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11-20-2014, 11:52 PM   #1
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K50 Multi exposure and astrophotography

I occasionally do a little astrophotography with my 1st DS (which is a bit noisy) and have just upgraded to the K50. Been looking at the Multi-exposure mode - has anyone tried this with astrophotography? Does anyone know how the K50 'stacks' the photos? (ie: are they all 50% transparency...)

In the past, I'd usually take 4 or 5 shots of the same thing (on a eq tracking mount) then put them in photoshop and stack them one on top of the other with 50% transparency on the second, 33% on the third photo and 25% on the fourth etc. This reinforces the actual image and reduces the noise. Having seen the multi exposure mode on the k50, I'm wondering if it can do the same thing in camera. ie: take 5 30 second photos at iso800 and allow the camera to 'stack' them with the end result being a much cleaner image with less noise that I can tweak a little harder in photoshop. Not sure if I'm on the right track here or not....

The sensor noise is much, much less evident on the K50 than the 1st DS. With the earlier Pentax, I'd sometimes take lightning photos and if I had the camera open for any length of time (which is unavoidable), then the sensor noise was pretty horrible - the warmer the weather, the worse it got. The K50 looks really clean by comparison so I'm very keen to see what sort of results I can get out of it.

It's an eye opener to see all the different modes and effects on the new model - I think my 1st DS was around $1400au several years ago - for less than half that, the K50 has bigger and better everything! Remind me not to invest in technology!

Cheers,

John

11-21-2014, 02:36 AM   #2
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I'd personally go manual anyway...
You can also take one (two, three, four...) dark frame and use the "difference" blending mode in Photoshop to reduce noise even more, and you don't even need a tracking mount for that...
Waiting for someone with a K50 to answer regarding the blending modes.
11-21-2014, 04:06 AM   #3
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QuoteOriginally posted by quedecree Quote
Having seen the multi exposure mode on the k50, I'm wondering if it can do the same thing in camera. ie: take 5 30 second photos at iso800 and allow the camera to 'stack' them with the end result being a much cleaner image with less noise that I can tweak a little harder in photoshop. Not sure if I'm on the right track here or not....
I am pretty sure that you can. Here's an example by nighfly with 6 images stacked the way you contemplate:

https://www.pentaxforums.com/forums/groups/135-astrophotography/2201-k-01-ast...#gmessage28013

But you might also consider using Deep Sky Stacker (it's freeware) to automatically align and stack before you do your post-processing:

DeepSkyStacker Download

Congratulations with your upgrade! These sensors are really good for astrophotography.
11-21-2014, 03:53 PM   #4
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Thanks guys. Had a bit of a session last night and some of the photos turned out ok considering I didn't have any guiding rigged up. I've also had to mark or make note of my infinity focus points - I'd forgotten how hard it was to focus the telescope sharply through the viewfinder! The multi exposure seemed to work pretty well and was probably only held back by light pollution. Here's a few of last night's pics... 1st pic's Andromeda. Second, I think that's NGC 672 to the lower left in Aries, 3rd's M42 with the camera attached to the 600mm Orion Apo (about 155 seconds at iso 800) and the last is Orion with the Pentax SMC 1.4 50mm lens (a very old lens with no auto anything but seems pretty good at 2.4 and up.

By the way, any recommendations on good prime lenses for this caper? I'm thinking Sigma's 1.8 28mm might be worth a shot?

---------- Post added 11-22-14 at 09:56 AM ----------

oops...last pic's my 18-125mm sigma DC lens, not the Pentax!

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12-10-2014, 12:47 PM   #5
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Don't know much about the Sigma 28 lens but I recently sold my FA 28/2.8 lens as I just was not using it enough to justify keeping.
Personally, I enjoy the Pentax DA lens so I would take a look at their wide angles in this category. As for Sigma, I have had a 50/2.8 macro that I have used it extensively over the years. It has and is performing extremely well.
Let us know what you decide upon! BTW, I enjoyed seeing your astro pics!
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