3.5mm 1.25" 72° field Delos

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The 3.5mm TeleVue Delos is designed to produce very high power/high contrast/high quality images with any telescope. It has a long 20mm eye relief that makes it ideal for eyeglass wearers. The majority of eyepieces in this focal length range have much shorter eye relief that makes them problematical for eyeglass use, but that is not an issue with the Delos. With 20mm of eye relief, its full 72° apparent field is easily usable with glasses.

The 3.5mm Delos has an adjustable height eyeguard with a soft rolldown eyecup to shield the eye from ambient light (from a neighbor’s security light, for example) and improve the image contrast. The eyeguard height can be locked in place at any point desired. The Delos can be used with with TeleVue Dioptrx astigmatism correcting lenses, should you desire to observe without glasses.

As a longer eye relief 72° field version of the acclaimed 110° field 3.7mm TeleVue Ethos SX, the 3.5mm Delos has all the virtues that astronomers have come to expect from an Ethos: high contrast, a neutral color balance, and full field sharpness – with well-controlled astigmatism, field curvature, lateral color, angular magnification distortion correction, and low pupil sensitivity (kidney bean effect) for daytime use.

The 3.5mm TeleVue Delos has a 1.25” barrel that is threaded for standard 1.25” eyepiece filters. A safety groove is machined into the chrome barrel to engage your focuser thumbscrew. This will help prevent the eyepiece from falling should the thumbscrew accidentally loosen while observing. The main eyepiece barrel is narrow enough to comfortably use a pair of 3.5mm Delos in a binoviewer. Rubber grip rings provide a sure grip in cold weather when wearing gloves or mittens. Dust covers are provided for both ends of the eyepiece.

You can see how wide your actual field of view will be when you use this Delos with your telescope by using the eyepiece field calculator under the "formula" tab above.

Field of view:
The field of view (FOV) is the amount of observable world one can see at any given moment.
72°
Eye Relief:
Eye relief is the distance from the last surface of the eye lens of an eyepiece to the plane behind the eyepiece where all the light rays of the exit pupil come to a focus and the circular image is formed, sometimes called the “Ramsden Disk.” This is where your eye should be positioned to see the full field of view of the eyepiece. If you must wear glasses because of astigmatism, you’ll usually need at least 15mm of eye relief or longer if you want to see the full field of view with your glasses on.

A note on our eye relief figures: Quite often, our eye relief figures will differ from those of the manufacturer. This is because we measure the “usable” eye relief, while the manufacturers specify their usually-longer (but technically correct) “designed” eye relief.

The eye lens of the eyepiece is normally recessed below the rubber eyeguard or rubber rim of the eyepiece to keep the lens from being scratched during use. An eyepiece might have a “designed” eye relief of 15mm (and the eye relief will truly measure 15mm from the eye lens to where the image forms). However, if the eye lens is recessed 3mm below the eye guard, the Ramsden Disk forms only 12mm above the eyepiece body (the 15mm “designed” eye relief, less the 3mm of eye relief made unusable by having the eye lens recessed into the body of the eyepiece). This “usable” eye relief of 12mm (measured from the rolled-down eyeguard – the closest point you can get your eye to the eye lens – to where the image forms) is the eye relief figure we would measure and list in this website.

Why is it important to list the “usable” eye relief? For those people who don’t wear eyeglasses while observing, a few mm difference between the eye relief they expect from the manufacturer’s literature and the shorter eye relief they actually get in real life doesn’t mean a lot. They can simply move a little closer to the eyepiece to see the full field, and never realize that the eye relief is a little shorter than they expected. However, some people must wear eyeglasses while observing, because of severe astigmatism. These observers can’t move closer to the eyepiece if the eye relief is shorter than expected because their glasses get in the way. For these people, the real life “usable” eye relief is more important than the technically correct but sometimes not fully usable “designed” eye relief. We measure and list the actual usable eye relief so that people in the real world can pick the eyepieces that will work best for them.

20mm
Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

3.5mm
Barrel Size:
The industry standard diameter, as of 2011, is 1.25" and is the most common.  Other sizes available are .965" and 2".
1.25"
Weight:
The weight of this product.
17.6 oz.
Warranty:
Limited Lifetime
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65mm x 120mm eyepiece container
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Helpful Formulas
Telescope Eyepiece Formula
To calculate the magnification and approximate actual field of view of this eyepiece on your telescope, enter the focal length of your telescope below and press the "Calculate" button.

Enter your telescope's focal length: mm   



TeleVue - 3.5mm 1.25" 72° field Delos

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TeleVue - 3.5mm 1.25" 72° field DelosImage showing three possible positions of the infinitely adjustable height eyeguard on a typical Delos, showing the reference marks on the barrel.
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Our Product #: TD03
Manufacturer Product #: EDL-03.5
Price: $370.00
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The 3.5mm TeleVue Delos eyepiece brings acclaimed Ethos image quality to a long eye relief 72° field eyepiece for comfortable eyeglass use during very high power planetary, lunar, and binary star observing . . .






. . . our 34th year