Jump to content

1564402927_Comet2021Banner.jpg.a8d9e102cd65f969b635e8061096d211.jpg

SW 300P Flextube Auto First Light Report - 4th March 2010


Astro Adj
 Share

Recommended Posts

Date: 4th March 2010

Time: 2100 ~ 2300

Site: Dark Site nr Assington

Weather: Clear

Limiting Magnitude: 5.5

Seeing: 5/10

Transparency: 7/10

Guidance: None

Site Notes:

My first proper observing session with my new scope deserved a spot somewhat more conducive to DSO hunting than my back yard, and so I went for a drive and ended up at a spot just north of Colchester. There was a single tree to the northwest, but aside from that I had viewing that was completely unobstructed.

Observation Summary:

Today’s session had both highs and lows. Starting with the former, I had some splendid views of M42. I was also able to spend time looking at Mars, Saturn, M44 and M45. I’ve recently invested in an OIII filter as well as some new EPs, and pleasingly they all performed admirably. Unfortunately, I was rather disappointed with my views of M31, and had a number of teething problems with my new scope.

Comments / Report:

First of all, this report is…enormous! I don’t know how it happened, only that I started typing and ended up with pages and pages before I knew it! Sorry in advance for such a massive post, but after writing it all I couldn’t decide which bits to chop out so figured I’d just include everything. Please forgive the terribly unscientific presentation!

Due to various reasons I’d not been able to get out to observe properly (i.e. at a site that had acceptable levels of LP!) for some time. However my new scope arrived last week and so I was desperate to get out there and see what it was made of. The scope is a Skywatcher Skyliner 300P Flextube Auto – the name is almost as long as the scope! Anyway, my reasons for buying it were that I wanted to spend more time DSO hunting, whilst still having a scope that could provide good views of the planets. After reading some reviews I decided this was the scope for me. I am going to write a mini-review of sorts, so I won’t go on at length about the scopes merits here!

I set up at about 2030, and began observing at around 2100. Once again I managed to leave my star map at home, so had no material to use as a guide. However, sadistic as this sounds, I actually quite enjoy hunting for my prey so I didn’t let this worry me! I used a HoTech laser collimator to collimate the scope, and performed the alignment routine as advised by the manual (basically, point the scope North, turn it off then back on again – slightly easier than the procedure for the 130PM on its equatorial mount!). I immediately tried for M31, as I’ve been itching to get a proper look at this galaxy for ages. Unfortunately, even though I aligned the finderscope before heading out, it was way out of sync with my scope. I decided to use Mars as my target for alignment purposes, and after about 15 minutes had the finderscope crosshairs and my EP FOV aligned. I decided to study Mars as I was already pointing to it. Unfortunately I was unable to discern any detail, and found that there was a wash of light over and around the planet which impeded my viewing. It looked as though Mars was emitting light of its own as it extended from the planet out to about 4 or 5 times its diameter. I’d not seen this in my old scope, and the same effect was present when I viewed Saturn later too.

At this point I decided to try for M31 again. At this point I’d like to quickly say I am going to swap my finderscope for an RDF or similar zero power device ASAP. Finding targets is so much more difficult without the RDF! I moved the scope in azimuth first, aligning the centre of M31 with the centre of the OTA. I then used the hand controller to slew slowly up and down until the fuzzy revealed itself. This took about 10 minutes, due in part to the problems I encountered with the auto system. Whilst trying to make fine adjustments the motors frequently failed to respond to my inputs, and this caused me to ‘over-shoot’ my target my some margin when they did eventually respond! I’m not sure if this is due to the clutch not engaging properly or if there is just a certain amount of slack in the system, but it did make centering objects more difficult than it should have been.

Eventually I had M31 in the centre of my 32mm plossl. This gave 47x magnification, and I could make out the bright central core but little else. I then changed EPs to give varying degrees of magnification from 150x to 300x. Unfortunately I was unable to see any further detail than the original 32mm EP had displayed. I was rather hoping to see dust lanes, and the shape of the galaxy. At this point M31 was at an altitude of around 18 degrees. I wondered (out loud, as I recall!) if this was too low for the detail I was seeking to be revealed. I also questioned the collimation of my scope (as I was completely reliant on the HoTech working accurately) and even the optics of the 300 itself.

Feeling slightly disheartened at the view my scope provided of its first DSO, I decided to move on to a new target. There was only one option – M42. This looked stunning in my 5” 130PM, so with an additional 7” of light-gathering power (equivalent, I believe to around 5.5 times that of my other scope) I hoped this would be better. And it was. Again I started at 47x magnification, and could immediately notice more detail than I’d ever seen before. I decided that M42 would be the perfect object to test my new SW OIII filter on, and set about popping it into the 32mm. Back at the EP, and I could definitely see the difference. The outer edge of the large, curved part of the nebula was more apparent and the nebula itself stood out much more than the stars it contained. In fact, this effect was so apparent I now refer to M42 as The Angry Shrimp. You know, those little devils that have antennae specially adapted for boxing? Well that’s what it looked like – the stars themselves were leant a blue/green tint by the filter, further adding to The Angry Shrimp’s menacing appearance. The core of the nebula looked like the shrimp’s shell, and the curved could resembled his antennae, one sprouting in one direction and one in the other! I was so scared of his fearsome visage I decided to switch EPs in order to zoom in and change the view! Again I used every EP in my arsenal, and also combined a couple with my new Ultima 2x barlow. I was extremely impressed – whereas my old SW one clearly affected the image this Celestron model seemed to not impact the view whatsoever. I even popped my 5mm Hyperion into it (for 600x magnification) in order to study the trapezium further but was thwarted by my inability to a) focus the image and :headbang: keep up with the rotation of the Earth!

After that, I decided I would scan a few old favourites, hopeful that they would be as enjoyable. I had a look at The Pleiades and the Double Cluster in Perseus. Both were splendid. I then decided to have a look for M44, as I’d not seen it before. I could clearly see the 3 stars that form a triangle around it, and could make out a fuzzy patch by using averted vision. Thus began the process of manually moving the dob in azimuth before going to work with the hand controller. Again it took some time, but I was able to home in on M44. I enjoyed the view through my 32mm EP most, as at a TFOV of c. 1.11 degrees I could fit the majority of M44 into my FOV.

Next on my hit-list was Saturn. It looked splendid through my 10mm SW plossl, and I decided to combine my William Optics 20mm with the Ultima to see how the image changed. I felt the contrast was improved slightly, and where in the 10mm the body of the planet and the section of the rings that passed over it looked uniform, in the 20mm combo I could differentiate between ring and planet. I tried to push the magnification to 300x but met with little success. The peculiar light that impaired my viewing of Mars also made an unwelcome return, again extending 4-5 times the diameter of Saturn.

By this point I had lost all sensation in my toes. The prospect of a nice cuppa and a crumpet or two was commanding my legs to jump into the car and return home with all haste. However, I had one final target I wanted to observe. This, like M31, was one of the reasons I bought my new scope. I hoped it was visible, and began scanning the sky for Hercules. This took much longer than I’d hoped! The last time I looked at him, Hercules’ body was almost perpendicular to the horizon. This time I think he’d had slightly too much vino as he was at a very curious angle! As a result I was looking between the wrong stars for my target - M13. To add insult to injury when I did find the correct 2 stars I realized that a tree (in fact, the only tree anyway near me!) was completely blocking the view. I spent a few minutes wondering if I could move the scope, but as it would need to be literally in the middle of the road I decided against it. I asked the offending tree to move over several times but it was intractable. I took the fact I was talking to a tree as a sign that it was time to pack up, and decided to leave M13 for another night.

Overall I found the session to be a good learning experience. I have enormous respect for those brave souls who use a dobsonian without any kind of automated support. How they manage to nudge their scopes along when tracking targets is beyond me! I didn’t get the results I was hoping for, but I think that the seeing may have contributed to this. When performing a star test early in the night I the concentric circles surrounding the star at both intra- and extra-focus were jumping wildly, which I think indicates pretty average seeing. Unless this was caused by poor collimation? I’ve still got so much to learn!

I’m looking forward to my next session, hopefully it will be under more steady skies. I am also going to spend some time with the scope in order to get accustomed to the tracking (currently, even in tracking mode, I have to hold down a directional button in order to keep the object centered – a trick which isn’t particularly effective when I am at high magnifications) and the slack I encounter when trying to make small adjustments.

I’d also be extremely interested in hearing from anyone who can help me with any of the problems I encountered – I am sure at least half of the issues are down to errors on my part!

Thanks for reading, and apologies again for the wall of text.

Link to comment
Share on other sites

  • Replies 32
  • Created
  • Last Reply

Top Posters In This Topic

Adrian

Nice report :headbang:

It sounds like you have found a good observing site :p

Not sure what happend when you pushed the mag up on the planets. Could be ghosting in the eyepiece/barlow combination?

Cheers

Ian

Link to comment
Share on other sites

Good report - lots of learning going on there :p

On M31, I think you are using too much power to see it properly. It's a huge object - 8x the diameter of the full moon - even your lowest power will only be showing you the core area.

Interesting what you say about non-motorised / automated dobs - I've been tracking double stars at 340x with a non-motorised alt-azimuth mount tonight so it is possible and even enjoyable once you get the hang of it. It's only in the last 12 months that motorised, goto, dobs have been available so many of us have had to get by with "nudging" for years :headbang:

Do have another go at M13 - larger aperture scopes really do globular clusters justice. I was observing it with my 10" scope last night and it's really stunning at 92x with my Tele Vue Ethos 13mm eyepiece.

Link to comment
Share on other sites

Great report, entertaining, written well and not too long at all!

It's going to take a little time to get used to your new scope but I'm sure you'll suss it out in the end.

This may sound like a daft question but are you certain the "wash of light" over Mars and Saturn was not caused by a build up of condensation on the EP? I found this last night when I placed a dark, heavy blanket over my head and EP to block out any unwanted light - the moisture and heat from my breath kept generating condensation on the EP, causing a similar view to what you experienced.

Link to comment
Share on other sites

Nice report Sir! The length is fine. However, you are BADLY in need of a few (cheap) upgrades; Two Fleece jumpers, A thick fur-lined lumberjack coat and most important of all - a fleece hat, gloves and scarf (from a 99p shop.) Don't ignore the scarf - its the best bit of all. Also wear two pairs of trousers and socks.

I'm not kidding, for less than the price of an eyepiece you can upgrade your viewing ability no end! :-)

Steve

Edited by Steve922
Link to comment
Share on other sites

A large scope commands a large report :headbang: The auto dob is something i've fantasised about (if thats the right word) so i shall be watching your progress with interest. My Skywatcher AZ Goto mount has a certain amount of play in the gears when using high magnification i.e. when the object drifts to the right and the left directional control is used to bring it back the object will sometimes carry on moving left until i use the right control to bring it to a standstill then it settles down again.

Link to comment
Share on other sites

Thanks for the comments everyone. I love this forum as I learn so much in such every time I log on!

Ian, I've heard of ghosting, but need to look into it further. Am I right that it's caused by light moving through the inside the of the EP being dispersed? I will try again to see if it is the magnification that was causing the problem (regardless of EP) or whether it only occurs with specific EPs. That might help isolate the issue!

Seb, I'm hoping the 300P will indeed open up so new objects. Ideally I'd like to work my way through the Messier list for a start. I like the idea of having set objects to locate, and the Messiers seem as good a place to start as any!

John, are you able to go up to 340x regularly? I understand that ordinarily 300x is about the most we can use in the UK? I was rather hoping this was not the case! I will definitely try for M13 again soon. I think your Ethos (very jealous, btw) should give a TFOV of around 1.08 degrees, and with a 32mm EP I believe my TFOV is around 1.11 degrees. So it sounds like that would be a good place to start!

Is there an accepted 'best' magnification for M31? I have been thinking about getting another EP to give a wider FOV, however I think I'm right in saying that if I push the focal length of the EP past 35mm I'll end up with an exit pupil in excess of 7mm. What sort of effect would this have on the image?

Steve, thanks for the tip! If it is indeed condensation, are there any paricular ways to let the EPs rid themselves of it?

Steve - good suggestion! I actually found a lumberjack jacket in Asda for £8 2 weeks ago, and it was lovely and warm. I usually wear walking boots with 2 pairs of socks, but stupidly forgot to wear them!

Link to comment
Share on other sites

Fantastically written and enjoyable report. A 12" scope under 5.5 skies will show you so much it's hard to believe. As for having enormous respect for those brave souls who use a dobsonian without any kind of automated support. How they manage to nudge their scopes along when tracking targets is beyond me. This part is simple to answer it is balancing. If your scope is perfectly balanced in Alt and Az then it's a doddle to track objects.

Link to comment
Share on other sites

Great report and a very entertaining read.

I'm sure as time goes on you will get to know your scope better and sort out some of the issues you have identified.

I am a 'nudger' myself and have never found it difficult - it's what you get used to I guess.

I'm looking forward to your next report now :headbang:

Link to comment
Share on other sites

Nice to hear about your new scope Adrian. And I am only slightly jealous! :headbang: The Angry Shrimp Nebula is going to be difficult to forget from now on, very funny.

I was interested to hear about your halo experiences with Mars, I get the exact same thing with Mars and Saturn. Yet I didn't have the same problem with Jupiter which was every bit as bright. I am thinking the misting up of the lens is going to be the problem as WebSentinal suggested.

Looking forward to reading more of your experiences with this scope.

Link to comment
Share on other sites

Stuart, that issue sounds similar to the one I experienced. Do you also find that sometimes you need to hold the button down for a certain period of time (maybe a second or 2) before the scope responds? That is the main problem I have, as the movement takes me by surprise and I end up over-shooting my target by some margin! I am going to try 'stabbing' the buttons rather than holding them now - I am hoping I can learn how many stabs it takes to get the scope moving, and therefore be more accurate when it comes to stopping the movement. If that doesn't work I'll just keep practicing in order to learn when the scope will begin moving.

Mick, thanks so much for the link you provided. That list is an incredibly useful aid, and I've already printed it out and popped it into the folder I keep all my maps/sketches etc in. I think it will rapidly become my number 1 tool when I'm out and away from the wonders of Stellarium!

I've given some thought to balancing my scope. With my 130 it is simply a process of adjusting the counterweight, but I imagine balancing a dob requires a little DIY? I was thinking of attaching some circular weights to the end of the OTA, but then realised I'd need a method of actually testing how much weight I required and a way to adjust the load depending on what EP / camera set-up I was using. Not to mention a way to actually get the weights themselves on the scope without them tumbling off each time it is moved! Any ideas? Also, I think I'm right in saying that this will only balance the scope in Altitude - how should I go about Azimuth balancing?

Steph, you are probably bang on the money there! My first scope had slow motion cables, so in a way I have been spoiled when it comes to fine adjustment! Having said that I am looking forward to becoming more proficient with the new scope - it will just make any successes I have even more satisfying as I'm having to earn them!

Julian, very interesting to hear you experienced the same problem when observing. I also didn't see this effect when looking at Jupiter, but attributed this to the scope as opposed to conditions. But now I think about it, I was able to pop out in little more than a t-shirt when Jupiter was visible, whereas observing now requires Eskimo impersonation. Do you think the EPs also need time to cool down in order to work optimally?

I've attached a couple of pics below, I realise everyone has probably seen this scope before, but thought it might be useful to show a size comparison between the 130 and the 300. I am pleased with how compact it is when collapsed - when you take into account the space needed for the tripod and mount, the 300 doesn't really take up more floor space than the 130 with all its bits!

post-16962-133877431511_thumb.jpg

post-16962-133877431521_thumb.jpg

Link to comment
Share on other sites

I've been wondering about my nudging skills and realised that I'm more of a 'drifter' (as in let the object I'm looking at simply drift through my FOV).

:headbang:

ha ha

I'm a drifter too. this is the main advantage of the better eyepieces I think - esp. with faster scopes like dobs.

great report - very much mirrors my own experiences but not got round to writing a report yet - will do eventually. I even found something 'all on my own' the other night a small patch of nebulosity called VDB53 http://stargazerslounge.com/observing-deep-sky/99041-nebulosity-south-orion.html

the other night I was watching also Saturn drift across my view at about 220x - Cassini division - at least three moons - just awesome.

Edited by Moonshane
Link to comment
Share on other sites

Regarding the problems with planetary views, I've had similar issues with my Flextube 300P (which I've been using for about a year). The four diffraction spikes are very bright round all stars, and around planets they turn into searchlight beams, while the planets themselves show a lack of contrast by comparison with the views I had in my 8-inch.

The spider seems suitably thin and the arms in mine are properly aligned, so although one option would be to replace it with a curved-vane spider (eliminating spikes), it wouldn't necessarily deal with the poor contrast, which seems to be coming from somewhere else. There are various possibilities:

1. Collimation (easily checked - mine's fine).

2. Excess stray light.

3. Defective mirrors.

4. Other things I haven't thought of.

I'm currently looking into option 2, if that doesn't work then the answer could be 3 or 4.

Regarding 2, there's certainly a lot of stray light reaching the focusser of the Flextube. This is not necessarily because of the open-tube design: I have the Astrozap shroud and it doesn't make much difference to contrast, nor does my dewshield. The low-profile 2" focusser is a big hole that lets in a lot of light from places other than the secondary.

Looking through the empty focusser in daylight (see photo below) there are three sources of visual noise:

1. The edge of the secondary (left of centre).

2. Light inside the drawtube.

3. Light on the tube wall opposite the focusser (including a shiny screw on the black tube rim, seen right of centre).

The pic shows the view that a 1.25" eyepiece gets. Without the 1.25" adaptor you see a lot more tube wall. All my eyepieces are 1.25" so that's sufficient problem for me to deal with.

Since taking the pic I've blackened the secondary edge with a Sharpie pen, and am about to put flocking inside the drawtube, then I'll flock the visible patch of tube wall opposite the focusser (and paint the shiny screw black). I might also add an annular baffle to the bottom of the focusser drawtube. If that doesn't improve planetary views then I'll just have to keep trying. The primary mirror clips may also be adding some diffraction noise. If the problem is incorrectly figured mirrors then masking the outer edge of the primary might help. Really, you could go on forever with this stuff- though since I got the scope for deep sky I'm not in a hurry and won't try too hard.

But your report underpins something I've felt ever since acquiring this scope: it's great for deep sky but not great for planets, and not a scope for someone who wants an "all rounder". My 8-inch f/6 was better for that.

Andrew

post-14602-133877431843_thumb.jpg

Link to comment
Share on other sites

Andrew,

the image you posted shows the secondary needs to be rotated slightly to appear concentric with the primary.

You can easily check the accuracy of your optics using a Ronchi ( Ron-kee) grating at the prime focus. These simple gratings, usually 100 lines/ inch will quickly show any under/ over correction - turned edges- dog biscuit etc on the optics.... only takes a minute to check.

Ken

Link to comment
Share on other sites

Thanks - actually I just held my camera up to the focusser so the secondary looks rotated: the camera wasn't exactly square to the focal plane. I should try a Ronchi grating though - any idea where I can get one?

Edit: Just saw them on Orion Optics UK, £75. Ouch!

Edited by acey
Link to comment
Share on other sites

I have one you can borrow...

Just drop me a PM.

Ken

ps You don't need anything more sophisticated than a fine mesh.... I've used fly mesh door screen and tea strainers in the past....you can also print a suitable 80 or 100 line/ inch on a transparency...

Link to comment
Share on other sites

Twotter, I can definitely see the appeal of wider FOV EPs! I may well invest in an ultra-wide EP, but first need to discover what focal length I will get the most use out of.

Shane, it would be good to hear how you got on - do get a report posted if you can find the time. It's the best feeling to find something unassisted, isn't it? It was one of the main reasons I decided against a scope with GOTO capability. I also stumbled across the link to the TriAtlas charts through your post - so thanks for that!

I had a look for the Cassini division but couldn't make it out. I hoped this was because the rings were almost completely edge on, but perhaps the combination of my inexperience and contrast issues conspired against me. Did okay on moons though - I counted 5 at the EP, but a session on Stellarium the next day revealed that one of my moons might well have been a star. But I'm certain I spotted Rhea, Enceladus, Dione and Titan. :headbang:

Andrew, thank you for the very informative post. Interesting to hear you have experienced similar problems to me, and it adds some assurance that it's not just my scope that has an issue - I'd hate to think my mirrors are at fault but it's a difficult thing to test, especially as I don't yet know what the scope should be capable of.

I did a little research on the subject of curved-vane secondary supports, and found an interesting image which I've posted below. Although I do get the classic 4 spikes when viewing bright stars, the effect that blighted my viewing of Saturn was very similar to the picture showing how the diffraction looks with a curved support - a roughly circular haze engulfing the planet! Very strange.

On collimation, although I'm happy the scope is collimated as accurately as it can be (cross-hair is bang in the middle of the doughnut, laser reflected by the primary is dead-centre on the grid on the collimator) I understand it could still be out of alignment if there is even the slightest discrepancy with the collimator itself. How do you typically test your collimation? I tried intra- and extra-focus on Sirius, but the concentric rings were moving too much for me to see if they were spaced correctly. Are there any other techniques I can use as a test?

I'd be very interested in seeing if you experience any success with your DIY projects to eliminate stray light. I am THE most cack-handed buffoon when it comes to things like this, and would almost certainly do more harm than good if I tried to do something like this. However, if you get on well with it I might have to give it a go!

Chris, I think I might have caught filter fever now. I've not had the chance to use my LPR filter yet, but I was really pleased with the OIII. Next on the list is a set of coloured filters for planetary viewing, I just need to learn more about them in order to decide exactly which set to buy.

Ken, would you be kind enough to expand on your post regarding rotating the secondary? I was just wondering if my mirror needs attention, but I'm not 100% what it should look like in relation to the primary.

post-16962-133877431882_thumb.gif

Link to comment
Share on other sites

The LPR filters are a great asset (I have the UHC which is the same thing) as I am sure you will find out...

I have limited LP but do have a glow in one direction...but for contrast it certainly adds to the experience and makes observation of feint objects much more pleasing to the eye.

As for coloured filters try and pin down a set - as for planets different filters bring out different essences of the planet you are observing...

Chris

Link to comment
Share on other sites

Stuart, that issue sounds similar to the one I experienced. Do you also find that sometimes you need to hold the button down for a certain period of time (maybe a second or 2) before the scope responds? That is the main problem I have, as the movement takes me by surprise and I end up over-shooting my target by some margin! I am going to try 'stabbing' the buttons rather than holding them now - I am hoping I can learn how many stabs it takes to get the scope moving, and therefore be more accurate when it comes to stopping the movement. If that doesn't work I'll just keep practicing in order to learn when the scope will begin moving.

You know i think that could be where i've been going wrong i've been holding instead of stabbing the buttons. Maybe the term "clicking" would be a less violent expression....having said that in times of frustration i have considering shaking my fist at the sky and thrashing my scope with a tree branch Basil Fawlty style! Seriously though it may just be a delay in the signal from hand control to mount making one instinctively hold down the button which then causes it to over shoot. I had this happen with Saturn the other night...moving left then right then left again....like i was playing video tennis! So last night i clicked......it moved after a moment then stopped i clicked again and after a second or two it moved and stopped again, so no over shooting!

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.