Superzoom focal length test (1 Viewer)

[Roy C]

But haven't you had to add some form of extension tube to your astroscope and would that not in effect extend its focal length .. is it a true like for like comparison with an actual prime DSLR lens?

No it would not,if the extension was between the Camera and the tc then it would affect the focal length but with the extension between the tc and the scope it does not alter the focal length - best explained by one if the experts in the astroscoping section "If you add an extension tube then you have to move the focus in by that amount to focus on the same subject so the tube length would just be cancelled out.". The extension tube is needed because there is no prism or mirror diagonal in the back of the scope. The distance light travels through the the extension tube would take up the length of the tube.
Like I said above I have even tried the Canon 400/5.6 on the 7D v the SX40 at full optical zoom with the same results - the DSLR combo was longer.
I wish the extension did give me a longer focal length but it does not.

 

[Binastro]

What may be of some relevance to image quality is I have found that using various compacts, bridge cameras and DSLRs the ultimate resolution achievable is closely related to the clear front aperture of the lens.
This is how it should be in theory.
With older cameras say 5 to 7 years the ISO limits were less and the computing power less.

I have not yet tried a camera with more than a 24x zoom ratio.

So if you look at the front diameter or clear aperture you will get a good idea of the quality obtainable from a good make camera.
One has to use the lowest ISO value for best quality.
And I mainly use JPEG finest.

I have done these tests on Canon, Panasonic, Konica Minolta and Sony cameras.

These best resolutions are achieved at full optical zoom and sometimes 2x sometimes 4x digital zoom.

The aperture of wide angle lenses is not relevant as many are oversize because of optical characteristics.

So you cannot expect very fine resolution from a lens with a very small front clear diameter.

Of course lens quality, contrast, image processor all play their part and high ISO images are improving.

My tests are at far distances usually 400 feet plus and I sometimes use a clock tower at about 400 yards.
But I think the same should apply close up. I.e. the larger front clear diameter lens at the telephoto end will give best resolution.
In small compacts the smallest f stop is often f/8 as losses would result from diffraction if the lens stopped down further.

So something like a fine quality modern Canon 400mm f/5.6 will outresolve a Superzoom camera with a smaller lens front diameter.
It might need a 1.4x or 2x zoom on the prime lens.

I have seen really excellent hand held images from a Canon 400mm f/5.6 at full aperture with no stablization, but image stabilizers or tripods often help.

 

[Wildmoreway]

What may be of some relevance to image quality is I have found that using various compacts, bridge cameras and DSLRs the ultimate resolution achievable is closely related to the clear front aperture of the lens..

We are talking about focal lengths here, image quality is a separate issue, in the right conditions a DSLR camera and lens is almost certain to give better image quality than a superzoom. Whilst I was happy with what my SX40 managed yesterday a competant person with a DSLR and a good lens would have almost certainly have obtained better images in every instance. I will not be getting rid of my DSLRs any time soon.