George Gearless

I have access to a summerhouse on a small island. Not only is it very dark, since there are only about 100 local inhabitants and no public lightning. But I've often found that when people on the mainland complain about grey skies or even rain, it's (almost) clear skies over the island. There's propably a meteological explanation for this, although I don't know it. In fairness, if the whole region is covered in thick heavy clouds, then so are the skies over the islands. It's not like islands are perpetualy cloudfree (if they were, I'd quit my job and move there tomorrow  ). I just think they're more likely to have clear skies than mainland areas.

Island weather and costal weather are propably not the same. But then again neither is costal and inland weather. So it's an interesting issue to ponder when searching for a good site.

1 hour ago, IanL said:

The problem won't be whether you can get a few hours out of it at first, I'd think you will. The issue will be that the battery performance will degrade fairly rapidly with repeated charging/discharging cycles. Car batteries are made to provide a lot of current for a short period of time after which they are recharged whilst still mostly full. Deep-cycle batteries are designed to be used continuously over a much longer period and will withstand repeated heavy discharge/charge cycles.

Yeah, I understand. 

Given my poor record of having the night off when there, quite exceptionaly, are clear skies I'm probably looking at 3 maybe 4 nights until the summer sun starts ruining nightviewing. If this solution can tide me over until then, I'll have the summer to save up for a propper powerbank. The car battery is just sitting there anyway. So I might as well get out of it what I can.

39 minutes ago, IanL said:

You can certainly do as you propose if you use the right sort of battery. I use one of these, but any sealed 12V AGM mobility scooter or golf buggy battery would do the trick:

https://www.amazon.co.uk/gp/product/B07GDPPMNP/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

Avoid any type of wet battery (traditional lead acid for example) as they're not good for transporting and can generate explosive gas when charging. Non-deep cycle batteries will die fairly quickly if used as astronomers tend to use them

To charge up I use a cheap 'smart charger' - just connect the clips to the terminals and leave it plugged in when not using and it will keep the battery charged and in good condition. You do not want the battery to discharge too much as that will also kill it (and they tend to discharge over time):

https://www.amazon.co.uk/gp/product/B01MY5UT1E/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

I use a wheeled tool case to lug around all my astro gear, and the battery and charger are just fixed inside that. Just be careful that nothing metallic can sit on the battery terminals and short them out or it'll be a barbecue. You will definitely want a 12V fuse of the appropriate rating set in the positive wire as close to the battery as possible. Just add up the amps drawn by all your gear and go for the same or nearest rating up from that. Do ensure that the wiring is thick enough to take the current.

Yes, it's sealed. And yes, I've got an impulse charger that should allow perpetual 'recharging' without causing damage or overload. As I said, I'll give it a whirl and see what I can get out of it. If I can get 2-3 hours worth of operating time, I'm good.

22 minutes ago, theropod said:

Hey,

Car starting batteries are not designed for deep cycling, and will have a very short life in that application. Starting batteries are designed to provide short bursts of high amperage, and to have the power removed to start the engine rapidly replaced.

Your mount has internal voltage regulation and should accept direct current voltage up to a specified point, and down to a certain point. Your owners manual should detail these specs. Stepping motors will work with a supply voltage that can vary quite a bit, but whether the driver will accept these voltage swings is another matter. Again, the user instructions should  make this clear.

I would look for a battery pack designed for the task, reference the user manual and be sure to install an in-line fuse rated about 20% over the expected running load to protect your mount from those “Oh no!” moments. A battery SHOULD provide the smoothest direct current possible for your mount. Just be sure what the mount will accept.

Hmm, hadn't thought about the deep cycling issue. I suspected there was a reason why the powerpacks designed for this use, were so expensive compared to the price of a car battery. Apart from the lightweight benefits, ofcourse. But hadn't thought about how differently they operate.

I had, in my mind, considered some sort of safety in order to protect the equipment against powersurges. Was thinking a 0.5 A fuse would do the trick.

Anyway, thanks for your reply. Since I already have everything needed, I'll propably do a dry-test run at the house anyway, and see how long it'll keep things running. But with your post in mind, I find it likely that I will be browsing the web for a lithium based powertank. Thanks.

I'm often frustrated that my 'targets' of the evening are hidden behind my neighbours big tree or my own house. So, I've been doing some reconnaissance around my neighbourhood to find a suitable site for setting up shop. I've found a spot a good 1 km away. Needless to say, power will be an issue.

After doing some research into how much power I'm going to need, I figured I'll be needing a rather large powerpack. Mount, heatbands, Stellarmate/laptop (I'm currently without a Stellarmate because I dropped it and broke it 😰).

As you are no doubt aware, a 'proper' powerpack designed for this type of use, is rather expensive. They are, as far as I can tell, Lithium based for easy lightweight handling. But since I'll be hauling my equipment in the trunk of my car anyway, I figured a car battery would serve the purpose. I have a brand new car battery (660 Wh/55Ah) that my girlfriend bought by mistake and could not return. That would give me all the power I need. And then some. So if I fitted two 12v sockets on that, I could plug in my mount and my heatbands directly to the battery. I also have a 12v DC to 230V AC inverter, which I could potentialy use for powering my Stellarmate (when I get a new one) or extra power for a laptop.

But I am worried that a car battery will mess up the electronics of my mount motor. Also, if the voltage of the battery isn't precisely 12v, what will that do to the siderial tracking rate? The question is, if the controlbox of the stepping motor can handle a somewhat unequal voltage? Or will that not matter significantly?

Anyone got any experience with this?

Great picture. You must be very pleased with the result.

I know I would be.

As far as photoshop skills are concerned; once you have the data on your harddrive,  you can sit and fiddle about with it as much as you want. It's not going anywhere.

14 hours ago, rickwayne said:

I agree -- while people do manage to do deep-sky and planets with one scope, they are much more advanced imagers than I, with bigger budgets.

Planets are tiny, so you need a lot of focal length, and greater aperture helps resolve finer detail. But they're bright, sunlit objects, so exposure times can be minimal. And successful planetary imaging leans heavily on software that processes hundreds of frames, picking out the transient sharp bits of each to assemble a high-quality image.

Deep-sky objects can be tiny too, of course, but many of them are HUGE compared to planets. But they're very very dim, so imaging them involves sensitive cameras, low noise, and absurdly long exposure time compared to planets. That's why everybody is banging on so about mounts. For a good "starter" equatorial mount with goto, you're already spending around $1000.

HOWEVER.

You can get started for less. A LOT less. Since computers let us stack multiple short exposures into a picture equivalent to one long one, you don't have to have something that enables two-hour exposures. A minute or two suffices, and you can get there several ways:

1. Use a camera tracker. I'm more familiar with iOptron products so the SkyTracker and SkyGuider are what I think of, but there are others. You can go even cheaper with "barn door" trackers such as the Nyx mount.
2. Use shorter focal lengths. At 500mm, tiny angular deflections are pixel-sized and visible. Plenty of excellent targets are out there for shorter lengths, however (North America nebula, Milky Way...). You can get old "prime" telephotos for just about every DSLR for a song on the used market, if you hunt.
3. Accept some image flaws. No, really. Astrophotographers tend to be really detail-oriented pixel-peepers, but normal people won't notice or care about tiny tracking imperfections. They'll look at the glorious nebula on your wall and say, in that wonderful slightly-confused tone of voice, "...you took that. Yourself."

The book recommendation is excellent. Understanding what's going on is a healthy immunization against wasting money on the wrong gear. I also really like Bracken's The Deep Sky Imaging Primer.

Example: This image has all manner of flaws, so (3) applies. Boy, does it ever! It was taken with a DSLR, a $125 500mm mirror lens, and a $300 SkyTracker. But I tell ya, it wows the normies.

 

This is an excellent post.

We (as in 'I') tend to get bogged down in all the wonderous stuff that is readily available for purchase at various supplier sites. You will NEVER have enough gear!

I actualy thought about it the other night when I was setting up to take some pictures of the moon. It takes me about 30-45 mins just to set up everything the way I want it. I caught myself thinking "things were so much simpler in the old days". By the old days I mean only a couple of years ago when all I had was a Wifi Alt-Az mount, a 127mm Maksutov and a realy old DSLR. The enjoyment of watching the skies and making a 'good catch photo' with that equipment, was just as great as it is for me today with much more advanced (and expensive) tools at my disposal.

I know that your post was directed at a beginner who sought specific advice (and I think he got some good advice from you). But I think that intermediates as well as experts could stand a bit of 'grounding' every once in a while. 

On 14/12/2019 at 10:48, Miguel1983 said:

Personally i have no experience with it, but i've been looking at the EQ35M mount lately as a lightweight second mount for wide field AP.

I think it has a reasonable price tag on it and i like the modular aspect of it, its like a beefy staradventurer  and capable EQ mount all in one.

This way you can start imaging with your DSLR and go from there.

Edit: i would not recommend starting AP with the Starblast, sure it's possible, but you're going to have a hard time balancing, focussing, collimation, ... a smal refractor is the way to go i learnt the hard way.

 

I have that mount as my primary mount. EQM35-Pro.

One of the parameters I chose it from, was definately the price. Money is a huge issue for me :). But as a first equatorial go-to mount, it does allow you to grow, kit wise.

I started out with a Mak127. I then got the Evostar 80ED Pro. And this summer I got a Skywatcher 180mm Mak.

The max additional load is listed at 10Kg. So with the Mak 180mm (7 kg tubeweight), DSLR, finderscope and heatbands, I'm realy stretching its capabilities. But so far it has performed without missing a step. I have taken some great shots of the moon with it, but have yet to record my first planet. Which is the real test with this scope.

Of the features that you would not normaly get with a mount of that pricerange I'd like to mention:

Built in polar scope.

Com port for guided photography.

10 kg payload.

Idealy, I'd have bought an EQ6 for the greater payload. But it was, for me, prohibitively expensive at the time. Or put another way; if I had bought an EQ6, I wouldn't have been able to afford neither the Evostar 80 refractor nor the Mak 180mm. At the time it didn't make much sense to put a Mak127 on an EQ6 when you're still just starting out. In rounded numbers the EQ6 is twice as expensive as the EQM35.

I whole heartedly recommend the EQM35 to beginners and experienced users alike. 

Belated congratulations on a stunning photo. 'Wow' is the most appropriate word I can think of.

Wow.

10 minutes ago, Merlin66 said:

It’s very easy to measure the focal length of a Barlow.

Draw a circle on a piece of card twice the diameter of the Barlow lens, focus the sun’s image on the piece of card - when the image fills the circle, the distance between the card and the lens of the Barlow is the focal of the Barlow.

 

Brilliant. Just...brilliant.

35 minutes ago, vlaiv said:

For best image quality you want to avoid using eyepiece projection and go for prime focus like explained above.

There is a number of ways you can achieve different "magnification", but for start let's discuss why that is wrong term in this context.

Magnification is the term that we use for visual applications - it explains how much something is magnified in the sense of - what would it look like to naked eye if it was X times larger or closer. It can be technically described as ratio of angular size of object.

With imaging things are different - we no longer have two angular sizes to compare - angular size with naked eye and angular size with telescope and eyepiece, we now have a different process - mapping angular size to pixels (or sampling points). That is called sampling resolution. Given an image of certain sampling resolution - you can still make thing in the image appear small or large by using different projection on device that is used to display things - like this:

 

Above is the same image (it is Voyager 1 image of Jupiter in high resolution so credits to NASA for that one) but displayed at different scale. What is the "magnification" of that image?

Now do an "experiment" - stand really close to monitor and observe these two images, and then walk away 3-4 meters and again look at that image, compare "magnifications" of those images again (they will look less magnified from 3-4 meters away although we did nothing to them).

Above was written just to show that "magnification" is meaningless term in imaging - it is related to visual and should not be used when imaging.

Proper term for imaging is pixel scale, or sampling resolution and it is expressed in case of astro photography in arc seconds per pixel ("/px for short).

Ok, now that we know what we are working with - let's see what would be the proper answer to the question "how one might change magnification". It is really about two things - changing pixel scale and changing FOV.

First you need to understand that there is something called native sampling rate for camera and telescope. It depends on telescope focal length and size of pixels on camera chip. Native FOV depends again on telescope focal length and size of sensor. Since you can't physically change number of pixels sensor has - native sampling rate and native FOV are related in the same way pixel size, sensor size and number of pixels are related (sensor size = number of pixels x pixel size).

Native sampling rate is your "baseline" - that is basic "magnification" that we can modify via different methods to obtain other "magnifications". It is calculated as 206.3 * pixel_size / focal_length.

I would like to mention one more thing that is important - that is critical sampling rate. Due to physics of light there is only so much detail that a telescope of a given aperture will show, and if you are sampling too fine (high sampling rate) - you will be just "wasting pixels" simply because there is no finer detail to be recorded. In reality oversampling has both benefits and drawbacks, but that is another discussion. Once you match your sampling rate to level of detail that aperture can provide under ideal circumstances (not guaranteed that you will actually record that level of detail - it does depend on atmosphere and quality of optics) - we say you are at critical sampling rate. There is simply no benefit in detail capture if going with "higher magnification" - or rather higher sampling rate.

Here is guide formula for critical sampling - you want your focal length to be equal or less to pixel * aperture * 3.857281 (this last number is 510nm and 2.4 and 1.22 combined into single constant to make things easy).

For example - if your camera is 3.75um pixels and you have 150mm aperture (not sure if your mak is 150mm, but let's say it's that one) - max focal length is 2170mm - that is ~ F/14.5. In fact you will find that F/ratio for critical sampling depends only on pixel size of camera.

How to change sampling resolution - to answer finally your question on magnification:

- use barlow lens. You can change magnification of barlow lens by changing distance of barlow element to sensor. Add more distance - larger magnification you get (finer sampling rate).

- use of binning - this process joins few adjacent pixels into "larger pixel". This method will not change FOV but will change sampling rate

- use of mosaics - shooting multiple panels and stitching them together. This technique is useful for larger FOV - something you will want for the Moon for example.

Most planetary imagers opt to sample at critical sampling rate and make mosaics for lunar and solar - only two planetary targets that are not tiny (please make sure you have proper filters when trying solar imaging!).

 

What a great and useful reply!

It's a lot to process (pun intended), but I think I follow. 

It's like the Canon Powershot camera I have with 50X optical zoom lens. I can push the 'magnification' to over 50 with the digital zoom. But this is just the camera processing it in the same way I would use the magnifying glass in the Windows Paint program. I can digitaly magnify it ad infinitum or until I'm blue in the face. But the picture will just become grainier and grainier until I'm looking at one single pixel.

Sampling rate is a term that I've been missing in my vocabulary. While I may have had an intuitiv but somewhat misguided understanding of it, it is extrememly helpful to have it explained all the way down to a mathematical formula.

I guess the trick is to accurately distance the camera to the Barlow lense to achieve critical sampling. Or 'the sweet spot' as I've dubbed it in my mind :). I'm sure there is a mathematical formular to calculate the exact theoretical distance. But since I have no way of accurately determining or adjusting the distance between the camera and the lense, that would just be an academic exercise. Trial and error will suffice, now that I know what to look for.

So, armed with my Mak180, my Barlow, my 385MC camera AND my new gotten knowledge, I now stand a fighting chance in getting some 'award winning and never seen better before' pictures of the moon :).

Thanks a bunch Vlaiv.

On 07/12/2019 at 13:38, JOC said:

Great photo's I sometimes have a bash, but I'm just not in the same league as the best on SGL.

Well, as my father says: "The best picture is the one you never took".

Glad I'm not on the commitee to pick the winner. An almost impossible task.

I say 'almost' because the moon eclipse is particularly stunning in my oppinion.

Thanks Vlaiv.

The bottom of the Mak does indeed have a T2 male thread. And yes, I can screw the camera on directly to that. Good tip about the nose piece , btw.

But without eyepieces I will not be able to achieve different magnifications. Which was kind of the point of inserting the tube in the first place. Particularly for moon photography but also for planetary photography.

I understand your point about the smaller sensor on the 385 vs my DSLR. But it does still surprise me that the difference in aberation is so pronounced. In fact, I had not noticed it at all until the problems with the 385 came about. To be honest, even knowing what I know now, I'm still struggling to see it.

So, it still leave the question:

How do I achieve different magnifications for moon/planet photography with my 385?

10 hours ago, vlaiv said:

Posting resulting images can help determine the cause.

Also - a bit better description of each setup or possibly a picture of it would be good.

Ok, here we go.

The moon picture. I only have one of the moon taken with the Mak. Even as compressed file it should be obvious that the edge is out of focus whereas the center is not. Unfortunately I don't have one with the refractor and the completely elongated stars. Same problem but much more pronounced. It was so bad that the stars at the edges looked like rainbow coloured comets. Tail and all (no, it wasn't drifting. The center was fine pinpoints of stars)

The three following pictures are of:

1. My diagonal mirror at the bottom of the Mak.

2. The nose/extension/eyepiece/camera coupling/camera laid out in order of assembly.

3. The whole setup assembled.

It is not clear on the picture because the camera is lying upside down, but the extra 150 deg lens is indeed off  the camera (and always was).

George

14 minutes ago, vlaiv said:

Having images would really help, I think.

Its hard to imagine what could be wrong because you mention that DSLR image is ok, while 385 image is not and behaves like there are optical aberrations in system (both refractor and mak) - field curvature or something else.

385 sensor is much smaller than DSLR sensor and it should be much less sensitive to aberrations that are inherent for particular optics (image is best in center of properly collimated scope).

Only thing that I can think of is that you are not used to seeing stars / image detail at that scale and that you have same level of aberrations (probably due to tilt, or defocus or similar) on both cameras but 385 being much smaller shows them larger (think crop factor here, although I don't really like to use that term).

What ever it is, I think we can sort it out, but like I said - best thing would be to record an image of star field / star (if you don't have any saved) and post it here so we get idea of what we are dealing with.

I get what you mean about crop factor, and your explanation makes sense.

The aberations were so severe that I remember thinking there was no reason to save the pictures until I got the problem sorted. But as I said, I'll check when I get home tonight and revisit this thread.

2 minutes ago, vlaiv said:

Posting resulting images can help determine the cause.

Also - a bit better description of each setup or possibly a picture of it would be good.

Not sure I saved any of them. I know I didn't for the moon pictures. I'll check.

I'll post some pictures of the setup when I get home tonight. Propably easier than to describe it.

7 minutes ago, don4l said:

Have you taken off the lens that comes with the ASI?

 

Yes. But was actualy wondering if I should put it on. But I guess not then :).

Ok, so this is a little embarrassing. A couple of months ago, I bought a Zwo ASI385MC. Particularly for planetary/moon photography on my Mak 180. But judging by results posted on Astrobin, it is very much possible to do some DS objects as well.

The past months have not offered much opportunity. If the skies weren’t cloudy, I could be sure I’d be working the nightshift. But a couple of days ago I got lucky and had somewhat clear skies (and managed to smash my Stellarmate in my uncontrolled excitement 😭).

I tried a globular cluster first with my trusty 80mm Evostar. The stars at the edges were extremely elongated and distorted. The center was fine. This wasn’t a problem when I used my DSLR. Or at least not as pronounced.

Then I switched to my Mak and pointed at the moon. When the center was focused, the edges were not. Once again I’ll point out that I never had this problem with my DSLR.

The only thing I’ve changed is substituting my DSLR with the 385MC. Why are the results so different? And what do I do about it?

George

PS: If anyone has an extra Stellarmate lying around that they don’t know what to do with, I’ll be happy to take it off your hands 😁.

2 hours ago, happy-kat said:

That's a shame, but you don't need to guide for the Moon, so can still play while you try to fix your stellarmate

I operate my camera through Stellarmate (Ekos) too 😩. I'm in the process of looking into if I have the cables required to connect my camera to my tablet/mini-laptop. And even then I have no idea if it'll work. I should be able to fire up K-stars/Ekos that is running on my tablet. Obviously it'll only be able to connect to the camera. But I suppose that'll do for now. IF I can get it to work.

In any case. Not gonna catch the moon for some time anyway because of its position. Or rather the position of my neighbours house. Neither are likely to move to accomodate me :).

Disaster!

The moon was too low so I had some houses in the way.  But that's not the disaster. I dropped my Stellarmate and now it doesn't send WiFi signal. I fear it's broken completely. Christmas comming up so I realy can't afford a new one. Argh!

🤬🤬🤬🤬

Until I can afford a new one (or this one magicaly decides to work again), I'm gonna have to go back to basics with unguided photographing with my DSLR.

Thanks everyone for the very good replies.

As I said, I'm not in any immediate need for purchase advice. Regardless whether I go for the Quark or a 'proper' solar telescope. Ever since I bought a foil filter for viewing sunspots I've wondered why I didn't see what I saw on professional photos of the sun. You know, that deep orange hue with lots of details of the surface and beautiful prominences.

I was a bit surprised about the quality control of the Quark that Davey-T mentioned. Even if the Quark is the cheaper alternative (if you already have a scope) it's not exactly pocket change we're talking about. So you would have thought a better quality control would be included in the price.

The Coronado Solarmax definately looks the business. But being a one trick horse (as solar telescopes are) the price seems extravagant. The Daystar Scout looks more likely to be in the realm of financial possebility for me. Or the Quark, combined with my trusty Evostar 80. Once I've sold a kidney, that is :).

Thanks again everyone.

Ok, so I'm sitting here on the nightshift and there realy isn't much to do or keep an eye on. So naturaly I started browsing various telescope sellers websites (such as FLO)  to see what I can spend the money I don't have on :).

Long story short: I was looking at solar telescopes. Yikes 😱 ! It seems that I need to win the lottery (twice!) to be able to afford one of those.  So I started looking for alternatives. The Quark Daystar seems like a viable and quite good alternative. They are not within my immediate financial means. But with a bit of planning they don't pose an insurmountable obstacle  (i.e living in a tent for a year and selling a kidney on the Chinese black market).

Since I already own a Maksutov (Skywatcher 180mm and also a 127mm)  the Daystar Quark Combo seemed ideal. So I read the description. And as expected, I ended up with more questions than when I started reading.

1. It seems strange to me that there is one for Chromosphere and one for Prominence. I have understood that this has something to do with wavelength (Ångstrøm). But is it realy beond the wit of man, or in this case Daystar, to create something that can do both?

2. In the description I read the following relevant to my telescope: "Maktsutov telescopes operating at a native ~F/15 focal ratio do not need to reduce the aperture of the telescope but must use front mount energy rejection to prevent overheating of the optical tube assembly". It begs the question: What the heck is front mount energy rejection? Could it be like the solar filter that I already have that you mount at the front of the telescope (you know, the foil sheet you can buy and cut to fit)? Or is it a special filter that you put on the Quark like the filter on an eyepiece?

3. Apart from my telescope, my mount and the abovementioned 'front mount energy rejection', what else would I need in order to start observing/photographing the sun?

Hoping to hear from some of the 'I-used-to-be-rich-before-I-bought-a-solar-telescope' members in here.

18 minutes ago, cletrac1922 said:

George

First of all welcome from Land Down Under

I am out a couple of times per month with my club doing presentations in primary schools and scout groups

When observing planets and other DSO objects with my 10" flex Dob, I use either a 15mm or 17mm wide angle eyepiece

When comes to the moon, as lot closer to us, and brighter, I find if use 25mm eyepiece gives you nice view, without cutting off the edge, as happens with 15mm or higher eyepiece

John 

 

Thanks John.

My goal is somewhat different than what you describe. I am going to 'stress test' my Mak and new camera to see how close I can get, and still get a useful picture out of it. For this I need to be as precise as I possibly can.

But I readily agree with you that for pure moon gazing (which I will propably never grow tired of) a 20mm or 25mm would grant the best overall view. 

26 minutes ago, AKB said:

An interesting thread (with some sidetracks, and, indeed some misconceptions by yours truly) here...

 

Thanks AKB. It did actualy help. Shame on me for not doing a propper forum search :).

It seems to be the consensus that if properly focused on a star, it should also be properly focused on the moon. In theory. However, different optical 'illusions' may give the impression of not being in focus over the entire plain. The trick being to find the middleground.

Since I will be using my Mak 180 (and possibly even a barlow to get a good crater shot), I will be looking at a very limited plane. So I am hoping that I can use my Bahtinov mask on a star, and the use the focus on a specific part of the moon that I wish to photograph.

I will revisit this thread when I have some 'hands on experience' to report on the matter.

Keeping fingers crossed for the promised clear skies 🤞 on friday.