Telescope or Camera Lens

[Rossco72]

For widefield images, is a Telescope or a Camera Lens more practical?

I have a number of Canon Lenses at various focal lengths and from f1.4 - f5.6.

For shooting large wide DSO's using a DSLR, is there an advantage to using a telescope over a camera Lens?

Cheers

[jgs001]

The thing that will define what you need is the field of view provided. The optical quality will be tested for deep sky, so you might find that lenses that work great for daytime, may not be quite so good for deep sky. But give it a try and see how you get on.

[Rossco72]

The thing is these are all L series professional lenses with flourite elements etc. so I am expecting the quality to be good. I mean will a £2000 camera Lens at f4 have a chance against a £2000 telescope at f7?

[jgs001]

In theory, it should beat it soundly into submission as it lets in nearly 4 times as much light...

Only one way to find out... My nifty fifty (£70 worth) did a great job on Orion at f/4... got all the Ha stuff with an unmodded camera...

[Matthew.Blake]

I would have thought the big difference will be field of view though. I'm assuming your F1.4 lens is the 50mm prime: how many telescopes do you know of focal length 50mm? I rather imagine, given the typically shorter focal lengths you will have with camera lenses, the quality will be at least as good as an expensive refracting telescope but you will have access to lower focal ratios.

[E621Keith]

I don't think telescope and camera lens have that much overlap in terms of focal length. If I needed 50mm or 100mm for constallations I'd use a camera lens. If I needed 500 mm for a nebula I'd use a telescope.

The smallest telescope I can think of is the WO ZS 66 f5.9 which had a focal length of 388mm. For me that's where most camera lens stop.

Of course, you may get 400/2.8 and 600/4, but their price are so outragous that I'd not consider them to be competitor with telescope. For the price of one 600mm f4L, you can get two C11 with hyperstars (560mm f2) on 2 CGEM. Or a Tak Epsilon ED180 (500mm f2.8) on a G11.

Also, when you get a camera lens, you are paying a lot for stuff you don't need in astrophotograpy, like AF-S and VR. Your choice of camera will also be limited to a single DSLR brand.

[simon84]

It all really depends on your target and how you want the image to come out. How widefield are you needing to go? A 20mm lens will give much more fov than say a WO66 which in turns gives you much more than a 120mm APO.

I am at the moment imaging exclusively with lenses with my longest focal length being 800mm (500mm x 1.6 crop factor) and my shortest focal length being 32mm (20mm x 1.6 crop factor) with a fair few sizes in between.

[Rossco72]

I am not really talking about buying any extra lenses, I have a number of lenses and telescopes. I am just wondering if a 400mm Canon L Lens which I already have would be better than using a telescope at prime focus.

[Beyond_Vision]

There are scopes like Borg and Televue that overlap the typical camera lens focal length territory. The problem with camera lenses are that they contain several glass elements and therefore have more glass to air surfaces. I would expect the scopes to perform better than the camera lenses in terms of CA and distortion.

Regards

Kevin

[E621Keith]

Here is a site that will answer your question about the 400/2.8L

Canon EOS EF 400mm f/2.8 L USM IS Astrophotography Tests

[mijijim]

Here is a site that will answer your question about the 400/2.8L

Canon EOS EF 400mm f/2.8 L USM IS Astrophotography Tests

Hi,

The above lens will cost you the best part of £7000.00.

mijijim

[riklaunim]

You can even use a CS lens with an industry camera (like DMK/DFK/DBK) and do H-alpha DS imaging like so. And they can be f/1.6 - f/2.0 so faster than Takahashi astrographs :)

[Coco]

I remember reading Richard (astrotrac) was un impressed with a very large Canon L lens ( 400/2.8) as I remember, lots of CA

quote

''we celebrated too soon, Gain’s mumblings soon revealed that the Canon 400 mm f2.8L was useless at f2.8, exhibiting every kind of optical aberration in the book. He tried stopping it down to f4 and beyond, but still no good. Only the very centre of the lens was use able, and then only just. Luckily I had brought the 2 x tele-converter and Gain had the cunning plan to jump to 800 mm focal length and image ‘close-up’ using the central area of the lens.''

Read here:

The AstroTrac Blog

Put me right off buying one

Guy..

[Matthew.Blake]

The problem with camera lenses are that they contain several glass elements and therefore have more glass to air surfaces. I would expect the scopes to perform better than the camera lenses in terms of CA and distortion.

Regards

Kevin

Surely by that logic the best telescopes will be those with a single lens? Is not the extra glass in the camera lenses (certainly for prime focus anyway) there to reduce the optical abberations?

Perhaps some of the weak performance compared to telescopes can be put down to the fact they are not really designed to be focused at infinity so their performance is optimised for object distances far closer than stars?

[ollypenrice]

I agree that where you have a telescope that can offer the FOV, use it. My FSQ85 with reducer can get down to 328mm at f3.9 and I very much doubt that any camera lens could match it. I think the Mini Borg gets down to around 200mm?

But if you can't get down there with a scope, use a lens. I have a Samyang 85 which, according to camera reviews, has a spectacularly distortion-free field when wide open, better than a Zeiss equivalent. So they said. Maybe so, but I find it is a million miles away from giving clean edge stars in astronomy use until it is stopped down to f4 as an absolute minimum. Now I love it (see my All of Orion post on the DS board at the moment.) but as no camera expert I have a strong feeling that we ask a lot of lenses in astronomy. Really you just have to forget those daytime f ratios I think.

Olly

[Beyond_Vision]

Surely by that logic the best telescopes will be those with a single lens? Is not the extra glass in the camera lenses (certainly for prime focus anyway) there to reduce the optical abberations?

Perhaps some of the weak performance compared to telescopes can be put down to the fact they are not really designed to be focused at infinity so their performance is optimised for object distances far closer than stars?

A good doublet telescope and definitely a triplet scope will out perform a camera lens. The multiple elements in a camera lens are not all colour corrected and are there for distortion correction or to make it zoomable whilst keeping the lens compact. They often only have a single ED or Fluorite element to reduce chromatic abberation.

[E621Keith]

A good doublet telescope and definitely a triplet scope will out perform a camera lens. The multiple elements in a camera lens are not all colour corrected and are there for distortion correction or to make it zoomable whilst keeping the lens compact. They often only have a single ED or Fluorite element to reduce chromatic abberation.

I agree, Camera lens are designed for day time use. Not taking a photo of test charts or a field of point sources with a dark background. A lot of the lenses in a camera lens were designed for doing things that will make them more convenient for photographers at a small expense of image quality at infinity. Features such as close range correction, vibration reduction, internal focus ... all make a lens much better for normal photography, but worse for astrophotography