andyrawlins

I eventually solved this.  It was Third Axis balancing.  I came across this by chance - I had never heard of it before which amazes me because its so fundamental.  Maybe for a small refractor its fine but for a biggish Newtonian  stretching the mount towards its limit it makes a huge difference.  All I needed to do was rotate the tube so that the centre of gravity was in line with the axis of the mount (rather than having say all the weight of the focuser, finder etc on one side) and all of a sudden it tracks very well and also finds targets much better.  

Its difficult to describe in words but there are some great videos out there explaining the issue and how to solve it.  If I can re-find the one that solved this for me I'll  post the link.

Hi All, I'm looking for some advice about how to keep my subject in frame when imaging the moon.

I'm using a 1200mm f6 Newtonian on a HEQ5 Rowan with a 3x Televue Barlow, so 3600mm focal length ,and an ASI 224MC camera.  I am polar aligning with an iPolar which does seem to have issues with camera centering so I re-align when I'm at my target so polar alignment should be good. When imaging at this focal length with an IR pass filter, which gives the best results, I'm only getting 25fps so to get 15000 frames takes 10 minutes.   

The problem is, in this time, the image shifts and I lose some of the things I want to image.   The stacking takes care of this but I do lose some of my image, or at least the quality of the area at the edges of the image (I stack with ASI Studio which I find the best but I'm not sure how it deals with a shifting image) .

I can't use guiding as far as I know as obviously the moon is moving faster than the stars.  I can, and do, manually re-center the image during capture but this isn't ideal for several reasons.

So my questions: I

s some drift to be expected with this mount/focal length or do I have a problem with the mount?

If drift is to be expected, what do i do about it?  Obviously I can lower the focal length or just crop the image but that isn't fixing things, its just putting up with them.  I'd be grateful to hear what others are doing.

Cheers

Andy

On 04/10/2022 at 01:02, Mike Q said:

Eyepieces come and go but a good barlow will be with you forever.  I have 3 telecentic barlows and i wouldn't trade them for anything. 

I had to look that term up but thanks

Thanks all.  I'm using my current Barlow and it seems OK.  My question is really whether a 'premium' Barlow will make an appreciable difference over a 'standard' one.  I have only ever used the one I have and would be prepared to spend £100 or whatever if its going to make a big difference, but don't want to waste my money if it won't.  I have nothing to compare it to. vlaiv recommended 2.5x here 

Hi all. I have an 8" reflector which I use visually mainly with Vixen LV 5&12mm objectives. I also have a 'no name' 25mm and a no name 2xBarlow that came with the telescope. 

The Barlow seems OK. If I visually compare the 5mm on its own with the 12mm plus Barlow there is little if any difference in quality on Moon or planets. 

However, I have started imaging with an ASI 224mc that I believe is ideally used with a 2.5x Barlow (reflector is 1200mm f6)

So to my question: does the fact that I can't see any obvious image degradation visually with the Barlow mean that it is good enough for imaging too?  What is the difference between an ok Barlow and a premium one?  Should I upgrade to a better one or a Powemate?  Recommendations gratefully received. 

Cheers in advance 

I got the iPolar with the HEQ adaptor to go on my new HEQ5 Rowan which is 'on the way'.  It doesn't directly fit the Vixen mount (too small)  but I managed to make a collar or washer out of a stiff foam which allows me to seat it quite firmly and reasonably accurately - more than enough for my needs.  The iPolar worked a treat (once I entered long and lat the right way round) and the Starbook worked like a deamon finding targets with better than ever precision.  So it looks like after 16 years of owning it I've finally found out how to use it properly, just in time to replace it with the HEQ5

I took the Dec axis apart cleaned and re-greased it.  Actually the grease in it wasn't too bad and I had quite a bit of trouble getting it back together just tight enough to work properly.  I think what made more difference was carefully adjusting the worm gear.  The whole thing now moves far more smoothly and quietly.  There still seems to be a vibration which renders it useless for long exposures but that may be due to overloading.  It will probably spend its retirement as a posh equatorial mount for my DSLR.  

2 hours ago, pete_gamby said:

If you are using the alignment process in the Starbook S and the mount is not physically perfectly polar aligned, the controller will constantly "nudge" the DEC motor to maintain tracking. This "feature" was typically referred to as DEC jump.

The received wisdom for imaging with a Starbook or Starbook S was to not use the controller to align but to make sure physical polar alignment is spot on (polar scope, drift align etc) so that only the RA motor is in use to track/image.

I'd tend to agree that overloading is also not helping.

Cheers, Pete (who used to be Vixen product manager at Opticron)

Brilliant thanks Pete - I knew I'd heard something about it 'hunting'.  I can't use a polar scope (because I don't have on and because of my knees if I did) but am planning to get an iPolar for my new mount.  They don't do an adaptor for Vixen GP but would you happen to know if it is compatible with other mounts.? I seem to remember hearing that you can use another make of polar scope (maybe Skywatcher) on them so an adaptor of that make should do the trick.  Polemaster do a Vixen adaptor but they are more expensive and people seem to prefer iPolar. 

I have just had another fiddle with the mount with and without the scope on.  The vibrations in the dec axis are there all the time at a low level but much worse with the scope on. (which is a big metal tube after all)  The dec motor was slightly loose in its mounting which I have tightened.  However, the dec axis is incredibly stiff, with the RA one not much better.  Does anyone have any instructions for servicing this mount?  I assume its a case of take it apart, clean re-grease and reassemble but that may be easier said than done

6 hours ago, newbie alert said:

Never touched mine, wouldn't know what it looks like internally as I've never had to look

With skywatchers more or less everyone takes them apart, either to belt mod, re bearing or relube.. the older mounts are known for the sticky glue/ grease.. broken or modify the alt bolts.. even the new eq6 r pro has a puck that makes the scope sit at a funny angle( I'd say that's a design fault)

Before I purchased mine I did plenty of research,  and nothing flagged up on the cem 60..

 

Have you got yours on their 1.75" tripod?  Their mounts seem to come by default on a 1.5" but FLO recommended the 1.75" even for the GEM28 which puts the price up.

On 27/10/2021 at 11:12, vlaiv said:

I would look into iOptron offerings, but those that are in Heq5/Eq6 range tend to be more expensive.

Skywatcher models are really affordable for what they offer and if you base your budget on them - it is unlikely that you will find better match (at that price point).

I would still consider going iOptron way. I have now Heq5 mount, but looking into getting CEM120 (or possibly Mesu 200 next).

In my experience, SW mounts can be made to work good but it requires a lot of fiddling. Mechanical finish of these mounts is very rudimentary. I have sense (and also what I gather from feedback on internet) - iOptron is much better in that regard.

There are couple of features with iOptron mounts that make them better in my opinion. I don't care much for iGuider / iPolar / EC and all that iFancy stuff, but I do like that they have magnetic floating worm which is rather good solution for backlash. They also have belt drive (something that is after market addition on SW mounts - except for EQ6-R and AZEQ6 models). Stepper motor resolution is good (better than SW mounts).

You have piqued my interest there vlaiv. thanks  .  EG6 pro is too heavy for me (dodgy knees) so was going HEQ5 Rowan but that is getting tight for my 10Kg OTA plus camera.  Now looking at GEM28.  Do you/anyone have any information on them in use.  CEM26 looks interesting but slightly lower payload.

Cheers

Andy

3 hours ago, dweller25 said:

Hello @andyrawlins

I have the same green Vixen GP which I use for visual only.

I keep the scope weight down to around 6.5kg maximum for best results and use a counterweight big enough to allow good balance close to the EQ head rather than at the far end which can set up vibrations.

I also had the same tripod as you but found it not stable enough so changed to a Berlebach UNI.

10kg of kit is possibly a bit too much for imaging.

It s a very good mount used within it’s capabilities.

Perhaps you can look for a bigger Vixen GPDX - that will take 10kgs and you can use your existing Starbook.

Or consider a lighter more compact scope - I use a Mewlon 180 on mine and it is very stable at x400.

Hope that helps.

Good tip about keeping the weight close to the mount.  I'll see if I can get another one second hand.  Matching of course!  Thanks David

2 hours ago, F15Rules said:

Hi Andy,

I know this will sound like a dumb question, but your photo doesn't show a counterweight on the c/w bar.. so, a) are you using one and b) is it heavy enough to properly balance your scope? 

If the answer to either of these questions is no, then that could be part or all of your problem.

Lovely mount.. I have one and really like it. A 10kg load for visual IF perfectly balanced would probably work. I'm not an imager though, so can't comment on that aspect.

Hope you get it sorted.

Dave

Thanks Dave

Yes I have one 7.5kg weight.  It not quite enough to balance the scope with the camera on (its fine without) but that motor seems very strong.  It's the Dec motor/movement that seems to cause the problems.  I did report it to Orion Optics when I bought it - I'm not sure what they said or why never sent it back (or indeed why they sold me that scope with that mount).  I'll have a play with just the camera and no telescope and see if it behaves which will confirm the overloading problem.  I originally bought the mount with a single axis motor that was fine.  It was when I added the Starbook and motors it all went wrong.  I'm guessing that motor is faulty.  I might take it to bits.  That always helps

PS yes it is a lovely mount - beautifully finished and pristine apart from some of the plastic bits.  I have seen several HEQ6/tripods with rusty bits.  The mount does have a bit of play on both axis and always did but its way better than the GEM starter mount I had on my first scope.  

Hello all

I have one of the old olive coloured Vixen GP mounts which I have been using mainly for visual and photos of the moon since 2012.  Ever since I got the Starbook-S for it there has been a tendency for a vibration to be set up after fine movement in the Dec minus direction.  This can usually be cancelled my nudging Dec + and has't been a problem for short exposure photos of the moon with my 8" Europa Orion Optics tube.  However, with longer exposures, even say 5 seconds, I get non round stars.  Now I should say that its probably overloaded - I think it is rated at 7Kg whereas my rig plus camera is about 10Kg.  I believe that the vibration thing would happen with lower weights/nothing  (I need to check)  but the overweight could be affecting it in other ways I guess.  I have more luck with the tube nearly horizontal than with it nearly vertical.  

I will probably upgrade and keep this one for more casual use or a later lighter scope but I'd be interested to know if anyone has used this successfully for images with any setup.  The Starbook-S 'chart mode' feature is a nice one but I think I read somewhere that the way the Starbook works makes it unsuitable for imaging.  It would be nice to hear that it is actually a good mount if used within its capabilities. 

The obvious answer is a better mount and I'll probably get an HEQ5-R though I have considered the Explore Scientific EXOS-2 PMC-Eight GOTO Mount.  Any thoughts?

Cheers

Andy

forgot to say, they have a 50% off sale at the moment.  I got it a few months back in a 30% off sale but its very good value even outside a sale. 

I am a relatively new Affinity Photo user (can't afford Photoshop!) and am very impressed with their dedicated astrophotography enhancements to the new version 1.9 that has just come out.  They now support stacking plus a lot of the tools I've seen used in Photoshop - star reduction etc.  A 20min video walking through the workflow is on this page  .  I hope that they continue to specifically support astrophotography and maybe they will even become leaders.  Now if only it would stop raining...

On 26/01/2021 at 18:50, LukeSkywatcher said:

I used to use a Horizon 8115 for my 20x90 bins. The quick release plate and pan and tilt handle developed a bit of slack/slip. 

I then bought a Ravelli pistol grip/ball mount and tripod. Its brilliant. It was a steal at the time. I couldn't resist.

 

I have it too - its excellent

Great thanks for your help all.  I'll keep trying with my DSLR but capturing a lot more images for stacking.  If and when money becomes available I'll probably get a planetary camera. 

7 hours ago, vlaiv said:

Not sure which part you don't understand, so I'll do a quick intro on all three possible.

1. Sampling rate

Telescope + camera is projection device and angle in the sky is mapped onto linear distance on the surface of the sensor. Scale factor related to this mapping can be expressed as arc seconds (measure of angle - 1/60th of arc minute which is itself 1/60th of a degree) per pixel.

It can be thought of as "zoom" although technically it is not zoom (zoom is ratio of angles, and here we convert angles to linear distance)

Above is formula to calculate it. Real formula should include Tan trig function but we are using small angle approximation that tan x = x for small angles (like mentioned arc seconds) for simplicity (above formula is good enough).

It is useful both in planetary and regular imaging

2. F/ratio of telescope, sometimes also called "speed" of telescope is ratio of aperture and focal length. It is useful in these calculations because sampling rate depends on focal length and actual detail resolved depends on aperture size. It turns out that certain pixel size has fixed F/ratio for what is called critical sampling

3. Telescope resolution / critical sampling

Maximum details that can be resolved by a telescope depends on aperture size. In fact there is relationship that defines maximum spatial frequency of signal at focal plane and is given as 1/ (lambda * f_ratio) - where lambda is wavelength of light and f_ratio is F/ratio of telescope.

Nyquist-Shannon sampling theorem says that we should be sampling the band limited signal at twice its highest frequency (regardless of what you might read elsewhere - this applies to 2d case as well), we can derive expression for needed F/ratio for critical sampling.

Critical sampling is resolution at which we can capture all theoretically possible detail for telescope of given aperture.

If 1 / (lambda * f_ratio) is highest frequency component, then associated wavelength is lambda * f_ratio. We need to sample twice per that wavelength (two times higher frequency) - so our pixel needs to be half that.

lambda * f_ratio = 2 * pixel_size

f_ratio = 2 * pixel_size / lambda

lambda is usually taken to be 500nm for broadband / RGB type of imaging, although you can put actual wavelength if you are using narrowband filter like Ha to stabilize seeing (in that case lambda would be 656nm).

f_ratio = 2 * 3.75mm / 0.5µm = 15

So F/ratio for critical sampling with  3.75µm pixel size = F/15

Brilliant vlaiv, a very full description.  The Astronomy Tools calculator that AstroMuni pointed me to suggests that if anything I should use a focus reducer in this set up rather than a Barlow.  Is this related to the default of 'ok seeing conditions'.  if I change it to 'exceptional conditions' it does indeed suggest a 2.5x Barlow.  

10 hours ago, AstroMuni said:

Here is a link that gives you info on relationship between Telescope & Camera https://astronomy.tools/calculators/ccd_suitability and this link should help you with the calculations https://astronomy.tools/calculators/ccd

Brilliant, thanks AstroMuni, I hadn't come across those sites.   Its good to see Nyquist here -  I know him well from my interest in HiFi - though in that sphere many now consider his 2x sampling requirement to be too low for music reproduction. A quite different environment though for a very different forum

7 hours ago, vlaiv said:

Say you go for camera like ASI224 and you use 3.75µm pixel size. You then need ~ F/15 telescope or in your case x2.5 barlow.

I've heard about this pixel ratio but I don't fully understand it.  Could you point me to chapter and verse please?  

3 hours ago, CraigT82 said:

Lucky imaging with a planetary camera is definitely the way to go, along with utilising a barlow. There is no point getting closer in by adding more barlow power and capturing still images as the atmosphere will be the limiting factor, you need to capture video and selct/stack the best frames as outlined by Vlaiv in order to get past the atmosphere limit.

Doing it that way you will get much closer in (i.e. capture fewer arc seconds of sky per pixel, due both to more barlow power and smaller pixels) but unfortunately you wont get anywhere near as much of the lunar surface in shot as you do with the 5D.  Saying that there are astro cameras with large APS-C size sensors (eg. ZWO ASI1600) but they do cost a small fortune.

Vlaiv's image linked to above is a cracker, especially for a 100mm scope.  I've taken a screenshot of his image alongside my own image captured with a 220mm scope to give you a taste of the resolving power increase going from 100mm to 200mm (ish). Do bear in mind that at this image scale I had to shoot 25 panels and stitch them together to cover just half of the lunar surface (full image can be seen my my astrobin link in my signature). As I mentioned you could get larger sensor cameras but costs go up rapidly.

 

 

Another excellent shot Craig, thanks very much.  I'm not too bothered about getting large lunarscapes, its detail I'm interested in. 

What tools do you guys use for stacking etc?  I have always used Registax but people now seem to use something else for stacking (eg Autostakkert) and then Registax for wavelets.  Why is that?  I've been dabbling with APT which seems to be an amazing tool.

4 hours ago, vlaiv said:

There is a limit imposed by physics of light and size of aperture on level of detail that you can record.

For any given pixel size - there is maximum focal length that you can use on certain aperture.

In most cases, limiting factor is atmosphere and if you want to shoot highest resolution images possible for a given telescope - you need to use lucky imaging approach. Again, in order to do that - you need very specific type of camera - dedicated planetary camera.

For dedicated planetary camera, few things are important:

- QE of sensor

- low read noise

- fast readout rate

Pixel size is not important as you can use barlow lens to get required focal length for any pixel size.

Moon does not have any significant color detail so you can use mono sensors that are more sensitive.

ASI224 is excellent choice because it has great stats on above quoted three properties. It has good QE at around 80%, it has very low read noise and it can deliver extraordinary high FPS.

Say you go for camera like ASI224 and you use 3.75µm pixel size. You then need ~ F/15 telescope or in your case x2.5 barlow. Use exposure length of about 5-6ms and get tens of thousands of frames. Stack the best 10-15% (judge how many based on quality of your frames) and apply some sort of frequency restoration process (say wavelet sharpening).

This will get you very close to theoretical limit of 200mm aperture.

Using that technique, I captured this image:

http://serve.trimacka.net/astro/Forum/2020-07-30/moon.png

(SGL no longer allows embedding non https images - so I'm providing link only - but you can view it in full resolution by enlarging it to 100%).

Above image was taken with 100mm telescope. This means that you should be able to go twice higher resolution with 200mm telescope.

Brilliant, thanks vlaiv.  I'd be very happy with a picture like that  Was it taken with a 224? Is it a mosaic? I thought they have a very tight fov. 

Hi All, I'm looking for advice on getting more resolution when taking photos, primarily of the moon.

I'm using an 8" Newtonian Reflector, 1200mm focal length, with a full frame Canon 5D III and 2x teleconverter.  This gives me nice sharp images that almost fill the frame but, even with 22.3 megapixels, I get limited 'zoom in' on photos before pixilation sets in.   

I have also been using APT and EOS Camera Movie Record to record the live view at 5x.  This also gives good results but as far as I know this just optimises the resolution (and allows stacking).  It can't actually increase the native resolution of the system surely?

I have also tried with a 2x Barlow, with and without the teleconverter, but this requires the use of extension tubes which leaves a heavy camera hanging on a long stalk of tubes that is neither stable nor safe for my camera.  My SLR adaptor allows me to insert objectives but this gives poor results, from uneven lighting to images severely stretched from the centre.  An adjustable length adaptor might be more successful, I don't know.  

Another possibility would be a dedicated astrophotography camera such as the ZWO ASI 120MC-S or the 224MC.  The field of view would be very much smaller and so far more 'zoomed in' but zoom doesn't imply resolution. The 'magnification' (I've read the threads about whether its real magnification or not!) produced by the telescope would, of course, be the same.  However, I assume that resolution is at least partly controlled by pixel density?  The pixel size of the above cameras is 3.75µm against 6.25µm for the Canon.  Would this then give me 1 2/3x the resolution of the Canon?  I'm hoping that an astro camera would work better with a Barlow so could match the 'magnification' but in theory be able to zoom in almost twice as far without losing detail.  What do people think?

Also, do people have views on whether the ASI224 is worth the additional £70 over the 120? The main advantages seem to be fps and noise which may not be that important for lunar (though when I get to planetary I guess would be more useful).

I'd be grateful for thoughts on the above and any suggestions for getting higher resolution.  Major expenditure (eg a 'bigger' telescope)  is not an option.

Many thanks in advance.

Here is a review and then a couple of questions to the forum

The experience I gained assessing my new Nikon Action EX 10x50s https://stargazerslounge.com/topic/369052-comparison-of-pentax-sp-50-wp-10x50-and-nikon-action-ex-10x50-cf/?tab=comments#comment-4009551 led me to dig out my old Vivitar Series 1 8x25.  I bought these in 1995 for £99, so not an insignificant amount then.  Series 1 was Vivitar's premium range at a time when (I believe) they were well regarded for their optics (now they seem to sell basically children's toy binoculars). Anyway, despite their price/apparent pedigree and excellent build (made in Japan) I never got on with them, finding them very difficult to focus and to keep in focus.  They rarely got used and indeed got superseded for general use by the Inpro 10x50 mentioned in the thread above.
    
Using what I learned when assessing the Nikon's I decided that the focus problems were down to four things: 1. a small exit pupil, quoted as 3.12mm, so you need to have the eyepieces correctly positioned over each eye; 2. a short eye relief that I estimated to be about 11mm. I found the view (without glasses) to be best with the short (4.5mm) rubber eye cups folded down.  Wearing glasses, it was like looking down a drain pipe with a severely vignetted view; 3. difficulties getting the interpupillary distance right: for some reason the image is significantly brighter when the binoculars are set wider than the correct distance.  However, at this, what would appear to be the correct separation, they will not come completely to focus. When they are brought down to the correct distance (60mm for me)  the image suddenly gets darker but actually focusses well; 4. a very 'low geared' focus wheel and seemingly very short depth of field which necessitates a lot of focus twiddling every time you change view (not for objects at infinity, obviously).  Because of these things, its crucial to get the binoculars correctly positioned over the eyes and to keep them in that position.  Once they are correct the image is actually not bad.  To be specific, the image is almost exactly like it looks with the naked eye: the same colour balance, the same detail and resolution, the same clarity, the same brightness - just a bit bigger.  Its quite uncanny really. In contrast, the Nikons give an almost hyper-real clarity, detail and brightness and as serious wow factor. 

Compared to the 10x50s they really didn't seem to magnify that much  (I found the objectives to actually be 23mm so 7.4x not 😎 but maybe this is something to do with AFoV. FoV is quoted as 'Wide Field 8.2°'.

So basically they magnify the image but not the brightness which is fine for daylight use but fairly useless as night.  The big advantage, however, is that whereas the Nikon's are over a kilogram and will only just fit inside my zipped up coat when round my neck, these weigh a third as much (350g) and are a fraction of the size (105x120mm).  They easily fit in my coat pocket.  

So I think I should give them more of a chance by keeping them in my coat pocket so they are there when I need them (the best binocular is the one you have with you!). 

On to my question then: does anyone know anything more about these older Vivitars: whether they are actually any good and when and why the company seemed to give up with proper optics?  I can find nothing on the internet.  All I have is the Vivitar brochure from the time (attached) in which the certainly seem to regard themselves as makers of 'proper optics'. 

I'd also welcome comments on the issues I found and whether my conclusions are correct.  

IMG_20210113_0002.pdf

On 31/12/2020 at 15:13, BinocularSky said:

Late to the party as usual - I must have been having a Xmas break 🙂  

I see from posts elsewhere that you've made your own mind up about this already. Nice review! For reasons best known to S@N, the "best 6 under £200" has now been incorporated into a "best 10", one of which is a 20x80 : https://www.skyatnightmagazine.com/advice/best-binoculars-for-astronomy/.  There's a version of "best 6" (and lots of other bino reviews, mostly by Alan Dyer and me) on Astrogear Today: https://astrogeartoday.com/comparison-review-six-10x50-binoculars/

Most kind thank you