Aperture

[Stephenbells]

Hello everyone, this is my first post as new member. I have a 114mm reflector but am considering upgrading in the future but I have never looked through a telescope larger than mine so don't really know what to expect. The feeling I get is perhaps to progress to a 6 inch there wouldn't be too much point, so perhaps an 8 inch? I suffer from arthritis! Good days and bad and at least my 114 is easy to cart about, I can have it up and running in a few minutes! How much heavier are 8 inch scopes? And is the performance significantly better. I am attached to my existing telescope, a goto and would probably keep it.

[umadog]

The rule of thumb is that you want to double the light gathering power (i.e. the mirror surface area) to see a significant difference at the eyepiece. In your case your case:

6^2/4.5^2 = 1.78x the light

8^2/4.5^2 = 3.16x the light

Both will provide a difference. You'll see the difference at 6", but the 8" a substantial difference. Particularly for sizes below about 8" or 10" you see a noticeable increase as you pile on the aperture. Not only are you gathering more light but you're increasing your resolution. Over above about 8" the scope is always seeing limited, so the resolution improvement is less pronounced.

A 6" Dob will weigh in at around 35 lbs the 8" at around 41 lbs. This is total weight, though. In both cases the weight of the heaviest component is about 21 lbs. So the the most you will lift for both 8" and 6" is the same. I'm basing those numbers on Orion's Dobs (i.e. the US company which also sells in the UK. Not Orion Optics UK). If weight is an issue and you can afford to spend more then look into scopes made more locally (Europe). A nicer design can lead to weight savings of about 30%.

[Stargazer33]

Hi Stephen,

This site shows a good indication of what you might see with different scopes and eyepiece combinations:

www.12dstring.me.uk/foveyepiece.php

Bryan

[umadog]

That's a nice site if you want to get an idea of what will fit into the field of the view (particularly useful for imaging) but it doesn't provide any information on what the objects will actually look like through the eyepiece. The site just scales and crops photographs.

These sketches provide a good impression of what an experienced observer sees from dark skies with an 8" telescope: http://www.deepskywatch.com/deepsky-sketches.html The emphasis is on dark skies. From light polluted locations you will see a lot less, I'm afraid.

[cotterless45]

Afraid aperture is king to see more faint objects.

However, seeing conditions, including light pollution is Queen. I've been lucky

to have seen some of our darkest skies.Nights when the brightest thing that you can see is the light from the Milky Way on the back of your hand.Western Isles, nice.#

Nick.

[Bizibilder]

Your choice will also be determined by the kinds of objects that you want to observe. For Lunar and planetry you may prefer a short tube type (Maksutov or Cassegrain) for convenience. Aparture is also a consideration for resolution but less so for any light gathering need with these sorts of objects. These scopes may not be lighter in terms of actual weight but can be far less clumbersome to move about or lift.