miguel87

For me the 300 would just be too bulky and unwieldy. I dunno where I would store it let alone getting it nice an steady for imaging.

I agree. I dont think you could get anything better under £150.

I think if you needed to spend only £100 you would be best with some good binoculars.

✌

12 minutes ago, John said:

Just a small point but, visually, details within Jupiters belts tend to get better defined when you back off the magnification rather than increase it. I think this is because they are low contrast features rather than the high contrast of, say, the Cassini Division.

Probably not really relevant to the overall topic though.

 

 

Maybe not too relevant but still interesting. I love to learn anything that I didnt know already!

I am missing a nice high-in-the-sky planet at the moment 🙁

8 minutes ago, Ags said:

Rural location matters because that determines how bright your sky background is. The contrast technique people are talking about on this thread works by attenuating the sky background but as yours is already dark I don't know if you will see the effect.

M13 is a star cluster - I am talking about reolving the individual stars in M13, which is possible for scopes of 4 inches aperture and up, roughly. Technically, the greater magnification will attenuate the fuzzy glow of M13 itself, so I will stick my neck out and say that you should resolve more stars at high mag in M13 from your location.

I'm not sure it 'resolves' any better under high mag but details such as individual stars will be easier to see as they will be spaced further apart and the glow of the core will be dimmed.

Think about a planet, details within Jupiter's belts or the cassini division in Saturn's rings is easier under higher mag even though these both dim appreciably under higher mag. Seeing individual small details, such as a single star within a globular cluster are easier with some magnification.

I am not disputing any of that. This whole discussion is just me saying;

"Stars dim under magnification"

Many people dont think they do, at all, and believe they function as an actual point source in a telescope.

The truth is they appear to dim less than some other objects and the dimming can be hard to detect due to contrast. But they grow in size and dim just like any other object.

15 minutes ago, vlaiv said:

 

If one had two scopes next to each other - one having eyepiece with x50 and one having eyepiece with x130 magnification - and switched between them - they should be able to see the dimming of the star by almost a magnitude due to spreading of light from star.

If you however use a single scope and switch the eyepiece - chances of spotting the difference are slim to none - since contrast of whole view sill be altered and we remember relative brightness differences much more than absolute brightness.

 

I agree completely. As I said before the subjective process of viewing is very complex and involves a lot of factors.

But the fact remains that a star dims under magnification. The effect may be very difficult to see visually.

Even under modest magnification despite claims that it would have to be extreme.

20 minutes ago, Ags said:

 

M13 is easily visible at the moment. Why not look at it with an eyepiece giving a 7mm exit pupil and one giving a 1 mm exit pupil and see which resolves more stars in the cluster? I am assuming you are in an urban/suburban location.

I am in a rural location but o dont know why that matters. And you are now talking about an extended object which is different to an individual star.

The more extended an object is, the more it appears to dim.with magnification because it's relative area increase is greater (doubling mag on orion could cause it to go from an apparent 30 degrees to 60 degrees whereas a star might go from an apparent1 arc second to 2 arc seconds). The spread of light is hugely different.

Just because stars appear to dim less does not mean that they do not dim.

14 minutes ago, Ags said:

 

It is astronomy 101 that you use high magnification to resolve faint stars in star clusters. This is a technique used by most observers. Who is wrong - your theory or all those observers?

All those observers.

Limiting magnitude is dictated by the aperture of the telescope, not the magnification being used.

The reality involves the effect of contrast and overall image brightness. So yes some dim stars are easier to see with the human eye under high mag. But they are not any brighter.

2 minutes ago, Ags said:

There is no other light to cause "increased brightness". The image you see in the eye is described fully by the light in the exit pupil. 

If you are correct, then why would a smaller exit pupil (I.e. higher mag) dim the image of a planet? If a 2mm and a 4mm exit pupil both fit entirely in your pupil and you are getting all of the light, then why is jupiter dimmer in a 2mm exit pupil than in a 4mm?

It is do do with light being stretched over larger areas. In a really big exit pupil, the light is being condensed to a smaller area, so any object appears smaller and brighter.

You previously said that the airy disc of a star in an 8 inch scope is around 1.4 arc seconds.

Let's use an example of my 20mm eyepiece in my 200p, a magnification of 50x, a AFOV of 50° and a TFOV of 1°.

The 1.4 arc second airy disc would fit 42.9 times across an arc minute and 2571.4 times across the diameter of the 1° TFOV.

Human monocular vision is around 120° horizontally with a resolution according to Rayleigh's criterion of 50 arc seconds (based on a 4mm pupil which is what this eyepiece provides).

This suggests the eye has 3600 'pixels' across the diameter of the eyepieces apparent 50°

These pixels are smaller than the 2571 stars we could stretch across.

So even at only 50x mag we have the ability to see the increasing size of the airy disc. And to me this seems apparent as the pin sharp small stars in my 32mm eyepiece slowly become slightly rounder as I move up through 20mm, 10mm, 6mm eyepieces until there is a very obvious round airy disc in the 3mm at 333x.

9 hours ago, Don Pensack said:

But to the eye, 

 

As soon as you have said that, we are unable to discuss anything objectively. The eye is subjective, non linear and individual. We cant have an objective discussion about how thing appear "to the eye" because there are too many factors.

Also you say that "the eye needs to resolve the airy disc with a visible size before magnification treats it as an extended object"

Well, of course we are talking about visible stars! We dont know or care if the ones that aren't visible are brightening or dimming. And if you are talking about there not being a visible 'airy disc' at low mag? Then what do you think we are seeing at low mag? The airy disc is the only image of the star that the telescope has, just smaller or bigger versions. Yes there might be a size at which the human eye cannot see it as a disc, but that doesnt mean it isn't. It also doesnt mean that is isnt getting brighter or dimmer.

Also the telescope does what the telescope does based on physics. It would treat a star the same even if there was no eye looking through the telescope. Magnification plays by certain rules. Yes our subjective experiences vary but that is a totally different conversation. The moon appears bigger closer to the horizon but it isn't. If you say the stars don't 'appear' to dim with magnification then I will take your word for it. The physical truth is that they do.

Nice telescope, I'm sure would give amazing results. Really good mount too.

My only minor criticism is that because it is designed for photography, it is a 'fast' telescope (f4 I think but could be wrong). This means you get a bit more blurring of stars/objects that are not in the middle of the field of view.

Having said that, my scope is f5, only slightly slower and it doesnt really bother me at all.

👍

EDIT: just checked and it is f4.7 which is not too bad in my opinion.

Yoi could go cheaper if you dont want GoTo but that's a personal preference.

1 hour ago, bomberbaz said:

Fair comments there. I thought a dslr was a lot heavier tbh, there you go. 

I also guess it depends on what the end game is going to be for the OP. 

Your solution above is a great one, no doubt there. My own idea was also worthwhile based on my own experiences using something which is maybe a little outside the conventional box of thinking, more EEVA tbh.

If the OP goes onto more serious astrophotography though, I would agree the HEQ/200p option wins out hands down.

Balls in your court @Scorpion Rob

Steve

Yep absolutely.

Why its such a hard one to answer, quite a few solutions with various pros and cons really.

And if there is one thing I know nothing about, it is refractors!

Let us know what you decide 👍

31 minutes ago, bomberbaz said:

Surely though once you start hanging a camera off a scope, the extra stuff you are still going into the realms of a HEQ type mount are you not?

My pentax DSLR is lighter than my 2inch 32mm eyepiece!

Definitely the best intro to photography especially if you already have a DSLR.

If I had to give a specific recommendation I would get a skywatcher 200p explorer and  a HEQ5 mount. That comes out at about £1030 all brand new.

You've got a perfectly capable mount for started some astrophotography.

A good 8 inch aperture for seeing a huge range of DSO's.

And a very capable (if not quite as sharp as a refractor) planetary viewer.

Only my opinion tho.

5 minutes ago, John said:

With the long refractor, you need them !

Yeah I had never really thought about it until I saw your picture. But then, I have never looked through a refractor (disregarding the supermarket 60mm I started with). 

I might try to keep it that way or I will end up wanting one! 😄

4 hours ago, John said:

Mine is even smaller !

 

The longest slo mo cables I have ever seen! 😉

26 minutes ago, merlin100 said:

I'm guessing a 3.6mm EP?

A barlowed 6mm Vixen SLV gets me 333x in my 200p EQ 👍

23 minutes ago, John said:

I guess we will have to stop advising newbies that very high magnification is not going to bring any benefits ?

But then again, with entry level scopes and inexperienced eyes, perhaps that is still sound advice ?

 

Yeah, I remember with my very first telescope, plastic, terrible 60mm frac. The realisation that stuff doesnt just stay nice and still to be observed!

It wobbles, jumps, moves out of frame, gets knocked out of frame, gets knocked by my eye, won't focus etc etc.

That's why you begin to understand the challenges of high mag. And yes, equipment and experience improve this massively.

I take my hat off to Mike and his 800x mag on Venus. But I think this should be considered the exception and not the rule. I can't imagine how unsteady and blurry that would look on my eq5 mount with modest eyepieces.

I reckon if you averaged everybody's comments we are looking at about 300x maximum useful.

✌

Hi Rob,

It's a pretty big question to answer and I'm not sure how much previous experience you have.

I think the main topic of discussion will be the astrophotography because the other categories should be well covered by pretty much any well made scope in that price bracket.

People often say they have a small interest in astrophotography so would like a scope that can do "a bit".

The way I see it, a scope can either do AP or it can't. Unless of course by just a bit you mean you would be happy with less high quality images in which case there are many different options.

How well your scope will do astrophotography is mostly dependent on your mount. I.e. how accurately can it track an object in the sky without wobbling.

People with more experience might give specific examples but I say £1000  will buy a great scope from any good manufacturer. How much of that you spend on the mount will dictate the quality of any photos you want to take (generally speaking).

As above. I think up to about 4 or 6 inches the 50x/inch rule is about right. Above that is more limited by conditions to somewhere between 250x and 350x in my experience.

Sometimes you CAN zoom in more and get an image but it often isnt worth it as no detail is gained and brightness is lost.

My current scope and eyepiece setup tops out at 333x and I never feel the need for more. It is very rare that I end up viewing at 333x for more than a minute or 2.

This mostly relates to my experience with an 8 inch scope.

✌

Welcome Rob from another living west of the border ✌

2 hours ago, Jennifere20 said:

Does anybody know if anything will be visible tonight? Planet wise 

Changes from one night to the next are small. So a planet might only move a few degrees a day across the sky.

Venus will get lower each evening, slowly, until we can no longer see it as it will be too close to the sun by June.

Jupiter, Saturn and Mars rise in the early hours but stay very low. They will slowly rise earlier and earlier over the next few months.

Definitely get to know your garden and where your clearest horizons are. I have a brilliant NW view but a poor SE view, so I tend to catch things as they are setting much easier than when they are rising.

✌

Just now, DaveL59 said:

epoxy/araldite would be better, superglue will break down eventually from moisture.

If the whole thing has come off what's the end of the bolt like, you might be able to file a flat/square end and get a small T-bar fitted onto it, maybe even silver solder it on yourself...

Its rounded but with grip/tiny gear teeth around it.

Thanks so much for looking at it for me.

I am best trying to super glue a replacement plastic handle on then I guess.

Very grateful for the info 👍

Incidentally, now that I've got a few eq5 people listening. Does anybody know what gauge the finger screws on the counter weights are?

The plastic knob broke off one of mine months ago and it's a right pain to tighten. There's tons on Ebay but I dont know what gauge it is and I am not technically minded enough to figure it out 😅