Highest power ?

[Dantooine]

What would be the highest magnification I could get on a good night with my 102ed f7 refractor? I’m asking as I’m considering a Barlow for those rare good conditions. Mainly for moon and planets. I normally max at 150x but have been up to 200x. 

[John]

Maybe 300x if its a decent one.

 

 

 

 

[Tenor Viol]

If you read old astronomy books from the 50s and 60s, they used to quote 100x per inch of aperture for refractors, less for reflectors. Modern view is that is way over the top as seeing is rarely good enough to get anywhere near that. I think modern view is in UK skies it is rare to get above 50x per inch (for refractors) so 200x for a 102mm would be a 'working' maximum with the odd occasion you can get more than that. There will be people with similar kit who will be able to provide 'real world' advice. 

[Dantooine]

That’s good to know. Another tv items twitching at my bank account then. Thanks John. 🤑

[Dantooine]

2 minutes ago, Tenor Viol said:

If you read old astronomy books from the 50s and 60s, they used to quote 100x per inch of aperture for refractors, less for reflectors. Modern view is that is way over the top as seeing is rarely good enough to get anywhere near that. I think modern view is in UK skies it is rare to get above 50x per inch (for refractors) so 200x for a 102mm would be a 'working' maximum with the odd occasion you can get more than that. There will be people with similar kit who will be able to provide 'real world' advice. 

I’ve been to 200x so maybe I’m being greedy then. 

[vlaiv]

It actually depends on your eyesight.

For 20/20 person - you don't really need to go very high to be able to see everything there is to be seen. For 102mm of aperture we are talking about resolving features the size of 1.26".

20/20 vision person will see 1' detail - that is 60". In principle you will be able to see it all with about x47.62. Any higher magnification will not show you more - just make it easier to see what is already there.

People often use x2-x3 that magnification because it just makes things easier to see (you don't have to work that hard like reading last line in eye doctor's office ) but after that, things just become too soft (not because optics is poor - rather things are naturally blurry because there is no additional detail).

[Dantooine]

11 minutes ago, vlaiv said:

It actually depends on your eyesight.

For 20/20 person - you don't really need to go very high to be able to see everything there is to be seen. For 102mm of aperture we are talking about resolving features the size of 1.26".

20/20 vision person will see 1' detail - that is 60". In principle you will be able to see it all with about x47.62. Any higher magnification will not show you more - just make it easier to see what is already there.

People often use x2-x3 that magnification because it just makes things easier to see (you don't have to work that hard like reading last line in eye doctor's office ) but after that, things just become too soft (not because optics is poor - rather things are naturally blurry because there is no additional detail).

That’s interesting. What magnification do you find suits you for most observing?

[vlaiv]

5 minutes ago, Dantooine said:

That’s interesting. What magnification do you find suits you for most observing?

I like when image is sharp rather than magnified.

x200 with my 8" scope and about x100 with 4" scope.

I was observing two days ago after quite a long time - had my 4" Mak setup on balcony and took a glance at Moon, Jupiter and Mars. I found that ES82 11mm gave most pleasing views, although I also used ES82 6.7mm and BCO 6mm. On Moon I preferred 6.7mm but on Jupiter and Saturn - 11mm was more pleasing.

That gave something like x118 magnification with 11mm and x194 with 6.7mm.

Just to clarify - when I observed Jupiter - it was Europa transit at that moment and I caught second part of it. Seeing could have been better but it was relatively good. I could see Europa shadow with both 11mm and 6.7mm and the moment it emerged from in front of Jupiter - I could clearly see Europa itself - but actual disk was only clear to me with 6.7mm. However at that magnification and with 4" scope - you can't really be sure if you actually resolved the disk - it just looks different than star, a bit fatter but with airy rings around it - which is a clear sign that we are entering too much magnification territory.

 

[Dantooine]

3 minutes ago, vlaiv said:

I like when image is sharp rather than magnified.

x200 with my 8" scope and about x100 with 4" scope.

I was observing two days ago after quite a long time - had my 4" Mak setup on balcony and took a glance at Moon, Jupiter and Mars. I found that ES82 11mm gave most pleasing views, although I also used ES82 6.7mm and BCO 6mm. On Moon I preferred 6.7mm but on Jupiter and Saturn - 11mm was more pleasing.

That gave something like x118 magnification with 11mm and x194 with 6.7mm.

Just to clarify - when I observed Jupiter - it was Europa transit at that moment and I caught second part of it. Seeing could have been better but it was relatively good. I could see Europa shadow with both 11mm and 6.7mm and the moment it emerged from in front of Jupiter - I could clearly see Europa itself - but actual disk was only clear to me with 6.7mm. However at that magnification and with 4" scope - you can't really be sure if you actually resolved the disk - it just looks different than star, a bit fatter but with airy rings around it - which is a clear sign that we are entering too much magnification territory.

 

I quite understand where you are coming from. I like the views of planets anywhere up from 55x. Nice from 90x-120x. At 150x it’s a little bigger but it does not always give anything more in detail. Some people on here are saying 400x etc, I just can’t get my head around those magnifications and things would be moving too fast with my manual setup so I don’t even try. 

[vlaiv]

1 minute ago, Dantooine said:

I quite understand where you are coming from. I like the views of planets anywhere up from 55x. Nice from 90x-120x. At 150x it’s a little bigger but it does not always give anything more in detail. Some people on here are saying 400x etc, I just can’t get my head around those magnifications and things would be moving too fast with my manual setup so I don’t even try. 

I pushed my 8" to ridiculous powers like x500+ just to see that moment when image "falls apart" - could not understand why people call it that, and I still can't.

For me, image did no fall apart - it just became magnified / larger with the same level of blurriness (and darker of course).

Best views of Jupiter to date were with 8" at x200, so again - no crazy powers required.

[Kyle Allen]

With my 8 inch Dobsonian, the highest power I use is 220x. I don’t feel the need to go any higher than that and often prefer the view at 150x. I have noticed that when reducing the magnification, the detail I have been observing is still visible just smaller, which agrees with what vlaiv says. Higher power makes it easier to see though. 🙂

[mikeDnight]

I feel the Moon can take high powers well when its high in the sky and the atmosphere is steady. Although you are unlikely to see more at 300X than you will at 200X,  high magnifications can present some really spectacular views and can be fun to use. And because there is plenty of light, you can push your scope until the seeing conditions put a limit to any improvement. I remember my stomach rolling as I drifted across the shear cliff face of the lunar Appenine mountains at 474X using my 100mm refractor a few years ago. The mountains looked almost 3D and because of the high mag I didn't see the sudden drop over the edge coming. 

Edited July 30, 2020 by mikeDnight

[Sunshine]

22 hours ago, Tenor Viol said:

If you read old astronomy books from the 50s and 60s, they used to quote 100x per inch of aperture for refractors, less for reflectors.

Oh don't i wish!

[Dantooine]

mikeDnight, wow 474x, what focal length is the 100mm?

Edited July 29, 2020 by Dantooine

[mikeDnight]

16 minutes ago, Dantooine said:

mikeDnight, wow 474x, what focal length is the 100mm?

It was a 100mm F7.4 with a focal 1.6X extender-Q plus 2X barlow and a 5mm Pentax XW eyepiece, giving X473.6 

[paulastro]

23 hours ago, Tenor Viol said:

If you read old astronomy books from the 50s and 60s, they used to quote 100x per inch of aperture for refractors, less for reflectors. Modern view is that is way over the top as seeing is rarely good enough to get anywhere near that. I think modern view is in UK skies it is rare to get above 50x per inch (for refractors) so 200x for a 102mm would be a 'working' maximum with the odd occasion you can get more than that. There will be people with similar kit who will be able to provide 'real world' advice. 

In my view x100 per inch of aperture in a high quality refractor isn't out of the question in instruments up to about five inches.  

However, this is only on those rare nights when the seeing is just about perfect, when the images look tack sharp with no visible seeing effects.  At such times the image looks motionless, like a fine etching.  Alas, they are VERY rare.  About once every 3 to five years in my experience.  Even then, they may last only a few minutes.

Having said that, with my ED refractors ranging from 72mm to 120mm, it's not that unusual to be able to usefully use x75 per inch.  That is with a binoviewer, without it would be less often.

And we're talking about the wild weather of Yorkshire here 🙂.

 

 

Edited July 29, 2020 by paulastro

[John]

I find that my Tak 100 is just getting into its stride at 200x and sails up to 300x fairly easily on the right targets. I was using 450x on the Moon with this scope last night when observing crater chains. Most of the time it was less than this but the "crazy" magnification was surprisingly sharp though it does get a bit dim.

My Vixen ED102 F/6.5 starts to run out of puff at about 200x - 250x though so I guess the figuring and polish of the Tak is a bit better

 

 

[paulastro]

You're right about the images getting dim at such powers John - and of course, the older your eyes the more likely you are to be troubled by floaters as the image becomes dimmer.  Though, using a binoviewer does help aleviate the floaters for me.

[BGazing]

On 28/07/2020 at 23:41, Dantooine said:

What would be the highest magnification I could get on a good night with my 102ed f7 refractor? I’m asking as I’m considering a Barlow for those rare good conditions. Mainly for moon and planets. I normally max at 150x but have been up to 200x. 

150x is perfect for that aperture, 200x if seeing is really good, or even higher if the floaters do not bother you.