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long exposure without guiding


Guest sharpie78

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Guest sharpie78

Hi Guys, Just wondering if anyone could give me an idea of how long (roughly) I'll be able to image before having to switch over to guiding please ?


I'm using a Skywatcher 130 Newt with Canon EOS 450D attached, mounted on an HEQ5 pro running off laptop with EQ MOD. 


 


I have a CCTV CCD camera which is capable of imaging stars very well and DSO's reasonably well by simulating long exposures and stacking them on the fly internally. My intention (eventually) is to attach that to a 9x50 finder and use it as a finderguider. 


 


I don't want to over complicate things yet by throwing guiding into the mix. I'm still learning how to use the things I've already got so any help with exposure length on my current rig would be greatly appreciated.


 


Clear skies


Jack 


:)


 


ps. if i image comet lovejoy while using stellarium to GOTO it.....will stellarium track it ok or will i have to use a specific tracking rate ?


 


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Hi Jack - Mike (Perkil8r) has had great success doing up to 5min subs without guiding - so he would be the one to comment. His PA though is terribly accurate (I have yet to find out how he achieves this).


 


For imaging comets I've seen that folks use an adjusted rate cos comets move quicker through the night sky than sidereal or any of the standard rates - I guess guiding might a solution there. There may be a comets plugin for Stellarium (similar to the satellites plug in) but you'd have to confirm that cos I've not investigated it. :)


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Guest sharpie78

NIce one, thanks for that Kim. I'll rack Mike's brain next time I see him on here. 


My polar alignment is getting there so I'll have a crack at a 5 min sub next time i'm out there and see what happens. Probably get a few streaky stars but hey...trial and error...... :-)


I've seen comets on stellarium, whether it's a plugin or not I have no idea, so I'll just give it a shot unless someone posts some helpful info.


thanks again


:-)

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You can improve the accuracy of tracking by using PEC (Periodic Error Correction) some mounts have it in the handset others you can use separate  software. It is basically a macro which you run when your on a star. With the mount Polar aligned as best as you can you slot a cross hair eyepiece of reasonable magnification into the scope and watch a star. You then start PEC training. If the star moves off cross hair you compensate with the direction buttons to put it back on. Then after the allotted time you stop recording.  


The PEC is now in the memory. This will enable longer subs without guiding when you come to image. All you do is run the PEC and start taking pics.


It sounds easy but there are a few things you have to watch for. Ive never done it on my mounts, although they both possess PEC I went straight into guiding


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Guest Kheldar

Re: Mike - he also did a lot of engineering on his mount, taking it apart and fettling :screwloose: Even then he would be the first to admit 5 minutes was only good about 50% of the time (and now guides.)


 


Throw in things like a gust of wind, atmospherics ... aspiring to long exposures without guiding is a thankless and painstaking task :(


 


Re: PEC - I do believe that's there no benefit (in fact probably detriment) unless you have a permanent set up or dual encoders .... if you drop the clutches, PEC is changed. If your PA differs from night to night, PEC will also change :( Granted you can get round this by PEC training every night ...


 


For the sake of sub £100 you can be up and guiding in no time with a simple finder guider setup :)


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Mike would not be the first to admit that ;)


 


At 5 mins I had a success rate of around 80-90%, at 6 mins it dropped to 50% hence my sticking with 5 mins in the end. The HEQ5 should be a little better, however, that was at 400mm focal length. At 600 I was really pushing it at 5 mins, and at 1000mm it was about 2 mins max before I started to get issues.


 


I would hope to achieve around 4 mins with a HEQ5 and the 130p in reality. You will need patience to get the setting up just so, good balance and a calm night in order to do it though.


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surely if the idea is to get longer and longer subs then guiding is the answer, you will always be fighting the mount and PA and everything,  is that not


why most imager's guide?  Even you Mike have gone to guiding with an NEQ6?  


 


Well apart from me, i dont guide as yet, but the mount i use is totally different to HEQ5 or the NEQ6


 


Just asking the question, please dont shoot the messenger :lol:


 


Sheila


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Lots of people want to image without guiding, i suspect because they do not want to extra perceived hassle of guiding, or the additional costs to get the guiding kit.

I probably have the money, i just can't face learning anything new just yet as my brain is already fried from this hobby :)

James

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Lots of people want to image without guiding, i suspect because they do not want to extra perceived hassle of guiding, or the additional costs to get the guiding kit.

I probably have the money, i just can't face learning anything new just yet as my brain is already fried from this hobby :)

James

 

but to have to get everything exactly right etc etc to produce long subs takes more effort and swearing than i think guiding does once learned.

And it is not so expensive to get set up as previous threads on here have explained. :)

 

I have seen Kheldar set his guiding up in bout 5 minutes...  so it cant be that much of a problem.. it only becomes a problem if

its cloudy :(

Edited by Sheila
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I do appreciate that it can be set up quickly and doesn't need to cost the earth, i'm just explaining what many of us non-guiders think, which i acknowledge is mis-guided [haha, mis-guided, get it?!].

There must be a learning curve, however easy or difficult that is. I was scared of equatorial mounts but took to it like a pig in muck, dog with a bone, or whatever the saying it....

Personally i have laptop issues too; it's a load of cr%p, so that puts me off using my laptop to guide too.

But yes i'm sure it's not really as tricky as i think. But i think these are the reasons people are put off it.

James

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surely if the idea is to get longer and longer subs then guiding is the answer, you will always be fighting the mount and PA and everything, is that not

why most imager's guide? Even you Mike have gone to guiding with an NEQ6?

Well apart from me, i dont guide as yet, but the mount i use is totally different to HEQ5 or the NEQ6

Just asking the question, please dont shoot the messenger :lol:

Sheila

Well we don't all have awesome mounts like yours Sheila ;) I bet you could get 10-15mons unguided from your mount? It is a thing of beauty both engineering-wise and aesthetically

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Guest sharpie78

thanks for the info peeps. very handy


..........looks like I'm switching to guiding. Truly over to the darkside now.  :geek:


 


I can do 3 minute subs, 4 minutes at a stretch, at the moment so will carry on with that until I get the couple of bits I need for guiding. looks like the learning curve just got steeper though  :facepalm:. In for a penny eh.........good job I'm a techno geek I reckon.


 


Out of interest phil.......do i have to have the synscan handset plugged in for PEC or can it be done through EQ MOD ? something to play around with while I'm waiting to get setup for guiding.......


 


thanks again everyone. such a wealth of knowledge on here.  :D


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Well we don't all have awesome mounts like yours Sheila ;) I bet you could get 10-15mons unguided from your mount? It is a thing of beauty both engineering-wise and aesthetically

 

 

well 10 mins is easy, 15 mins a little harder but quite possible, once got 30 mins but i think i was just lucky with the PA then :o

I am just idle really :lol:

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thanks for the info peeps. very handy

..........looks like I'm switching to guiding. Truly over to the darkside now.  :geek:

 

I can do 3 minute subs, 4 minutes at a stretch, at the moment so will carry on with that until I get the couple of bits I need for guiding. looks like the learning curve just got steeper though  :facepalm:. In for a penny eh.........good job I'm a techno geek I reckon.

 

Out of interest phil.......do i have to have the synscan handset plugged in for PEC or can it be done through EQ MOD ? something to play around with while I'm waiting to get setup for guiding.......

 

thanks again everyone. such a wealth of knowledge on here.  :D

 

 

good decision i think there :thumbsup:

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what mount are you using Sheila ?

 

 

I have a GM1000 mount which has encoders and geek stuff in it, so it tracks to an error of less than i think its 0.5 arcsecs.  It does

take time to PA and run models of the sky, but once that is done, its start it off and walk away, until pier flip is due.  If it coulds

over or anything, it does not bother the mount it still tracks.

 

Fortunately i got mine before the 50% price hike over the last 6 months :o

 

 

Sheila

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Uh oh! Don go and google the GM1000!! I did and now every time I get my mount out I wish it was a GM1000 :(

If I am at a dark site and Sheila is there she let's me look at her GM1000-well I look when she's not looking :D

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Guest sharpie78

very nice. I've just had a look at it online and I think I have mount envy  :lol:


 


mount envy + aperture fever = very big hole in my pocket !!! 


 


time to exercise some self control and prioritise......it's a good job christmas is coming and I've got presents to get for the kids. that's a big enough hole in my pocket already.


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very nice. I've just had a look at it online and I think I have mount envy  :lol:

 

mount envy + aperture fever = very big hole in my pocket !!! 

 

time to exercise some self control and prioritise......it's a good job christmas is coming and I've got presents to get for the kids. that's a big enough hole in my pocket already.

 

only advice i can give is mount is most important, but you have the HEQ5 so you should do fine :)

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Guest sharpie78

it's served me well so far. been accurate with the goto, when i've got my alignment right, and is very solid with my little newt on it. It'll be going on a pillar soon so should improve things a little there too.  :)

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Hi Jack, I did my first guided subs last week and although I had a few teething troubles it worked really well and I wondered why I had not started it sooner!!


I have been doing unguided images for about a year and found 120 secs was the best I could get without getting star trails, last week I started on 5 min +.


I am using a QHY5 mono and a 9x50 finderscope with an adaptor from 'Modern Astronomy' on a HEQ5 goto mount.


 


Cheers


Ron


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Guest peepshow

I have a GM1000 mount which has encoders and geek stuff in it, so it tracks to an error of less than i think its 0.5 arcsecs.

 

 

Sheila

The write up on that super duper mount states,  " Up to 0.5 "RMS tracking accuracy" 

  I wondered what RMS refers too as tracking accuracy is a  function of time too is it not ?

 

.5" over a minute or hour or what?

For 6k odd it is probably over a year. :)

 

Anyway, I now have  a bench mark for my barn door tracker. :D

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The write up on that super duper mount states,  " Up to 0.5 "RMS tracking accuracy" 

  I wondered what RMS refers too as tracking accuracy is a  function of time too is it not ?

 

.5" over a minute or hour or what?

For 6k odd it is probably over a year. :)

 

Anyway, I now have  a bench mark for my barn door tracker. :D

 

 

RMS means root mean square.... no good asking me... ask a geek or maths geek, just know its works :D  all i need to know really

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Philjay, with the PEC training with a reticle eye piece, with all its limitations, how does handset know which errors are down to periodic errors, and which are down to poor polar alignment (there will always be some however carefully i polar align)?

James

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Guest Kheldar

Philjay, with the PEC training with a reticle eye piece, with all its limitations, how does handset know which errors are down to periodic errors, and which are down to poor polar alignment (there will always be some however carefully i polar align)?

James

 

There-in lies my point above ... you have to recreate the same PA each time ...

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