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Issues imaging fainter objects

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#1 AstroWizard

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Posted 25 February 2020 - 11:28 PM

I am having issues imaging with my DSLR camera: fainter objects do not even appear in my photos. My current setup is a 6" 1216mm Meade Starfinder (f/8) with a Telrad and my camera is a Nikon D5300 mounted using an Orion combined camera adapter with an H20mm lens.

 

The issue is I don’t seem to be gathering sufficient light.  I can view stars that are bright and visible to the naked eye and image them through my camera. My camera is properly focused and that I can see the bright stars I was imaging. But when attempting to image any other object (M31 for example) my camera is completely dark. I have my camera in manual mode and have tried tweaking both my ISO and exposure with no apparent improvement. From what few images I have been able to take there appears to be some chromatic aberration in the stars. I am quite new to Astrophotography (at least with a dobsonian) and therefore may have a flawed setup to begin with. Below I have attached a picture I took of Sirius (It's not the best).

 

I'm not sure if it's a mechanical or an electronic issue that is causing me a lack of light but I would appreciate any advice.  Thanks!

 

DSC_5417.jpg

 



#2 Oyaji

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Posted 26 February 2020 - 12:15 AM

Astrophotography with a Dobsonian mount is difficult if not impossible. 

 

I suggest you start your astrophotography journey by consulting www.astrobackyard.com.   There is a wealth of information there.  And although there are lots of other websites pertaining to astrophotography, I don't know that you will find one better than that to get you started.  

 

Good luck, and clear skies!  


Edited by Oyaji, 26 February 2020 - 12:17 AM.

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#3 scadvice

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Posted 26 February 2020 - 01:02 AM

I think it's focus. Reflectors can be difficult imaging with. I think you cannot get close enough inward to focus. Hopefully people who images with reflectors can give you some pointers. Trevor Jones Astrobackyard is a good starting point as Oyaji said to learn AP.



#4 Sammy

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Posted 26 February 2020 - 01:35 AM

The problem is more than likely trying to image using that H20mm lens.... Get a t-adaptor and do prime focus. You may have to move the primary further up the tube to reach focus but the results will be better....
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#5 bobzeq25

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Posted 26 February 2020 - 01:37 AM

The way astrophotography works is this.  Simplified version.

 

You take a number of fairly long exposures ('lights").  Say 30 seconds to 5 minutes.  In order to do that (if you're using a telescope, which magnifies motion as well as astronomical objects), you have to track the stars extremely precisely.  The mount is of the utmost importance.  Almost everyone uses an equatorial mount, with motor drives.

 

You take enough of them to add up to at least half an hour.

 

You load all the exposures into a computer, stack them, and process them, using specialized software.

 

Key point.  The camera doesn't work because it's better than your eyes, it works because it's different.  It can patiently gather a lot of light.  IF you can keep it precisely pointed for a long time.  Unlike your eyes, it doesn't work immediately, it takes time.  At least half an hour.

 

The telescope doesn't really help you without that excellent (and expensive) mount to keep things extremely precisely pointed.  1/1000 of an inch of error is too much, and your target is moving.  Assuming you don't have a mount like that, a far better way to do this is with a camera and a lens.  That can work even if the camera and lens are sitting on a fixed tripod.

 

This book will get you started, and explain much more.  I _strongly_ recommend it to you. 

 

http://www.astropix....bgda/index.html

 

Here's what it takes to get a good image of M31 with a telescope.  I used a D5500 and a 70mm telescope.  It's 37 2 minute exposures, a little over an hour.  That was at F4.8, it would need more like 3 hours at F8.  I spent a few hours stacking and processing the 37 exposures on a computer, it's pretty complicated.  The telescope was on a mount that cost well over $1000.

 

Start with the D5300 and a lens (a 50mm would be good), using the technique in that book.  Your scope doesn't help you, it just makes things very difficult.

 

M31 SV70T smaller.jpg


Edited by bobzeq25, 26 February 2020 - 02:08 AM.


#6 B 26354

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Posted 26 February 2020 - 01:39 AM

Order this book:

 

https://www.amazon.c...=dp_ob_title_bk




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