Autoguiders..

[AweSIM]

hi everyone.. first off.. thanks to all the people on this forum whove helped me decide on the gear that i should be getting for my first scope.. really.. if it werent for you people.. i would never have been able to get this far so quickly.. this forum has literally turned out to be the holy grail for me.. .. thank you all of you people..

ive pretty much decided about the kit i wanna have.. excluding the accessories.. (EPs, filters, bells and whistles).. the equipment is this..

- SkyWatcher Explorer 200PDS..

- NEQ6 Pro SynScan..

im particularly interested in long exposure astrophotography and im trying to get a kit that can be adapted to photography too.. so called future proofing.. ..

ive learnt from people here that an HEQ5 is the bare minimum for photography and even it doesnt warrant exposures longer than 2 or 3 mins.. and that autoguiders are the only way to take exposures of any length.. but since autoguiders have weight too.. the HEQ5 might prove inadequate for 200P plus all the guiding equipment.. so im trying to go for NEQ6..

that aside.. im looking for some answers to questions regarding autoguiding thatve been popping in my head.. please clarify my confusions and guide me to the right path.. .. thank you all so much..

here is what i already know.. for autoguiding.. you need..

1. a mount that can support the weight of the OTA and the guiding equipment..

2. a guide scope..

3. camera for the guide scope..

4. some software that connects to the mount and the guide camera and analyses the image.. if there is a shift the software tells the mount the corrections it should make to track the object perfectly..

here is what i dont know.. or am confused about..

1. a guide scope is typically smaller than the main OTA.. so for 200PDS.. what sort of aperture would be appropriate for the guide scope? and should it be refractor or reflector or anything?

2. since the guide scope is smaller than the main OTA.. its magnification will hence be lesser than the main OTA.. that mean that the guide scope is looking at a wider section of the sky and tracking that image.. what i wanna know is that isnt that inaccurate? i mean i know for mount alignment we use the highest magnifications we can to center the alignment stars.. cuz its more accurate.. if the main OTAs magnification is ten times that of the guidescope.. the image from the OTA would need to shift ten pixels for the guide scope image to register a shift of one pixel.. so if the OTA image shifts by 5 pixels or less the guide scope image remains the same.. so isnt that inaccurate?

3. if im using a 10MP DSLR camera for the main OTA.. what sort of camera should i use for the guide scope? obviously 10MP for guide scope isnt feasible.. and if it is something like 1MP or something.. that should further reduce the accuracy of guiding as pointed out in point 2.

4. what sort of software is used for guiding? what interface does it have to the equipment? im guessing the software needs to communicate with the mount and guide camera at the least.. what hardware is required?

5. if the mount has not been aligned up PERFECTLY.. the view WILL suffer from field rotation even if its a little bit.. an autoguider cant do anything about it right? and please tell me.. WHAT DOES AN AUTOGUIDER DO IN THE FIRST PLACE? as in how does it exactly work?

6. if you guys could post images of your autoguider setups and their specifications.. it would help clear out a lot of my confusions..

thank you all.. ..

asim sohail..

pakistan..

[Paxo]

Hi Asim,

It is common today to use a short refractor as a guidescope coupled together with a relatively small chipped camera as a guidecamera (for example a QHY5 camera). These cameras have been designed specifically for guiding, they are highly responsive and give exceptional results.

You mentioned in your post the differences in magnification. Originally when guiding was done by eye and the mount manually moved after following a guidestar visually against a crosshair (usually via an off axis guider) it was usual to use a longer focal length guidescope. Advances in software (such as PhD, which is free) allow sub pixel calculations of the star movement which gives very accurate results (typically my own setup only varies by about 0.1 pixels while guiding which is probably down to seeing).

As for why use an autguider, it is likely with a good alignment you may get 5 mins without any noticeable star trails, but probably no more. Basically the autoguider takes an image (typicall 1 to 5 second duration) and then checks the position of the guidestar (which us either selected automatically by the software, or manually by yourself) against its original position, if it has moved, it automatically moves the mount to place the guide star back to it's original position.

If you do this every couple of seconds, and with a good alignment, the star may never move more than 0.5 pixels from its starting position, resulting in nice round stars in your image, and you can do extremely long exposures (typically I do 20 minute subs for narrowband, and TJ does up to 1 hour), you just couldn't do this relying only on the mount.

The mount itself, being mechanical, has errors (periodic errors from the worm drive) in it which can be removed by guiding also.

Hope this helps

Steve

[beamer3.6m]

I have an HEQ5 which I load with an Explorer 200p as my imaging scope and I use a C80ED mounted side by side as the guidescope.

I have managed 10 minute subs unguided with just the Explorer 200p but when guided long subs are easy.

The C80ED has is f7.5 whilst the 200p is f5.

Hope that might help.

[AweSIM]

@paxo and @beamer3.6m..

thanks guys.. yes it certainly helped a lot..

@paxo..

brother.. that was a very good piece of information.. you explained it quite well.. could you explain your setup in detail? or better yet.. post an image of it so i can see it in action?

@beamer3.6m..

my friend.. you have the same OTA as the one im hoping to buy.. but you have an HEQ5 mount.. i was going for an NEQ6 cuz i believed that HEQ5 isnt good enough for heavy weight and accurate tracking.. can you tell me the following..

1. how much does the OTA, guide scope, cameras etc weigh individually and combined?

2. how has your experience been with HEQ5? unguided and guided? has it felt inadequate at all? does it bear the weight well? or does it strain?

3. could you kindly post a couple of images of your setup? itll help me understand better "what goes where and how"..

4. how long have the longest exposures that youve been able to get by guiding?

5. if you could also post some images youve taken unguided and guided.. so that i can visually see the difference autoguiding adds to your experience..

6. what is the condition of light pollution at your site? at my home if i take a 30s dslr image at 400 ISO at an elevation angle of about 45 degrees, my exposures turn up bright orange.. but i do go on summer trips to northen hilly areas where conditions are much better..

as an addendum.. please also take time out to address these.. since you have the same setup as im trying to aquire..

1. what are the dimensions of the box that OTA was originally packaged in?

2. how well was it packaged? i intend to have the scope shipped from germany to norway to a friends place.. whos coming back to pakistan.. im very much worried about potential damage so im trying to have the OTA hand carried thru the flights.. how real are my concerns? is the packaging good enough to bear a little abuse that can be expected at airport security checks?

[beamer3.6m]

I will try to answer your questions but bare with me as it is 20 to 1 in the morning.

I am not sure the Explorer 200p and the Explorer 200PDS are the same and you need to check that. However I have found that the HEQ5 can easily handle the 200p on its own. In fact it does not even break a sweat.

I believe that the load capacity of the HEQ5 is 13 to 18kgs. The reason for the range is that imagers and observers place different values on their setup needs weight wise as imagers like to allow more room for the scope to operate below its max.

However, I am aware that the C80ED weighs in at around 3.7kgs I believe (or at least the web tells me so). I believe that the 200p (my version) is about 10kgs which puts me slightly over the imaging weight, however on top of this I have a DSLR which I hand on the Explorer and a QHY5 guide camera.

I have never found any problems with guiding with this setup although it might be 'too heavy' for some.

In terms of guiding my skies dont normally allow for more than 10 mins subs and the accuracy of your guiding will come down more to set up than the weight (assuming you dont go crazy).

However, if I were 6 foot tall and stronger (and had more funds) I would go for an EQ6 (or whatever it is called these days) as they allow for room to increase your scope size and payload. I would struggle to lift the EQ6 and this was important due to my previous need to setup and packdown my kit.

As for the box size they come in, you wont carry it home on your own on the train lets put it that way. The boxes are large and heavy. Delivery to home or work (if you have a car) is a good idea. My OTA is 1m long so the box will be longer to allow for packaging. I doubt you will get this on a plane as the tube is 8 inches in diameter so you have to imagine that the box will be 12inches square and over 1 meter long.

Hope that helps.

[AweSIM]

@beamer3.6m.. my apologies brother for inconveniencing you.. but thanks for the explanation.. .. it clears some things but i need to know a few things more.. ill wait at the convenience of your own schedule.. .. but whenever you can get time to respond.. kindly elaborate on the following points.. not now though.. this is just a reminder and a kind request ..or shall we say.. a check list.. ..

- an image of your setup..

- guided and unguided images youve taken with this setup..

- how well was the OTA packaged? youve made it clear it cant be hand carried.. that means itll have to go in the baggage.. is the packaging good enough to be safely stored in luggage? or should i rather not risk it..

many thanks in advance.. have a good night..

[AweSIM]

@paxo.. hey.. the software you mentioned.. PHD.. it looks very good.. although i dont have the mount or the camera it requires for operation.. it still looks great..

[Veracocha]

You might consider using a finderscope for guiding to cut down on weight. I went from a ST 80 to a 8 x 50 for guiding. Saves on weight/bulk.

[AweSIM]

@veracocha.. that was new info.. and not weight saving but money saving info too.. .. i couldnt however view the images you posted.. all images from imageshack appear as a frog inside an ice cube.. i suspect that imageshack has blocked a certain geographical range of IPs.. ..

[AweSIM]

addendum.. yay.. .. for sale forum now accessible to me.. ..

[ollypenrice]

I have an HEQ5 which I load with an Explorer 200p as my imaging scope and I use a C80ED mounted side by side as the guidescope.

I have managed 10 minute subs unguided with just the Explorer 200p but when guided long subs are easy.

The C80ED has is f7.5 whilst the 200p is f5.

Hope that might help.

10 minutes? Really? That would be good for an AP1200 let alone an HEQ5! How tight were the stars?

Olly

[beamer3.6m]

Verracocha how do you attach the camera to the finderscope.

[Veracocha]

Verracocha how do you attach the camera to the finderscope.

The adaptor at the top of this page. "t" type.

Accessories @ Modern Astronomy

[AweSIM]

can you guys post images of your autoguider setups please? or provide links to their uploads? im really interested in seeing how the whole setup looks and works.. if you guys could also take out time to explain the equipment youre using (guide scope, guide camera, OTA, OTA camera, mount, and software).. thatll be great.. .. thank a lot.. ..

asim sohail..

[ollypenrice]

can you guys post images of your autoguider setups please? or provide links to their uploads? im really interested in seeing how the whole setup looks and works.. if you guys could also take out time to explain the equipment youre using (guide scope, guide camera, OTA, OTA camera, mount, and software).. thatll be great.. .. thank a lot.. ..

asim sohail..

Sure,

Firstly on an NEQ6 we have, next to the mount, a Tak FSQ85. Piggybacked on that is an ST80 guidescope and piggybacked on the ST80 is a Geoptik camera lens holder with ATIK4000 in residence at the time of the pic. They are all rigidly mounted to each other but I always have a guidestar because the guidescope is F5 and the guide camera is a cooled Atik 16ic. The ST80 carries a finderscope aligned to the Takahashi.

This setup looks a bit top heavy but in fact works very well. I don't have to leave lens or camera on the Geoptik adapter if we are imaging in the Tak.

Then this is a TEC 140 apo with a WO ZS66 piggybacked, again rigidly, for guiding a Takahashi EM200 mount. I have actually swapped the 66 for a second ST80 because I want to use the 66 as a parallel imaging scope next to the Tak and use two cameras. Note that the guidescopes attach via these useful things http://www.baader-planetarium.de/sektion/s03/bilder/1530_gross.jpg from Baader so you can take them off and swap them round easily. (For some reason one of the 16ic guide cameras does not like one of the laptops and sometimes acts the goat so an instant swap of guidescopes is faster than a reboot/reinstallation when this happens.)

The ST80s both have the de-lensed Barlow they come with as extenders to bring the cameras to focus. They are excellent guidescopes provided everything is tight, notably the cast back section whose crosshead screws into the main tube must be tight. I also put a dob of epoxy resin on the Barlow extenders to keep them rigid, though it isn't really necessary. Mine will only ever be guidescopes. The fact that they can take the cheap and effective SW finder, for aligning to the imaging scope, is a big bonus in view of the price of Takahashi and TEC finders...

I guide in AstroArt at the moment but aim to try alternatives.

Olly

ollypenrice's Photos

[AweSIM]

@veracocha.. hey.. i just refreshed the page the blocked images suddenly are now accessible.. i guess you changed the image links.. .. and wow.. nice setup.. very nice.. .. how do you mount a second scope to the main OTA though? these look like double tube ring type thingys.. are these two separate tube rings screwed to each other instead of dovetail bars? the 8x50 and guide cam setup looks neat.. and your HEQ5 mount doesnt seem over-weighed.. maybe thats cuz the OTAs you have on this setup are short scopes whose turning moments arent that great.. i suspect if you had 100cm long newtonian like 200P and mount a second scope on that one.. the mount may not be as stable.. but the setup works for you.. and thats just great.. wow.. awesome setup.. good job pal.. nicely done..

@ollypenrice.. wow again.. impressive setup.. .. i doubt ill be able to get to that level anytime soon.. maybe in a year or so and 5000 EUR later.. .. but a couple of questions bug me.. regarding your setup and veracocha's setup too..

1. you guys are using refractors.. i understand that these must be apochromatic but why not reflectors? refractors are way more expensive than reflectors for the same aperture.. both of you guys are using refractors of apertures less than may 150mm i guess.. wouldnt you guys have been better off had you used 200mm or more aperture reflectors? why refractors?

2. i cant think of anything else.. .. awesome setups.. (drooling already).. .. thanks for sharing guys..

asim sohail..

pakistan..

[ollypenrice]

Oh no, not refractors versus reflectors! This is astro dynamite.

Speaking personally I use refractors for these reasons;

-plug and play. They don't need collimating, they have excellent mechanical integrity (keeping things lined up) and are totally predictable. Focus is easy, image shift doesn't exist.

-no diffraction spikes. I just don't like them and, more importantly, I regularly combine high res with widefield images which could not be done with diff spikes on one or both.

You are right that a Newt is cheaper and has higher theoretical resolution if, as is likely, it has more aperture. But it will need a high order of coma correction to match a Takahashi FSQ. This will mean that it will no longer be cheap and will be very fussy over orthogonality. Big tubes also catch the wind.

However, reflectors take great pictures too, but as a professional provider I need things to work, not to work 'when I have just fiddled with this for a bit...'

Olly

[AweSIM]

@ollypenrice.. thanks for that insight.. you listed them pretty well.. reflector vs refractor points.. i had a bad "departmental" refractor scope as my first.. and the experience has taught me to quietly stay away from them.. but seeing so many people with refractors and being able to get such good images from them.. im guessing it wont be long till i get a good refractor too.. once i have attained a complete SkyWatcher Explorer 200P DS kit first and learnt to use it properly that is.. ..

as a side note.. i just checked the cost of your Tak FSQ85.. its more than 3500 GBP.. the 200PDS im planning on is less than 350 GBP.. i know itll suffer from coma and other things.. but if it were for a comparable price id expect it to perform better too.. but i guess portability and wind cross section is important for you too which a newtonian cant match.. so why not go for an SCT or MCT? those tubes are closed, small, and im told perform better than refractors? does the decision come down to a personal preference (like initially mine towards newtonians) or to some quantifiable parameter (like now mine towards cost vs aperture)?.. thanks again..

[Veracocha]

My setup has the WO rings and a WO mounting plate/dovetail. On top the ring is threaded to take another scope via mounting rings. I had the 200mm newt on it before and wind more than weight was my problem.

[AweSIM]

aahh.. that explains it well.. .. thank you veracocha.. .. and thanks for sharing your setup.. both you and ollypenrice.. it helps a novice like myself to

1. understand what goes where and how..

2. realize how expensive is this hobby..

3. decide upon what new threads to start next.. ..

4. plan for the future.. what equipment i might be needing..

5. drool.. =)..

asim sohail..

[ollypenrice]

I know our Tak was crazy expensive but look; http://ollypenrice.smugmug.com/Other/Nebulae-and-clusters/M42CCBOV2010/1100345185_HHd4m-X3.jpg

http://ollypenrice.smugmug.com/Photography/Widefield-images-including/COCOON-450-980-2010/940313387_yM9Fg-X3.jpg

In my book it performs.

Imaging with an SCT (we do have one) is very hard work and the optics of the pre Edge/ACF ones are distictly ordinary once off axis. Also the long focal length makes them galaxy and planetary nebula hunters provided you have the accurate mount needed to guide at the long FL. And the seeing on the night. And a flattener reducer, and an aftermarket focuser, and the collimation is right, and you can keep the dew at bay.... All possible but not plug and play.

Olly

[AweSIM]

hi olly.. i checked your site out.. truly beautiful images.. lovely work.. three cheers mate.. you rock!!!.. .. and yea youre right.. SCTs are long FL scopes.. i forgot that.. my bad..

[AweSIM]

Hi,

I was just revisiting this post and wanted to thank you guys for your valuable advice and suggestions. Thank you so much. =)