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12-31-2014, 10:29 AM   #1
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Astrophotography... Telescope vs telephoto

Is there a difference in a 600mm telescope and 600mm lens? If I want to try some astrophotography would one produce a better result all other factors considered? A telescope is basically a telephoto lens with an eyepiece vs. a camera correct?

12-31-2014, 10:47 AM   #2
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There is a lot of difference. Camera lenses have multiple elements to correct for different aberrations, such as CA. Unless you buy a very top end refractor telescope, you will definitely have corrections to make in PP.
Reflecting telescopes generally don't suffer CA that much. But they tend to have problems with coma anywhere outside a central area of perfect focus. Not to mention being more difficult to mount a camera to.
12-31-2014, 11:54 AM   #3
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You'll also more likely have more control of aperture with a lens than a telescope.
12-31-2014, 12:00 PM   #4
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I replaced my SMC K 400mm with an 80mm ED scope (500mm f6.25). The scope itself was only 100 more than the lens to purchase (sales&#128522 and you can use your camera in place of an eyepiece (prime focus). The IQ difference is very noticeable.
The only issue then is the cost/choice of mount, diagonal, eyepieces! Yet another form of LBA.

12-31-2014, 12:00 PM   #5
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Good point. I use aperture masks to increase f stops. My scopes start at F5/F6. I've made masks to be able to get up to F10. This enables me to focus wide open, and then shoot at tighter aperture.
12-31-2014, 12:11 PM   #6
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QuoteOriginally posted by wildlifephotog Quote
There is a lot of difference. Camera lenses have multiple elements to correct for different aberrations, such as CA. Unless you buy a very top end refractor telescope, you will definitely have corrections to make in PP.
Reflecting telescopes generally don't suffer CA that much. But they tend to have problems with coma anywhere outside a central area of perfect focus. Not to mention being more difficult to mount a camera to.
QuoteOriginally posted by W412ren Quote
I replaced my SMC K 400mm with an 80mm ED scope (500mm f6.25). The scope itself was only 100 more than the lens to purchase (sales��) and you can use your camera in place of an eyepiece (prime focus). The IQ difference is very noticeable.
The only issue then is the cost/choice of mount, diagonal, eyepieces! Yet another form of LBA.
Hmm . from wildlifephotog post I get the feeling a lens would be better... from W412ren I get the feeling a telescope is better unles you are saying the IQ difference is worse...
Diffence in opinion or am I not understanding?
Thanks

Last edited by soycory; 12-31-2014 at 12:13 PM. Reason: clarification
12-31-2014, 12:17 PM   #7
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There is a rather large learning curve to using scopes for astro photos. The use of lenses is easier, but guiding is still an issue.
I use both lenses and scopes. They each have an area of best use.

The moon is fairly easy. It's the rest that challenges one's abilities.
12-31-2014, 12:21 PM   #8
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For me the scope IQ is far superior. Depends on the lens you compare with I suppose.
There are some top quality refractors available though for a lot less than "Star" lenses.

---------- Post added 31st Dec 2014 at 19:43 ----------

Not the greatest images in the world but these show an example.
First one with K400 and 2x TC, second with scope.





12-31-2014, 12:49 PM   #9
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Kenko Lens2Scope Adapter for Pentax Mount Lenses - Angled Eyepiece K-LS10-PKAB will let you use your lens AS a telescope, no camera required.

Vello T Mount Lens to Pentax K Camera Adapter LA-PK-T B&H Photo lets you connect your pentax camera to a telescope that uses the T mount.
12-31-2014, 12:59 PM   #10
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QuoteOriginally posted by narual Quote
Kenko Lens2Scope Adapter for Pentax Mount Lenses - Angled Eyepiece K-LS10-PKAB will let you use your lens AS a telescope, no camera required.

Vello T Mount Lens to Pentax K Camera Adapter LA-PK-T B&H Photo lets you connect your pentax camera to a telescope that uses the T mount.
Is this the same "T" mount as for Tamron lenses?
12-31-2014, 01:09 PM   #11
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T mount for many Celestron scopes. We have a C90 that is effectively ~1200mm at f13. Again, each has their uses but if variable aperture is important lenses are superior in that regard. For plantets and the moon we find the scope is better overall, for wide field star photos the best are high speed wide angle lenses (30/1.4 is my best for that sort of thing).
12-31-2014, 01:20 PM   #12
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QuoteOriginally posted by W412ren Quote
For me the scope IQ is far superior. Depends on the lens you compare with I suppose.
There are some top quality refractors available though for a lot less than "Star" lenses.

---------- Post added 31st Dec 2014 at 19:43 ----------

Not the greatest images in the world but these show an example.
First one with K400 and 2x TC, second with scope.



Big difference. The scope looks much better.
12-31-2014, 01:36 PM   #13
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QuoteOriginally posted by W412ren Quote
For me the scope IQ is far superior
mmmm .. what scope are you using?
12-31-2014, 02:23 PM - 1 Like   #14
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A couple of thoughts. Be careful about nomenclature when comparing scopes and camera lenses. When people refer to a "600 mm lens", they are usually talking about the focal length of the lens. OTOH, when you see mention of an "80mm spotting scope" they are usually referring to the diameter of the objective lens (i.e., the large lens at the front of the scope." The focal length of the lens divided by the objective diameter is the focal ratio. For example, a 66mm spotting scope with an focal ratio of 6 will have a focal length of 396mm. When you talk about a "600mm lens", that is a nice telephoto lens indeed, but not too unusual. A "600mm scope" would be a really large amateur telescope that would probably need a pickup truck or trailer to transport. (600mm is 23.6 inches--Google "Yard Scope").

A "T mount adapter" is a gadget that is used to connect a camera to T mount accessories. Each camera mount has a specific T mount adapter that you can buy for it. The T mount for the Pentax K bayonets onto the the lens mount in the same way as a lens, but it has no electrical contacts or anything for connecting the camera to the internals of the lens. On the other side of the mount is a specific thread (42mm, I think) that can be used to connect T mount lenses, of telescopes that have a corresponding adapter. Of course, everything T mount is strictly manual focus and manual exposure.

In general, I agree with the statement that scopes are best for planets and the moon, wide angle lenses are best for wide star field photography. Also, if you want to good closeup pictures of planets, you need to use a scope and eyepiece with a technique called "eyepiece projection". For this you need a really sturdy mount and a way of focusing very carefully, because the magnification you get is phenomenal, which magnifies camera shake and minimizes depth of field.

---------- Post added 12-31-2014 at 05:14 PM ----------

After giving this more thought, I decided to recommend some reading. There is a book that is now about 15 years old. "Astrophotography for the Amateur" by Michael Covington. It was written pre-digital, but it does contain a lot of information about scopes and connecting them in various ways to cameras, effective focal length, magnification, etc., that is still relevant, since digital did not repeal the laws of optics. It is also written for non-experts. Checking Amazon, it looks like it is out of print, but available used and as an ebook (for a seemingly high price). You might also find it at your local library. It is worth reading. What it doesn't cover are post-digital developments such as the stacking of many short exposures of a dim object to get a useful image without a lot of noise. Since I got away from this stuff since I went digital, I can't recommend a single reading source for the more recent developments
12-31-2014, 03:26 PM   #15
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QuoteOriginally posted by soycory Quote
Is there a difference in a 600mm telescope and 600mm lens? If I want to try some astrophotography would one produce a better result all other factors considered? A telescope is basically a telephoto lens with an eyepiece vs. a camera correct?


Dollar for dollar you're going to be able to gather more light more accurately with a good telescope. You can purchase some telescope focusers which have software designed to change focus with temperature and camera lenses do not. On top of that you can find extremely fast or long focal ratio telescopes which would be prohibitively expensive as camera lenses. You can also cool down a telescope and control tube currents in order to limit distortions caused by heat waves and air currents.


The plus side of a camera lens for wide field astrophotography is that the setup time is quicker than with a telescope. The downside is that the camera lens is not as versatile for stellar photography as a real astrograph.


By the way I should mention I own eight telescopes and built my own 4.5" astrograph just for taking pictures of satellites.

obin

Last edited by Obin Robinson; 12-31-2014 at 03:31 PM.
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