miguel87

Thanks chaps. I have never bought any extra mounting parts so it must have come with two options. Unless of course rother valley optics very kindly gave me an upgrade without telling me.

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13 minutes ago, DaveL59 said:

does look like the one on my EQ5 that fits in the saddle for the tube rings to fix onto

Ok thanks, maybe it came with two different size options of something.

👍

Advice please,

Been having a proper clear out of the loft. Found a box of astronomy bits and sorting it out.

What is this and do I need it? It must be from my eq5 mount.

Thanks! ✌

Very nice 👍

9 hours ago, Don Pensack said:

OK.  We know the size of the Airy disc in a scope isn't relevant because then we'd all use only short f/ratio scopes, where the Airy disc is smaller.

 

You are proving my point here; yes the airy disc is smaller in a faster scope precisely because the image created at the focal plane is on a smaller scale (less mag).

So we have evidence here that the size of the best focussed star image in a telescope gets bigger with magnification.

Why else would the airy disc be bigger on longer f/ratios?

If it behaved like a point source f/ratio would not affect it's image.

9 hours ago, Don Pensack said:

 

At whatever magnification the Airy Disc becomes an extended object, you have to exceed that before the surface brightness dims with increasing magnification.

 

It is always an extended object, just a small one.

As soon as the primary has focussed the star at the focal plane it has become a non point source. Due to the airy disc, diffraction of light and any aberrations present. The image of the star on the focal plane is not a point source. Not at any magnification.

The book I have linked states that a point source is not physically realizable.   https://books.google.co.uk/books?id=8P4gBQAAQBAJ&pg=PA74&lpg=PA74&dq=a+star+is+not+a+true+point+source&source=bl&ots=CZj7YUxKkF&sig=ACfU3U1CbyTW-qgS33AQTjSEyACGEcYUQw&hl=en&sa=X&ved=2ahUKEwil2LP-67fpAhX2TxUIHSvTC9AQ6AEwAHoECAEQAQ#v=onepage&q=a star is not a true point source&f=false

Yes, it is a small object so even doubling its radius by doubling magnification will move it from about 0.7 arc seconds to 1.4. So still tiny. But the dimming process as with any other objects is still taking place.

The light source remains the same so it has to dim, there is no way around that unless you argue that...

1.) it is indeed a true point source at the focal plane.

Or

2.) It does not increase in size with magnification. (Which is impossible unless the focal plane image contains a point source)

5 minutes ago, Jennifere20 said:

Can you guys zoom right into it?? I just kept getting a white blob! I used the 20mm tried my 9mm and could just see even more blur 

Venus is covered in cloud so remains a beautiful white blob even under higher magnification.

I guess I would normally view it around 100-150 magnification but depends on alot of factors.

Vlaiv was able to give the size of the airy disc for a given aperture. This is in arc seconds (0.7 for 8inch scope if I remember), so objectively not a point source.

You could do the maths of the TFOV of any eyepiece divided by the airy disc diameter to figure out it's apparent angular size in the eyepiece.

You could in theory then roughly estimate its surface brightness which would decrease with greater apparent angular size.

11 minutes ago, Don Pensack said:

That could have been the eyepieces in question.  Assuming your scope is f/5, I would guess a 1mm exit pupil (5mm eyepiece) would be about the minimum for the Airy Disc to present a noticeable size.

At 6mm, you should not have detected any decrease in brightness of Vega.  The overall field brightness would be dimmer, but Vega?  I would suspect your 6mm eyepiece may have a significantly lower transmission.

Nope. The 6mm has less glass and is much more expensive so I doubt it.

Also you dont just suddenly get to a certain magnification and boom, from a tiny dot to an airy disc. Its grows and shrinks with magnification (obviously you need high mag to see this).

Either way. It is not a true point source at the focal plane. Because the mirros/lenses just arent that accurate.

And the airy disc depends on the size of the aperture. So as you zoom in or out, the disc gets larger or smaller, hence dimmer or brighter.

4 minutes ago, vlaiv said:

I just jumped in this discussion again and I'm not quite sure what is being discussed, but star is point like for quite a large span of magnifications.

If you want to get somewhat more technical - most people resolve at about 1 minute of arc. Airy disk size for 8" scope is 1.28" - we can say that most of light is concentrated under half of that so about let's say 0.7". We need about x85 magnifi8cation to get into region of 1 arc minute. To start resolving airy disk - you need couple times that. This is why people say - 

Yes, you will see star dim when you crank up magnification - but you need to use crazy powers to see it clearly.

This is all I was saying, that it will dim with magnification.

I know it's not huge because they are such ti y objects.

Having said that, the brightness of Vega last night in my 32mm and 6mm was very noticeably different.

9 minutes ago, vlaiv said:

I have to be very careful here as there are different answers depending on context.

If you increase magnification for anything that has surface - surface brightness with respect to apparent angular size will decrease. On the other hand - surface brightness with respect to actual angular size will not change.

What does this mean?

Take sky for example - we have sky that has certain brightness - like mag21 - which means magnitude 21 per arc second squared brightness. Increase magnification - it will look darker. Measure it, regardless of magnification or pixel scale - you will always get mag21 per arc second squared.

So in absolute terms - brightness does not change. In relative terms it does change - if you spread light over more receptors (eye cone cells or camera pixels) - same amount of brightness gets registered by more receptors - each receptors gets less photons - in that sense - each receptor registers lower signal - but total number of photons remains the same.

Makes sense?

Yeah I get that, obviously  I'm not gonna actually change the brightness of the object.

But we all agree that planets are dimmer under higher magnification, because that same amount of light is spread out.

If you increase mag enough on a star then you will resolve the airy disc. It will not remain a point of light because you are not examining the star itself. You are imaging the image created at the focal plane. 

The image on the focal plane is a disc, it has dimensions and therefore the image of it in an eyepiece will dim as it is spread out under higher mag.

If the image of the star at the focal plane was an actual physical point then fine. This would need literally perfect optics. But it isnt, not even close really.

1 minute ago, vlaiv said:

 

This does not mean that star will be point like in a telescope - telescope optics can't resolve something past airy disk sizes - and airy disk size depends on aperture size.

 

 

Agreed. So anything that has its light source spread over an area will dim as that spread increases?

44 minutes ago, Don Pensack said:

 

1 hour ago, RichardHurst said:

Thank you so much for your help and advice, as you know its all a bit of a head scrambler. I want to start off like you just using my Nikon D810A DSLR and the Redcat which has a 250mm focal length. With your Sony and 30 second exposures is that long enough to capture a nebula image?

Capture many 30 second images (maybe an hour exposure in total I.e. 120 exposures) then stack them together with free software.

Stacking is how most of the images you see have been achieved.

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2 minutes ago, Skipper Billy said:

This document might help you

https://drive.google.com/file/d/1IuxD4QFi9wOfRbrxfXrls3Eas9SevJ1a/view

It's just a manual eq5, same as mine. Computer programs will not work.

On 28/03/2020 at 00:06, IamLost said:

Basically Polaris is blocked by my house so I cannot use it to align and I was wondering whether or not there is a way to align without seeing Polaris. I’d like to do some imaging so it would have to be aligned well enough that there won’t be noticeable trails. Thanks!

I would mark a spot where I put my telescope (3 tripod leg marks) to use everytime.

Once you have done one fairly accurate drift align I would then mark an artificial north celestial pole on your house based on what is showing through your mount's polar scope!

Sounds crazy but will be very worthwhile in the long run.

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If you have a slightly larger budget then I personally find the vixen SLV's are another step up in quality without breaking the bank

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You seem well committed so I'm sure you will get it sorted with a systematic approach. I just dont like to see astrophotographers spending hours and getting results that they're disappointed with.

Dont forget to stick an eyepiece in the telescope every now and them. Take a look and chill out. 

There comes a point where you have to be impressed with what YOU have achieved. Comparing to other results is a downward spiral.

It is very difficult to put a personal spin on AP. With normal photography you can take from a  different angle, put something interesting in the foreground, alter composition etc. With telescope AP, the object is just the object, same size, same angle, no foreground, no background.

That is what ultimately put me off; the idea that if I got an exceptionally good photograph and spent hours on exposures, flats, parks, bias, processing. At best, I would end up with something identical to what has already been done.

Anyway, I ramble! But trying to say, enjoy the results from your setup, you are never gonna get the best photo you have ever seen of M42, M57 etc etc, it's just not possible. But, it is YOUR picture.

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Keep going with the visual! It's an amazing hobby. One of the best things is the lack of power needed. I see many people people with laptops, cameras, guiding scopes, battery packs and heavy power banks.

All I have is one battery pack the size of a TV remote which last 3-4months just to track the sky.

For the 3 star align at this time of year I would just look at the plough which is virtually overhead. The stars are bright and won't be blocked by anything. You could learn all 7 pretty quickly.

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Call me old fashioned (I'm 90% a visual observer) but sometimes you have to take a step back and realise that there's very little wrong with those stars (other than colour perhaps).

If you are a perfectionist then I guess it is an issue. But you will get beautiful pictures with the setup just as you have it. I often see stunning images of stacked 30s frames so maybe just stay shorter.

Only my opinion.

The best power option for you will depend on what you are powering.

Just a mount? Or cameras, dew heaters, laptop etc. If you can tell people what you need to power I'm sure you will get some good recommendations.

If tracking is a priority go with an eq mount. They are not as difficult as everybody makes out.

12 minutes ago, MarkAR said:

Well FLO sell the 150P-DS with the EQ5 so that should be sufficient but I would be tempted to put it on the HEQ5 or an EQ6 of some sort.

I dont think the OP is mounting the 150pds. Just a camera at the moment.

Also I use the 200p on just an eq5 and for visual its absolutely great. Many people use this combo with no issues. The tracking motors will do the trick for a piggyback DSLR too.

1 minute ago, Barry-W-Fenner said:

Is this known by any other name? I've searched Skysafari for IC3568 and it's not finding anything. I'm keen to have a look tonight.

On a slightly different note. Anyone attempting Mercury after sun set? It looks to be in a very high position by its standards.

Baz

 

Yep around the 21st of may I'm gonna go for mercury. The only planet I havent observed with the scope. It is going to be pretty near Venus then and easier to find.

Short answer is more magnification, so either a 2x barlow or an eyepiece in the 4-6mm range perhaps.

The long answer is, how much are you expecting. I have a 200mm telescope and as for seeing detail to the level of ice caps (must be talking about mars) that is a once in 4-5 years sort of detail for me.

I would say that Saturn will always look small in that scope but on a good night you might be able to split the rings. 

Jupiter, on a good night you might catch 2 or 3 bands on the planet, the great red spot is difficult but possible.

I owned a 130 reflector for a long time and found 200x magnification to be pretty much the worthwhile limit. And this could only be used on rare occasions, very often you will find that zooming out a bit and observing at 150x or 100x although smaller will be so much sharper and brighter, often with more detail.

In your shoes I would get a quality eyepiece around 6mm and a decent barlow lens. You will then have 25mm, 12.5mm, 10mm, 6mm, 5mm and 3mm!