Telescope vs. telephoto??

Does the terminology...200 power in telescope language have a relationship to 200 mm in 35mm Photography lenses..

how do I relate a telescope to a telephoto..
say you are shooting the moon with a 200mm telephoto..
What would that be the Equiv to in a telescope power rated lens..
or are Telescopes rated in another terminology?

 

[ame=http://www.youtube.com/watch?v=wPVFPI4hIMs]Swarovski Digiscoping Part 1 - YouTube[/ame]

thinking about a scope

 

Telescope magnification is determined by the ratio of the telescope's objective focal length to the eyepiece focal length. So if you have a telescope with a 2000m objective focal length (say an 8" Celestron at f/10) and a 10mm eyepiece focal length, the magnification is 200x.

Camera lens magnification is based on the ratio of the telephoto lens focal length to the "normal" image lens focal length. So if your normal lens in 35mm photography (full-frame sensor) is 50mm, then a 200mm lens would give you a 4x magnification (relative to the 50mm lens). If you have less than a full-frame sensor, then apply the sensor ratio (usually 1.3x, 1.5x, etc). As an example, Nikon usually has a 1.5x sensor ratio for DX cameras, resulting in a 6x relative magnification to the "normal" lens (which is closer to 35mm in a DX) with a 200mm telephoto.

 

Big magnification sounds enticing, but there are some issues to be aware of.

Large magnification results in light loss, so you will need a combination of slow shutter speeds and fast ISO, which will degrade the image somewhat.

It may also be hard to preview the image due to small effective aperture (try looking at an image at dawn or twilight with your camera lens stopped down to f/16 or f/32).

Despite the small effective aperture, you'll have more limited depth of field than you might expect and focusing might be sensitive (depending on the number of turns you get on the focus ring or knob).

Slow shutter speeds require a remote shutter release, super-stable tripod and calm air (and a static/slow moving subject).

Calm air can be mistier and hazier, resulting in less snap (contrast and color saturation) in photos. Differential heating in the landscape might be seen as shimmering and mirage like distortions in the image. In other words, atmospheric conditions will be a limitation on when you will be able to get good photos.

Large magnification makes it hard to find your subject, so you'll want a really good ball head, which can be locked down rock solid to take the shot, otherwise it can still be done, but expect some frustration.

 

Do you teach this???

You're Good!

I will spend the next 30 minutes decifering what you just said..
thank You!

can you tell me, if I shot the moon with a full frame camera, what magnification in a scope would equal that magnification by a 200mm telephoto...???

 

It really depends on what your goals are. Mine are to do deep sky longer exposures with filters at some point with a sky tracking system, and the Canon T Mount.

Canon have a fantastic infra-red adjusted sensor in the 60Da, but you can do great shots with any current SLR IMHO.

If I had a very large budget, I'd get something like this...

http://www.celestron.com/portal/celestron-c14-af-xlt-cge.html
with a mount like this
Celestron CGE-Pro Motorized Equatorial Telescope Mount 91527 B&H
http://www.celestron.com/astronomy/celestron-cge-pro-mount.html

Yeah... epic results would ensue! Probobly would even get a comet named after me

 

If I answer exactly as you've asked it, then as mentioned above, a 200mm telephoto on a full-frame camera has a magnification of 4x, so you would need to set your spotting scope configuration to 4x to match it. This would not be possible with the Swarovski zoom eyepiece as the video clip you linked says the combination has a zoom range of 25x to 60x. So at the minimum magnification setting of the Swarovski at 25x, it would still be 8x more than the 200mm telephoto, or the equivalent of a 1600mm telephoto.

If you're asking what magnification you need to get the moon to be full frame in the camera, then we can estimate that via angle of view. The moon has a 0.5 degrees (30 minutes) angle of view, give or take. A 1200mm telephoto lens has a 2.5 degree angle of view.

Angles-of-View | B&H Photo Video Pro Audio

It's not exact, but doubling the the focal length approximately halves the angle of view. So you would need the equivalent of a 10,000mm telephoto on a 35mm camera to get the moon to be full frame, which is roughly 150x-200x.

 

Wow!
What college do you teach at?
Very well stated.
You have answered my primary question.
In retrospect i understand.
The human eye sees at 54 mm
A 200 mm lens is 4 times that.
Hence the power rating in telescopic
Terms would be 4X
I just wanted to relate how much closer to the
Surface of the moon i would be seeing with 60 or 100
Power.
Thank you.
Michael

 

Actually celestron makes an equivelent scope
To swarovski for 1/4 the price.
It is rated quite well in its class

 

Optics are quite a science! Now if only I could figure out how the hell aperture blades actually accomplish what they do.

 

It's all about tracing the light rays This diagram couldn't make it much simpler I think. It also shows why the exposure needs to be compensated for a higher aperature.
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I suspect he meant "how does it work mechanically?". In which event, this video may help...

[ame=http://www.youtube.com/watch?v=VnYQCBQHt-Q]???????? ????????? (Iris diaphragm) - YouTube[/ame]

In a camera, the aperture leaves are flexible and overlapped rather than butted as in the video, but mechanically the mechanism is similar - a control ring which causes an end of each aperture leaf to pivot on a second ring so that the body of each leaf swings in or out. This next video shows the overlapped leaves, but the mechanism is less obvious as the two rings are overlapped.

[ame]http://www.youtube.com/watch?v=jYcSwjvwe3E[/ame]

 

This should be interesting !

A camera that can see around corners - CNN.com

 

Wow, I didn't know there were other amature astronomers on the forum.

When thinking of taking the plunge into astro photography, I read everything I could for about 2 months straight. unfortunately, I forgot most of it.

 

Some time back, I did a hydrogen line and oxygen line scan with a 40 ft. Dish at the NRAO in WV of the crab nebula. Very cool stuff for X Y and Z coordinate graphing.

I've been an enthusiast of optical astronomy since I got my first Newtonian reflector I still haven't taken the plunge into astro-photography though.

 

Back when I was in college and studying astronomy/cosmology I had the opportunity to use a Questar 3.5" scope the department had. They had built an incredibly beefy tripod for use with the telescope. I had fun photographing the moon as well as the sun. I think the focal length of the Questar was about 1500mm and the size of the moon on the negative didn't fill the frame. However, the scope was a decent macro lens as it had a minimum focus of 10' give or take. I taped a dollar bill to a wall and George W filled the frame nicely. I wish I could afford to get one as they are a jewel of manufacturing.

 

I am actually looking to share the astronomical heavens with my 8 year old boy..
A spotting scope is not ideal for stars and planets..although for the moon it is perfect.
Can anyone suggest a quality piece of equipment...non computerized that will be able to hook up to my DSLR and go beyond moon photography..

Quality and portability is what I seek, a heavy reflecting scope is not my Idea of portability..his patience is short, so I need to set up , View..and head for bed in the evenings..

Bench mark would be to see Saturns rings. clearly.

 

If the whole spotting scope question was solely astronomically targeted, I would consider a Celestron C90 (3.5" aperture) as a low cost way to get into it. The current C90 has gotten very good reviews for the optics, considering the price. This 3-way review between a Questar, C90 and Meade ETX concluded by saying the C90 is almost as good as a Questar at 1/20th the price.

90 mm Maksutov Comparo

You can pick up a basic C90 for the ridiculously low price of $150! It's also threaded for a T-adapter, so you only need the matching ring for your camera mount. It comes standard with a 32mm eyepiece that will give you 39x magnification (though the standard eyepiece is apparently from their dirt cheap line, with poor eye relief and narrow field of view). The usual rule of thumb is aperture (in inches) times 50x is the useful magnification limit. So with a 3.5" aperture, the useful magnification limit is 175x. So you can add a 7mm eyepiece and get 180x, and maybe also pick up a better 32mm Plossl.

Amazon.com: Celestron 52268 C90 Mak Spotting scope (Black): Camera & Photo

Celestron C90 MAK Spotting Scope 52268 B&H Photo Video

The C90 will be good for planetary observation (should be able to see Saturn's rings), but probably less so for Messier objects. You'll want large aperture for those to gather all the light you can, in which case you're talking about 6" to 11" or larger (which won't be easily portable).

You'll also need a good tripod with az-el motion, the Celestron tripod gets mixed reviews but is also low cost.

 

Actually, even better might be a Celestron Nextar 102. For $430, you get slightly bigger aperture, a refractor (more direct optical path and faster optics f/6.6 vs f/13.9 for the C90), 2 eyepieces plus a computerized mount and tripod.

Celestron NexStar 102 SLT Telescope 22096

The 660mm focal length of the 102 versus 1250mm focal length of the C90, means you'll get about half the magnification for the same eyepiece, but the viewing should be brighter and clearer (although a low cost refractor like this will likely show slight green color fringing on very bright objects). The computerized mount should be a fast setup and you can direct it to find planets without having to look for them, which can take a lot of time (for your son to get fidgety) if you're not used to it. The faster optics will also help you to see more Messier objects.

 

Id also consider an Orion ST120. 4.5 ish" of apeture, f/5, short focus length, and will give WIIIIIDDDDEEEEEE views of the heavens. Should be a great scope for mounting a camera to. Comes with a manual equitorial mount.

I have been meaning to pick one of these up for wide views with out having to shell out the big bucks for an APO refractor

 

AstroView 120ST Equatorial Refractor Telescope | Orion Telescopes


Nice old world style

 

Thanks for posting the link. I tried, but I guess I was doing it wrong lol.

 

Meade 20" MAX ACF Telescope w/ Starlock, MAX German EQ Mount & AZ Pier - OPT Telescopes


I know my son would like this one...OMG

 

about 4 seconds of exposure with my 70-200 IS L II @ 200mm on my 5D MK II. Cropped. no filters. Not bad, but I need some real equipment to do this better.
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