#1  
Old 13-10-2009, 09:04 PM
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telecasterguru (Frank)
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DSI II and focus

I have spent a number of hours trying to get Jupiter to focus in my DSI II and have been singularly unsuccessful.
I am using a Bintel 252 Dob on an eq platform and no matter what settings I use all I get is a blown out blob.
I follow the instructions in the manual for planetary imaging. Gain, offsets no matter what I try it won't become clear. It is perfectly clear with an EP.

Any suggestions greatly appreciated.

Frank
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  #2  
Old 13-10-2009, 10:03 PM
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[1ponders] (Paul)
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Try a focusing aid on a star first. Try a simple hartmann mask and see if you can focus on a bright star.
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Old 14-10-2009, 07:04 AM
Dennis
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Hi Frank

Assuming that you can achieve focus with the DSI on stars as Paul suggested, I think that the DSI is a very sensitive camera compared to typical webcams such as the DMK series so if you are imaging Jupiter at the prime focus I suspect that you are just saturating the chip, which is why you can’t see any details.

You should be able to see the Galilean moons though, if they are a reasonable distance from the disc?

I have an SBIG ST7 and the shortest exposure it takes is 0.01 sec and that also blows Jupiter out at the prime focus of my ‘scope, until I insert a Barlow which increases the magnification and consequently dims the image and I can then see the cloud belts.

Webcams are the preferred cameras for imaging Jupiter due to their ability to grab between 100’s and 1000’s of frames for stacking.

Cheers

Dennis
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Old 14-10-2009, 09:30 AM
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telecasterguru (Frank)
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Thanks for the info. I have tried a 2x and a 5x barlow to no avail. The DSI II has a planetary setting which I assume is different to it's DS settings. Its very strange that when I look at the image of Jupiter standing straight in front of the computer screen it is a blob but when I move to the side and look at the monitor from a side on angle it looks in focus. Why would this be? I'm sure I'm doing something wrong.

Frank
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Old 14-10-2009, 09:43 AM
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You have to set the exposure of the DSI II to ~1/1000 of a second to get Jupiter anything else than a blob. At too high an exposure its just a huge circle of light. For focus us a Bahtinov mask on a bright star then go to Jupiter without touching your focus, set exposure to 1/1000 sec and you will see the bands.The DSI II is very sensitive.
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Old 14-10-2009, 09:53 AM
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telecasterguru (Frank)
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Allan,

I will have another go again tonight. I believe the exposure was set to .008 seconds. I will drop it down to .001. Auto exposure didn't seem to produce any results at all.

Thanks

Frank
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Old 14-10-2009, 10:23 AM
Dennis
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Hi Frank

In terrestrial cameras, auto exposure is (generally) not suited to astronomical scenes. Auto exposure algorithms attempt to integrate the tones in a scene and average them out to a mid-grey. On my Canon 40D this works very well on most day time scenes where there is a nice spread of tones from blacks through greys through whites.

With Jupiter, all you have is a black sky and a white blob for the planet with few (none?) in-between tones so this fools the exposure meter which then over exposes when it “sees” all that black and attempts to let more light in, to lighten the blacks to make them approach a tonal value of mid-grey.

Cheers

Dennis
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Old 14-10-2009, 12:17 PM
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I know exactly what your talking about. It's pain in the @#$$ trying to fucus that camera. I do it with the moon and still I can never get looking sharp, there always seems to be a softness to the focus. I've tried with refractors and newts, same thing.

I havent got a mask though, thats next on my list. Hopefully that will make it easier.

Sandy
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Old 14-10-2009, 12:42 PM
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Frank

I bought a second-hand DSI II recently. The best move I made was to buy Nebulosity from Craig Stark. It has a fine focus function which give a continuous FWHM readout that makes focussing so much easier.

It works better on stars than Juppiter but it will make a difference.

Let me know if you need the link.

Pete
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Old 14-10-2009, 01:04 PM
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telecasterguru (Frank)
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Pete,

That is a great idea as I already have nebulosity2. I never thought to use it.

Frank
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Old 14-10-2009, 03:34 PM
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Envisage works well with a Bahtinov mask and focusing. Just increase the levels (LHS control) til you see the spikes and take it from there. Far better than Nebulosity's fine focus (in my experience). Cant take the time to make a Bahtinov mask? then just take 3 pieces of tape or string and place them across the front of your scope in a Y - easiest thing to do.
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Old 14-10-2009, 06:44 PM
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Ide go with nebulosity every time over envisage. IMHO envisage sucks badly. nebulosity allows you to frame, focus, take batch images and a whole lot more. make sure you have updated to the latest version.
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Old 14-10-2009, 07:01 PM
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kinetic (Steve)
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Quote:
Originally Posted by Dennis View Post
Assuming that you can achieve focus with the DSI on stars as Paul suggested....

Dennis
Frank,

As Dennis and Paul alluded to.....we are assuming this scope CAN
already bring things to focus?

My GSO Dob and most others, I assume, need the '50mm chop'
before I could bring something to focus (DSLR, DSII etc).
I followed Clive's (Alchemy) guide in the articles section on
how to do it to a 12" F5 Dob.

OK.....assuming your's already does focus ok, I found quite a few
weeks back that Jupiter and the DSI II needed a manual exposure
setting of 0.0005 sec in Nebulosity to bring surface features on
Jupiter in, perfectly exposed.
Anything slower and it blew out into a blob.

Hope this helps,

Steve
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Old 15-10-2009, 05:40 AM
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telecasterguru (Frank)
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I have no problem focusing with my DSLR.
Unfortunately could not try anything last night and I am away now until Sunday. Will have a go with nebulosity then and let everyone know what happens.

I definitely do not want to give the scope the snip.

Frank
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Old 15-10-2009, 08:30 AM
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Quote:
Originally Posted by bmitchell82 View Post
Ide go with nebulosity every time over envisage. IMHO envisage sucks badly. nebulosity allows you to frame, focus, take batch images and a whole lot more. make sure you have updated to the latest version.

Agreed!!!
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