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M Astronomy

Imaging with a Star Adventurer

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Posted (edited)
23 minutes ago, tooth_dr said:

I’ve just started imaging on a SA with a Nikkor 180mm. The total weight of my camera and lens and dovetail and remote trigger is 4 1/4 pounds ? (1.92kg)

The lens seems to present no trouble without a bracket holder. I took this last week - 16 x 120s ISO400 F2.8

 

Very cool shot, and nice lens! You have the AF version which is a little lighter than the AIS version I bought. Mine's not AF so probably not usable outside of AP, but mine was probably quite a bit less expensive at $200 used. Good to hear that your camera has no trouble holding it, though.

Edited by bokchoy ninja

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Hi, after a 2yr absence (sold my Celestron 8" scope to fund baby things) I have ordered a Star Adventurer which hopefully should be arriving tomorrow. 

I have a Canon 700d with 3 lenses. 18-55mm f3.5-5.6. 55-250mm f4-5.6 and a 50mm F1.8 

Does anybody have tips, must do's or extra things to buy to aid my experience?

 

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It's a good idea to fit some sort of RDF in the hotshoe, get a bright star centred in live view and then centre the RDF on it as it's quite tricky figuring out where it's pointing.

Dave

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Posted (edited)
9 hours ago, Radders said:

Hi, after a 2yr absence (sold my Celestron 8" scope to fund baby things) I have ordered a Star Adventurer which hopefully should be arriving tomorrow. 

I have a Canon 700d with 3 lenses. 18-55mm f3.5-5.6. 55-250mm f4-5.6 and a 50mm F1.8 

Does anybody have tips, must do's or extra things to buy to aid my experience?

 

Hi, and thanks for posting.

I’ve had my Star Adventurer (SA) mount since April 2017 and found it a lovely piece of equipment for taking wide field images. Used within its operational capabilities it works extremely well, the tendency is to push too long a FL optic or payload weight onto it.

You will need to factor in a suitable, rigid tripod to hold the SA and your experience with the SA’s wedge will vary. Mine was very stiff to use and coarse so I did away with it and used an old Celestron heavy duty Alt-Az mount which is way smoother when polar aligning. Your experience will of course vary.

The large clutch on the SA can get over tightened but Sky Watcher produced this video to help rectify the matter-

 

You soon get to judge what tightness is needed on the clutch and how to do things in the dark!

When polar aligning the SA’s polar scope is very decent and if you employ the SkyWatcher Star Adventurer Mini App you can use the polar clock capability to accurately set Polaris. My advice would be to finish polar alignment when Polaris is at either a major division (eg 0, 10, 20, 30 ,40 ,50 minutes) or at the half way point (5, 15 etc.). This accuracy can make the difference when using longer FL lenses. I was able to increase the exposure time at 300 mm FL from 150 to 180 seconds using this technique.

The polar illuminator that comes with the SA is annoying and has a tendency to drop off until you use some tape to secure it.

Using the SA you come to the point wondering what sub-exposure length to adopt as with short FL lenses you find you can track for ages. There’s a law of diminishing returns as far as exposure time goes, especially if your location is controlled by local light pollution. With shorter FL lenses such as 135 mm I’ve been quite able to obtain exposures of 15 minutes but depending on the light pollution where you image a much shorter exposure time may suffice. Here the speed of your optics will come into play. I generally use a 135 mm Samyang f/2 lens with a clip-in Astronomik 12nm Ha filter and find 300 seconds an optimum exposure time, I have done longer but 300 second sub-exposures do the job and now a spoilt frame due to cloud only loses 5 minutes of the session. The 300 seconds sub-exposure time came partly out of extensive imaging and using the histogram in BYEOS to best judge what I considered was an optimum exposure time, it comes out pretty close to what is explained and calculated in the presentation below. 

You might find this sky fog calculator useful- http://tools.sharpcap.co.uk/ with it you can determine the amount of light pollution at your imaging site and employ the value to provide a value for your optimum sub-exposure duration depending on your optics, local light pollution level, type of camera (colour/monochrome) and any filter you are using. This presentation is very rewarding on the matter of what sub-exposure lengths to try and well worth watching all the way through-

 

You could skip the very interesting presentation and go to 49.12 in the video where the formula for calculating your Optimum sub-exposure time is given. Provided you know the read noise of your DSLR, how much sky glow you have and how much extra noise you can tolerate in the image you can quickly work out your sub-exposure length. For my set up the sub-exposure time calculates to 312 seconds if I accept a 3% added noise so close to my 'suck it and see 300 seconds actually used.

I hope this all helps, I’m sure you will really enjoy the SA mount and look forward to seeing your posts on SGL in the future.

Best Regards,
Steve

Edited by SteveNickolls
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Posted (edited)

Hi Steve, are you getting  consistente 300" subs @ 135 MM unguided?

The same for 150-180" @300mm, unguided too?

If so I find that you have an exceptionally good sample. Mine, even with perfect Polar Alignment, doesn't even get close to that due to Periodic Error and high frequency harmonics... 

You lucky guy! 

Fabio 

Edited by FaDG

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5 hours ago, FaDG said:

Hi Steve, are you getting  consistente 300" subs @ 135 MM unguided?

The same for 150-180" @300mm, unguided too?

If so I find that you have an exceptionally good sample. Mine, even with perfect Polar Alignment, doesn't even get close to that due to Periodic Error and high frequency harmonics... 

You lucky guy! 

Hi Fabio, Sorry to hear your experience with the SA has not been so good.  I have only just recently been working to bring my old CG-5 Go-To mount back into use and learning how to use PHD2 and decipher its graph to check how the mount is performing. I've not thought it necessary to use it on the SA so no idea what its PE etc are like. Are you using a PoleMaster accessory to obtain your alignment on the SA mount?

I have been very pleased with how the SA tracks finding the supplied polar scope so much better than the old Celestron types. It didn't need any adjustment from the factory when checking the polar scope was aligned in the mount. As I mentioned in an earlier post I did find the SA wedge quite poor so it's very likely that quality varies with each part of the assembly, luckily I replaced the wedge for an old Celestron Alt-Az mount/tripod I had lying around which is so much smoother to operate for polar alignment and probably more sturdy than a photographic tripod. I didn't mention before but a house brick (about 3kg) is placed on the eyepiece tray to keep everything steady. 

Regarding subs at 135mm yes my standard exposure length is 300 seconds and unguided the only time I had an issue was when I had not balanced the set up properly to image at a high elevation and found a few slipped frames.  Most of my imaging is relatively wide field with the Samyang 135mm lens at around 6 x 10 degrees but good for making mosaics. Here's a 4-pane mosaic of part of Cygnus from last October each pane was made from between 18-24 300 second light frames with matching dark frames from my library and master bias and flat frames, I've used StarTools to turn it into an inverted image so you can see the stars better, the Samyang gives good star shapes-

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As I've been busy on the few decent nights this season making mosaics I've not used my 75-300 mm lens much to follow consistently up on the 150 and 180 second exposures performance but may next season give this lens more of a try. After imaging at f/2 using the stock zoom at around f/6 is so ponderous.

Again I'm sorry to hear you have had less fortune with your SA mount. Just a thought, is it still under warranty to return it to the retailer?

Best regards,
Steve

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Posted (edited)
22 minutes ago, SteveNickolls said:

Are you using a PoleMaster accessory to obtain your alignment on the SA mount?

No, PA done with the stock polarscope which is perfect. I had zero (0!) dec drift in 10 minutes. 

Differently from yours, my wedge works great, no wobble at all, and is associated to a sturdy wooden tripod. 

The issue is in the head though: the total value of the PE isn't bad, but there is a high frequency harmonic preventing longer FL. it can track without limits below 100mm, but above it's a pain. 

The mount is out of warranty period, but anyway Skywatcher does not commit on a performance, so actually it works. 

With their QA Level and at this price tag, it's just a matter of luck in getting one that works BETTER! 

I'm happy for you. 

Edited by FaDG
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8 hours ago, SteveNickolls said:

With shorter FL lenses such as 135 mm I’ve been quite able to obtain exposures of 15 minutes

That's pretty darn impressive, 900s exposures.

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1 hour ago, FaDG said:

The mount is out of warranty period, but anyway Skywatcher does not commit on a performance, so actually it works. 

With their QA Level and at this price tag, it's just a matter of luck in getting one that works BETTER! 

Sorry to hear this if I'd known performance could vary so much I'm not sure I'd have committed to getting one. I'm aware there are a number of different maker alternatives out there on the market for this caliber of mount.

Best Regards,
Steve

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I'm fairly new to my Adventurer - I bought it last October/November so that I can take it abroad but I've been monitoring this thread for some time and have to say I'm very enthused about the prospects .  With a mate's assistance, we took mine out for a test last weekend - The transparency was atrocious, but we went through the process of setting it up and all seemed to perform pretty much in line with what I expect to be using it for...

However, as I've always used a goto mount (and/or platesolve), I knew that was one thing I was going to miss badly when trying to find DSO's at longer FL - To my shame, starhopping doesn't come naturally to me :icon_redface:.  However, we thought we'd see how a 70-200/f2.8 would perform - No problem getting Arcturus in the frame and again, tracking / focus looked promising, so we thought we'd see if we could get M3 on the sensor @ 200mm...  and failed miserably... even when zoomed out to 70mm!

Unfortunately using setting circles was / is also beyond us both (again, FAR too used to the simplicity of goto / EQMOD / platesolving!), but I did find an interesting article for manual goto using dead reckoning on DPReview, so thought I'd post it here in case anyone else is in the same boat as me. 

A “Manual Goto” method for use with the Star Adventurer mount

When using a simple mount like the Skywatcher Star Adventurer with a telephoto lens to photograph faint deep sky objects, the problem arises of how to locate the target.

This is a manual GoTo method that allows the mount to be moved from a known position to a desired new target position using dead reckoning.  It only works if the camera is mounted on the Star Adventurer “Fine Tuning Mounting Assembly”: the necessary control is lost if the camera is mounted on a ballhead.

The method makes use of the fact that object coordinates in the RA/Dec system are readily available (ie Stellarium app) so that a move from one place to another can be easily described in terms of a change in RA and a change in Dec coordinates. The key is that the motor on the mount only moves the imaging camera in RA, and the control knob on the Dec bracket only moves the camera in Dec. Thus, the necessary RA correction is made with the motor (and the N/S direction slider) and then the necessary Dec correction is made by turning the control knob on the Dec bracket.

The detailed procedure is as follows.

·         Find the coordinates (RA in hours / minutes / seconds; Dec in degrees / arcminutes / arcseconds) of an “easily identifiable star” near the target

·         Find the coordinates (RA, Dec) of the target.

·         Work out how many minutes RA must change to move from the initial star to the target and how many degrees Dec must change to move from the initial star to the target

·         Calculate the direction (S or N on the mount three position slider) and time that the mount needs to run at 12x speed to make the necessary RA correction:

·         Observers in Northern Hemisphere:

For every minute increase in RA coordinate, the SA has to run [S, 12x] for 4.62 seconds.

For every minute decrease in RA coordinate, the SA has to run [N, 12x] for 5.45 seconds

      NOTE:  Opposite for Southern Hemisphere

·         Calculate the number of rotations of the Dec adjustment knob that are needed to make the Dec correction, given that I measured one full rotation of the knob to be equivalent to 2.95 degrees.  The knob has 10 ridges on it, so it’s easy to make 1/10 of a turn, or about 0.3 degrees.

If Dec needs to increase, the knob must be turned so that the camera turns towards the N celestial pole.

If Dec needs to decrease, the knob must be turned so that camera turns away from the N celestial pole

 

·         Get the mount polar aligned and turn tracking on at the normal 1x rate and direction

·       Centre the camera on the “easily identifiable star”

·       Make the RA adjustment [turn tracker off; set N-S slider appropriately; set speed to 12x; wait the required time; turn tracker off, set N-S slider appropriately for normal tracking; turn normal tracking back on]

·         Make the Dec adjustment

 

I’ve tested the procedure (Northern hemisphere settings) by moving from Elnach to a point between the Jellyfish nebula and the Shoe-buckle cluster.

·         The overall angle between Elnach and the target was 11 degrees and 45 minutes

Initial star (Elnath) is at:                      RA 5h 27m 31s   Dec 28 degrees 37’ 15”

      The target was at:                                RA 6h 14m 56s   Dec 23 degrees 28’ 19”

      Difference:                                            RA + 47.5m         Dec - 5 degrees 9 m

·         Location after the GoTo move:          RA 6h 11m 25s,   Dec 23 degrees 40’ 15”

Error:                                                   RA – 3.5m            Dec + 12m

Overall, these errors mean that the image centre was about 50 arcminutes from the desired target.  A 300mm lens on an APS-C camera has an angle of view of about 5 degrees so an error of less than a degree means, with this sensor size and focal length, that the target will be within the field of view after the GoTo move.

Has anyone used a process such as this (or something similar?).  If anyone has any experience/tips on framing at longer FL, please pile in :).

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7 minutes ago, AndyUK said:

If anyone has any experience/tips on framing at longer FL, please pile in

It's a whole lot quicker to fit an RDF in the camera hotshoe then start on a bright star near the target and centre it in live view and in the RDF it's then a simple matter to take images and star hop to the target using Stellarium or similar, fine adjustment can be done 2 arrow buttons and the screw adjuster on Dec.

I just filed down a cheap RDF but purpose made adapters are available

Dave

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Hi Dave, I do have a hot-shoe mounted RDF and of course once calibrated that makes it easy to get to the closest high mag/named star (which I can just about manage using my phone to help :))... it’s just that hop from that star to the DSO I struggle with, especially when I’ve been trying to use the ball-head (ie not RA buttons / DEC  knob on the adjuster)...

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Hi Andy, I use this method with the 300mm lens mounted on the dovetail bar, no ball head, once the star is centred I move half a frame at a time, taking short exposures, towards the target so trying not to get lost and comparing stars to Sky Safari on the phone as I go until arriving at the target, recently found some dim comets using this method that weren't really visible in one exposure unless comparing the stars to the SF screen to pinpoint them then taking longer exposures.

Dave

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Thanks Dave - It looks as though my error is trying to use the ball-head for framing rather than relying on the "fine tuning mount assembly"...

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Ball head is fine for wide angle lenses in fact they need it for framing but tele lenses with the rotating mounting foot work pretty well for framing stuff.

Dave

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Got my Star Adventurer the other day. Not had a chance to try it out yet although debating whether to tonight but the near full Moon is putting me off. 

 

Do people most commonly attach their ball head directly to mount itself or the L bracket? I tried to attach my ball head to the black thing on the end of the L bracket but the thread was too big on the ball head. Is there a way round this or just attach my dslr directly to it? 

 

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Posted (edited)

You can get tripod thread adapters to reduce the thread.

I use mine on the dovetail bar so I can still check the PA during imaging.

Dave

https://www.ebay.co.uk/itm/Tripod-Head-Thread-Reducer-3-8-Female-to-1-4-Female-Adapter-German-Made/380716541010?hash=item58a4796452:g:08AAAOxyhs5SMEpR&frcectupt=true

Edited by Davey-T

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Cheers Dave I'll order one of them. Is that how you mount yours? On the black thing or with ball head on the end of L bracket? 

How about your polar scope illuminator? Special adaptor to fit the L bracket? 

 

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Yes I mount the ball head on the L bracket, I filed the slot out to fit the polar scope illuminator as adapters weren't available at that time.

Dave

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34 minutes ago, Radders said:

I'll order one

you sure it wasn't in the kit? I had one with mine

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12 minutes ago, Radders said:

Hmmm. I'll have a look.. 

Usually comes with the ball head.

Dave

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Managed to try the Star Adventurer for the 1st time last night. Put a 18-55mm lens at 18mm, done a rough Polar Alignment ie just facing North at the right latitude and level tripod didn't use the Polar Scope. I was getting trails at 30 seconds. I thought this can't be right. It took me 10 mins of faffing around before I realised it was set for the Southern Hemisphere. Duh! Anyway I took 8 subs at 2 mins each, no darks and stacked them in DSS. Quick edit in Lightroom. 

Do the Stars look ok? I find focusing on live view at x10 really hard to get pin sharp. 

 

LRM_EXPORT_23808052222855_20190422_225451922.thumb.jpeg.8465753af2864cf952245ef2afb57dd4.jpeg

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Just a quick question, is it essential that you calibrate the Polar Scope? 

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