4 inch refractor vs 4.75 inch refractor vs 6-inch reflector vs 5-inch mak

[Superdavo]

Hi everyone!

A while ago I made a topic asking whether a 4-inch refracting telescope would be better than my 6-inch reflector for planets, and I have a few more questions.

Firstly, last time, people said the aperture of my 6-inch would make more difference than the quality of the 4-inch, but is there any difference between a 4-inch and 4.75?

Secondly, does the aperture difference affect photography, where I could just increase the gain or exposure?

Thirdly, many people recommended a mak last time, so how would, say, a 5-inch compare for photography with the other does?

Lastly, if none of these, what would be the best scope to buy for a budget of about £300-350?

Thanks for reading, and please help

David

[Superdavo]

Thirdly, many people recommended a mak last time, so how would, say, a 5-inch compare for photography with the other does?

I meant other scopes, predictive text was messing about, sorry about that

[Moonshane]

there are basically three differentiations when it comes to astronomy:

1) visual - aperture best for faint objects - focal ratio does not affect the image visually at the same magnification - some objects respond better to a certain type of scope

2) webcam imaging of solar system - needs slow or very slow focal ratio - aperture governs resolution - more = better but more = bigger mount

3) DSO/faint imaging - quality of mount and focal ratio are key - aperture is to a large extent irrelevant but focal length will determine the field and a good match to chip size. faster focal ratio will gather light more quickly like photography.

in 2) and 3) chromatic aberration will be an issue if not using an apochromatic refractor or a reflector (includes SCTs/Maks) although you can shoot in mono and combine images afterwards.

in all imaging processing is what takes the time.

[ronin]

Which 4" refractor ?

Visually an ST 102 would be worse for planets, the TAL would possibly be better.

The ST 102 would give too much CA for AP and the TAL is a bit too long for AP.

If the idea is AP of planets then the Mak is a better choice as you simply stick a webcam on and take a video.

If you are looking at AP of DSO's then the Mak is the wrong scope and very likely on the wrong mount (Alt/AZ I suspect).

Thing is if you are goung to do AP even half seriously you need a different scope to that used on the visual side. Like many things a visual scope will do some AP but won't do it wonderfully well.

Consider a track day at Brands. 2 cars, both open top 2 seaters. Mazda MX5 and Caterham 7 - which would get round quickest ?

If AP is what you want (it seems to be) then you want a good mount (EQ5, better HEQ5) and a short fast scope. A short fast refractor means an ED or apo scope at least.

Of all mentioned the 150P is probably the fastest scope you list.

[Superdavo]

The 4 inch would be second hand from rother valley optics, and the rest would probably be skywatcher telescopes, and the refractors would be achromatic and have a slow focal ratio

[RikM]

The 4 inch would be second hand from rother valley optics, and the rest would probably be skywatcher telescopes, and the refractors would be achromatic and have a slow focal ratio

Being achromats, they would be very poor for photography.

Since you are interested in imaging planets, how about something like a second hand C8 and a 2.5x Powermate? You already have a good camera in the DMK 21. Otherwise, get your collimation bang-on and use the longer 5x Powermate with your 150P.

[ollypenrice]

Refractors only become truly virtous when apochromatic and expensive. Note that there is no watertight definition of apochromatic since no refractors are perfect, so a refractor may be visually apochromatic but not photographically so.

If you are not talking about a very costly apo refractor then get a reflector.

Also, do you intend to image the deep sky or the planets? The two activities are poles apart as Shane has explained.

Olly

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2277139556&k=FGgG233

[Superdavo]

Are second-hand scopes a good idea, or are they risky?

[RikM]

Are second-hand scopes a good idea, or are they risky?

Second hand scopes can be great. Most people look after their astronomy equipment but it often pays to visit in person and make sure you know what you are buying before parting with any cash. About a third to half my equipment has been bought second hand.

[Superdavo]

How much would I expect to pay for a second-hand C8?

[John]

How much would I expect to pay for a second-hand C8?

A reasonable rule of thumb is 60%-70% the new cost.

Virtually all my astro equipment has been bought used.

[Polar Bear]

How much would I expect to pay for a second-hand C8?

I just picked one up (20 year old C8 Ultima) for £500 primarily for Solar System visual and imaging. It came with many extras worth approx £250.00

It also came with the original huge tripod and fork mount with RA tracking courtesy of a built in DC drive (9v PP9 powered) and is ideal for what I want.

The drive is reputedly accurate enough for DSO imaging if aligned correctly and with use of the PEC function.

Having used a 120mm Evostar on a EQ3-2 there is no comparison as regards ease of use and solidity, or the quality of image / view.