rl

superb..

There might be some merit in working out the field you will get with various scopes, correctors and cameras, just to get an idea of what will fit in. You would need to choose a coma corrector for the 130PDS, or a flattener for the ED72. These extras frequently modify the focal length. Are you planning on using a Canon DSLR or a proper astro cooled camera? Most midrange Canons come with an APSC-size sensor which is 16 by 24mm ...with a 420mm focal length this gives you roughly 2 by 3 degrees on the sky. This is fine for M42 but too small for M31 unless you're planning on doing a mosaic. Globulars like M13 show up reasonably well but are a bit small on that scale. The moon looks a bit on the small side and could use a Barlow. If the HEQ5 is ruled out on cost, then an ED72 on an EQ5 pro isn't a bad place to start. The ED72 also makes a robust travel scope and comes in a nice case. They come up fairly frequently secondhand for about £250.

It's probably early days yet if you're just starting imaging, but do you expect to stick with it? Or are you just testing the water at this stage? If you do stick then you will probably want to upgrade fairly quickly from an EQ5.....to a HEQ5 or maybe even an EQ6 mount depending on portability requirements. You are possibly more likely to stick with it starting with a good mount...there will be enough other problems to get right. I just wonder if it's worth taking the financial hit trading up...or just save up for the HEQ5 in the first place. If you can find a secondhand HEQ5 it won't be that much more than the basic EQ5pro..they generally change hands for about £600-700 if you can afford to wait. As I've put in another thread somewhere, the 130PDS is a real giantkiller in skilled hands. By AP standards it's an absolute bargain. But you might not get on with the diffraction spikes, and collimation is just something else to go wrong and ruin an otherwise excellent imaging session. The HEQ5 leaves you with more options if you do choose to change the scope. Small refractors have a reliability that Newtonians always struggle to match. I'm the Newt's biggest fan but for AP in the less than half-metre focal length range I'd take a small apo/ed frac any day, cost permitting. Vlaiv's point is a very good one....the HEQ5 was actually designed to do AP rather than the facility being added on as an afterthought. Best of luck whichever way you go...there is a lot of support available on this site.

@geeklee Thanks! As you've already got the mount it costs nothing to try.... It's nice sometimes to have an alternative widefield shot alongside the main event on the Newt. I wouldn't advocate using a C8 on the counterweight bar and expecting it to work or using the extension rod either...but as shown mine works just fine.

@geeklee Yep..I know, it does rather break the rules for accurate guiding! I used the setup in the photo to take a spectrum of RS Ophiuci last night. The gold box in the Newt focuser is a spectroscope. There is a red ZWO guide cam in the spectroscope keeping the star on the slit. On the counterweight bar is my TS65Q. So.. the mechanical connection between the guide cam and the TS65 goes through the spectroscope, the Newtonian ( rigid carbon fibre), Newt cradles, AZEQ6, counterweight bar, extra saddle. It's tenuous at best but it does seem to be reliable; I've used the setup on several occasions now. I took 20 by 1 minute exposures and all came out with round stars....and this is the general experience. One of those subs is in the RS Ophiuci nova thread. The setup in the photo is pretty much perfectly balanced in both axes, and I use a polemaster which certainly helps...PHD2 does almost nothing in dec corrections. I think the move to a bigger diameter counterweight bar was a very good move over the EQ6. It's much more rigid. One man's experience with a sample of one mount. YMMV....

I've had the AZ-EQ6 for 6 years and never had a problem with it. It's been excellent. I thought the AZ feature might be useful but I've always used it in equatorial mode. Typical RMS errors measured with PHD2 are about 0.5 to 0.7 arcsec with a 12kg payload (8" Newt plus accessories), and that is without any mechanical modifications or faffing about with the PHD2 variables. The extra saddle is useful in that you can use a short/ medium focal length refractor plus camera as a counterweight which allows two exposures to be taken at the same time. The whole setup is rigid enough that guiding on the main scope is good enough for the secondary scope on the counterweight bar. The basic EQ6 has always been a good mount but the later AZ-EQ6 and EQ6R do address a lot of minor shortcomings, albeit at a price. If I were buying again I'd look carefully at the EQ6R simply because it can handle a couple of kilogrammes more.

Time well spent. Hope to see more of those!

Turning a bit redder now (12 August 2300 UT) ,Bright star in centre of image: 60 seconds, TS65Q (420mm focal length, Canon 1100D modded, iso 1600), Skyglow Imaging filter, north at top. Raw spectrum: Hydrogen markers in green.

One man's search for optical perfection is another man's OCD....we all have our own standards on this one. Getting it off is not a big deal but sometimes unwarranted perfectionism causes these jobs to snowball.. Can you blow it out? Camera shops sell proper clean compressed air cans for this purpose. Could you get your hand inside the tube without knocking the secondary? Do you feel happy removing the mirror / cell assembly? Once you get the mirror out, you often see a lot of stuff you can't see from the top, like water sleaks and dust, none of which really impact the view. But then you're into cleaning the mirror properly just to make the job worthwhile....not a big deal with a lint-free optical cloth, distilled water and a drop of washing up liquid. But it's still a risk. Do you feel happy recollimating after reassembly? There is a good case for leaving it alone at the moment. If it is a bit of leaf I can't see it doing much harm long term provided it's dry. Personally I'm not in the camp that recommends cleaning a mirror one every 20 years whether it needs it or not, I like my mirrors fairly clean and probably take them out about once a year for this purpose. Not sure that helps much...

@robin_astro.. Robin Thanks for the input; very helpful, with much food for thought. I checked the sensor response and there is indeed a bias towards the beta line: The rest of the telescope optics are all reflective (and clean). The spectroscope has a resolution of 400 which isn't great....it probably is good enough for looking at known lines but less so for identifying unknowns. I did take some spectra of Altair and Vega with the intention of normalising the instrument response but attempts so far to complete the process in Vspec have failed. The workflow process is quite involved, and the handbook is much better at explaining what the button do rather than explaining why I need them in the first place. Ken Harrison's book is the best "how to" reference I've found so far. I've been meaning to sit down and sort this out since Nova Herculis last month..it's becoming something of an ogre now! The instrument is known to be slightly nonlinear, so was calibrated against a neon lamp using about 20 lines..this particular bulb has some weak argon lines that help in the blue. I tried a 3rd and 4th order fit. Both show higher residuals in the blue so I'm wondering if the argon lines are real or not. The reference paper looks very interesting...

Any chance of it being astigmatism induced by something being tightened down too far over a high spot? You might find that just shimming the distance just transfers the fault to the other corners.

At least one professional telescope, the 2.7m at McDonald Observatory, is still in constant use despite the primary being shot seven times with a 9mm handgun at point blank range and then hit several times with a hammer. Beginners take note; less risky collimation techniques are available...

@JeremyS...Interesting... I could'nt get Iron to fit those peaks just to the right of Hbeta. . I stepped through the periodic table option. I'm sure the Japanese experts are right...probably something wrong with my calibration. Their H-alpha is much stronger as well.

A couple of raw data shots taken last night.. First one had Hydrogen wavelengths in green, the second has Silicon in orange. Looks like there is far more emission at the Hydrogen Beta wavelength (4861 angstrom) compared to the alpha (6563). When I've found out how to flatten the continuum in Vspec there should be some nice P Cygni features visible. The (possibly) Silicon lines roundabout 5000 ang look fairly prominent. The very narrow line peaks are probably not real. Eyeballing the H-beta peak comes up with a radial expansion of about 2000 km/sec.

Thanks for the heads-up chaps... Looking at the forecast here it's going to be a one-off chance tonight, and that's if I'm lucky. Checked the spectroscope collimation. Checked th emount and its cables..Renewed the dessicant tablet in the ancient Atik 314......now what else can Mr Murphy possibly bring to the party?

This review makes the Askar 400 look like the mutts proverbials for AP..in fact I'm very tempted myself.. However it makes little mention of the visual performance which is part of the op's requirement. The FLO site makes the following comment: Thus it's good visually for wide-field viewing. This is often a euphemism for "not good at high magnification". I might be overly suspicious but if the op is looking for an all-round instrument then this scope might be a disappointment on planets while excelling in its intended role for wide field AP. Owner input required!

That would be an excellent choice. 3kg...small and short, r+p focuser. It looks like a mini GT81 which has a good reputation. The focuser travel is enormous and should accomodate a 2" diagonal without issues for visual. And there is a customer return on offer....

The usual advice is to focus on the mount first, since it will determine your total payload limit.. Do you need it to be portable? The HEQ5 has a brilliant reputation for doing photography with smaller scopes. It's portable in the back of a car, but not as Easyjet hand luggage. But to answer your question more directly... The ZS61 is an excellent choice for widefield photography (I've had one) and it's really light at about 1.4 kg. . But you may find 60mm a bit limiting for visual . Fitting a finder can be awkward; a red dot on the DSLR hotshoe is a common solution. A better compromise may be something a bit bigger like the proverbial Skywatcher ED80. The extra few millimetres aperture do count in this range. Remember to budget for the field flattener. The really big argument in favour of the ZS61 is its airline portability. If you're not flying then maybe have a look at something a bit bigger...after you've looked at the mount! I have TS 65Q (no longer in production but there is something similar) which in my opinion has better build quality for AP than WO even if there is a lot less bling. Don't get me wrong; WO are very good but the TS65Q was specifically engineered for AP; the flattener is included, the focuser is rigid rack-and-pinion and locks properly, the camera can be rotated easily to frame the subject. And there is a finder bracket. And the dewcap has a locking screw (lack of such is a pet hate of mine). Triplets are better at colour correction than doublets but the difference with ED glass is small. The difference is more important with faster scopes; a big plus for a triplet is that it is possible to make fast scopes relatively colour-free. A GT81 triplet is f/5.9 native, compared to f/7.5 for an ED80 doublet which virtually halves the time for a given amount of exposure, assuming the reduced image scale is acceptable. But again, there are many excellent shots taken with doublets so I don't see any point in making a triplet an essential requirement. A good doublet is still an excellent AP choice. Triplets are absolutely fine for visual. Some claim a good doublet will beat a good triplet on visual contrast just because there is less glass. This argument also trades on the fact that the eye is sensitive over a much small range of colours compared to a CCD, the more so as the light intensity goes down. Your eye peaks at about 500-550 nm wavelength whereas the camera can see 400 to 1000 nm at all levels of illumination. In my opinion there is not much point in paying for premium brands unless you are a real perfectionist, but many will disagree. Scopes like the Takahashi quad Petzval designs are wonderful pieces of engineering that will fill a massive sensor, but if you're using a humble APSC scale DSLR camera then a WO GT81 with flattener will do just fine. There is a convenience argument for a premium astrograph in that the flattener spacing adjustment is done for you and fixed. And because the flattener is built-in there is more flexibility in adding filter wheels, off-axis guiders. You will find almost as many posts on flattener spacing as there are on Newtonian collimation... Not all proper astrographs will allow you to use a 2" diagonal for visual, though 1.25" is usually ok. The TS65Q wont, nor the older Pentax SDHF75, though both will work with 1.25". I believe there are complications with the Tak quads on this score as well for visual. Make sure whatever you choose will do both, preferably with 2" diagonal. Hope this helps...

It's not that you see "nothing" so much as "nothing extra". Leaving the usual seeing limits out, once you've matched the resolving power of your scope to the resolving power of your eye, all you end up doing is spreading the same amount of detail over a larger part of your retina. The view doesn't necessarily fall apart, but it loses sharpness because the limited amount of detail is oversampled by the cells on your retina. The resolving power of your eye is a very individual thing; I've seen numbers between 1 and 4 arcminutes (= 60 to 240 arcseconds) in the literature. It also depends on illumination..whether you are using the rods or cones. So for a 4" scope with a resolving power of 1 arcsecond, a magnification somewhere 60 and 240 will allow the eye to see all that the scope can reveal.

No...the obstruction percentage refers to the linear dimension. We need to be clear not to confuse linear and area numbers. Using your example, the area of the primary would be Pi* radius squared...= 314 square inches. The obstruction is 30%, or a circle of 30% * 20 inches = 6 inches. The area of the obstruction is Pi * radius squared, = 28.3 square inches. Thus the secondary obstructs 28.3/314 of the incoming light = 9% This is a fairly small fraction which you will hardly notice. The effective area is 314 - 28.3 square inches = 285.7 square inches. Working the circle area formula backwards, this equates to an unobstructed diameter of 19.1 inches. So the effective diameter changes very little for quite a big central obstruction. The theoretical resolution remains the same as a 20 inch unobstructed, but you would notice a loss of contrast since diffraction off the edges of the secondary causes a small amount of light spillage..a small amount goes where it should'nt so dark areas in the image aren't as dark as they should be, and light areas aren't quite as bright

Thanks for putting up this post. I saw the advert and was not sure whether to be sympathetic or suspicious; others with a similarly cynical disposition as myself may have had the same dilemma. Let's wish him and his wife well and be grateful for what we've got.....

The ES 30mm 100 degree needs a 3" focuser...and it weighs a ton. Of the few reports I've read...most say it's a good eyepiece. Few call it a great eyepiece..it just does not seem to attract the universal praise some other eyepieces do. I'd speak to someone who owns one first. You might have trouble selling it on without taking a big hit if you can't get on with it.

Have you had previous success with the same setup? What does a star at the zenith look like? The seeing was so bad on Jupiter after the rain yesterday I just gave up..

I like the organized way you have put together a list if kit that should work together. Most of us just accumulate kit as and when it becomes available cheaply and then regret it when it won't all work together....I'm in that category! Looking at your post count, you are possibly new to the hobby. Assuming you are just starting AP, I'd be inclined to keep things as simple as possible. There is a lot to learn (both hardware and software) and it's probably best to stick to the essentials. Getting some success early on with simple kit is a good motivator to keep going up the rather steep learning curve and avoid wasting the all-to-few good nights we get in this country. Poor nights are good for testing out guiding and practising mount alignment. I'd avoid "niche" kit and stick to to popular commonly available stuff simply because there is a wealth of experience out there to help you out. The usual advice is to concentrate first on the mount and guiding, rather than the imaging scope. The HEQ5 is a good choice for small scopes. The logic is that you will probably keep the mount for a long time while swapping out the scope as tastes change. Not sure if aa HEQ5 will handle a C9.25 though...worth a check. The SCT might need an EQ6 level mount. Personally I'd ditch the EAF for the moment...manual focusing with a Bahtinov mask is a simple enough procedure. Earl's comment about the SW 130PDS is very valid. In skilled hands it's an absolute giantkiller but you need to be able to collimate it, and diffraction spikes are not to everyone's taste. The traditional way in is a SW ED80 refractor with a flattener..it's reliable every time you take it out. It's almost a rite of passage when starting AP. I would guess you are more likely to keep the ED80 as a second scope than the 130PDS, as and when you get the Celestron 9.25. At this sort of focal length you will need to guide. A guidescope is fine..but possibly better suited to a refractor imaging scope. Reflectors can have mirror slop which the guidescope can't correct for. Newtonians often use an off-axis guider (OAG) for this reason, but the OAG generally offers a smaller choice of guide stars compared to a guidescope. There is quite a lot of merit in buying kit secondhand. At least if something does not work out you can shift it on without too much of a loss. Sticking to this site and ABS I've not had many problems. And the best of luck....!

In 1986 I was working in Oman, when Halley's comet was making its last appearance. Beautiful clear night, took a bunch of friends 25 miles into the desert at 3am to view the much heralded apparition with my 60mm refractor. Got to site, only to find I'd left the diagonal behind... It was some time before I was allowed to live that one down!