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New Red Dot Finder

JamesF

By JamesF
in DIY Astronomer

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JamesF

JamesF

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I had an RDF die on me recently and as I had a variable brightness red/green dot rifle sight sitting about doing nothing I decided to have a go at fitting it to a scope.

I took the mount from the old RDF, cut a piece of aluminium sheet to act as the mounting rail for the sight and screwed that flat to the top, then just bolted the sight on. Initial tests suggest that the light transmission is far better than the old RDF despite having two pieces of glass for the light to pass through. I wonder what the chances are of testing it "for real" before the end of the year though...

rdf.jpg

James

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  • 1 month later...
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JamesF

JamesF

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I have the same RDF and have been thinking of converting it to fit my scope, just wondering would it be better to have it closer to the scope I see your mount fitting is about 2 1/2 inches long.

It may be. I just used the original base from the dead RDF because that's what I had available.

James

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  • 8 months later...
bambuko

bambuko

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Hi James,

Have you had a chance to test this contraption yet?

I bought very similar one and so far found that red dot is too bright even on min setting (but this I am sure can be sorted out)

The main problem is some yellowy coating on the glass - might be OK in the daylight, but at night I can't see very well through it :embarassed:

BTW, here is mine:

IMG_7461.jpg

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JamesF

JamesF

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Hi James,

Have you had a chance to test this contraption yet?

I bought very similar one and so far found that red dot is too bright even on min setting (but this I am sure can be sorted out)

The main problem is some yellowy coating on the glass - might be OK in the daylight, but at night I can't see very well through it :embarassed:

BTW, here is mine:

Looks very similar indeed to mine :)

I've found mine to work ok, but the sky is very dark here.  I guess it's possible that the coatings on the glass might reduce the contrast too much otherwise.  It looks like it might be possible to replace the glass with something thinner and uncoated if the end(s) could be removed, but I've not tried to do that.

James

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Naemeth

Naemeth

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Looks very similar indeed to mine :)

I've found mine to work ok, but the sky is very dark here.  I guess it's possible that the coatings on the glass might reduce the contrast too much otherwise.  It looks like it might be possible to replace the glass with something thinner and uncoated if the end(s) could be removed, but I've not tried to do that.

James

Surely that would add to the cost though?

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JamesF

JamesF

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Yes... Mine doesn't have an orange coating, though it is clearly coated.  Holding it up to the window I can see a slight loss of light, but the view through it also looks a little sharper than without (it's not on a scope at the moment because it has been temporarily replaced by a finder-guider).

James

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bambuko

bambuko

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...I've found mine to work ok, but the sky is very dark here.  I guess it's possible that the coatings on the glass might reduce the contrast too much otherwise.  It looks like it might be possible to replace the glass with something thinner and uncoated if the end(s) could be removed, but I've not tried to do that...

Thanks James,

I have no problem with dark skies here (North Devon). I looked thorough it last night and it was not acceptable.

I wonder indeed if the ends can be removed?

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bambuko

bambuko

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Well... you win some, you loose some, and this one is definitely the case of £18 down the toilet.

I have managed to take it (partially) apart, using heat gun and brute force:

IMG_7466.jpg

It's the reflex mirror that's yellow coated and I guess there is little I can do about it, plus getting to the PCB for LED control seems equally impossible (must be also thread locked like everything else on this xxxx thing :evil:)

My advice would be - it is unuseable for astro purposes as delivered (because of the coating and brightness of the LED) and there is little that can be done about it easily.

So it is £90 for Baader 40mm Super Sky Surfer V if you want something like this and no shortcuts :huh:

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JamesF

JamesF

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Blimey, that's fairly bright :(

Is it not possible to remove that and reassemble the rest.  I'd have thought against a dark sky the reflection of the LED on the outer glass would still show up?

All credit to you for being prepared to get so aggressive with it.

James

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bambuko

bambuko

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It was pretty useless to me as it was :mad: so I had to have a go.

No it is not possible to use outer glass because the angles wouldn't work (the mirror is not straight - it is at a slight angle to account for LED being on the side at the rear) - at least I don;t think so...

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Naemeth

Naemeth

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It was pretty useless to me as it was :mad: so I had to have a go.

No it is not possible to use outer glass because the angles wouldn't work (the mirror is not straight - it is at a slight angle to account for LED being on the side at the rear) - at least I don;t think so...

I suppose at least you know not to spend any more time on it :).

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John

John

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I was thinking about getting something like that quite recently so it's good to have this information on it's suitability, or lack of it, for astronomy purposes.

Thanks for taking the trouble to examine one and post your findings - it's what make forums like this indispensable I think  :smiley:   

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JamesF

JamesF

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It does seem that the suitability of the finder can't be guaranteed.  Mine worked as well as any of my other "normal" RDFs when I was using it, but perhaps different vendors require different coatings or different optical standards or perhaps the design has changed.  Maybe I just got lucky.  Looks like it's an idea best avoided for the time being, in any case :(

James

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