Use of Telescope for Nature Photography

I have recently invested in a Meade ETX-90 Astro Telescope. It comes

with a fitting to take my Nikon F50 and can be converted for

photography of the night sky. I am not interested in pictures of the

stars but wonder whether anybody has had any experience in using a

scope for nature photography and the quality of the pictures that

resulted.

You can do this but my experience with it gave images that I would not share with my dog. These things are not optically designed to give what most nature photographers would consider a sharp quality image.

They will get you the magnification but thats about all.

Look at the price you will pay for less magnification in a 500mm or 600mm camera lens and that should tell you something.

Gerald - that was Halletts Comment that just went by you there.

Doesn't often come by and well worth looking at when it does!

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It depends on the telescope. I have a Televue Gensis telescope.

It's a 4" f5 fluorite refractor, equal to a 500mm f5 lens.

It produces superb 35mm images, but it weighs 10lbs, is about

36" lens (longer then the focal length!!) and I think the

current price (for a 550mm f5.5 version) is a little over $2000.

I'm not very familair with the ETX-90, but I'm guess ing it's a

90mm objective. I'm also guessing it will be slow and the focal

length will be long, making it difficult to support well and hard

to get fast shutter speeds. Most telescopes are too long and too

slow to make really useful lenses. It may be nice to have a 1000mm

f11 lens on the odd occasion, but 95% of the time or more you will want something

shorter and faster.

Yes, you can get good results from a telescope, but there is no free lunch.

As is true for most questions like this ("I have an X...."), those with the equipment in hand are in a FAR better position to answer the question than those of us who don't.

Unfortunately, the ETX-90 isn't much good for astro or terrestial photography. It has a focal length of 1250mm and a fixed f/stop of f/14. That's very slow. I've used my Canon FD 400mm f/2.8L for astrophotography and nature photography. For astrophotography, I typically take exposures between 10 and 30 minutes at f/2.8. At f/14 you would need exposures almost 16 times that long (even longer, actually, because of reciprocity failure). The only exception is the Moon. Your ETX-90 will take good photos of the Moon with 100ASA film. You should try exposures between 1/15 to 1/60 sec, depending on the phase of the Moon.

For nature photography, the focal length is a bit long. Its difficult to keep a lens with that focal length steady. I have on occassion (but reluctantly) used my 400mm f/2.8 with a 1.4X teleconverter to take it to 560mm. Even with a very steady mount, I try to shoot at least 1/500 sec at that focal length and have gotten some pretty sharp images. I have even taken a few shots at 1/250 sec with reasonable results (but most shots are too blurred for me). The ETX-90 focal length is more than twice that. I wouldn't try to take nature photos with anything less than at least 1/500sec. Consequently, if you shoot 400 to 800ASA film you could take pictures of subjects in open sunlight at f/14. Slower film speed and more desireable lighting conditions during early morning or late afternoon would require you to work at prohibitively slow speeds. All of your photos would undoubtably be very blurred from motion.

So unless you want to take lots of photos of the Moon, I would not recommend buying the Nikon accessories.

However, as mentioned above, faster, highly corrected refractors such at the Genesis make great lenses. But if you are going to spend that much money, you might as well consider lenses that were designed for the job.

I would agree that a real lens is better than a telescope if you just want a real lens!

However, on a number of occasions (before I owned "real" telephoto lenses) I used the Genesis as both a superb telescope AND a telephoto lens. In a place like Yellowstone for example, a very good telescope might well be something you wanted to take along anyway, both for viewing wildllife and looking at some REALLY dark skies! The Genesis is a bit cheaper than a similar lens (e.g. 500/4.5 or 500/4), but

I'd agree that if you really want a lens, buy a lens! The telescope has a fixed f-stop of course, but with a telephoto that's rarely a problem. It's worth noting though that the Genesis used as a telephoto lens had higher resolution and contrast than any similar "real" telephoto lens ever tested by Modern Photography, back in the days when they did lens tests.

Now I carry a real lens AND a telescope (not the Genesis though, something a little smaller and lighter). The only other telescope I'd consider would be an AstroPhysics Traveller. As I recall it's a 600mm f6, also priced over $2000 and with a 6 month waiting list last time I checked.

The main optical problem with scopes used for photography is excessive chromatic aberration, color around the object. The ETX is a catadioptric scope (a Maksutov type like the legendary Questar) and has essentially none of this color. Even the best refractors have some color, although the latest offerings from Tele Vue and Astro Physics are extremely good in this respect (and their prices reflect this). For a daytime test, focus on a telephone wire against a bright sky and look for a purple and/or green fringe around the wire. Even my f/5 Genesis will show a bit of this color. A cheap Meade 4" cassegrain reflecting scope will not. The best small commercial refractor I've seen is the Astro Physics Traveler, which is a highly color-corrected triplet and uses ED glass. The very latest Tele Vues are also in this class and use ED glass or, in the case of the TV101, ED and fluorite. There are others (Zeiss, Takahashi, etc.) but they are even more expensive and not obviously better for most purposes.

As already stated, the large f number and lack of stability will be your most challenging problems in practical use.

By the way, Bob, the last time I inquired, you couldn't even order a Traveler. My friend recently sold two of these (used) for over $3000 each! Production is off and on due to demand for their other scopes and mounts. I think Astro Physics makes different model scopes available on a rotating schedule. I was on a list for over two years before I was put on the official waiting list to order a 6" scope. A few months ago, they called me and said I had until noon the next day to put down the deposit to reserve the scope. Mine is due in March, 2000.

<p>Times certainly have changed since the last response of this thread. The Traveler is no longer produced and there appears to be no direct replacement in the lineup. In 1998/99, a telescope company by the name of Takahashi introduced the 4 inch f/5 double fluorite refractor. 530mm at f/5 or 850mm at f/8 with the ExtendQ 1.6x optic. The color correction is nothing short of astounding for an optic as "fast" as f/5. Plus the sharpness, contrast and resolution are also top notch. I routinely photograph nature photography with this telescope and it has proven to be an optical wonder. A quick internet search on the traveler will produce some results for astrophotography, but the takahashi FSQ (N and ED) have become the standard for serious astro imagers. <br>

Probably THE most color correct telescope on the market, refractor wise, would be the TOA series from Takahashi. If I remember correctly, it's a cooke triplet that has double ED glass. <br>

Using a mirror optic presents it's own set of problems. For one thing, you get a HUGE loss of contrast due to the aluminum coating. If you examine the aluminum coating, you will find that the metal itself (or any coated metal) has a columnar like structure which will cause plenty of light scatter. It's the nature of the beast and no amount of "flocking" or baffles, etc will help in this regard. A high end refractor with the equivalent aperture area will always outperform a mirror optic. True, a mirror optic will be essentially "color correct" and free of chromatic aberration, but they definitely have their own set of cons to the list. Another thing to consider - the corrector plate on many mirror optic hybrids (SCT/Schmidt Cassegrain, schmidt cameras, maksutov cassegrains, etc) will introduce chromatic aberration due to the fact that it's a piece of glass doing some, but not all of the correction.<br>

I've had quite a few chances to shoot with the new Canon 800 IS lens and I've been severely disappointed with it's optical quality when compared to a high end telescope. Lack of contrast, lack of resolution, etc. The only thing good about it is the autofocus, the lighter weight of the optic (when compared to my 15 pounded fully loaded takahashi FSQ106N) the image stabilization and the aperture control. Optically speaking, Canon has ALOT to improve, despite what the famous Canon bird photographer says. But then he doesn't shoot with a high end Takahashi, Astro Physics or TEC telescope in the field. I definitely do. <br>

Put it this way. Let's say you went from consumer glass to a high end telephoto lens, say an "ED" or "L" series glass. Quite a bit of difference. Huge. Now take that same difference and then some more when going over from a L glass (or ED if you're shooting the other system) to the highly corrected telescope. It's quite shocking and definitely shows up when printing 8x10. Lots of microdetails.<br>

A factor to consider is that the high end telescopes are made with extreme precision. Companies like Tak, TEC and AP will take each batch of glass and measure out the melt data for the production run. The melt data for each type of glass or even crystal (pure fluorite) is quite critical. After the melt data is considered and plugged into their optical formula, the grinding and polishing (figuring) of each element takes place. Mind you, this isn't the high speed polishing/grinding that Canon, Nikon, Leica, Zeiss will use. They can blast out parts in 20 minutes or less with plenty of zonal errors. With the t-scope guys, it takes many hours, even DAYS to get the figure of the lens where they want it. <br>

Whenever you high speed grind a lens, it generates plenty of heat. More than enough to distort the figure of the lens. But most of the time, the camera manufacturers will do this to meet production numbers. Many thousands of rpms vs a few hundred rpms of the t-scope optic. <br>

Camera lens manufacturers will NOT have the time to measure out the melt data of each specific glass, but instead, rely on the "slop" or tolerance of the air spaced design. With a camera brand telephoto lens, most people aren't really looking for that last bit of contrast, or sharpness or saturation. Also note that camera lens makers will not give you the wavefront error or even a measurement of how good the lens is. One of the measurements is called Strehl Ratio.<br>

A perfect optic will have a 1.00 strehl ratio. When a lens is pointed at a true point source (star or simulated star) it will have the ideal Airy disc with very little energy in the second ring. High contrast, high sharpness, all the good stuff. Now with an optic that has low strehl ratio, you will get a significant amount of smeared details, lowered contrast, etc. A link to an optical test (with strehl ratio) is listed below.<br>

http://www.astro-physics.com/products/accessories/software/atmos/atmosfringe.htm<br>

About the ONLY lens that I know of that advertised "diffraction limited" optics were the Leica R series telephotos. Diffraction limited means 0.8 out of 1.0, which is respectable for an optic. Not the best, but at least they're advertising. With the other brands, they won't list it. I wouldn't be surprised if the new Canon 800 lens had a strehl of .3 or lower. Takahashi and AP as well as TEC have strehl ratios of .95 (for the Tak FSQ ED and N) and .99 for the AP, TEC and TOA triplets. Truly remarkable.<br>

Something that isn't well known about optics - you can either have the color correction (for the melt data, if it's designed correctly) or the focal length. In other words, if you get a different batch that has different melt data, you can have one or the other, not both. So if it's a 500mm optic (or thereabouts), you can keep the perfect 500mm focal length or you can vary the focal length to achieve the color correction you want. There is no free lunch.<br>

High end telescopes will NOT play "second fiddle" to ANY commercially made camera manufacturer (or even lens manufacturer) optic out there, at least not in terms of ultimate optical quality. Times have changed!<br>

Astro Physics now has an 8+ year waiting list. <br>

For more info on nature photography with telescopes, you can check out my article in Nature Photographer, Winter issue, 2009. The article is labeled "ultra high resolution optics". </p>