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Prime focus.


ozboyz1

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I have been inspired by the photos taken by many contributors from this forum; it was two weeks ago I made my first attempt using my un-modded Nikon-90 after a long cold and cloudy winter. I chose prime focus, with ISO 400, 30 second un-guided sub. (i.e. every 30s, I used 'goto' to re-align the scope before taking another shot.)

Attached is the photo of the Orion, my house is at the corner and polluted with street light, so I used UHC filter. Please kindly let me know what I can do to improve it? .... like sell the house and move to the country  ....   :laugh:

oh, a bit about my scope, it's SW carbon fiber, f4, 8" with 800 mm FL, HEQ5 SW mount.

Thanks heaps. 

post-36583-0-33171300-1414818277_thumb.j

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very nice first image, it looks like it lacks a bit of focusing, others can tell better than i do.

does your camera have liveview with zoom? it helps a lot to zoom in liveview and do the focus adjustments, if not, try taking some short exposures, check the focus and make the necessary adjustments.

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So your 30 second sub is unguided but, presumably, also no tracking? Looks like your stars are trailing. I'm a novice too, so I may be wrong, but I think you will struggle to get clean stars without some sort of tracking if you are shooting 30 second subs.

You can probably get away with 30 seconds if you are imaging widefield with just the DSLR, but through the scope you are going to get trailing very quickly.

I may be wrong, I'm just learning, so I am sure someone with more knowledge Will be along to let you know.

Nice first effort though. I fancy a go at Orion soon!

Good luck!

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Hi AtretaMarky1973

yes, I had problem focusing that night, but didn't think of using liveview .... thanks for the tip :-) Sorry for a silly question, I thought tracking and guiding are the same ? I just bought a 2nd hand Meade DSI-C camera, and trying to set it up for autoguding.

Billy,

I took this photo without lens.

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Ozboyz1,as I said, I am a novice, but my simple understanding is that tracking does just that, tracks the item in the RA axis to keep it in view. Guiding works with the tracking to provide adjustment to the tracking to counter periodic error in the tracking. By which I mean, over time, if just tracking, the target will drift from the centre of view due to imprecise polar alignment and gearing inaccuracy on the mount.

So two things that work together to keep the target central for longer exposures.

I have an EQ3-2 which just tracks in the RA axis with a single motor. It is not set up to guide so I am limited to shorter exposures.

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Hi AtretaMarky1973

yes, I had problem focusing that night, but didn't think of using liveview .... thanks for the tip :-) Sorry for a silly question, I thought tracking and guiding are the same ? I just bought a 2nd hand Meade DSI-C camera, and trying to set it up for autoguding.

Billy,

I took this photo without lens.

Sorry - completely overlooked that you said "prime focus".

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Marky1973,

you were right, tracking & autoguiding are 2 different things (I should have read the manual carefully :-)). My HEQ5 Synscan mount has auto-tracking function + PEC.

Is autoguiding more accurate and if I use autoguiding, do I need to turn auto-tracking on my mount off  ???

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Hi

You should be able to get 30s subs unguided provided your polar alignment is spot on and everything is properly balanced. I wonder how you operated the shutter - you at least need some sort of remote shutter control to prevent vibration. You could probably put together a decent image from stacking many 30s subs though it's a bit tedious. The heq5 tracks quite well but ideally you want autoguiding to correct tracking errors via computer control with a laptop - running planetarium software e.g. Stellarium, and guide software e,g. PHD or PHD2. Guiding will enable you to take longer subs :)

Louise

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The hook shaped stars in your image are not from periodic error - or not prinicipally so. They are caused by the scope shaking on the mount. PE trails are straight lines. How were you triggering the exposures? It is absolutely impossible to do this by touching the camera. That will cause it to dance all over the place. The only way to do it is electronically, either by using a cable release or via PC and control software.

It is very hard to comprehend the phenomenal tracking precision required to take a photo at telescopic focal lengths but imagine trying to pick up a pea with two metre long chopsticks. It's a bit like that. The HEQ5 it as its limit with an 8 inch Newt and possibly a bit beyond its limit, but something should be possible.

Regarding focus, which is critical, try Googling Bahtinov Mask. These work superbly.

Olly

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2266922474&k=Sc3kgzc

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Billy, I am afraid I don't know about the mount that you have and how the Synscan stuff all works, but I am sure you will be able to find some helpful hints from the people on this site! I have just an EQ3-2 but, so far, have managed 90 second exposres with clean stars with just a polar alignment and an RA tracking motor - no guiding. So you shoudl be able to do a bit better with just polar alignment and tracking while you sort out the guiding side of things. I'm just getting used to getting images together before I jump into guiding - that'll be next year's project! ;-)

Good luck!

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I can manage 30sec unguided with 1" pixels (1200mmFL) on a rather ancient HEQ5 before periodic error wrecks too many subs, so you should be OK at 800mm. M42 is quite near zero Dec, so the worst possible place for periodic error, mind you.

NigelM

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