Telrad only just illuminates when fully on?

[Zermelo]

I've just taken delivery of a Telrad, never used one before.

I thought I'd been sent a dud at first, I couldn't see anything when I switched it on. But it seems that I need to turn the rotary switch very nearly to maximum (it has a 270 degree range) before the reticle starts to light at all. At maximum setting I can see the rings clearly in the window and it certainly seems bright enough to work with, but I have only the last 10-15% of the 270 degrees in which to set the brightness from zero to max (to be clear, I haven't tried this in the field yet, I was just testing that it worked in a darkened room. The way the weather is looking, it won't be seeing any real action for a while).

My question for experienced users: is this normal behaviour for a Telrad? It seems a bit odd to configure the potentiometer circuit so that the LED fires up only at the very top end like this (I know semiconductors do have different characteristics from filaments). One concern is that I'm testing it now with new batteries at 25°C, so the voltage is unlikely to be as healthy come midnight in January - if it's only just lighting at the top end now, might it fail to at all, in more taxing conditions?

[AdeKing]

I have a couple of Telrads and I think both of mine light up towards the end of the potentiometer travel range and don't kick in instantly when you turn the dial.

It looks like its going to be clear tonight so I'll have check for you when I go out later.

Ade

[John]

Talrads and the Rigel Quikfinder are calibrated for use in darkness, unlike other red dot finders, which are usually too bright at night even on the minimum setting. So it is very hard to see the Telrad / Rigel reticules in daylight even at full brightness but at night they are just right.

 

[Astro-Geek]

Mine too.....

As John and Ade have said, you can only notice the full range of dimming over the full range of the rotary control in darkness.

You'll find it's right round at the "lower" end when you're trying to centre a dim "fuzzy".

In fact you can buy a very useful add-on for them that adds the ability to flash on and off at variable rates.  This helps even more, allowing your eyesight to pick out very feint objects during the "dark" pulse and centre them accurately.

https://www.firstlightoptics.com/finders/telrad-pulsar-reticle-module.html

(shameless plug for FLO 🙂, who's price for it is very competitive, and quick delivery)

[niallk]

Sounds normal (I've 2).  I think they may use a logarithmic potentiometer.  Geared for use in the dark, where greater control for dimness is very useful. If using before dark, I'd normally have it on near full!

I've owned a Telrad for >10yrs, and never had an issue vs temperature.

Edited June 3, 2020 by niallk

[NGC 1502]

As above, my Telrad operation is the same, most of the brightness obtained close to maximum movement of the switch.

Brilliant piece of kit.

Ed.

[Alan White]

Same here, and I would add that in daylight you will not see it.
Go into a dark room, then try it, probably just night dim that does not show in daylight.
And check your batteries, they also give similar control issues as voltage drops on my Telrad,
just becuase they are new does not mean they are fresh and full.

Edited June 3, 2020 by Alan White

[Zermelo]

Thanks all, I won't be sending it back then.
To be clear, the batteries are definitely fresh (tested with battery tester) and I was trying it out in a pitch black room.
But I'm reassured that the operation seems to be typical of the brand - a logarithmic pot seems to be a good call, niallk.
And Astro-Geek, the pulsar add-on looks a really neat idea, I wish you hadn't mentioned it ! There are just too many gadgets in this hobby, and not enough pennies.

[Alan White]

Just now, Zermelo said:

There are just too many gadgets in this hobby, and not enough pennies.

You hit the nail on the head with that one 👍

[Louis D]

My original Telrad from 1998 worked well until the batteries corroded and somehow destroyed the rest of the unit despite splicing in a fresh battery holder.  It had a nice, smoothly increasing brightness when it was working.

I recently bought two used Telrads of much more recent vintage, and both behave as you describe.  They only turn on in the last few degrees of travel.  I would have to conclude that the potentiometer was changed out for a different unit over the past 15 to 20 years.

For everyone who chimed in to say theirs is working fine, in what year did you purchase your Telrad new?

[2STAR]

On 03/06/2020 at 09:22, Alan White said:

Same here, and I would add that in daylight you will not see it.
Go into a dark room, then try it, probably just night dim that does not show in daylight.
And check your batteries, they also give similar control issues as voltage drops on my Telrad,
just becuase they are new does not mean they are fresh and full.

I have aligned my Telrad to Scope in daylight, just hold your hand over the front of the Telrad and the circle appears, align & adjust it by looking through a couple of fingers keeping the outer circles showing on your fingers, until the center circle is in tune with your eyepiece. 

As for turning on, sometimes i have to rotate to full, back, and then full again to get the circle illuminated, also I have found it best to not have the circle on full power but adjust its brightness depending on which star you are aligning.

regard

eric

Edited June 12, 2020 by 2STAR