miguel87

My follow up question would be. If you continue to reduce aperture to silly amounts, say 1 inch or less, do you start to limit TFOV?

Because the mirror physically cant see past the narrowing tube. I imagine being a primary mirror looking at a tiny hole at the other end of the scope. I cant imagine fitting the seven sisters into that view?

I think some further googling has cleared my mind a little. It is wrong of me to think of the image existing on the primary mirror. The image exists at the focal point in the focussed tube and the eyepieces examine this image in different ways, they do not 'look' at the mirror.

All parts of the mirror can see the whole aperture (minus the secondary obstruction). So larger aperture just means any individual object is shining off a larger surface and focussed to a brighter point within the final image.

And as you said before, that is why recolimation is not needed, every part of the mirror sees all of the aperture, so...

stopping down the scope doesnt actually put any part of the mirror in the dark.

1 minute ago, John said:

It does work but I've had a couple of glasses of decent wine so I can't attempt to explain the optics behind it. But it does work !

 

You will have to attempt to explain it to me on a less eventful evening!

It got me onto thinking about the primary mirror and how when we use higher magnification we must only be looking at a small area of the mirror? 

If that is true, I dont understand how more aperture (adding extra unused mirror) makes that image any brighter.

It must all be down to how focussing works

I cant wrap my brain around this! Need someone with a few more brain cells to explain.

I dont understand how part of the produced final image doesnt include the underside of the cap? With the aperture now being off centre, how does it still appear in the centre of the eyepiece?

If the small aperture still uses all of the primary mirror, how can the aperture make any difference at all? 😖

I guess what I am failing to understand is how the image on the primary (as seen from the secondary) relates to the final image. I presume with no eyepiece in, you could look down the empty focuser and see the off-centre, small aperture surrounded by the underside of the telescope tube cap? If the eyepiece forms its image from this information, how can we not see the cap.

My twisted logic assumes that a smaller aperture reflector has a more curved primary mirror to relate to the width of the opening.

Somebody help my brain!

Mike

Thanks James,

If I ever sketch all 110 my plan is to print a photo-book of the negative images. It has added a little extra excitement to my observing sessions AND the biggest difference I have noticed is that the sketching really makes me stay on one object for longer, studying it in detail rather than flying around the night sky too fast.

After many years of visual observing and one half-hearted attempt to get into astrophotography I have decided to keep a record of my observations by sketching. Partly spurred on by my desire to tick of all 110 messier objects.

These are my very first sketches from the last week or so.

2 minutes ago, Pankaj said:

I would say that your plan to buy a 10" dob is perfect. The Skywatcher 10" dob is good piece of equipment. I have it too and its my best mate for ''a grab & go'' observing session. Though to some members here, this scope may sound a bit heavy to carry. Its got great resolution and splits the tightest of doubles easily. All planets are within reach except of course Uranus & Neptune. Its 1200mm FL with a modest 25mm eyepiece will easily show the rings of saturn, bands on jupiter and the moons of both planets. Increase the magnification using 2x barlow and eyepieces till 6mm (400x) and you'll get blown away with what you see. 

Due to its aperture, almost all nebulas and galaxies are within reach though watching the details in some dimmer ones may require dark skies. 

The only problem with a Dob is that as you increase the magnification, the planets quickly pass through the field of view. So with time and practice, you will have to learn to follow the planets movement through the fov by turning the dob mount. 

Uranus and Neptune are definitely within reach. I have seen them many time with 8 inches. Not much to look at and obviously smaller than our closer neighbours but I have resolved Uranus as a crisp disc and Neptune appears more star-like.

They give good reviews because they dont want to waste pages on showing people a telescope NOT to buy. Venus will not show detail but the phases are enjoyable to see. I would have thought you could pick some colour out on saturn with that scope.

As for Saturn's rings, the planet should be obviously not round and of golden colour in the 3 inch scope. I doubt you would be able to see the cassini division but you should be able to get a small crisp view.

If your main interests are planetary then maybe stick with a refractor as they give sharper, more accurately coloured images of planets. 

Dont expect magic with 8 or 10 inches. I have had an 8 inch newt for many years. Maybe only 3 times out of 10 I can make out the cassini division in the rings. The quality of your sky will make a huge difference and the declination of the planet.

Views will never get worse with more aperture unless the optical quality of the scope is worse. Like for like, more aperture is always a better view.

I have heard similar things about 'optimal aperture' it is nonsense. If it was true, all professional observatory telescopes would be 8 inches or smaller so that they have optimal views!

Sounds ridiculous. Just barely visible in my 8inch under bortle 4 last night.

That's not F8, works out as F3.2, I know very little about telescopes but that is very fast. Others will be able to tell you if this is causing problems.

What are you viewing that is showing you a blurred image?

Where did you the get the mirror?

Mike

I did enjoy last night too!

Spent most of my time in leo with the triplet and M66/65.

A quick trip to the black eye also was very nice.

However, I am most chuffed with finally finding M1! The crab has eluded me until now. But I must say that I had to catch it quite early into the night as it is now so low and with my 8 inch newt it was an averted vision only object, VERY faint smudge with no detail at all but a slight suggestion of elongated shape.

Not much to see but a big one off the list 😁

Enjoyed reading your report

Mike

Another 2 inches will always give you better views so you have to set a budget and stick with it. Also, a 10 inch Dob is a fairly chunky piece of kit so depends where you planning on taking it and storing it. 

I would love 10, 12, 16, 20 inches! But after moving from 2 inches, to 5, now 8. I know that anything bigger would start to cross the line for impractical. That's only based my personal situation tho with storage, ease of use, transportability etc. I think if I went bigger I would use it less. Which defeats the point. 

Also if you are new to telescopes, the longer the scope, the more magnification you will have for any particular eyepiece. So nudging a dob will get increasingly difficult to start with. Depends if you like very wide field views too; my longest eyepiece is 32mm and I can only just fit the seven sisters in frame with a 70° AFOV. If my scope was longer I would be looking at much more expensive eyepieces to frame the whole thing.

I'm not saying stick to 8, just think about practicality. 

Brilliant thankyou!

Hi everyone?

Sorry to hijack this thread but I cant figure out how to start a new topic in a group.

I notice the south wales group has the most members 👏

I have been stargazing for 10 years or so, been living in Gower, south wales for 3 years now. Really enjoying the skies compared to living in Birmingham.

Hope to connect with other local people too. Does this group ever meet? If not it will at least be nice to compare experiences with others in the same part of the world.

Had a great night on Monday and chose Leo as my target. Saw the triplet as well as M105, 66 and 65. A quick hop to coma berenices for the black eye galaxy and a quick globular.

Really enjoyed although maybe expected a little more in detail from my 8inch newt. Perhaps expecting too much or maybe it wasnt quite a s clear as I thought.

Anyway! Nice to be part of the group ✌

Hi,

Didnt know where to post this but I am finding it impossible to find groups on this website? I am on mobile and have looked everywhere.

Thanks

Amazing, insightful read!

Just have to be pedantic and point out the small mathematical error right at the start;

A billion is only a thousand million, or a 1 with 9 zeros.

Sorry ✌

Brilliant, the best I have ever seen from an undriven mount.

Well done!

How long were your exposures on a non driven mount? I am intrigued as this picture seems impossible! Great picture by the way, would love to know how you achieved it.

34 minutes ago, sarahsmiffy said:

Thank you very much.

basically I want to see a bit of everything. Maybe not right away but just to know this scope can.

can I add a motor or goto later ?

Yep the motor is pretty cheap and reliable and easy to fit. I prefer this to constantly nudging along a dobsonian which is a skill in itself. There is something great about located an object and just relaxing to observe for as long as you want without adjusting the telescope, even at high magnification.

Newtonoans are definite all rounders I would say.

16 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 ??!!??

Looks like a great scope. Very similar to what I use really. I think you can expect nice views from home.

I dismantle my set up every time but it really doesnt take too long to setup. Mainly a space issue for me, you would need to leave the tripod legs spread and that takes a lot of space. I would definitely take the weights off if the actual telescope is off too.

I would second a medium size reflector on an EQ mount. But I think we have proved that alot is down to individual preference.

More money  is going to improve things but you can enjoy even a 100 pound scope.

Stargazing is a funny hobby. It often involves standing around in the dark and cold british weather and waiting for clouds to move. But if you have a genuine interest in what is above us and the movement of light across the universe then it is totally addictive.

At some point you have to pick based on preference. As long as you understand the main differences of scopes and mounts. Spending 250 quid on any well made scope will give good views of many objects, regardless of it's type. But if you are in it purely for visuals, you will get bored after a few looks at the moon, jupiter and saturn.

Sadly, telescopes are one of the mostly neglected purchases. I know so many people who bought one and it never left the shed/loft. It's not a glamorous hobby.

I started with a 2 inch supermarket reflector on a trip about 6 inches tall. Terrible lenses, awful views and incredibly unsteady. But I loved it! And have kept upgrading ever since.

I'm sure you will make a good choice but dont over think it. Just get out there and use it!

When you say see nebula, I just want to make sure you know what that means.

No colour (very very rarely a little bit)

A vague grey smudge that is often so faint that it disappears when you look directly at it.

You will not be able to take any photos of nebula without spending approx 1000 plus. Not even a little snapshot here and there.

There are a handful of nebula, maybe 5 or 10 that are brighter than this, but still a brighter grey smudge, no sharply defined edges.

Alot of the enjoyment, for me at least, comes what WHAT you are looking at, not how it looks.

And in terms of planets, you are looking at the size of a lentil in the palm of your hand. Maybe a pea if we are talking about jupiter, but that would drift out of view in around 20 seconds without a motor drive.

I'm not being a debbie downer here, just trying to be realistic.

Mike

6 hours ago, Jakerm1995 said:

Hey Mike, 

That's not far at all, I really appreciate your offer and will probably take you up on grabbing some tips off you! I am a complete noob to this world, astronomy has always fascinated me but i've never got around to buying a telescope. So I hope you'll excuse my lack of knowledge. Upon looking at the map, it does show that where I am is in the orange/yellow area, I hope that it isn't too bad.

Are there any local astronomy clubs at all? 

Again thanks for the help!

Jake 
 

No it's not too bad, depends what you compare it too. I'm actually from birmingham and started my hobby there before moving to wales. My skies were much worse there but I still enjoyed you hobby. 

You will probably find plenty of things to observe at home and every now and then you might drive for 30 mins or so to a dark spot. Heading north we are very lucky as within about 45 mins we are in world class dark skies. I tend to use Usk reservoir which is Bortle 2.

I once met up with Seansea astronomical society at the university but to be honest it wasnt what I was looking for although it's probably not fair to judge on just one visit. 

Hope you enjoy it!

✌

Hi Jake,

Shouldn't be a bad spot at all. If you need any advice I live over near penclawdd!

Also this website https://www.lightpollutionmap.info/#zoom=4&lat=5759860&lon=1619364&layers=B0FFFFFTFFFFFFFF

Great light pollution map of the UK. Very detailed.

Hope you keep at it!

Mike