Michael:
Here are my thoughts, I have owned several small MAKs over the years including the ETX-125 and currently own a C-5 OTA (the telescope part)SCT. I don't recommend small MAKs like the ETX-125 as a general use scope... If you are thinking of one of these scopes, give it try before you buy..
The story goes like this:
I caution anyone considering small MAK to consider the importance of the long focal length/slow focal ratio combined with the 1.25 inch focuser. This places significant restrictions on the capabilities of the scope for both astro and terrestial use.
These things combine to make a scope that has a very narrow Maximum possible field of view as well as one that is limited to a small exit pupil. I will discuss mostly the ETX-125 because it is the scope I am most familar with, the C130 has a somewhat shorter focal length so things are somewhat better. (The C-130 has some other issues I believe, something about an optical window in the rear...)
The maximum possible field of view for the ETX-125 is about 0.83 degrees or about 1.6 times the diameter of the moon and less than half the diameter of the Pleiades. This is quite small, particularly for terrestial applications, at 200ft you are looking at a field of view of less than 3feet. This makes finding your target difficult, particularly with the stock finder. Autostar does not help you locate a bird at 200feet...
Add in the fact that you are stuck at relatively high magnifications/small exit pupils. With the 32mm Plossl that provides that 0.83 degree field, the magnification is 60x with a 2mm exit pupil. Terrestially most viewing is done between 15x and 60x because most often the atmosphere does not support the high magnifications during the day.
Astronomically, these factors also have their ramifications. With a smaller scope, a widefield of view with a large exit pupil is nice because it allows scanning of the big targets like the Milky Way, roaming the Milky Way at 20x with a 3+ degree field of view is, IMHO, one of the best reasons to use a 5 inch scope.
Other issues that are important to consider are the large central obstruction of these MAKs. When Sky and Telescope tested the ETX-125 they found that the secondary obstruction to be 40%, this is quite large, it affects the contrast of the image and means that there will be a hole in the center of the exit pupil that is 40% of the exit pupil. The eye adjusts for this, in a fast scope this is a problem but at F15, the exit pupil is small. There is also the issue of thermal equilibrium, these scopes need to cool down for quite sometime to achieve optimal performance, especially at high magnifications.
There are other issues to be aware of such as "through-put". In the end you are looking through 3 mirrors and one piece of glass and there is light lost due to that large Central Obstruction. The result is that even with enhanced coatings on the mirrors, less than 75% of the light is transmitted, making for an even dimmer image...
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So, these are all factors to be aware of and considered seriously before purchase. In order to get that compact size, there is a definite price to pay.
My own personal choice as a combination terrestial/astronomical scope is a small relatively fast refractor. These provide those wide fields of view and low magnifications, are extremely efficient at getting all the light to your eye and since the introduction of the Orion ED-80, APO color free performance is affordable. Terrestially scopes like the ED-80 are great for viewing targets both close up and far away, 20x, even 15x with a 4 plus degree field of view makes birding fun and at the same time a 125x clear and sharp high magnification views are there to be had.
Astronomically, one is losing some aperture so possible resolution is lost but the lack of a central obstruction (=high contrast) and high efficiency goes a long way to make up for it and the ability to provide the widefield views allows these scopes to do stuff that the small MAKs just cannot do.
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So, I have painted a rather glum picture here. There is certainly some bias, mostly in the fact that I own larger scopes so that the long focal length of the MAKs are not of interest, even a 6 inch F/5 Newtonian with a 29% central obstruction will provide significantly better astro-performance. My longest focal length scope is a 12.5 inch F6 but it has a 2 inch focuser so it is capable of 1.3 degrees with a large exit pupil... Of course it takes a ladder...,
I think I have presented the basic issues that anyone considering a small MAK should be aware of. Others may sing the virtues of the small MAK, personally my first dark sky experience with my ETX-125 was disappointing when compared to small refractors and a similar sized Newtonian...
Jon
PS: For terrestial viewing, I am quite happy with the views a star diagonal provides in a MAK, SCT or refractor. The image is correct top to bottom but reversed right to left. Correct image diagonals are available but these normally degrade the image, particularly at high magnifications so for astro use, the star diagonal is best and for terrestial use, I am perfectly comfortable with the left-right reversal...
