Reducing red dot finder brightness

[cuivenion]

I thought I'd take a punt on this:

https://www.amazon.co.uk/Pinty-Tactical-1x40mm-Reflex-Riflescope/dp/B06XT11W79

Its fits the 11mm rail from  my broken skywatcher finder, so no problems there. The good points are the build quality is good and it comes with lens caps. The cons are that the it dims the stars when you look through it, and worse of all the lowest setting for the red dot is way too bright for astro use.

I'm guessing there's not to much I can do about the stars being dimmed but if anyone has any advice on how to reduce the red dot led output it may be useable.

[Dr_Ju_ju]

Depends on how brave\determined you are.

If it can already be adjusted, then it should be possible to modify it, by upping the value of some(?) resistors, thereby lowering the voltage\current fed to the LED, creating the desired effect. But you'd have to dismantle the device to get at the electronics....

[Davey-T]

Cheap ones have a variable resistor so easy to add a suitable resistor in line with it.

Dave

[cuivenion]

I was wondering if there was a lower voltage battery that would fit in the compartment, it takes 2032's. I wouldn't mind fitting an inline resistor although I admit I've no idea how to do it. I don't mind learning though.

[NGC 1502]

 

Indeed, some cheaper RDFs don’t go dim enough.  Probably the ideal solution is an electronic one. However I’ve had good results from painting red nail varnish on the light source. Allow each coat to dry before adding more.

If you’re of male gender, you risk a sideways glance in the shop if you buy nail varnish.....?

I’ve also tried placing transparent red sweet wrapper in front of the light source, but that’s no good, just gives a huge blurry blob. Better is transparent red sheet.

More money, but Telrads, Rigel Quickfinder and those better quality metal RDFs do go dim enough.

HTH Ed.

[cuivenion]

It has parallax unfortunately so essentially useless for astro. Looks like I'll have to move it on to an airsoft user.

[dlastro]

I have struggled with this problem with red dot finders for years. As has been mentioned, most RDFs are repurposed gun sights. As such they have an interference coating on the concave lens at the front that both enhances the reflection of the red LED light and dims the light from the target star.  This is exactly what we don't need in an astronomical finder. The problem could be solved if the importers of RDFs stipulated that the lens NOT be coated and that a higher resistance potentiometer be used.  My first RDF did not have a coated lens and the dimmest setting was very dim. 

If you want to dim the light of the LED either of the two methods suggested will work, introducing another resistor into the dimming circuit or putting a transparent cyan (minus red) filter in the LED light path.  Red filters are transmit red light and will not dim it.  Photographic color correction filters such as a CC50 or CP50 filter are ideal.  More than one layer may be necessary and requires a bit of experimentation. The filter should be cut to fit and placed in the housing at the back of the finder where the red LED light is emitted so that it interrupts the beam. I folded mine into a "U" shape and inserted it into the channel in the forward part of the rear housing. A piece of tape holds it in place. This should work with other RDF designs proved the filter can be placed in the LED beam.  Unfortunately nothing can be done about the coating on the lens short of the importers stipulating RDFs without coated lenses.  I have not experimented with the resistor modification since inserting a filter is much easier.