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Telrad Dew Shield +

Posted by Jerry McBride   11/03/2004 12:00AM

Telrad Dew Shield +
P.M. Research Inc
Street Price: $25
Available through most astronomical outlets

Before I get going full speed, let me say that I do not work for or have any involvement in P.M. Research, the product, any seller of this product, and I purchased it like everyone else.

One of the amateur astronomer’s arch-enemies is dew – and when temperature and dew point get too friendly, the wet menace starts to collect on everything, including the venerable Telrad. That’s where the standard Dew Shield (DS for short) and the Dew Shield + come in handy.

See Figure 1. When you are not aiming your scope, you push the hood-like DS to cover the projection panel. When you need to aim your scope, you flip the shield up.

Notice the cathedral-type arch you sight through. This feels a little claustrophobic and reduces your view a small amount. Although the main sighting reticles can still be clearly seen. Notice the two metal flanges – this is how the DS mounts to the Telrad, using the existing screws.

Say Goodbye to Neck Cramps

The DS+ cleverly adds a hinged mirror for 90 degree viewing. When your scope is pointing near zenith, the hood can be folded past the rear of the Telrad. You then turn a little knob which swings the mirror into place. Now you have a 90 degree Telrad! Not bad for an extra few bucks. The only other unity finder I know of that has the 90 degree feature costs much, much more.


Installation is theoretically simple. Remove two existing screws on the back of the Telrad, place the Dew Shield’s two metal flanges over the holes, and replace the screws. Don’t over-tighten!

Now we get to the negatives I discovered with the product. The fit of the dew shield leaves much to be desired, but with some TLC, the product works very well.


The DS+ does just what it advertises – it quite effectively protects your Telrad against dew. It also provides a 90 degree view capability which makes finding sky objects much more comfortable. I recommend this product for these reasons.


Chiefly I was not impressed with the initial mechanical fit and alignment. These issues were not difficult to overcome, but it took around 45 minutes of experimentation, and prudent application of a hobby tool.

#1 – Mirror rubs Telrad frame when closing DS+

Refer to Figure 5. Notice the “ski rails” that hold the clear projection panel. When you fold the DS+ into “dew protect” position, the top corner of these rails rub firmly against the mirror. I immediately got out my hobby tool and rounded off the edges.

#2 – Required fiddling with hood alignment

I had to experiment with the positioning of the two mounting flanges or the hood wouldn’t sit squarely. This causes an off-kilter view through the 90 degree mirror. After about 15 minutes of experimenting I had it positioned nicely.

#3 – Slip-on rubber sleeve easily comes off the mirror flip bar

The mirror hinges on a bar that passes sideways through the hood. You can see this in Figure 4. Part of this bar protrudes from the side, so you can use it to flip the mirror in or out of position. This plastic bar has a rubber slip-on sleeve. This is not glued on and slips off fairly easily. A little silicon adhesive fixes the issue. This should be done at the factory.

#4 – Appearance of Installation Documentation

The one page (front & back) installation note won’t win any beauty contests with it’s hand drawn illustrations and 1950’s mimeographed look, but explains the basic install process well enough.


The Dew Shield Plus is still a good and very useful product, even if, in my opinion, you need to tweak a few things yourself. The alternative is one of the following:

1. Live with a dewed-up finder and/or a sore neck.

2. Pay much more for the top of the line unity finder, which has a straight through/90 degree viewing feature.

As an amateur astronomer, I thank P.M. Research for creating the DS+, it greatly enhances the already great Telrad. As a “consumer” I think the design has a lot of room for improvement. After some tweaking everything works very well – but I should not have to do this.

Those with the extra cash might be happier with the upscale competition. But for my money, the DS+ is a very usable product which I am glad I purchased.

Clear Skies
Jerry McBride