telescope as a lens?

[adrian tyler]

to complete a project i would like to make some pictures from the top of the sierra nevada looking down into granada. however none of my long lenses are going to work as they don't have sufficient magnification. i have been looking at the "Leica APO-TELEVID 82 angled telescope with VARIO 20 - 50x WW ASPH ocular"

http://www.company7.com/leica/telesc...televid82.html

if there is anyone who knows the focal length equivelant in 35mm format of this optic i'd be grateful...

thanks

adrian

[Struan Gray]

Those are sexy scopes.

The total magnification of a telescope is the focal length of the main optic divided by the focal length of the eyepiece. In this case, 440 mm divided by 8.8-17.6, which roughly works out as 25-50 x (hence the name of the eyepiece :-).

Roughly speaking, for a given format, its normal lens gives 1x magnification at infinity. Multiply other magnifications by the normal focal length to get an effective focal length. So, for 35 mm film, assuming a 'normal lens' is 50 mm, the equivalent focal length of the Leica scope is 1250-2500 mm. Use appropriate factors if your camera is a non full-frame digital.

Hearsay has it that the dedicated camera adapters for these scope (http://www.company7.com/leica/televcam.html) give better results that photographing through an eyepiece made for viewing, but then you are limited to a single focal length, 800 mm. It all depends on how pernickerty you want to be: astro photographers are generally unhappy with the results from even these exalted terrestrial scopes.

[adrian tyler]

thanks struan i appreciate it !

they do look good don't they, pretty un-versatile but it may be my best solution if i can swing the budget, also after looking through the "brought to light: photography of the invisible" SFMOMA catalogue there are a possiblity of other applications which could provide hours of fun!

it'd be interesting to see the difference between photographs made through the eyepiece viewer and the dedicated adaptor.

i suppose astro photograhers need more magnification?

[Struan Gray]

The biggest problem is that telescopes are usually optimised for on-axis performance, and even the relatively small area of a digicam sensor gets you far enough off-axis that the aberrations turn ugly. When looking through a telescope with your eyes, their adaptation covers errors which can make a photograph look horrible, and you tend to be more indulgent to centred compositions and things like colour fringes at the edge of the field.

You will need a beefier support than the usual sorts of tripods used by birdwatchers. In fact, support and air quality between you and the town will be your biggest headaches.

You might also want to look into local options for renting the big sports glass by Canon and Nikon. The APO wunderskops from Zeiss and Leica have quite good reputations as telephoto replacements when compared to other spotting scopes, but I've never seen anyone suggest they compete with the dedicated long lenses, even once you have to crop and interpolate the images taken with the telephoto lens.

PS: if you want to do things 'right', here's some telescope porn:

http://www.takahashi-europe.com/en/p...refractors.php

[Archphoto]

There is a crude way of finding out the lengh you want: take a picture of the area you want with your longest lens and enlarge the full frame of it to say 40x50, deterimine the size of the area you realy want and start calculating.

Original hight of the print at ...mm /new hight of the area choosen = your factor k
...mm x k = new/needed focal lengh

For 35mm a mirror lens with extender (focal lengh converter) could do the trick, for 4x5 you would need a Sinar P2 with multiple bellows and inbetween standards and a bit more....

You allso need quiet air as has been said, a sturdy tripod and expect a loss of contrast if you are phtographing an object miles away.

Peter

[jp]

There is a crude way of finding out the lengh you want: take a picture of the area you want with your longest lens and enlarge the full frame of it to say 40x50, deterimine the size of the area you realy want and start calculating.

Original hight of the print at ...mm /new hight of the area choosen = your factor k
...mm x k = new/needed focal lengh

For 35mm a mirror lens with extender (focal lengh converter) could do the trick, for 4x5 you would need a Sinar P2 with multiple bellows and inbetween standards and a bit more....

You allso need quiet air as has been said, a sturdy tripod and expect a loss of contrast if you are phtographing an object miles away.

Peter

I've used a cheap russian mirror lens + teleconverter (2000mm) on a 35mm dslr for these sort of shots. In addition to these reqiurements, you'll also want a darkcloth, as they aren't that bright for focusing. The distance compression is uncanny.

You can get almost as good results shooting with a high quality tele lens (300 2.8) and digital zooming/cropping in post processing if you've got a decent camera sensor.

[GPS]

Adrian, are you speaking 35mm photography or LF photography?

[Peter K]

Adrian, are you speaking 35mm photography or LF photography?

That's no difference if one uses the telescope mounted in the way the exit pupil of the telescope meets the entrance pupil of the camera's standard lens, focussed at infinity.

In this case the telescope is an afocal device and the subject is, in Adrian's case magnified 20 - 50x compared with the standard lens.

This is also the case with other afocal devices like microscopes, dove turn-over prisms, fisheye converters etc.

Peter

[Drew Wiley]

A real expert at adapting cameras to telescopes is a fellow here in the SF Bay area
named Francis Sakamoto. Originally he adapted Nikon and Pentax 6x7 cameras for
Celestron telescopes, but now he uses a 8x10 Toyo view camera with a long bellows,
puts Apo-Nikkor graphics lenses on the front, and a 6x7 camera at the film position.
Has a website.

[Glenn Thoreson]

Be advised that atmospheric haze is greatly enhanced using ultra long lenses. Something to consider.