Telephoto vs Telescope

The purpose of this article is to compare photographs taken with a Canon 100 – 400mm 4.5-5.6 L IS II lens to four different telescopes.  The goal is to help people venturing into astrophotography decide what equipment will best suit their needs.

Methodology

• The same Canon 5DS R body was used for all the photographs.
• All photographs were taken with a tripod.
• At least five photographs were taken of each subject with each telescope. Refocusing was performed after two or three frames in sequence. The best photograph from each sequence was selected for this article.
• Focusing was achieved using the cameras on screen display as well as the displays magnification. The Canon was focused using the camera autofocus feature.
• No retouching / sharpening was performed except to blur the faces of people and license plates which may have been in the photograph.
• While I will not name the individual telescopes tested I will provide the following data;
  • The four telescopes ranged in price from $250 to $4000.
  • Telescope designs included Schmidt–Cassegrain 2000mm equivalent, costing approximately $1000.
  • Three of the telescopes were refractors.
  • The $4000 Refractor was a 4 element APO.

Test 1: a Church at 436 yards

Above: full frame shot with the Schmidt–Cassegrain 2000mm equivalent on the left, and on the right the full frame shot with the Canon 100-400mm set at 400. Both photographs were taken at 1/500sec., f10, ISO 200.

Below: The same two photographs with the Canon photograph enlarged to match the photograph taken with the telescope.

Test 2: a store front at approximately 200 yards

Above: Canon telephoto lens set at 400mm on the left, three refractor telescopes to the right of the Canon. All four photographs were cropped significantly to show the area with the most detail. Photographs were taken at ISO 400, 1/400 – 1/500, f8.0.  Fluctuations in shutter speed were due to the different f-stop equivalent of the telescopes.

Test 3: a radio antenna on hilltop

Above: Canon telephoto lens set at 400mm on the right, three refractor telescopes to the left of the Canon. All four photographs were cropped significantly to show the area with the most detail. Photographs were taken at ISO 400, 1/2000 – 1/5000, f8.0. Canon 1/2500, ISO 400, f8.0. Fluctuations in shutter speed were due to the different f-stop equivalent of the telescopes.

Conclusion 

In the conditions shown above the Canon telephoto lens presents better contrast, sharpness, and color saturation when compared to the four different telescopes tested.

Astrophotography is has a very different set of requirements when compared to viewing astronomical objects. When it comes to astrophotography one of the most important pieces of equipment is high precision German Equatorial Mount also known as a GEM. Without a high precision mount, long exposures will produce blurs and streaks due to the rotation of the earth. Most likely you already have the lenses in your camera bag to get started in astrophotography. Wide field astrophotography will generally utilize lenses in the 16mm – 24mm range on a full frame DSLR. Deep field astrophotography will utilize lenses in the ranging from 100mm for larger objects to 2000mm for smaller objects.

If you are starting out in astrophotography you would be well advised to put your money in a good precision GEM mount and make use of your existing lenses. As you become more heavily involved in astrophotography and want to photograph the smaller deep space objects you will most likely need to move up to a telescope for its increased magnification power.

Also for viewing, not photography, the increased magnification power of a telescope will allow you to observe details in planets and other objects which you will not be able to view with all but the most powerful telephoto lenses.

I want to extent my thanks to Ted and Bob from Skies Unlimited in Pottstown PA. Without their help, professionalism, and equipment, this article would not have been possible.

Take care, and keep experimenting.