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DPChallenge Forums >> Tips, Tricks, and Q&A >> how do i combine multiple exposures?
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03/19/2009 12:21:26 AM · #1
Hello everyone! how do I combine multiple exposures to try and make this kind of picture

//www.dpchallenge.com/image.php?IMAGE_ID=684408
//www.dpchallenge.com/image.php?IMAGE_ID=684061

should I just make layers and change their opacity? Is there software that can line them up with markers that I can set?

thank you
03/19/2009 12:45:55 AM · #2
You can try that, but you will usually have a really hard time aligning the images and/or have a lot of noise. There are programs out there that help in astrophotography. I am no expert but 1 my friend uses is registax.
03/19/2009 12:56:22 AM · #3
The photos you used as an example was shot with a microscope that connects to a camera. What you're trying to do needs to be done a different way. But to make a composite it's easier to lay one image on top of the other and then make a mask over it so you can paint away area's or bring them back if you want.

The photos:
Copyrighted_Image_Reuse_Prohibited_684408.jpg Copyrighted_Image_Reuse_Prohibited_684061.jpg

Message edited by author 2009-03-19 00:59:12.
03/19/2009 01:15:51 AM · #4
the description quite said 5 times 6 minute exposures so i thought they were good examples...

but are there software to line up pictures to make a composites?

Message edited by author 2009-03-19 01:16:12.
03/19/2009 01:41:17 AM · #5
Originally posted by Dirt_Diver:

The photos you used as an example was shot with a microscope that connects to a camera.


not to be picky but don't you mean telescope?
03/19/2009 02:24:11 AM · #6
Originally posted by smardaz:

Originally posted by Dirt_Diver:

The photos you used as an example was shot with a microscope that connects to a camera.


not to be picky but don't you mean telescope?


HEHEHE I was going to bring that up. but you beat me to it. :P
03/19/2009 02:38:01 AM · #7
Double post somehow....

Message edited by author 2009-03-19 02:40:28.
03/19/2009 02:40:10 AM · #8
Originally posted by spiritualspatula:

Well, those two photos were taken differently. Though they both used telescopes in one fashion or another, it wasn't the same. The first photo was taken using an DSLR mounted to a telescope. The second was a DSLR mated to a tracking device, using a 17-55f2.8 lens. If you thought photography was expensive, you will really be amazed by the costs of astrophotography. Here is a thread with some useful information, as well as the links to two useful tutorials. Thread. "Night Photography" Tutorial "An Astrophotography Primer"
Copyrighted_Image_Reuse_Prohibited_750369.jpg There is a good explanation for the process with this one too, as well as 594259.jpg
21.gif jlanoue may give you some pointers if you ask, as well.


ETA: I forgot to add that you should definitely check out John's page if you haven't already, linked to his image, as well as here.
03/19/2009 12:08:36 PM · #9
wow.... thanks allot for the link to that site! :)

is doing say.. 100 3 seconds exposures going to give the same result as 10 30 second exposures? (My gut feeling says absolutely not but I just felt it was worth asking... and regardless of the answer I will probably try both just to compare the difference by myself sometime this summer :p)
03/19/2009 12:19:19 PM · #10
No, that isn't the same. You still need the info to reach the sensor, so if 3 seconds isn't enough time to "see" the detail, no matter how many images you shoot, you won't ever get that detail. Also, with 30 second exposures you will obviously get a lot of noise and motion that may wash out the detail you were going for. It is all about trial and error to find the "sweet spot", so by all means, try both.

Rule of thumb (from a very non-expert): planetary photography you want a lot of short exposures (that is why people use webcams). For galaxies, nebulas, etc. you want longer exposures (as there isn't nearly as much light).

Best of luck!
03/19/2009 12:21:22 PM · #11
Originally posted by smardaz:

Originally posted by Dirt_Diver:

The photos you used as an example was shot with a microscope that connects to a camera.


not to be picky but don't you mean telescope?


HAHAHA yeah that's what I meant. It was late when I typed it
03/19/2009 02:19:38 PM · #12
Originally posted by mshimer5:

No, that isn't the same. You still need the info to reach the sensor, so if 3 seconds isn't enough time to "see" the detail, no matter how many images you shoot, you won't ever get that detail. Also, with 30 second exposures you will obviously get a lot of noise and motion that may wash out the detail you were going for.

The purpose of programs like RegiStax is to reduce the noise by stacking several images and combining them -- the detail areas (stars) will remain, but the noisy pixels will cancel each other out (assuming it's really random noise and not something with the sensor).
03/19/2009 02:45:32 PM · #13
True...but there is only so much RegiStax can do. If you can get the details that you want (or the exposure that you want) with a shorter exposure, it is better to do that. Webcam images of planets are much better than trying a stack of 30 second exposure.

Regardless...the point still remains that 100 x 3 sec exposures is not the same as 10 x 30 second exposure.
03/20/2009 04:07:23 PM · #14
Originally posted by julienrl:

Hello everyone! how do I combine multiple exposures to try and make this kind of picture

//www.dpchallenge.com/image.php?IMAGE_ID=684408
//www.dpchallenge.com/image.php?IMAGE_ID=684061

should I just make layers and change their opacity? Is there software that can line them up with markers that I can set?

thank you


Hi Julienrl,

I wrote up a tutorial a while back on noise reduction using photoshop, you can find it here.

john
03/21/2009 12:15:04 AM · #15
Thanks allot for the help everyone! :)

so why would a webcam picture of planets be better than with an SLR exactly?
03/21/2009 09:15:50 AM · #16
Originally posted by julienrl:

Thanks allot for the help everyone! :)

so why would a webcam picture of planets be better than with an SLR exactly?


I'm not sure it's better so much as easier and cheaper. When shooting a planet only a small amount of the sensor is receiving light, the rest is background dark sky so you don't really need a high MP sensor. Also when shooting a planet, you typically take hundreds, if not thousands, of small images. There are software packages that will take these input frames (.avi file) and automatically pick out the best images and align and average them and give you back your image. As rudimentary as this sounds, some of the best planetary images out there on the web are done this way. Finally, when photographing a planet, the exposure time is typically around 1/32nd of a second, NTSC video is about 30 frames per second, matches up well.
03/21/2009 09:54:54 AM · #17
Originally posted by julienrl:

Thanks allot for the help everyone! :)

so why would a webcam picture of planets be better than with an SLR exactly?


No problem. For the webcam: just to add something (as everything that was just said is exactly right) when taking a picture of planets you want to make sure that your exposure is very short and the length of time that you are photographing them is short also. You want to take hundreds (if not more) of pictures in a short a mount of time. This is very easy to do on a webcam, but very difficult to do (if not impossible) on a dSLR. The reason you want to do this is a short amount of time is because the planets are rotating (duh...but seriously consider this). If you take to long to photograph, say Jupiter, the planet is rotating pretty fast and will get slightly blurred. This doesn't mean it is impossible to take pictures of the planets with a dSLR, just much easier to do with a webcam.
03/21/2009 11:35:32 AM · #18
huh... that is pretty cool! I guess the new SLRS with video will be more apt at taking pictures of planets then (that is if its not interlaced video)
03/21/2009 11:43:58 AM · #19
To amplify what Matt posted in the last post, a webcam has a very small sensor, so the pixel pitch is very small. That means more pixels on a very small object. The high noise of webcams makes very little difference for planetary photography, because you are almost always averaging dozens if not hundreds of frames.
Another advantage of capturing video and stacking frames is that only those frames with "good seeing" need be used. The atmosphere is turbulent, but moments of clarity happen even on bad-seeing nights.
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