Magnification vs Focal length (1 Viewer)

[mahgnitton]

OK this post may get a few chuckles but everyones got to find out someway 8-P

I havn't used a spotter scope or binoculars etc in my life but have shot with A Canon 300D, 10D and have now got a IR converted 350D, I would like to try digiscoping but would like to know how xMag relates to xFocal length Ie...

To get a good quality 600mm L lens from Canon it will cost me £8,000, for just over 3x as much I could buy myself a low milage Aston martin Volante convertible!, I know there isn't such thing as a x600MAG spotter scope though so I would like to know what magnification will relate to 600mm, if say 30x is the same as 600mm then I could get a £300-400 spotter scope and keep the rest for the volante

Also am I right in thinking that like geting a DSLR body and buying lenses from other manufacturers I can buy a spotting scope and buy any manufacturers eye piece to gain extra magnification or quality?

 

[Ultra Lite]

about 3x per 100mm of focal length

thus a 600mm telephoto on a APC sensor camera would give you about 18x.

 

[SteveClifton]

OK this post may get a few chuckles but everyones got to find out someway 8-P

Also am I right in thinking that like geting a DSLR body and buying lenses from other manufacturers I can buy a spotting scope and buy any manufacturers eye piece to gain extra magnification or quality?

This might go some way towards answering your question. Most birding scopes have a dedicated set of eyepieces made by the same manufacturer to fit them. Typically, you might get 20x wide, 30x wide and 20x-60x zoom. Others like Nikon also produce fixed wide angles that are good for 50x, 60x etc. up to 75x. It's unusual to be able to swap eyepieces to use on others makes of scope, unlike astro scopes which use a standardised eyepiece fitting.

As far as your other question goes, I feel less qualified to answer. I tend to think of 50mm in old 35mm terms as being roughly equal to 1x, so 500mm should be around 10x by that same rule. Digital SLRs should be more than this, for example, my olympus has 2x crop factor, whereas most others are around 1.5x or 1.6x, so your 600mm lens might be 15x-16x equivalent.

Digiscoping with a scope is likely to get you far more reach, relatively cheaply. From personal experience it's easier digiscoping with a P&S compact camera with 3x zoom. With a 30x eyepiece this gives you 90x with the full zoom of the camera utilized. Zooming the scope (with a zoom eyepiece) up to 60x will get you to around 180x, though obviously you need very good glass and at least 80mm objective lens to get anything worthwhile. The optimum would probably be around 60-90x with a decent scope like the Swarovski.

If you buy a cheaper scope, without ed glass, you might find it unsuitable for digiscoping as digital cameras are far more more sensitive to chromatic aberrations at high mag than our own eyes. Therefore you would see colour fringing in your results.

Steve

 

[Paul Corfield]

The normal (1X) lens for a camera is basically the length of the diagonal of the film plane. In a 35mm camera this would be 43.2mm but the industry settled on 50mm as being the standard. On a 35mm camera anything from 40mm to 55mm can be considered normal as every person has a different field of view, it's not exactly the same for every individual. Everyone can see roughly 180° but your attention is brought to an angle of view much less and this is the part the brain concentrates on. A 50mm is roughly the same as this angle of view.

On a dslr, because of the smaller sensor, a 35mm is considered the normal. This would be about 52mm on a film camera. So on a 600mm lens it would be roughly 18X as Ultra Lite posted.

I use a 600mm ED astro scope mounted directly to my dslr, just as you would a camera lens. In conjunction with a 1.4X and a 2X teleconverter I get a range from 18X to 52X magnification. I generally work in the 24-37X bracket and this is good for 100m on a bird roughly the size of a chicken for an easy comparison. For a Swan sized bird then 200m would be possible. For clarity/quality though most digiscopers work in the 50m or less range but it all depends on the size of the subject and the air conditions. No matter what your magnification and galss quality being equal, air quality will always dictate the detail you are going to capture. In the summer months you will have to get as close as possible because the heat shimmer in the air will rob the subject of any detail. In the winter you can push out much further but not over water because the water is usually much warmer than the air above it and you get the heat shimmer effect again. Big magnifications just magnify the problems more so and while you might capture a close up image, it's not always the best image. A 600mm ED astro scope will get you very close to the quality of a 600mm Canon lens for around £250.

Paul.

 

[mahgnitton]

Thanks a lot steve for the info, yeah I know what you mean about low quality glass, I once bought a cheap 600mm lens with a 2x teleconverter from Ebay, I managed to Isolate a window from Wollaton hall, Nottingham full in the frame but it was hopelessly soft, I quess what I want now is to find out where to get a good quality option for a fraction of the price of a 600mm camera lens and it looks like I'm very close...

http://www.pulsar-optical.co.uk/prod/skywatcher/telescopes/equinox80proflouriteedrefractor.html

http://www.pulsar-optical.co.uk/prod/telescopes/sky-watcher/proseries/edrefractors3.html

http://www.pulsar-optical.co.uk/cat/telescopes/meade/sky-watcher/bresser/intes/celestron/tal.html#Sky-Watcher-Refractors

 

[mahgnitton]

Thanks Paul you've also been a great help and gave me something to look for.