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Old 16-02-2009, 08:48 AM
zumka (Daniel)
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DSI Pro Focusing

Hi Guys,

My First attempt at astrophotgraphy

I tried to take some shots with my DSI I PRO Cam and 12" Skywatcher DOB,
however for some reason I was unable to achieve full focus.
I was under impression that DSI was plug in and start taking shots as described in the manual. What am I missing here, do i need some sort of camera addon ?
I used Meade imaging software that came with the camera.
Thank you for your help.
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Old 16-02-2009, 08:57 AM
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Omaroo (Chris Malikoff)
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Hi Daniel

Are you reaching focus and having trouble making it precise, or are you lacking in travel such that you'd never reach focus to begin with? Given that you have a Newtonian, maybe your focuser assembly is too long and you need more in-focus travel that you've got. The only way to fix this (if it is indeed the problem) is to either swap the focuser assembly for a low-profile (read: shorter) focuser or physically relocate your primary mirror up the OTA towards the secondary a bit.

Well, a camera is just another device at the end of the optics train that tries to do the best it can with the light received - whether it's in focus or not. A camera isn't unlike the eye - you still need to focus it to see a clear image.

Do a search here on IIS for the "Bahtinov Mask". It's a simple device that you temporarily place on the end of your scope that, when pointed to a bright star, will show whether you are at focus or not by taking fast 1-second images and looking at them on-screen. As you move focus in either direction you will see the shape of the six-spiked diffused star change, and when everything is symmetrical you have reached focus. It's the fastest and easiest way in my opinion to get as close as you can to proper focus.
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Old 16-02-2009, 09:49 AM
zumka (Daniel)
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Hi Chris, yes focuser is lacking in travel. The star appears as a big white circle when reaching maximum. I have tried moving camera in or out of the focuser without any success.
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Old 16-02-2009, 12:24 PM
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peter_4059 (Peter)
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I had to move my mirror forward (long colimation bolts and springs) and modify the 1 1/4" - 2" adaptor (machine the lip off it) to get enough in-travel for my DSI II pro with a filter wheel fitted on the front. You will probably achieve focus by doing either of these mods with the standard DSI I pro with the filter slider. Happy to post some pics if you want to see what I did.

Peter
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Old 16-02-2009, 12:28 PM
zumka (Daniel)
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Is there other way that doesn't involve modifying telescope ?
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Old 16-02-2009, 05:28 PM
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You can achieve focus with a barlow but that will obviously reduce your FOV. The adaptor mod is quite easy and you can buy a new adaptor so not permanent. There's a photo of my modded adaptor in this thread.

http://www.iceinspace.com.au/forum/s...ad.php?t=25290
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Old 17-02-2009, 10:33 AM
zumka (Daniel)
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Quote:
Originally Posted by peter_4059 View Post
You can achieve focus with a barlow but that will obviously reduce your FOV. The adaptor mod is quite easy and you can buy a new adaptor so not permanent. There's a photo of my modded adaptor in this thread.

http://www.iceinspace.com.au/forum/s...ad.php?t=25290
Hi Peter,

I didn't fully understand from that post how exactly did you modify it.

Can you please give me more info.
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Old 17-02-2009, 05:27 PM
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Take the 2" - 1 1/4" adaptor and have the lip machined off it so the camera fits further into the focuser - you can gain 10mm of extra inward travel this way. You won't be able to use a thumb screw to lock the adaptor to the DSI nose piece but instead will need a grub screw (this is the small black dot on the silver part of the machined adaptor). I've attached two pictures each showing the adaptor before and after the lip is machined off. The after picture shows the DSI nosepiece installed in the adaptor.

Peter
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Old 19-02-2009, 09:42 AM
zumka (Daniel)
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Thank Peter,

Now I understand

Bintel suggested to buy this 2" camera adapter :

https://www.bintelshop.com.au/Images/Stock/7403X.jpg

Which will replace 1.25 adapter that comes with DSI.
In theory this will achieve same outcome.

Does anyone know who sells them beside Bintel.
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Old 19-02-2009, 04:51 PM
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Yep - that might work but you wont get the full 10mm extra as it still has a flange.
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