vlaiv

Very interesting. I have not noticed anything similar on my mount.

I wonder what sort of error could we be talking here?

You say that pulse happens every 0.5-0.6 seconds? Let's see what that corresponds to.

If I'm not mistaken, Heq5 has 64 micro steps per step, and one micro step is 0.143617 arc seconds. Sidereal rate is 15.041, right? This means that every second, we have 15.041 / 0.143617 = ~104.73 micro steps.

Interestingly enough - in 0.6s we have about ~62.83 micro steps. I bet that this period is actually 64 micro steps and that you see what happens on a full step.

Next thing that I would be interested in is how much absolute error there could be from such a motion. Since we have seen that it is indeed about 0.6s period - in that time frame, mount moves 9 arc seconds. From what I can see on the first video you posted - it looks like mount is going faster in one cycle than it ought to and then slows down in last 10-20%. Maybe it is doing what your oscilloscope is showing - in one "step cycle" maybe it is following sort of sine curve? I'm not sure how we could model this without precise measurement - like having a timed video against millimeter paper or something.

In any case, let's go with some very simple error model. Let's say that speed of mount is 20% larger than it should be and then it slows down. It is larger for 80% of time. In 0.48s it is moving at 18"/s instead of 15"/s. What sort of error could we expect?

0.48s * (18"/s - 15"/s) = 1.44

That is very large error and that should be easily noticed as oscillation by people guiding at 1s.

Have you tried measuring actual error from DEC drift experiment and pixel scale?

6 hours ago, oymd said:

Hi Vlad

Today I started my imaging session by setting up in the afternoon, and started by taking flats and dark flats.

I then went on to do the Lights when it got dark.

I have just realised that I took my flats and dark flats with the focuser all the way racked in, just as the scope was when I took it out of the case!!

I have a mark I did with a sharpie pen on the focuser tube to mark my focus, but I completely forgot to move the focuser out to that position!

Does that mean that the flats and dark flats I took today are rubbish and useless?

These were new flats with the reducer in place!

Like tooth_dr mentioned, flat darks don't care much about focus (but do take them regardless of the fact that they are short). I'm afraid that flats are probably going to be useless.

You know when you focus - star first is a circle then collapses into a single dot? Dust particles cast shadow that looks like this defocused star - this is because dust particles are some distance in front of the focus plane - they are "defocused" so they cast defocused shadow. Problem is of course that they are on optical element, like flattener or filter or whatever in optical train at a fixed distance to camera. When you bring sensor to focal plane - dust particles are at some exact distance from focal plane and cast shadows of certain diameters. If you change dust particle defocus - you make these shadows larger or smaller.  This makes an issue - larger shadows in flats (if flats were taken with focuser all the way in - dust the furthest from focal plane) can't properly calibrate out smaller shadows in lights.

Nope ...

Zwo website:

1 hour ago, johninderby said:

Another one worth considering. Not a bad price at the moment and a good R&P focuser.

https://www.teleskop-express.de/shop/product_info.php/info/p1151_TS-Optics-70-mm-F6-ED-Travel-Refractor-with-modern-2--RAP-Focuser.html

That one also does not have very good correction of CA. It is very good travel scope / small visual instrument, but SW 72ED is going to be much better for imaging.

There is TS photoline 72mm model that uses FPL53 and lanthanum glass that has much better color correction and is well suited for AP purposes (as the name of line suggests):

https://www.teleskop-express.de/shop/product_info.php/info/p8866_TS-Optics-Doublet-SD-APO-70mm-f-6---FPL-53---Lanthan-Objektiv.html

Btw, while I fully support the notion that ST80 is not imaging instrument, has a loads of CA and poor focuser - I have to say that with some careful application it can be used for imaging:

This image was taken with ST102 - bigger brother of ST80, and purple fringing was not removed in post processing. It was done with color camera (although small planetary cmos type - ASI185) and only tricks used were aperture stop and wratten #8 yellow filter stacked with UV/IR block filter.

2 minutes ago, johninderby said:

Still think the AZ5 130PS could be a good option and within budget.

I'm somewhat reserved about that 130PS and in general - SW scopes of latest series that come bundled with new mounts (like pronto, az5, AzGti).

It looks like they have been trying to cut down weight of these scopes to make them more stable, and for some inexplicable reason, they decided that collimation systems take too much weight, so these new scopes can't be collimated.

Take a look at back sides of some of them:

Here is quote from one unboxing post here on SGL:

Quote

 However one of the big things that I liked about this version of the 130p compared  to the others is that it does not require colimation as the back panel does not have any screws as you would see on a normal Newtonian.

I'm not sure I would like a scope that can't be adjusted if it goes out of collimation.

2 minutes ago, johninderby said:

If it wasn’t a bit over your budget would suggest a Skytee II alt-az mount with a 150p ota.

I was thinking along the same lines, but Skytee with tripod is already over budget. Unfortunately, I don't think any of smaller alt az mounts like Az4 or Az5 would hold such ota without issues (both size and fact that it would hit tripod close to zenith?).

Maybe watching this video will explain the size of that scope and eyepiece positions that you can encounter:

13 minutes ago, sarahsmiffy said:

Thank you.

yes, I understand about the nebulae and galaxies.

i do live in a medium polluted area but there are some no/low polluted areas nearby and I’m looking forward to drives down to the coast in the summer - if we are ever out of lockdown.

I’m not up for a dob if it’s heavy - I’m 4ft11 so am concerned about height.

also, this is something I am going to want to pursue. I’ve loved being out at night in the garden - it’s so peaceful and the stars never fail to amaze me and I’ve been lost the last few days without using my scope. 
I think I will put some more money towards it and get this. 
 

https://www.rothervalleyoptics.co.uk/skywatcher-explorer-150p-eq3-2-telescope.html

what are your views ?

 

also so you guys with EQ mounts leave them assembled at home or do you dismantle after each. I’m planning on leaving it assembled but I read somewhere it puts pressure on the mount from the weights ??!!??

That scope is not going to be considerably lighter than comparable aperture dobsonian telescope.

Mount head is 3.2kg, tripod is 3.3kg, tube weight is 5.3kg and there are at least 5kg worth of counterweights included. Fully assembled setup is going to be around 16-17kg.

That is pretty much the same as 6" dob version - which is (just checked) 5.8kg for tube and about 10kg for base - so total about 16kg.

Height is concern with such scope. Tripod has minimum height of 71cm, and there is at least about 25cm on top of that for mount head, so we are at 100cm without the scope. Scope is luckily shorter because of 750mm focal length, so at most about 40 additional cm. I suppose at lowest setting for tripod, eyepiece at highest position would be around 135 - 140cm - that should be ok for you?

Such scope is better if you plan to add motor tracking or goto later - it is fairly easy to do, there is kit for that.

However it is harder to operate while observing because EQ type mount can place telescope in awkward position for viewing. You will need to rotate scope in tube rings (which means loosen rings - but not too much for them to open, turn tube without it sliding to affect the balance and re tightening rings). You will also have issues with using finder scope as it is straight thru and will be also placed at awkward positions.

This is really my main objection to using newtonian scope on EQ mount - too large span of possible eyepiece heights and weird positions and need for rotating OTA in tube rings.

5 minutes ago, Ricochet said:

That's the focuser height at zenith for my dob in its current position (mine has tube rings so I change height for best balance).

What may be an issue is weight. I think the tubes generally weight about 15kg and are quite bulky so this should be considered before purchase. 

I measured my SW 200p tube to be around 10-11kg (as I recall it - it was 11kg something with 600g guide scope on it) and base is about 15kg so total 25-26kg when assembled, so yes, rather heavy, but from what I understand OP is not concerned with bulk and weight of the scope for both storage and transportation.

You need over x150 I think. If you have very sharp vision, you could do it at x100 but cells would be very tiny.

I think that most comfortable observing of granulation is at x200 or so. You also need very good seeing.

As a guide - single granule is about half the diameter of Great Red spot - so you can roughly fit x4 of them. I'm talking here in arc seconds when viewed from Earth - not actual physical size. Granule is about 2" while GRS about 4-5" depending on Jupiter's distance.

18 minutes ago, sarahsmiffy said:

Ok a dobsonian could be the way to go for me then.

only thing is I’m 4ft11 -I’m a bit concerned if the eye piece maybe too high in some positions. Any tips or experienc

Maybe best tip that I can offer here is to get height adjustable chair. Tube is about 120cm long and stands about 10-15cm from ground (maybe even less). Eyepiece is some 10-15cm away from the front of the tube, so I would say that at highest point, eyepiece is about 120cm from the floor. That is 3ft 11in or there about?

I'm sure that if you measure yourself sitting in regular office chair with your back straight - your eyes will be at somewhere around 110cm from the floor?

Hence you need adjustable height observing chair that has 15-20cm adjustment range and you'll be fine.

Just now, sarahsmiffy said:

will I be able to see nebulae and galaxies.

Most certainly. Larger telescope aperture (diameter) - more light it gathers and that makes faint galaxies and nebulae easier to see. However that is not the whole story. Dark skies really make a difference, but observing skill also makes quite a contribution. The more you observe - more you will see. Sound strange but it is true as you'll train your brain what to expect and what sort of level of contrast and detail you can expect.

2 minutes ago, sarahsmiffy said:

can I stand to view the eye piece and am guessing the eyepiece is 1.25 so can use other lenses.

I found it hard to look thru that scope while standing. It involves quite a bit of bending to reach eyepiece position with someone that is of my height (~6ft). Maybe this image will demonstrate this:

Btw, these are not my images - these are just screen grabs found online - so credits go to their respective owners. I'm just posting these to give you sense of what you can expect.

Bent over observing is not my cup of tea. Whatever puts physical strain on you - detracts from observing. You want to be as relaxed as possible to get the best views. That is why seated observing is much better with this sort of scopes.

4 minutes ago, sarahsmiffy said:

https://www.rothervalleyoptics.co.uk/skywatcher-evostar-90-eq3-2-telescope.html

what do you think of this for my wants and needs 

Since you had astromaster 130 - which is 5" scope, how did you find the views?

90mm aperture is going to show you less compared to 130mm.

I think it is nice scope except the fact that is somewhat limited in aperture. It will have some false color on bright object such as planets, the moon and bright stars, but not as much as some other refracting scopes out there (it is after all F/10 scope).

Other than that, I find that having only 1.25" focuser is limiting. That scope would be capable of wider field views if it had 2" focuser. Btw, you can use 1.25" eyepieces with 2" focuser - there is adapter included.

Btw, for less money, you can have something like this:

https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-150p-dobsonian.html

and for a bit more money you can have something like this:

https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-dobsonian.html

You mentioned that you don't want dobsonian type scope as you did not want to have to put them on table or anything. These two scopes are big scopes. They sit on the ground and you can comfortably sit in a chair next to them and observe. In my view one of the most comfortable observing positions. I have 200p version.

This image sums it up nicely:

Both of these scopes are going to outclass 90mm refractor in every aspect and also that Astromaster 130.

Their only drawback is the size and the bulk. Larger one weighs 25kg assembled. 150p is less than that, probably somewhere around 16-18kg. Both can be transported by a small car (easily split into two pieces - base and tube).

If you don't mind the size and bulk - then these are best options. You can still attach phone to eyepiece and take a shot - it will be as good as any other scope that is not driven (or rather poor / rudimentary).

Do you mind if we sort of step back here and just for the moment consider what do you want and expect in a telescope.

Telescope is not only about view (although arguably those make most of the experience of using telescope), it is also about how often it is used and how easy it is for you to use it.

I would start by asking you to define your priorities and also to state your expectations. Maybe there is a need to address those as well. If we can't fit everything in certain budget - it will be much easier if you let go of some of expectations instead of hoping that they will be met to a certain degree.

Do you know what you can expect to see in amateur telescope? Many people are influenced by high quality images they see on internet and in some cases people are better served by understanding what can realistically be seen thru telescope instead of chasing ultimate photo like views by changing telescopes. Your viewing location is very important - how much light pollution there is. Sometimes best upgrade to a telescope is "tank full of gas" - or means to get to dark location. Even small telescope is transformed under dark skies.

How about ease of use and transport. Would you be able to handle 25Kg telescope on a regular basis. Do you have storage for large telescope?

These are all things that need to be considered to properly answer what is suitable telescope.

Out of interest, what do other members thing of this alternative to 90/900 on Az3 mount?

https://www.firstlightoptics.com/sky-watcher-az-eq-avant/sky-watcher-skymax-102-az-eq-avant.html

I don't really like AZ3 mount - slow motion controls need rewinding and it is very uncomfortable to view up near zenith.

Az Eq avant mount can be used both in Az mode and Eq mode. Can be outfitted with tracking motor for planetary observation later on.

102mm Mak is going to offer similar performance to 90mm achromatic refractor but in considerably smaller package. Easier to mount. Just a tad narrower field of view - comparable to that of 6" F/8 and 8" F/6 scopes (both being 1200mm and mak being 1300mm - vs 900mm of 90mm F/10). Of course - on Moon and planets, Mak will be better due to lack of chromatic aberration.

Other types of pre processing like calibration?

I have SW Evostar 4" F/10 and have used it (only once so far) for white light solar with Lunt Herschel wedge (1.25") and Baader solar continuum filter.

I have to say - I was not pleased with it. I'm 99% certain that view was poor due to seeing. I was able to see some faculae, but nothing more (of course it was quiet time and no spots), but friend of mine - first time viewing - could not see them. Other than that - such a long scope on AZ4 mount is not what I would call rock solid.

Will need to test this combination further in better seeing and when some sun spots arrive ....

Don't use that calculator (that is wrong btw) for planetary critical sampling rate as it is aimed at deep sky imaging.

Don't choose planetary camera based on pixel size. You can always add much cheaper barlow to any camera and if you vary distance from barlow lens to sensor, you will vary magnification / sampling rate to suit your pixel size.

Just use quality barlow like Baader VIP that already has T2 connection and you are set - add a spacer of two to get to wanted distance. You have focal length of that barlow and it is easy to calculate magnification from that (I believe there is Baader pdf that explains that as well).

What you want to compare is max frame rate, QE and read noise. To lesser extent, you want to consider chip size as well if you do large targets like lunar and solar (you'll need less mosaic panels to cover whole target with larger sensor).

290 QE vs 178 QE - 80% vs 81, I would say that is pretty much a tie.

290 read noise vs 178 read noise - 1e vs 1.4e - here 290 is winner.

290 is winner in FPS as well, as it is capable of higher FPS, but 178 is not bad - it can also do over 200fps (that is enough not to loose frames on 5ms exposures - you won't go lower than that on any of the planets except on lunar and solar).

And finally - If you are interested in lunar and solar primarily - 178 has quite a bit larger sensor being 1/1.8" vs 1/3" 290 (or in diagonals  8.93 vs 6.45mm - almost 40% larger diagonal in 178 model - x1.9 by sensor surface ). Sensor size is also important in EEVA applications if that is of interest to you.

There you go - for planetary if lunar and solar are occasional thing and not primary concern - go with 290. If lunar / solar is primary thing and you do a lot of panels - go with 178.

Btw - optimal F/ratio for 178 is about F/10 due to pixel size, so you can just use it directly attached to EdgeHD 8" - since it is F/10 scope.

For 290 - it is about F/12, so you'll need a bit of barlowing.

Finally, just to clarify things - I'm giving you sampling rate recommendations based on theoretical resolving power of the telescope - for details see this thread:

2 minutes ago, johninderby said:

I’d hold out for an ED180 if I were you. 😁😁😁

If they ever did produce such a behemouth mointing it could be a bit of a problem. 🤣🤣🤣

I'm signing up for complementary ED200 - F/10 folded design refractor on dob mount (with tracking, why not? ).

Good point being raised - can you do side by side comparison of the two to rule out atmospheric influence on particular observing night?

I think it is probably collimation issue.

I have 8" F/6 dob and have been occasionally observing the moon (nothing serious, but had experience of what high power view of the moon looks like with that scope), and my new 102mm Mak made quite an impression on me after first use on luna. Image was very good / very sharp up to about x200 (1300mm scope and 5.5mm and 6.7mm EP). It did start to break a bit with 5.5mm but that was mostly due to seeing conditions.

8 hours ago, oymd said:

I redid my flats yesterday....

I think its a better result now?

This shows what happens when you take flats after taking your rig apart - you can never get everything back together as it was before (in terms of exact positions / orientations).

Dust shadows make that emboss signature because flats are slightly offset to lights (center is properly calibrated, one side is over corrected and opposite side is under corrected).

It is all however good practice - just make sure you take proper flats with scope & camera at same position and focus.

You should use FWHM/HFR on not so bright star - star that does not saturate in single exposure. You need nice star profile for software to be able to calculate these values properly. Saturated star will be clipped at the top and won't have nice shape.

Also - try to get at least a 1-2s exposures when looking at the value. When using less exposure, seeing can make star dance around and FWHM value will also change. This happens even with two second exposure - it is not unique value, it will change as seeing changes star profile. More it "dances" around - worse the seeing is (or at least tilt component of it).

Just mentally average FWHM value when you look for the smallest one (sometimes software has aid for that - like displaying "train" of values so you can know if you are getting lower or not).

If it was particularly windy night - it can impact results and image will look "smeared" a bit.

To me - image looks like it was stacked with some good subs and some smeared subs (stars have well defined core but also large wings - core comes for good frames, wings come from smeared subs). This means that it was either wind gusts or moments of rather poor seeing on some subs.

In poor seeing it is also hard to get perfect focus as it "moves" in and out because of the seeing.

What I'm more worried about is the fact that you took calibration frames but your image above looks like completely uncalibrated image. How so? Did you apply darks, flats and flat darks?

18 minutes ago, B4silio said:

Am I missing something? Is that really a Push-Pull system where I should be adjusting both?

I think that push pull is just misnomer - there is no such thing as push pull system (as far as I know - I would like to know how one can use two screws - one to push and one to pull without turning both at the same time to adjust collimation) - it's usually just collimation / lock.

Collimation can be spring loaded, or threaded version.

With spring loaded - collimation screw provides distance and spring makes sure mirror is held against that screw. In threaded version - it just behaves as worm or focus system on SCT/MCT type scope.

I remember collimation being lock / collimate type on my RC, but I've forgot - which ones are lock screws and which ones are collimation screws.

How about doing it without "assistant" or "wizard" or "helper" and such?

Just plain old "capture image" and you set exposure and parameters and capture some flats and then repeat with same parameters but this time cover the scope to capture flat darks.