography. unfortunately, they didn't even consider this a viable option (unlike canon in japan..) oh well, we have our own possible source of modifications ;-)

[ebw343]

The view of the milky way is dependent on the season first and the latitude of the observer second.

In the northern summer / southern winter the nighttime view (say around midnight locally) is looking inwards towards the centre of the galaxy. The centre is found in the constellation Sagittarius. The latitude effect means that for mid-northern viewers - such as us poor Brits - the centre is low on the horizon at best and a lot of the best views are below the local horizon. In the south, say Aus, NZ, SA that part of the sky is directly overhead at the same time of year and thus the view is much much better. However part of the Milky Way does pass overhead in the north through Cygnus and the view is pretty good if you have dark skies.

In the northern winter, southern summer we look outwards (with our backs to the centre) along the plane of the galaxy with the Milky Way passing near to Orion. Again this is low to the horizon at mid-northern latitudes and high above in the south.

During spring/autumn (both seasons for both hemispheres) the late evening view is perpendicular to the plane of the galaxy, so no Milky Way overhead anywhere and we look out at other galaxies instead.

Overall the south wins out with the best parts of the sky overhead plus lower light and chemical pollution due to the lower population density.

The saying goes that God put all of the best of the night sky in the south, and all of the Astronomers in the North!

Finally. Thank you Alec for posting that superb shot. It demonstrates a great deal of skill (and practice no doubt) notwithstanding your location.

[Rick_D]

Thanks Alec! Duly noted; my tiny brain is now busy interpreting it (IIUC the camera has to be able to follow using three axes of motion, not just two, for longish exposure times).

-Rick

acme, that's a neat mosaic from Axel Mellinger. On the left edge of the right hand circle you can pick out my image (above), although upside-down.

And Rick, if you didn't already find it, see my earlier post about the difference between tracking and guiding.

Cheers,
Alec

[PeterMG]

I was so bold to ask olympus europa of the possibility of "built to order" E410 cameras for astrophotography. unfortunately, they didn't even consider this a viable option (unlike canon in japan..) oh well, we have our own possible source of modifications ;-)

That is strange when they put a full page advert for the E400 in the BBC Sky at Night magazine. Strange bods marketing executives.

[3dpan]

Rick,

There are only two axes being corrected with the guide program, so I'm not sure which is the third you are referring to.

There are two types of mounts, Alt-Az, and Equatorial.

Alt-Az is like a pan-and-tilt head with the pan axis vertical.
So to find a star you pan around to the correct bearing, (the azimuth, somewhere between 0-360 degrees), and then tilt up, (the altitude, between 0-90 degrees). This type of mount is used most commonly on telescopes for visual observing, and with the computerised "Go To" program. Once you find a star that way, because its position in the eyepiece is not critical for visual observing, then simple hand controls are sufficient to tweak its position. Not so convenient for autoguiding programs though.

The Equatorial mount is like a pan-and-tilt head with the tilt axis in line with the celestial poles. A bit harder to set up, but much simpler to operate, and to guide with. On a tracking (equatorial) mount there is just one motor driving the tilt axis, at the same speed as the stars. The other axis (pan) is used only for minor corrections. And for short exposures and medium to wide angle lenses there is not usually any correction needed, (depending on the accuracy of your polar alignment).
For an Equatorial mount a guiding program will issue correction commands to the two axes, and is a "relatively" simple program.

Here endeth the lesson for today, hope it clears some confusion.

Cheers,
Alec

[3dpan]

ebw343,

Thanks for that explanation, I was trying to imagine the path/rotation/tilt of the earth through the seasons, relative to the Milky Way, and I got very lost.

And to obtain pics like that seems to require perseverance and a tolerance to cold, as much as skill/practice.
That picture was my third night of dodging showers and trying to point the camera in the right direction, and even then I got just two images to stack.

On the fourth night I managed to correct the framing and get five images to stack, then it rained.
And here is the result of the fourth night, a stack of five frames, which improves the signal/noise and makes the "kiwi" a bit more discernible.

Attachment 5620

Cheers,
Alec

[acme]

I was trying to imagine the path/rotation/tilt of the earth through the seasons, relative to the Milky Way, and I got very lost.

It might be easier for northerners, since we only only have reasonable hours for viewing of sagittarius for a few months a year. At a high latitude, waiting for much of the interesting stuff to creep above the horizon tends to imprint the position of the celestial equator, and how far "below" it one can see, fairly deeply in ones mind!