The eyepiece dilemma

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Canopus Lim
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Joined: Fri Jun 03, 2005 12:46 pm
Location: Macpherson

The eyepiece dilemma

Post by Canopus Lim »

I have been reading a lot of equipment reviews during my spare time and have found some truth and false statements in them. I think as people, we all have certain biases to different things and have different likings. Astronomy equipment I find is like food in that we all have different preferences and certain biases. For example some people may like durians, and I for one detest it. Haa.

There is no one eyepiece or one telescope that fulfills everything. Some people like super widefield and they go for big binoculars. Some people like to see more details and they go for large scopes. Some people like portability and they go for small portable apos. All have their pros and cons.

When it comes to eyepieces, it is a real dilemma actually. Eyepiece designs like all designs have certain goals. Some eyepieces are designed for the highest definition, others are designed for the most immersive and ‘wow’ factor. I have read many reviews and they usually compare the wrong eyepieces. It is like comparing a sports car with a SUV. Comparisons I feel should be of the same category, sports car to sports car and not only that the same size engine sports car. A sports car can go fast and accelerate fast but it can only fit two people and carry less goods compared to a SUV that can carry many more people and goods. It is a design and physics problem. Highest definition does not go with wide field and vice versa. There is a compromise and a balance the design has to take.

In general, the higher the AFOV and eye relief, the more lens elements are required to correct the field. This means that the contrast will drop due to more scatter as more elements and the throughput will drop due to more elements. In short, the definition goes down, how much depends on the eyepiece design and coatings. However, the big gain is the AFOV and eye relief which means more immersive at the expense of definition.

The smaller the AFOV and eye relief, the less lens elements and the greater throughput and contrast. Yes, there will be increase in definition but the field is not as corrected especially on fast scopes due to less lenses to correct the aberrations. However, the throughput will be the best and contrast will be the best. Take for example a 3 lens eyepiece and 30 degree AFOV. I am sure it has the highest definition, but the most pathetic eye relief and AFOV. If you want even more definition, the designer can just reduce the field stop and the AFOV becomes 20 degree. Surely well corrected and highest contrast but the object cannot even fit in the field.

Some people are moderate, they like high definition and high AFOV. Others are more clinical and they want the highest definition at the expense of the immersion. The other end of the spectrum is those who wants the most immersion but at the expense of highest definition. Good eyepieces do well in most categories and excel at some but they cannot excel in everything. There is a balance. For me, I prefer the immersion part which relates to enjoying the view and having the largest AFOV. I am not a scientist, so I do not want the narrowest of AFOV for the highest definition. It does not make a difference to see an ultra fine feature then not seeing it at all. I like the openness kind of view and to feel close to the object.

What kind of eyepiece preferences you guys have?
AstroDuck
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rlow
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Post by rlow »

Yang Beng, I am amazed that you manage to write a long essay on this!

Actually there is a simple solution: just get two different sets of eyepieces like I have, a set of orthos for planetary observing and a set of wide field EPs for deepsky observing. :)
Last edited by rlow on Thu Aug 17, 2006 9:57 pm, edited 2 times in total.
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weixing
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Favourite scope: Vixen R200SS & Celestron 6" F5 Achro Refractor
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Post by weixing »

Hi,
Most of my eyepiece are orthoscopics from KK Japan... good and cheap. They perform significantly better than most eyepiece at the same price range. I think I'm the only one in SingAstro that use orthoscopics eyepiece as my primary eyepiece. :)

For wide field, I use the 25mm Super Erfle and GSO 2" 42mm eyepiece... again good and cheap. :)

Have a nice day.
Yang Weixing
:mrgreen: "The universe is composed mainly of hydrogen and ignorance." :mrgreen:
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Canopus Lim
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Location: Macpherson

Post by Canopus Lim »

Rlow,
Haa. I have reached my astronomy budget already. Enough spending except on books. :P
AstroDuck
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VinSnr
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Location: Andromeda Galaxy

Post by VinSnr »

Forget eyepieces, go video!! haha

This eyepiece vs Video is going to be the next alt-azi vs GOTO kind of thing.
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chrisyeo
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Post by chrisyeo »

What kind of eyepiece preferences you guys have?
I'm a complete eyepiece amateur, but for me, budget comes first: a nice set of Plossls.

Next, a high powered Orthoscopic for planetary work.

Finally, after looking through some Tv eyepieces, I realise that a wide-field big AFOV long eye-relief eyepiece would be nice for the
space-walk' effect.
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