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New scope - view a bit...meh


Mr niall

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I’ve been trying out my new Meade 90/900 refractor with my Explore scientific solar filter today.

compared to my older 70mm frac (And the same filter) I found the view a bit... meh. The edges were sharply defined but I noticed a lot of what looked like some kind of light bleed - the background looked much more of a vague mustard colour and the sun maybe seemed a bit more washed out. With my old 70/900 it was a sharp circle on a dark background.

is this symptomatic of larger apertures and faster scopes in general or is there possibly something else going on? Maybe reflections or a lens issue maybe?

many thanks

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1 hour ago, Mr niall said:

I’ve been trying out my new Meade 90/900 refractor with my Explore scientific solar filter today.

compared to my older 70mm frac (And the same filter) I found the view a bit... meh. The edges were sharply defined but I noticed a lot of what looked like some kind of light bleed - the background looked much more of a vague mustard colour and the sun maybe seemed a bit more washed out. With my old 70/900 it was a sharp circle on a dark background.

is this symptomatic of larger apertures and faster scopes in general or is there possibly something else going on? Maybe reflections or a lens issue maybe?

many thanks

Did you try the two side by side yesterday or are you going on memory?

I ask because I’ve found the views the last couple of days to be quite poor despite the clear skies. Seeing has been poor with little granulation visible, certainly nothing like I normally see. So it may just be the conditions?

No reason why the new scope should be worse, it is still f10 so likely to be reasonable well corrected. Are you seeing a lot of CA?

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There are a lot of factors that can contribute to image degradation:

1. The seeing ( the usual culprit. )

2. Extinction i.e. the fact that the object you were observing(in this case, the Sun)was very low in the sky and thus the atmosphere degraded the image.

3.Inferior Eyepieces... Mostly the Eyepieces that are provided with a telescope range from being poor(kellner, ramsden, achromat lens etc) to fair(ortho, plossl)...so if you're observing with one of the cheaper ones... they could be the cause of the degraded images.

4. Even though your scope is an achromat, it has a focal ratio of F/10; at this ratio it should be very well color-corrected... however the sun is a bright object... so 'some' color fringing will occur.

Most probably, the color-fringing and washed-out effect is due to poor eyepieces. If its in the scope, you can check it at night by focusing on a bright star(vega, deneb) at high magnification, if the image is a perfect (tiny) disk, then you have nothing to worry about. If it does not come to a sharp focus, then your scope has spherical aberration... which is a fancy way of saying that the scope doesn't focus all the light to a point.

To answer your question, no bigger scopes do not usually suffer from bad images- if they are treated properly. They will usually provide you with a better image.

However, I'd recommend you get yourself a Newtonian if you want to get a bigger telescope (no color-fringing). Also you can get a Apochromat, but they're usually really expensive.

Edited by DanyalAG
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Seeing has been poor here for past couple of days too. Obviously that does t help. But the main reason for scattered light and a non-black, blurry background is high, thin cloud cover which may not always be visible from the ground. Like Stu says, I’d also hazard a guess that the problem isn’t your new telescope.

Edited by Highburymark
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30 minutes ago, DanyalAG said:

There are a lot of factors that can contribute to image degradation:

1. The seeing ( the usual culprit. )

2. Extinction i.e. the fact that the object you were observing(in this case, the Sun)was very low in the sky and thus the atmosphere degraded the image.

3.Inferior Eyepieces... Mostly the Eyepieces that are provided with a telescope range from being poor(kellner, ramsden, achromat lens etc) to fair(ortho, plossl)...so if you're observing with one of the cheaper ones... they could be the cause of the degraded images.

4. Even though your scope is an achromat, it has a focal ratio of F/10; at this ratio it should be very well color-corrected... however the sun is a bright object... so 'some' color fringing will occur.

Most probably, the color-fringing and washed-out effect is due to poor eyepieces. If its in the scope, you can check it at night by focusing on a bright star(vega, deneb) at high magnification, if the image is a perfect (tiny) disk, then you have nothing to worry about. If it does not come to a sharp focus, then your scope has spherical aberration... which is a fancy way of saying that the scope doesn't focus all the light to a point.

To answer your question, no bigger scopes do not usually suffer from bad images- if they are treated properly. They will usually provide you with a better image.

However, I'd recommend you get yourself a Newtonian if you want to get a bigger telescope (no color-fringing). Also you can get a Apochromat, but they're usually really expensive.

No there is no colour fringing at all. 

Eyepieces are Vixen NPL Plossls so I know they are not the problem.

I was having trouble focussing last night but SA didn't occur to me, I will investigate further thanks!

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33 minutes ago, Stu said:

Did you try the two side by side yesterday or are you going on memory?

I ask because I’ve found the views the last couple of days to be quite poor despite the clear skies. Seeing has been poor with little granulation visible, certainly nothing like I normally see. So it may just be the conditions?

No reason why the new scope should be worse, it is still f10 so likely to be reasonable well corrected. Are you seeing a lot of CA?

Yeah it is sort of memory I guess - but objectively speaking I'd definitely never noticed a yellow background before.

Funnily enough no noticeable CA at all. But I have never seen granulation and today was no exception!

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1 hour ago, Mr niall said:

Yeah it is sort of memory I guess - but objectively speaking I'd definitely never noticed a yellow background before.

Funnily enough no noticeable CA at all. But I have never seen granulation and today was no exception!

SA can definitely be an issue, killing the fine detail, but at f10 the risk of that is lower than a faster achro. Worth checking for I guess.

I had a couple of quick looks this afternoon and the seeing was better during one of them. Granulation showed a little better to the point of seeing some darker knots and swirls in it. A little but of interest anyway.

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1 hour ago, Stu said:

SA can definitely be an issue, killing the fine detail, but at f10 the risk of that is lower than a faster achro. Worth checking for I guess.

I had a couple of quick looks this afternoon and the seeing was better during one of them. Granulation showed a little better to the point of seeing some darker knots and swirls in it. A little but of interest anyway.

wowsers I've never seen anything like that. I need to up my game!

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2 hours ago, Stu said:

 

I had a couple of quick looks this afternoon and the seeing was better during one of them. Granulation showed a little better to the point of seeing some darker knots and swirls in it. A little but of interest anyway.

What sort of magnification were you using Stu?

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