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long exposure of constellations

neil groves

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neil groves

neil groves

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ok so i went out tonight specifically to look at M13 which i did and was suitably impressed, then i thought i'd take a 30 min or so exposure of the plough, so i mounted my camera onto the telescope and tried to get the plough in the FOV.....i couldn't, each time i tried i found i couldn't get the camera to the correct orientation to get the plough in the FOV, how is this done please so i can track for several 1 min exposures? i mean i had to have the mount positioned so as to polar align, so i couldn't move the mount right?

Neil.

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GuillermoBarrancos

GuillermoBarrancos

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ok so i went out tonight specifically to look at M13 which i did and was suitably impressed, then i thought i'd take a 30 min or so exposure of the plough, so i mounted my camera onto the telescope and tried to get the plough in the FOV.....i couldn't, each time i tried i found i couldn't get the camera to the correct orientation to get the plough in the FOV, how is this done please so i can track for several 1 min exposures? i mean i had to have the mount positioned so as to polar align, so i couldn't move the mount right?

Neil.

EDIT: found via post history that you have the CGEM and 120ED Pro Scope.

Do you have a clear view North to see Polaris?  If not, then you cannot use the polar Scope and will have to manually align as close as possible With Compass (true North) and mobile phone app (best possible latitude setting) and then do a drift alignment.

With the CGEM, you should also be able to do the All-Star Polar Alignment routine, instead of drift alignment (which can be a pain without autoguider. So lets not go there).

When doing unguided exposures of 1 minute (and ESPECIALLY at 900mm focal length with your 120ED Pro), perfect polar alignment is a must! If not, the target will still just drift in FOV and your exposures will be ruined.

PS. If you haven´t already. I strongly recommend you reading up on the subject first! There are many good articles and youtube videos to be found on the internet about Polar Alignment, Drift alignment and All-Star Polar Alignment Routine.

Getting a clear understanding of how each routine works before attempting it, will save you from frustration and dissapointment.

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michael.h.f.wilkinson

michael.h.f.wilkinson

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Which Mount did you have again? Do you have a polar Scope and have a clear view North to see Polaris?  If not, then you will have to align as close as possible with compass and then do a drift alignment.

Depending on the Mount you have (Advanced VX, HEQ5 Pro, N EQ6 Pro). You can also do the All-Star Polar Alignment routine.

When doing unguided exposures of 1 minute, perfect polar alignment is a must. If not, the target will still just drift in FOV and your exposures will be ruined.

That latter figure depends critically on the focal length used. I managed a 12 minute shot with an 85mm lens (on 35mm film, so roughly 50mm on APS-C) unguided.

hya1: Comet Hyakutake: Camera: Contax RTS II Lens: 85 mm f/1.4, Piggyback (on GP-C8) Exposure: 12 min at f/2.0 on 100 ASA Fujichrome Sensia film Time: March 27, 1996 at 01.00 GMT.

Came out nicely (100 ISO film used, hence the need for 12 minutes at F/2). Polar alignment was good, no doubt. For 1 minute exposures at short focal lengths used for entire constellations, alignment is much less critical.
With a 50mm lens, using the old 1000/focal length rule a 2 second exposure using a stationary camera will hardly show star trails. A 60 seconds exposure is merely 3 times as long, so a reasonably aligned polar axis would remove most of the problems. At longer focal lengths better alignment is needed.
Note that aiming the camera at a circumpolar constellation can be difficult  to impossible if the camera axis is not at 90 degrees of the declination axis.  That might have been your problem
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GuillermoBarrancos

GuillermoBarrancos

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Michael. See my just updated post. :)  I did some searching in his post history and found out he has the Celestron CGEM Mount and 120ED Pro refractor.

PS. Neil, With the long tube of the 120ED Pro and also having the camera hanging on the back. It´s important you balance your scope properly as well!

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michael.h.f.wilkinson

michael.h.f.wilkinson

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Michael. See my just updated post. :)  I did some searching in his post history and found out he has the Celestron CGEM Mount and 120ED Pro refractor.

PS. Neil, With the long tube of the 120ED Pro and also having the camera hanging on the back. It´s important you balance your scope properly as well!

I think you misunderstood the OP. It is impossible to image an entire constellation with a 120ED. A DSLR with short focal length lens is needed

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GuillermoBarrancos

GuillermoBarrancos

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I think you misunderstood the OP. It is impossible to image an entire constellation with a 120ED. A DSLR with short focal length lens is needed

Good point. I really need more coffee this morning. :D

As he mentioned the Polar Alignment, I thought he was struggling to keep the object (he talks about M13  :confused:  ) in view, which would indicate bad polar aligment.

But Yeah, if he also wants to frame the entire Constellation in FOV around it. Not going to happen at 900mm focal length.

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neil groves

neil groves

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Alan that sounds like what i need, can you recommend a ball head? preferably from Amazon since i do most of my purchasing there.

Yes sorry i didn't make myself clear in the original post, i had the camera set up on top of the 120ed on the thread on one of the OTA mounting rings, i am a newbie at this and it is going to be a LONG time before i attempt any imaging through the 120mm lol

I am just using a DSLR with a 70-200L for some wide field experiments at the moment, i did one last night but it looks like the camera slipped during one of the exposures so next time i will just fit the camera directly to the mount and leave the scope off, i am intending to use the 120ED just for observing at least till i get the hang of the mount.

Neil.

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Alien 13

Alien 13

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Hi Neil, I just use a cheap one similar to this http://www.amazon.co.uk/Camera-Tripod-Ballhead-Quick-Release/dp/B008H3XZ22/ref=sr_1_1?ie=UTF8&qid=1398785475&sr=8-1&keywords=camera+ball+head but i dont have anything heavier on it than my Canon 650D with 135mm lens.

This thread might give you an idea of what can be mounted on a ball head http://stargazerslounge.com/topic/212386-tracking-with-a-camera-only-setup/

Alan

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glowingturnip

glowingturnip

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you might need some of these as well - http://www.amazon.co.uk/Convert-Adapter-Tripod-camera-release/dp/B0089TYEIS/ref=pd_cp_ph_2

I got a ballhead like that, but haven't been able to use it in anger yet because the screws from my tube rings are 1/4" and the hole in the ballhead is 3/8"

once you're polar aligned on the scope btw, you can have the scope pointing in any random direction you like to get a good angle for the camera, then just turn the RA tracking on.  Doesn't matter what the scope's pointing at.

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GuillermoBarrancos

GuillermoBarrancos

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Alan that sounds like what i need, can you recommend a ball head? preferably from Amazon since i do most of my purchasing there.

Yes sorry i didn't make myself clear in the original post, i had the camera set up on top of the 120ed on the thread on one of the OTA mounting rings, i am a newbie at this and it is going to be a LONG time before i attempt any imaging through the 120mm lol

I am just using a DSLR with a 70-200L for some wide field experiments at the moment, i did one last night but it looks like the camera slipped during one of the exposures so next time i will just fit the camera directly to the mount and leave the scope off, i am intending to use the 120ED just for observing at least till i get the hang of the mount.

Neil.

Hehe no problem Neil. :)

You might have a look here. This is a piggy back finder holder to piggy back a DSLR on a Scope, With ability to rotate the camera for framing.

http://www.teleskop-express.de/shop/product_info.php/info/p733_Baader-Witty-1-adjustable-piggyback-camera-and-finder-holder.html

I am sure, As I don't think you want to order from Germany, that you can get something similar in the US! This piggy back adapter is from Baader.

At least it's a Visual example With description, to give you an idea what to look out for. :)

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Alien 13

Alien 13

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So am i right in thinking that after i polar align my mount, i leave it alone and just use the ball head to frame the camera on whatever i want to image anywhere in the sky and thats it? i just hit GO?

 

Neil.

 

Yes thats pretty much it you can have the main scope pointed in the most convinent position for the camera to get the best view of the target.

Alan

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idigitize

idigitize

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I found myself getting a plate on top of the tube rings (1/4 inch allum) to spread the weight as though it was a bit much on just the one tube ring. Much much sturdier now with a ball head fitted for wide field or can mount the lens foot straight on it too if needed.
Before and after...

image

image

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