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Is x428 crazy talk on an 8" Dob in the UK?


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Firstly I wanted to say a big thank you to everyone on here for all the help and advice given. This is my first post but I've been a regular visitor to this forum for a year now.

Ok so I have a Skywatcher 200p AutoDob and am very happy with it. I invested in a 10mm Bader Hyperion and a Skywatcher 2" 2x ED Deluxe Barlow.

Contrary to nearly every piece of advice I have ever read, I am feeling a huge temptation to go large with the Hyperion 3.5mm for planetary viewing :-) I only drag the dob out on very clear nights and have always found views of Saturn and Jupiter clear and crisp at x300. I should say at this point that I have good eyesight, am a keen photographer (not astrophotography) and a large part of my job is graphic design so I like image clarity. Despite everything I've read regarding x200 being as good as it gets in the UK, I have never been frustrated by clarity @ x300 but I am always frustrated by the size of what I'm looking at. Is it really madness to up my mag to x428? What % increase in object size will I achieve vis-a-vis % decrease in clarity?

I have 2 viewing locations, urban Hertfordshire and rural Norfolk.

Thanks in advance.

Z

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Well, I would have said, 'Yes, it would be crazy,' but if it works for you then stick with it. Very high magnification is often used by double star splitters who just want the separation but planetary observers like clarity. Even in very good scopes and at altitude and with good seeing I tend to stick at 250 but what works for me may not work for you.

Olly

Edited by ollypenrice
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Depends very much on the seeing conditions, state of scope cooling and collimation etc as well as the object being viewed. I find the sharpest views of the planets (depending on the above factors) are between 150x and 250x. With Jupiter around 180x seems optimum, for Mars and Saturn, 225x seems pretty good on a decent night. My most used scopes are a 4.7" refractor and a 10" newtonian.

Above these magnifications you loose clarity, contrast and resolution so even though the image of the planet gets bigger, the view is worse in my opinion.

Short answer - yes, 428x is crazy !

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Cheers Olly and John. I invested in a Hotech Laser Collimator (too good for the Skywatcher to be frank but plan to upgrade scope in a few years so figured I'd future proof my accessories) and meticulously collimate before every session and always leave the scope out for at least an hour before even attempting to view on cold nights. As I say I have always found Jupiter and Saturn bright and clear at x300. OK, maybe the image could be sharper at x300, but I would happily trade some clarity in return for a closer view. Am I likely to meet the edge of the viewing cliff between x300 and x428? Can clarity loss vs size gain be expressed as a %?

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.... Am I likely to meet the edge of the viewing cliff between x300 and x428? Can clarity loss vs size gain be expressed as a %?

As you are already using more magnification than I find useful at 300x, all I can suggest is try it and see :D

The seeing conditions have a massive effect on what can been seen on a given night on a given object, unless you view from the top of a mountain in Hawaii or similar.

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The maximum recommended mag for your scope is 400x and people don't normally get decent views anywhere near that. I have the same scope and on a very clear night I can use 300x on some planets and the moon so it maybe worth a shot but I would think probably not. I use an 8mm ep and a 2x barlow but a single ep would probably be better. I never expect the mag I can achieve with this scope on a good night, not in a million years. I have 'incredible' long range vision I've been told but I'm long sighted, don't know if this makes a difference.

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I thought using my 6mm eyepiece with a 2x barlow on my 200p dob to give 400x magnification would be crazy when I tried it the other night, but it gave me my best, clearest views of Mars so far. (My thread about it here: http://stargazerslounge.com/astro-lounge/179018-mars-last.html)

I might have just been lucky that seeing conditions at the time were exceptionally stable though.

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Thank you to everyone for taking the time to reply. @Wleshrob your post was really helpfull and I checked the other post you did re: Mars @ x400... Your sketch tells its own story for my money and this is why I think I might take a punt on the 3.5mm despite all the prevailing wisdom. Would you be good enough to try x400 on Jupiter next time you're out? I'd be really interested to know how it stacks up against the closest thing you have to x300 on the 200p? In any case I will duly report back once I get the 3.5mm and will gladly take it on the chin from prevailing wisdom if it ends up on Ebay :-)

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as already said, it's certainly possible to get and use very high magnification with your scope and I routinely use 400x and above with a 6" scope for some double stars as Olly says. I can generally use 250x and even ridiculous magnifications like 613x with my big dob and 3-6mm zoom on the moon but in truth, you can see what you get at much lower magnifications like around the 250x mark. Other than double stars i find that on objects like planets where you need to see contrast features, the magnification can only really be used to about 200-250x max.

it's great fun though and I really enjoy watching the moon slide across the field at 500x!

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If you stick a 5x power mate and a 5mm BST on the scope you get 1200x. Thats what the maths say and that is what the optics will "produce".

It will however be utterly and completely useless.

You can claim any magnification.

Give whatever you want a go, if it works then fine.

However asking will prove nothing, take the eyepiece, the scope, the barlow and try it.

What different people want is different. If you get an image at that magnification it will not be sharp. If you don't mind that then it will not be a problem for you, it would for me.

The image will not be much bigger, it will be dimmer.

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No harm at all in experimenting with very high magnifications. On rare occasions when the seeing is superb it's good fun to push things.

At the same time it's also worth comparing the views of the same object, under the same conditions, at lower power to see what difference that makes to the contrast of the more subtle features.

I guess what we a looking for is, on a given night, the optimum combination of magnification with crispness and contrast. That usually takes some experimentation to determine for each object being viewed and is why it's very useful to have a range of high magnification options available rather than just the one.

The advice that I generally give re: high magnifications tends to err on the cautious side to try and ensure satisfactory views under a wide range of seeing conditions rather than something which would be the ultimate possible under the best conditions.

Edited by John
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My usual maximum is x294. On some rare, steady nights, I can use x392 on the moon and doubles.

Generally i go up in small steps to find the optimum magnification for the conditions - x196, x235, x261, x294, x336, x392 - which is why I have so many eyepieces...

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Thank you to everyone for taking the time to reply. @Wleshrob your post was really helpfull and I checked the other post you did re: Mars @ x400... Your sketch tells its own story for my money and this is why I think I might take a punt on the 3.5mm despite all the prevailing wisdom. Would you be good enough to try x400 on Jupiter next time you're out? I'd be really interested to know how it stacks up against the closest thing you have to x300 on the 200p? In any case I will duly report back once I get the 3.5mm and will gladly take it on the chin from prevailing wisdom if it ends up on Ebay :-)

I will try but at the moment Jupiter disappears behind trees and neighbours' houses pretty quickly after it comes out. Plus it's quite low in the sky so there will be more atmosphere to look through.

I think the height of Mars in the sky and the seeing conditions conspired that night to allow good views of Mars at that magnification. But even so the features still didn't jump out at you, they were subtle.

I wouldn't go buying a really high magnification eyepiece though as the times you could use it are really low. Personally I would get a 7mm eyepiece that I could use with the barlow to get 3.5mm.

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the F number of your scope is a rough guide to the highset power ep you will be able to practically use ..

ie a f8 scope = 8mm ep

an f4 scope = 4mm ep

any given ep ie 8mm will give different mag in different scopes

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