Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-25-2014, 05:41 PM   #1
New Member




Join Date: Sep 2014
Location: Oregon
Posts: 9
Wanting to take astrophotography pictures

I want to experiment with taking pictures of stars. The more threads I've read about it the more confusing to me it has become. ex: Some will say set your f-stop high or low. Iso at 400 or 3200. You have to have a minimum of a 28mm lens or smaller. The 500 rule.
Here's my setup. Pentax k50, 18-135 lens, 50 1.8 lens. Sturdy tripod, remote controller, extra batteries, hot cocoa and a confused brain on how to start. I was hoping someone will lend me their knowledge on the basic settings to get started. Also the location where I will be at has very little light pollution. I know the lenses aren't ideal but I just want to dip my toes in the water without Megashark scaring me away -Michael

09-25-2014, 06:23 PM   #2
Loyal Site Supporter




Join Date: Jun 2009
Location: Tumbleweed, Arizona
Photos: Gallery | Albums
Posts: 5,091
Evening,

Well, here is what I do. The Earth rotates, making the stars appear to move. So, you can take two approaches: Star trails - aim the camera up and open up the shutter for a while. The second approach is shooting stars - like the Milky Way. In this case you don't want to have star trails, and that is the 500 rule. 500/the focal length of the lens = the number of seconds to leave your shutter open. So for your 18mm lens (500/18=27 second exposure). For your 50mm lens (500/50=10 second exposure).

In both cases, you are going to need to have a high ISO 1600, 3200, perhaps 6400. The higher the ISO, the more sensitive to light the sensor will be. For your 18mm lens at wide open (f4 I think) I would probably try both 3200 and 6400. For the 50mm @ f1.8 I would go with 1600 and perhaps 3200. The reason for the difference is that of the aperture wide open - one at f4 while the other is f1.8 - its a big difference.

The lens - 18mm for a wide field, like the Milky Way, 50mm for some tighter shots of stuff in the sky. The 50mm will do better with the f1.8 aperture. The 18-135 is a slower lens with something like a f4 aperture. You are going to want to shoot wide open - so as to capture as much light as possible.

You are going to have to do some experimentation to see what works best for your and your location. You want to shoot without any moon - like tonight. The New Moon was last weekend so its still pretty small. You want to use something like this web site to see what the Moon is doing. The darker the location the better. You can find some dark locations at the following maps....I was going to say that you are going to want to shoot on either Manual or Bulb, but your shutter speeds will be less than 30 seconds (for no star trails). For star trails you will want to use Bulb - since you are going to be shooting for minutes to get some trailing.

The best thing to do is to go out and give it a try. Also, a couple of good flashlights and a folding chair helps.


Last edited by interested_observer; 09-25-2014 at 06:30 PM.
09-25-2014, 07:04 PM   #3
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,068
I believe the 500 rule is for focal lengths on a 35mm format camera. An APS-C camera is seeing stars move through its field of view on an 18mm much like a FF camera sees them move in a 28mm lens. I'd take that into account.

And for where I live, if that is a factor in the 500 rule at all, you need to add a safety factor to that rule too. That rule has produced too much star trail for me so I use a shorter time.

Last edited by tuco; 09-25-2014 at 07:09 PM.
09-25-2014, 11:12 PM   #4
Site Supporter




Join Date: Aug 2014
Posts: 395
Here is one I took before reading any of the rules of astrophotography. I just put the camera out for a 30 second exposure at the widest aperture the kit lens would allow and then upped the exposure in lightroom afterwards. I will definitely have to try these rules tomorrow night and see how they work. I'm going out shooting with a friend tomorrow.



Definitely some star trail action here, but I was at ISO 100 to avoid noise. Still a beginner, so there is a lot for me to try!

09-25-2014, 11:46 PM   #5
Junior Member
nicomis's Avatar

Join Date: Oct 2013
Photos: Gallery | Albums
Posts: 41
QuoteOriginally posted by tuco Quote
I believe the 500 rule is for focal lengths on a 35mm format camera. An APS-C camera is seeing stars move through its field of view on an 18mm much like a FF camera sees them move in a 28mm lens. I'd take that into account.

And for where I live, if that is a factor in the 500 rule at all, you need to add a safety factor to that rule too. That rule has produced too much star trail for me so I use a shorter time.
For my night shots I follow the rule of the 500 in this way: 500/focal lenght/crop factor.
This is a shot taken a few nights ago @ 18mm
So: 500/18/1.5= 18secs
these are the settings I used: ISO 4000, 20 sec, f 3,5 (maybe 15 secs would have been a better choiche to avoid the little trails you can see in the bottom right)

Waiting for a wide angle lens, that would help me a lot



---------- Post added 26th Sep 2014 at 09:20 ----------

I think that there's not so much differece in using a 18 mm f 3.5 and a 50mm 1.8 lenses when photographing the stars.

Here's my calculation (I hope to get it right):
Diaphram = f/3.5 - f/1.8 = 2 stops difference

Secure TIMES
18mm = 500/18/1.5 => 18 sec
50mm = 500/50/1.5 => 7 sec

Times = 7sec - 18sec = about 1+1/3 stop difference

So 50mm (@ f/1.8 - 7 sec) is about 2/3 stop faster than 18mm (@ f/3.5 - 18 sec) for shooting stars without trails.
2/3 stop in ISO scale is the difference between ISO 3200 and 5000, and it's a significative difference!!!

However I'think that 50mm is too long for landscapes with stars but could be useful in some cases!

Last edited by nicomis; 09-26-2014 at 12:27 AM.
09-26-2014, 05:46 AM   #6
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,068
I also believe the 500 rule is for focal lengths under 50mm which is 35mm on an APS-C camera.
09-26-2014, 06:13 AM - 1 Like   #7
Pentaxian




Join Date: Jan 2011
Location: New York
Posts: 3,248
A good way to learn astrophotography is read first, which you've done, then experiment. Try the 18-135 first because wider is easier. Initial settings 18mm, 20 sec, wide open (f3.5 on that lens I think), ISO 1600. Experiment with ISO and shutter speed to see what you get.

I shoot in raw+jpg for astro. The jpg gives an initial idea of what's in the image, and if it looks promising then I do a lot of work on the raw to bring out Milky Way details. Astro is as much about processing as it is about image capture.

Good luck. Astro is one of the most technical photographic pursuits and I still don't know if it's fun or frustrating
09-26-2014, 09:18 AM   #8
Veteran Member
Kendigitize's Avatar

Join Date: Apr 2013
Photos: Gallery
Posts: 316
The 50mm would be a good lens to experiment with since it's faster and will give you some good results right off. I have the 18-135, but for me it's hard to focus at night, an I just don't like the results. Maybe it's my copy. I get better results with my 18-55 kit lens at F4, 15sec, iso800. Here's a shot of the Persieds from last month and the Milky Way a few months ago


09-27-2014, 12:26 PM   #9
New Member




Join Date: Sep 2014
Location: Oregon
Posts: 9
Original Poster
Thanks for all the informative help everyone. Did a quick camping trip last night and experimented with some shots. While waiting on an exposure shot, I heard a loud sound right next to me as if someone threw a boulder into the lake. Made me jump 5 feet back almost knocking over the tripod. There was no one else around. Just my lonesome self. Grabbed a flashlight and tiptoed towards the sound of the direction. Peering around a bush, it was a beaver. The sucker did not look happy. Came to a conclusion that the beaver must have slapped its tail to warn me off. Didn't have enough time to get a picture of it.
Anyways I ended up with some great shots. My fiancee liked the frame shot of this one, and wanted to get it printed. [IMG]<a href="https://www.flickr.com/photos/77722650@N06/15371739582" title="IMGP0981 by BuddhaRockin, on Flickr"><img src="https://farm3.staticflickr.com/2945/15371739582_42024516e1_s.jpg" width="75" height="75" alt="IMGP0981"></a>[/IMG]
I don't like how dark it turned out. Tried my best with lightroom and ended up with this. <a href="https://www.flickr.com/photos/77722650@N06/15368880661" title="mthood by BuddhaRockin, on Flickr"><img src="https://farm3.staticflickr.com/2944/15368880661_e74fa2c156_s.jpg" width="75" height="75" alt="mthood"></a>
If anyone of you want to take a stab at correcting the file anyway. The lady and I would be grateful
09-27-2014, 12:57 PM   #10
Site Supporter




Join Date: Aug 2014
Posts: 395
that brighter one is really cool!
09-27-2014, 02:09 PM   #11
Veteran Member
Kendigitize's Avatar

Join Date: Apr 2013
Photos: Gallery
Posts: 316
Nice composition and good work on the stars. It looks like you have the Corona Borealis (The Northern Crown) in the upper left corner, but I could be wrong. Now if you just had the beaver doing a backstroke across the lake, you'd be set. You could go higher on the iso next time and maybe bring the exp time down to 25sec. to get a little less startrail. But these are better results then I get with my 18-135. I'm going to have to try harder to make that lens work I guess.
I did some quick Lightroom processing on it. Keep up the good shots.
09-27-2014, 02:32 PM   #12
Pentaxian




Join Date: Jul 2009
Location: Seattle
Posts: 7,068
Single exposure astro landscapes are no more difficult than a regular landscapes really. It's digital! Take a shot and shoot again. Trial and error until you're there. How hard is that? Now finding a good astro landscape scene is difficult these days. Clear night, new moon and little to no city lights is hard to find where I live without driving a long ways away.
09-27-2014, 08:25 PM   #13
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,704
QuoteOriginally posted by interested_observer Quote
(500/18=27 second exposure)
interesting - I use 666 which gives you 37 seconds. I suppose the formula can be tweaked for your latitude. Though the increased resolution of cameras these days means that star trails that weren't apparent on a 10Mp camera will be visible on a 24mp camera.


Pentax K5IIs - Sigma 18-35mm f/1.8 ART @ 18mm f/1.8 ISO 800 40s

But when you have the Pentax GPS Astrotracer the need to do math is somewhat reduced:


Last edited by Digitalis; 09-27-2014 at 09:10 PM.
09-28-2014, 10:36 AM   #14
Loyal Site Supporter




Join Date: Jun 2009
Location: Tumbleweed, Arizona
Photos: Gallery | Albums
Posts: 5,091
In terms of the "500 rule", I take it as a flexible guideline - an initial approximation of where to start, if you will. Is it perfect for all occasions - no. Does it give a reasonable starting point - certainly, can it be better - of course. There are a lot of variables at play here too, and with them a lot of unstated assumptions. A lens with a pretty large aperture (f4, f3.5, f2.8, f2 - rather than stopped down at f8, f11, f16...), the ISO probably higher than what the user is use to - ISO 1600, 3200, etc. It helps with getting the user to a reasonable point in terms of the focal length they are using. From there it's experimentation time.

Are there variations - sure, using 600, 650, etc. while still others use divide by 1.5 if using a crop (or 2 for MFT's). They are all good initial estimates.

There are also a host of other conditions to consider - how dark is the location? Cloud cover? Phase of the Moon?, Type/age of camera and sensor? etc....

09-28-2014, 02:45 PM   #15
Veteran Member
Tan68's Avatar

Join Date: Sep 2014
Photos: Albums
Posts: 396
OP, pretty good first attempt, I think.

As far as rule.. I hadn't heard of it but I tried a long exposure picture in Death Valley and noticeable streaks at 30 seconds with 18mm. Little dashes. I think I had ISO 1600 and f/2.8 on first week of March. Certain it was only 30 sec. cause I had no cable release so could only go 30 sec... So, only adding to the point there is room for variance in the rule of thumb

I was just trying to light my campsite from light reflected from cloud and that worked okay. A quite spooky and shadowless look of early evening brightness. with cloud streaks and star dashes :^)
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
18mm, 50mm, camera, factor, iso, lens, pentax help, photography, pictures, rule, sec, stars, times
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to take pictures like this? song_hm Photographic Technique 20 07-28-2013 05:05 AM
Weatherman wants to take pictures of lightning. cloudoc Welcomes and Introductions 8 05-01-2012 12:47 PM
How to take Pictures like this? robtheprincess Photographic Technique 9 09-12-2011 11:42 AM
Wanting to try out astrophotography dmort Pentax Camera and Field Accessories 6 05-16-2011 09:36 PM
People Want to learn to take great family pictures kklabunde Photo Critique 3 10-11-2009 09:58 AM



All times are GMT -7. The time now is 12:22 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top