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Andrew*

Questions/Comments - Understanding and Choosing eyepieces

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Any feedback on my primer you are most welcome to post in this thread. I appreciate all your comments!

Cheers

Andrew

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Thanks Andrew that was a very well put together primer i will be expanding my eyepiece collection soon and i found it very helpfull i will have to read it a couple more times though.

Mick

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Oh come on you lot Andrew has worked hard on this project with some very good advise lets see some feedback.

Mick. :shocked:

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:shocked: Thanks Mik!

I'm glad it was helpful to you.

Andrew

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I think you could say a bit more about maximum mag. I've toyed with the idea of running through that one here explaining why and showing that it all holds together.

There is plenty of evidence on this board that peoples expectations are far higher than they will get.

It's a sad optical fact that as the exit pupil gets much below 1mm apparent planetary definition deteriorates. At 0.5mms that's obvious on all but the very best scopes and should be reserved for testing and aligning telescope. Even on the best scopes available there will be a noticeable drop in contrast. A realistic limit is something like 0.8mms. As usual with telescopes it varies. Much depends on the optics design/quality and general conditions. From the eyes point of view exit pupils can go a lot lower than that. Comfort has nothing to do with it.

The other factor is scope size. Some where around 8ins scopes working at these levels of magnification start being effected more and more by the atmosphere and general seeing conditions. Much depends on where one lives. While some one with a 6ins scope may be able to achieve maximum magnification they may well be severely disappointed if they move to 10ins and expect to achieve a similar exit pupil. They are more likely to achieve a similar object scale and a brighter image. The later is pointless on planets. It might help them image uranus. I have a 10ins sct that has done that. Not much detail putting it mildly. In practice an 8ins could do it as well. The exposure would just be longer.

Glad to see you have mentioned the cost aspects below something like F8. In my experience it becomes critical at F6. Skywatcher should be shot for supplying those super plossls with them. The old ones were better even at F8.

I wish you luck in finding some one with an 8mms pupil. 6 is a more realistic limit. A few manage 7. Not much chance of either if there is any ambient light. Reduced eye relief helps a lot with that. Some use a sort of light proof bag that fits to the scope. It helps a lot. Pupil size is a well researched area. The main argument against over sized exit pupils is that some of it doesn't enter the eye so light is wasted. Use the correct sort of eyepiece and one can move the eye around in the beam that comes out of it. Could also be that one can see what one wants to look at in the part of the beam that enters the eye. I do that a lot. The effective magnification is low so the contrast is very high.

John

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Thanks for taking the time and effort to put this together. Peoples opinions will differ and you can't please all the people all the time. :shocked:

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Thanks for the detailed response Ajohn. As this primer is designed more for beginners, I can't afford to go into great detail on many aspects, otherwise it would get too long and too complicated.

I will make adjustments where my figures were not accurate, but I am not comfortable with adding further complications. I already spent some time to make sure I kept it simple.

Cheers

Andrew

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Well done Andrew for writing such an informative article :thumbright:

My only reason for not commenting so far is that I haven't found the time to print it out and give it the attention it deserves. That said, I have had a quick scamper through it.

As you have asked for feedback: I think it would work better if it were separated into smaller, separate, mini-primers - magnification, FOV, suitability, etc. That way it would appear less intimidating. It is also quite 'wordy'. I used to write articles for a boating magazine and remember the editor saying 'never use two words where one will suffice'. The word 'that' is a good example, it can almost always be removed without harming the sentence. You have used almost 30 'thats' (the wordprocessor counted them, not me) and that is just one example. You can usually reduce the size of a first draft by around 30% without harming the meaning or context. Often whole sentences can be removed.

So, a useful primer with plenty of detail that would be easier to read if it were edited into smaller bite-sized chapters.

Hope that helps :cat:

PS: I shall be writing some primers for FLO's website later this year so you can get your own back then :shocked:

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Thanks for your advice Steve. How to reduce its length is just what it needs! :shocked:

I'll look into shortening it later.

Andrew

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I'm well used to my comments on forums sparking off primers and some times even web sites. These leave me feeling a bit dissatisfied if they don't get the points across. KIS is the usual reason offered too. No matter. I'm happy providing I've helped clear the mire and started people thinking. Like most people I eventually get fed up of typing the same answer over and over again.

John

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Nicely done Andrew. Just had the chance to finish reading it. Plenty of detail. Thanks.

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Ditto from me too. :cat: nice and easy read. Not too much specific terms and stuff, but good info. just right for the start :shocked:

Marius

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Thanks all! :cat:

Glad you got something from it.

Steve, I took 10 minutes this morning and cut about 200 words from the text by taking your advice :shocked: but I'm sure if I spent some more time on it I could cut another 200...

John, my suggestion would be to write an article targeted to a more an audience with a higher level of understanding to avoid having to type things over and over again. My primer covers the basics - to write anything more advanced is out of my depth and out of the depth of the potential audience. The last thing I want to do is mislead beginners, which is why I have heeded your advice to alter what is there.

cheers

Andrew

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A very useful addition to the guidance on SGL Andrew - it's almost impossible to get the level of detail "right" on these things but I think your primer stikes a good balance.

Thanks for putting it together :shocked:

John

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Andrew

I think you have captured the key points very well.

The work acn always be refined but it is excellent as it stands. :shocked:

Cheers

Ian

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Thanks Ian and John. I appreciate it.

Andrew

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just like to thank andrew and kaptain klevtsov for the posts which are very helpful especially for beginners like me because they have kept it easy to read and fairly simple to understand,

many thanks

ron.s.g

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