(Viewed 885 times)

[martyn2005]

Hi All,

I tried some very basic Astrophotography last week and wasn't very impressed with the results and I wondered if anyone had any tips or advice as to improvement.

My equipment was a Canon AE-1 camera with a 50mm lens on a tripod loaded with colour print 400ASA film. I had read a few articles in books and particularly a 'beginners' feature in Sky and Telescope magazine and felt confident that my equipment was fairly adequate for the job - at least for pictures of constellations and wide field views etc.

Whilst I'm still in the dark about many aspects of astronomy I used to work as a professional photographer and so was confident about the cameras use.

I used an F setting of 1.2 and focused the camera to infinity. Then I just picked some constellations and bracketed exposures of 25 seconds and then a second of 50 secs for each shot. I thought that both of these times would prevent star trail and for the most part they did but instead of the dark skies that I was seeing the prints came back looking like late afternoon skies! It was weird. I could see the stars I had pictured but the amount of light let into the pics was crippling.

On a plus point the 50 second exposures pulled out some detail of the milky way and some colour variations in the stars.

So heres my question - how do I make the sky black AND allow enough light in to pull out the constellations properly. Everything I had read said that exposures of at least 20 seconds with my type of equipment would be necessary.

Tips please! ;D

Martyn

[Chicago Astronomer - Astro Joe]

Martyn, I can totally sympathize with you.

As a kid, I used to take many star trail shots with my trusty bellows camera. Good results, as I only used black and white film.

When I got my 35mm SLR, I was eager to reproduce the shots, but in color. Man...was I quite disappointed!

I got what you are getting, a daylight sky in the middle of the night. I discovered it's a balance of exposure, film speed and aperture settings. Now you got to play and experiment with different combos...

What you are getting is the ambient light pollution that invades our skies. When leaving the shutter open, it's collecting all that pollution gunk..washing out a dark sky. What I have done is two extremes...

First, I used a fast film speed, 800/1200 ASA and a quicker exposure...oh 5 seconds to 10 seconds. It varies. Then I used a much slower speed, 100 ASA, open the iris all the way and a longer exposure time, 1 minute or so.

Now with a higher mm of lens (70-100mm +), it will darken the sky somewhat and increase the contrast, and ergo...a darker sky in the shot. The same can be said of the f-stops. Normally we would want to open it up all the way to gather as much light as possible, but again with the light pollution, it invades our shots. Try stopping down some to block out the LP, and allow the starshine to pierce thru, they should be bright enough to overcome the smaller iris. Time again is a factor, leave the exposure a a bit longer...say a second or two. A lot of variables to consider, but city astrophotography isn't easy.

I haven't played with film astrophotography in over 20 years, and this is all from memory. The old brain cells still work!....amazing... ;D

Not one method works all the time, as sky conditions vary with clarity, transparency and airborne gunk.

Now, I have seen C.A. Bill's astro photos of the night sky while piggybacked on his scope with excellent results. Perhaps he can share his techniques. They are very good.

Let us know of your results!

[jglover]

martyn2005 said:

I used an F setting of 1.2 and focused the camera to infinity. Then I just picked some constellations and bracketed exposures of 25 seconds and then a second of 50 secs for each shot. I thought that both of these times would prevent star trail and for the most part they did but

Hi Martyn,

With a 50mm lens, stars will start to trail at about 30-40 seconds exposure. A 28mm lens will give you about a minute, while a 100mm lens will cut that time to 10-15 seconds. You have to remember, the stars are moving and telephotos not only magnify the sky, they magnify the motion. Start here:

home.hiwaay.net/~krcool/Astro/asthwto/TriAst.htm

This goves you a good overview and has a bunch of decent links to help you get started.

As far as the washed out skies go, it is almost certainly the printers fault. If the prints were done on an automatic printer, the machine will see all that black sky and assumed you have severley underexposed the photo, so it will compensate by trying to lighten the overall exposure. Constellation portraits will almost have to be hand print. You need to let the photofinisher know these are images with lots of dark sky and that they will need to override the machine settings and adjust the first print manually, by dialing in some more density to the negative. They will need to set the machine to print all the subsequent photos with these custom settings and not let the machine decide. I had the same problem with some photos i took of both Comet Hale-Bopp and Hyakutake. The skies were washed out and a greenish-orange....just plain ugly. I took the photos back and told them to print it for black skies and the images were fine. But I had to make a point to tell them every time I brought in astrophotos to add the density.

I used a one hour minilab in a mall. i was *never* able to get a major markey photofinisher like a Walgreen's or K-mart to do a decent job. Their operators had no clue as to how to override the machine's auto settings.

[martyn2005]

Dear Joe and John,

Thanks for your comments guys.

Joe: We started to chat on Friday about this and you had some great advice about changing the speeds of the film and experimenting with exposure time. I think the standard technique of frame to frame bracketing may have to be changed to film to film!

John: You are spot on about the printing. i went CVS as it was only a test film and I even asked them to print everything as they were astronomical photos but they didn't . I'm sure that they also didn't know how to overide their machine. I only got 12 prints back from a 24 exposure roll so that was disappointing, I may try switching to a camera store or lab next time.

I think a combination of a faster film and shorter exposure time next time and I'll let you know the results!

By the way the site I used was west on 290/88 near DeKalb. I exited on Peace Road and turned left over the bridge. I then found myself in farm country so I set up by a dirt track in between two corn fields - great views and dark skies (or so i thought at the time! ;D)

Thanks again for your help, see you soon.
Martyn

[atomant]

Astrophotography from the city is tough

Here are a few samples using a 3.2MP digital camera and a manual 35mm SLR:


Orion and Sirius from city
2 sec exposure
Nikon 3.2MP on EQ mount


Subaru from city
2 sec exposure
Nikon 3.2MP thru 90mm refractor with 25mm Plossl eyepiece


Lyra from city
5 min exposure
Vivitar 35mm SLR with Fuji 200 color film on EQ mount
F3.5 at 70mm
processed by local drugstore chain


Sagittarius from city
5 min exposure
Vivitar 35mm SLR with Fuji 200 color film on EQ mount
F3.5 at 70mm
processed by local drugstore chain

my piggyback experience started with this surprise in 2002 [nothing has come close to this nirvana]


Sagittarius from Texas Star Party
20min exposure
Vivitar 35mm SLR with Fuji 200 color film on GM8 EQ mount
F3.5 at 70mm
processed at a Walmart!??!
[That dark vignette on left was caused by my refractor tube]

Clear skies,

[Chicago Astronomer - Astro Joe]

Bill,

I always smile when you show me your astrophotos, and even tho difficult, it still is quite possible to get cool shots like you have.

All great stuff, I wish I could accomplish the same.

[atomant]

Hey Joe,

Anything to inspire the next generation of city astronomers. We can't let light pollution defeat us.

Anyhow, the coffee is wearing off. Goodnight!