Excuse me for being dumb minded but...

[asteele3]

If you take off the visual back and eyepieces to make way for the dslr camera to go on then where's the zoom gone?

[Cornelius Varley]

The telescope now acts as one big telephoto lens, in the case of your C8 XLT a 2032mm F10.

Peter

[LukeSkywatcher]

The telescope now acts as one big telephoto lens, in the case of your C8 XLT a 2032mm F10.

Peter

Exactly. You focus with the camera, because the scope is essentially a large zoom lens.

It does feel odd in the beginning when you start imaging that you no longer have to focus the scope but rather the DSLR attached to it.

[asteele3]

So how would I get good close ups of Saturn? Can't I get any zoom? Why would I use the telescope for imaging when I can use the camera and get the same results? Sorry but this has been troubling me for a while.

[Starlight 1]

For Saturn its best to use a web cam.

[asteele3]

I've got a webcam so how do I attach it to the scope?

[Freddie]

Pop it in where the eye piece goes instead of the eye piece..

[kenmyers]

Check back through my posts on the asdacam mod for a guide on how to make one for less than £10

[Chris]

Hi, if you remove the lens from your webcam and attach a small piece of 32mm pipe to the front of the cam making sure its sitting square then it will insert where your eyepiece would normally go. To gain mag you can insert a 2x Barlow before you insert your webcam. Then you need to download some free software namely Sharpcap and Registax, use Sharpcap to film the planet and Registax to stack the individual frames from the film which will bring out the planetary detail by increasing the ratio of signal to noise and by also throwing out frames that have been badly effected by atmospheric turbulence. As mentioned above theres lots of info on here about webcams and which ones are best for Planetary imaging, not all are so its a good idea to check this out first. I did the mod on the ASDA cam as mentioned above its probably a good place to start as its minimum outlay:)

hth

Chris

[steppenwolf]

Can I just make a tiny correction to this - your telescope does indeed become a large telephoto lens for your camera but there is no zoom function, just a focus function.

[ollypenrice]

Yes, I think there's some confusion in the terminology. Zoom means variable focal length, as Steve says. A telescope is a prime (fixed focal length) lens. All lenses/scopes have a focal length and the longer it is the more a small target fills the chip. Avoid the term 'magnification' because it is meaningless in imaging (how big is your print, how big is your screen, etc etc) and think of arcseconds on the sky turned into mm on the chip. Image or Plate Scale.

For the planets amateur telescopes never have enough native focal length so you increase it by using an extra lens, whether an EP, a Barlow or two or three, or a Powermate. This changes the native focal length of the scope to a new effective focal length. It also slows the focal ratio enormously, limiting you to bright targets.

Focusing the scope or focusing the camera? Well, the 'camera' is the lens plus the body so that's what you are focusing! The control that you use is on the telescope.

Olly

[The Sailor]

Exactly. You focus with the camera, because the scope is essentially a large zoom lens.

It does feel odd in the beginning when you start imaging that you no longer have to focus the scope but rather the DSLR attached to it.

Bit puzzled here, surly you mean the camera becomes an eyepiece and you focus the telescope as normal through the camera, but no zoom whatsoever?

Jim

[steppenwolf]

I don't think you can really call the camera a replacement eyepiece because it doesn't contribute anything optically to the system, it literally just sits at the prime focus of the telescope as a passive device awaiting the fall of the photons whereas an eyepiece refracts the focused light from the telescope. The telescope is indeed focused in the same manner as with an eyepiece installed.

[The Sailor]

The telescope is indeed focused in the same manner as with an eyepiece installed.

Thank you for the tech data but as said the telescope is focused not the camera

Jim

[steppenwolf]

the telescope is focused not the camera

Not in dispute

[alan potts]

Look I'm not sure about this, I don't know much about putting a DSLR on a telescope but I know a a fair bit about photography.

I have a F4 500mm telephoto Canon and a top of the range albeit from a few years back, 1DS Mk 1 & 2 bodies. If I put this lens abn a body on my scope mount and point it at the sky I know it will show Saturn or any other bright planet only as point of light.

I don't think at 2000mm you will get a great deal either. I think you would have to go to 6000-8000mm to get an image on which any detail could be seen That is in effect F30-F40 on your scope. This can be done by using a Powermate or Barlow, I am not sure what the exposure time would be but I would guess at around 2-5 seconds, this of course depends on the ISO speed. As time increases you do then increase the need for accurate guidence.

Alan.

[michael.h.f.wilkinson]

At 2000 mm you get some detail, but I prefer to use a 2x TeleXtender (like a Tele-Vue PowerMate, a Barlow will do as well) to get a good 4000mm, or even a 3x TeleXtender at 6000mm. The latter gives a low surface brightness which is OK on Mars and Venus, but less so on Saturn), so I am looking for a 2.5x PowerMate, which I think would be ideal.

[asteele3]

So if I don't get any zoom? Then why would I use the scope and the slr when I could just use it without and get the same images? The only point I can see is the tracking function, which is vital. But how would I use the Barlow when the camera has to be attached with everything off including the diagonal and the back thing?

[steppenwolf]

So if I don't get any zoom?

I think we really do need to get some terms correct here. 'Zoom' does not equal 'magnification' which seems to be what you are talking about.

The apparent size of an object when captured on a sensor is directly proportional to the 'apparent' or 'real' focal length. If you compare the image captured by a 200mm telephoto lens with that taken by a telescope with a focal length of 400mm, the object will be twice the size on the sensor so displaying it on a given monitor, it will appear twice the size too.

Zoom, as Olly has stated above, is simply a description of a lens with a variable focal length.

Using a Barlow lens or a Powermate amplifier alters the light path thus altering the apparent focal length. If the apparent focal length increases, the image on the sensor will increase in size in the same way that a real change in focal length will increase the size of the image on the sensor.

[michael.h.f.wilkinson]

Perhaps the following explanation will help. In 35mm SLRs the apparent magnification of a lens is generally expressed as the ratio between its focal length and that of a standard lens (or 50mm for 35mm format). An 80-200mm zoom ran from 1.6x to 4x, a 400mm is equivalent to 8x (like binoculars), a 2,000mm is 40x (low magnification in my scope). I used to do planetary photography with my SLR and used about 18,000 mm or 360x, using eyepiece projection. The reason for this apporach is that 18,000mm of focal length gives you a 360x larger image of an object. In APS format, the standard lens is shorter (about 35mm), so you have to redo the calculations, but the same principle applies.

A DLSR will not help very much when taking pictures of planets. It is possible to do it, as my attempts on film show, webcams are just way better. My 640x480 webcam has sufficient resolution for all planets. What would help is higher sensitivity to improve the signal-to-noise ratio

[ollypenrice]

Thank you for the tech data but as said the telescope is focused not the camera

Jim

Well, I'd prefer to say that the telescope is focused onto the camera chip (or film.) You have to consider them as a unit - if you want the image to be in focus! When you focus a camera lens you move the glass elements. When you focus a telescope you move the camera back or forward relative to the glass. Same difference.

Olly

[The Sailor]

To be honest with you, when I put a camera on to the telescope I am not worried how I get focus as long as it gets there when I move the focuser on the telescope , this was really my point in the post as pointing out that the camera is focused to a novice will having him asking more questions. Like when a simple question is answered with loads of tech about focal ratios an suchlike, I honestly don't see a need for it as I feel it clutters up the novice with things not really required. I have been taking photos almost 50 years and have never felt to need to worry about all this if the camera was in focus .

Jim

[alan potts]

Perhaps the following explanation will help. In 35mm SLRs the apparent magnification of a lens is generally expressed as the ratio between its focal length and that of a standard lens (or 50mm for 35mm format). An 80-200mm zoom ran from 1.6x to 4x, a 400mm is equivalent to 8x (like binoculars), a 2,000mm is 40x (low magnification in my scope). I used to do planetary photography with my SLR and used about 18,000 mm or 360x, using eyepiece projection. The reason for this apporach is that 18,000mm of focal length gives you a 360x larger image of an object. In APS format, the standard lens is shorter (about 35mm), so you have to redo the calculations, but the same principle applies.

A DLSR will not help very much when taking pictures of planets. It is possible to do it, as my attempts on film show, webcams are just way better. My 640x480 webcam has sufficient resolution for all planets. What would help is higher sensitivity to improve the signal-to-noise ratio

Michael,

I have Canon DSLR's and I have a power mate 2inch X2. Could I put on the camera which have a mass of pixels, 11mil and 17mil if I remember correctly. My LX 200 with power mate would be 6096mm at F20, If so I will give it a try.

Alan.

[michael.h.f.wilkinson]

Michael,

I have Canon DSLR's and I have a power mate 2inch X2. Could I put on the camera which have a mass of pixels, 11mil and 17mil if I remember correctly. My LX 200 with power mate would be 6096mm at F20, If so I will give it a try.

Alan.

It can be done, but the planetary image will be quite small (but quite detailed). Note that F/20 to F/30 will be best for certain webcams with a pixel size of about 5-6 micron (which is common). If the pixel size of your camera is less, you can use a shorter focal ratio. The big advantage of webcams is that you shoot a whole string of short-exposure images, select the best and stack these after alignment. You could do this with the video mode of some DSLRs. If you use video mode of the camera, you must take the effective size of the binned pixels into account, and you might need an even slower F-ratio.

[ollypenrice]

To be honest with you, when I put a camera on to the telescope I am not worried how I get focus as long as it gets there when I move the focuser on the telescope , this was really my point in the post as pointing out that the camera is focused to a novice will having him asking more questions. Like when a simple question is answered with loads of tech about focal ratios an suchlike, I honestly don't see a need for it as I feel it clutters up the novice with things not really required. I have been taking photos almost 50 years and have never felt to need to worry about all this if the camera was in focus .

Jim

Jim, I don't think a term like focal ratio is 'tech.' It is a bog standard term in photography. F2.8, F5, etc etc. Here are the facts in as low tech a way as I think they can be rendered.

Focal length decides field of view. Short FL gives wide field, long FL gives a small field. For large objects you use a short FL. For small ones you use a long FL. The FL of a telescope can be increased using EPs, Barlows or Powermates.

Focal ratio determines exposure time, a fast (low number) giving shorter exposures.

Olly