Very small DIY erecting monocular

[angryowl]

Hi to all again

Being bored with some of my other projects(read that: there's major issues with them), I'm taking a "break" and resurrecting an old one which I've always wanted to start work on.

Back in 2016 I purchased from Surplus Shed in the US a small Beseler objective and two other unknown origin eyepiece lens assemblies. The objective sadly seems to no longer be available at Surplus shed but here's a link of it from the WayBack machine. It's a work of art, long FL with amazingly crisp and well colour corrected images given it's size. Front and back element diameters are both 8mm making this roughly an F15 objective, which explains the crispness of the images and overall good quality of the image.

At the same time I also got two of these. When they all arrived the objective was in pristine condition however as to the two eyepiece assemblies, well they were in overall awful condition. Brass casing was all green and corroded, on both lenses the front and back elements had grit dust and large deep scratches in them. Don't get me wrong I'm not slagging Surplus shed off, these things can happen and for $5 each you can't really say much. Anyway opened them up and cleaned them to the best of my abilities and they work well enough as they are now. 

What I wanted to do with them was a very small erecting monocular. Back in 2016 did a few tests to prove it would work and it did, however due to the horrible quality of the two eyepiece lenses I shelved the project.

A few days ago went back to Surplus Shed explaining the situation and they were very apologetic about it all and were genuinely sorry. Anyway I mentioned that I'd be ordering two more in the near future and need some assurance that these one will be of reasonable quality optically that is. They assured me they will be scrupulously inspecting each of them before shipping them off so I'm happy with that. 

I will post some pictures of the Beseler objective later today, it's got a nice screw section at the end making it easy to mount. Don't yet know how I'd mount all of these and what materials I'll use for the tubes.

When I did my testing using the two objective lenses I got no chromatic aberration whatsoever and the image was very sharp. The fun thing is that if I want to I could make this zoomable, as adjusting the distance between the erecting element and the eyepiece and then refocusing provides the potential of having a zoom function.

Of course due to the small aperture of the objective lens this is not intended for night time use, with the only exception being the Moon as it gave some nice views of the Moon at higher magnifications. This would be used mainly for daytime terrestrial viewing.

[angryowl]

Actually something I've been thinking of for a long time would be to replace the erecting lens with a single or doublet lens. I would imagine this would still work just fine, my only concern is would it impact the overall quality of the image in any way? The only reason I'm thinking of doing this is to try to use less glass as each piece of glass even if it's fully multi coated and what not is still absorbing light. So by having less elements for the erecting lens rather than the four elements as found in the eyepiece lens should in theory bump up the overall light transmission by a bit? 

[happy-kat]

This reads an interesting project, I look forward to your progress and pictures.

[angryowl]

Thanks happy-kat. Had a closer look at the Beseler objective and it looks like it's just an air-spaced doublet which is interesting, I thought it would have more elements inside. In the pictures the elements look a bit smudged/dirty but in reality inspecting them in bright light they look immaculate. Anyway pictures as promised including the two eyepiece assemblies:

 

[angryowl]

Looking on the SurplusShed's website I found several achromatic lenses all 11mm in diameter which is pretty much the perfect diameter. There's no description for the lenses apart from the FL, diameter, type and whether they're coated or not. That being said I assume "achromatic" means it's a doublet, right as it couldn't really be a singlet, could it?

Anyway the ones I found are the following:

       Type      Diam           FL        Coated

1.  ACH    10.9 mm    37 mm    Yes
2.  ACH    10.9 mm    19 mm    Yes
3.  ACH    10.9 mm    18 mm    Yes

Judging from my tests with my two eyepiece lenses which have 10mm FL, I'd say from the above selection the 18mm or 19mm FL ones would work best as an erecting lens rather than the 37mm FL one?

Need a bit of help from the optics experts on here. First, does achromatic lens usually mean doublet? And second would one of the 18mm or 19mm FL lenses I mentioned actually work equally or better as an erecting lens than the 4 element 10mm FL eyepiece assembly?

Thanks in advance for any help provided.

[Helen]

Interesting! Do you reckon you could use a camera instead of eyepiece and make a little electric microscope?  I've been looking at the little handheld microscopes, but then thought why couldn't I utilise my ASI planetary cam and just add a lens and light...?

Helen

[angryowl]

1 hour ago, Helen said:

Interesting! Do you reckon you could use a camera instead of eyepiece and make a little electric microscope?  I've been looking at the little handheld microscopes, but then thought why couldn't I utilise my ASI planetary cam and just add a lens and light...?

Helen

Hi Helen,

Absolutely, you could build a microscope out of this. 

In fact you've made me curious and did a quick test with my qhy5l-ii and the two eyepieces I have. This was just a random distance between the two eyepieces but if you lower the distance you get less magnification and if you increase it you get higher magnification.

This is the key on my keyboard I used as a "sample"

The lens arrangement

The results

Remember this was handheld and the eyepieces are dirty and scratched. This is 2ms exposure with 30 gain on the QHY.

I'm sure you could purchase two better quality lenses and build a proper electronic microscope with varying magnification. You're actually tempting me to add this to my project list 

[angryowl]

1 hour ago, Helen said:

Interesting! Do you reckon you could use a camera instead of eyepiece and make a little electric microscope?  I've been looking at the little handheld microscopes, but then thought why couldn't I utilise my ASI planetary cam and just add a lens and light...?

Helen

Of course you could also go the route of adding a lens in front of your camera, find the right distance, mount it and you've got your microscope. This however would be just a single magnification.

Actually you could have a system where you switch different FL lenses in front of the camera to get varying magnifications.

[angryowl]

Trying to calculate minimum and maximum practical magnifications with all potential erecting lenses. 

Post number three here and this will definitely help. 

The other thing I'm thinking of is, should it be 3D printed or use other materials like aluminium piping. From what I gather the erecting lens does not move, when changing the magnification factor the eyepiece goes in and out and then of course focus would need to be adjusted accordingly again via the objective. So two moving cylinders on a "static" middle one which contains the erecting lens. 

I think I'll purchase multiple achromatic doublets and two of the same eyepieces I already have from SurplusShed as they're relatively inexpensive.

I'll do some calculations and maybe produce a 3D design of the entire monocular and give 3D printing a shot first.

[angryowl]

Ordered the two eyepieces again from SurplusShed and two other achromats; 10.9mm Dia x 18mm FL and 9.9mm Dia x 20mm FL. It's good tom have that choice in diameters, 10.9 vs 9.9 as I haven't yet figured out how the casing would be constructed plus I have the two eyepieces available which if I sand the threads down I'm left with 9.8mm dia brass cylinders.  

Also couldn't resists for $10 I also got a 45 degree erecting prism With a focusing mechanism. Here's the item.

[angryowl]

After payment of a hefty customs charge the items have finally arrived. The 10.9mm achromat is spotless as is the 45 degree erecting prism unit.

However after asking Fred to inspect the two elements carefully before shipment, I still received a pair of horrible quality pieces of glass. Have emailed Fred about this...

I know brass (which I'm assuming is the casing material?) corrodes and that's fine, but looking at the description of the item on their page, no where do they mention they are in pretty bad shape.

 

 

Also the 9.9mm Dia achromat also shows signs of coating scratching or damage, not sure on this one, I still think it's usable the way it is, maybe I'm just being picky?

 

Last time I received the two brass lens assemblies I took them apart (obviously no damage whatsoever to the two internal elements was observed), set all lenses and spacers aside, then proceed to carefully clean the brass barrel. Then they were reassembled and looked much better but of course plenty of dust was trapped inside and the front and back elements still had the scratches on them so in the end I couldn't really use them. This time, if I'm going to attempt a cleanup, I won't disassemble the barrel. I'll await for Fred's reply and take it from there I suppose... 

 

[souls33k3r]

That is just disgusting mate. 

[angryowl]

1 minute ago, souls33k3r said:

That is just disgusting mate. 

Well, I mean, errors like these can happen, you know sending off a bad batch or something like that. What I want to know though is if SurplusShed actually have in stock some usable L1620 lenses!!!

[souls33k3r]

6 minutes ago, angryowl said:

Well, I mean, errors like these can happen, you know sending off a bad batch or something like that. What I want to know though is if SurplusShed actually have in stock some usable L1620 lenses!!!

Errors like these should "not" happen. Period! Unless they have blind employees packaging the stuff for them.

[angryowl]

8 minutes ago, souls33k3r said:

Errors like these should "not" happen. Period! Unless they have blind employees packaging the stuff for them.

Yeah I suppose you're right, and the whole hassle with this coming from the US make it even worse. I'll update once Fred replies. 

[souls33k3r]

3 minutes ago, angryowl said:

Yeah I suppose you're right, and the whole hassle with this coming from the US make it even worse. I'll update once Fred replies. 

especially when you're the one having to pay for the custom charges for "damaged" goods. Yes mate, keep us posted.

[angryowl]

Just got a reply back from Fred, paraphrasing:

"Yes they are all the same.  We cleaned the ones we sent you the best we could and I checked the optics (although not with a magnifying glass) and they both looked ok to us."

They'll also issue me with a refund for the two lenses. So I guess that's that! If that looks like an "ok" piece of glass then I must be bonkers!

I just wish they'd put in a little hint on the item page, like in the description or something similar, but oh well, such is life.

[Astrobits]

Have you considered irpoyser.co.uk for surplus optics? A bit more expensive on list prices but with no tariffs etc. might be useful.

Nigel

[angryowl]

2 hours ago, Astrobits said:

Have you considered irpoyser.co.uk for surplus optics? A bit more expensive on list prices but with no tariffs etc. might be useful.

Nigel

Looks promising, never heard of them, thank you. I'll be contacting them to see if they have something in the range of the diameter I'm looking for.

Thanks again for the link!

[souls33k3r]

On 4/27/2018 at 18:53, angryowl said:

Just got a reply back from Fred, paraphrasing:

"Yes they are all the same.  We cleaned the ones we sent you the best we could and I checked the optics (although not with a magnifying glass) and they both looked ok to us."

They'll also issue me with a refund for the two lenses. So I guess that's that! If that looks like an "ok" piece of glass then I must be bonkers!

I just wish they'd put in a little hint on the item page, like in the description or something similar, but oh well, such is life.

They clearly don't want to do business any more. Typical traits of shady businessmen.

[angryowl]

1 hour ago, souls33k3r said:

They clearly don't want to do business any more. Typical traits of shady businessmen.

Well, I ordered from them in the past and they were always spot on and fantastic to deal with.

I'm not happy with the lenses, but I'll be refunded for them which is more than I can ask given the circumstances. 

[angryowl]

Ha! Having a closer look at the other lens, the one in the black casing in the pictures above, turns out it's a singlet when I ordered a cemented doublet in no casing. Have any of you ever heard of a achromatic singlet? I sure haven't.

Of course asked for refund for this as well, but at this point to tell the truth I am annoyed and frustrated that I now have to go somewhere and look for another source as I was sent the wrong item!

This is what I was supposed to receive!

[souls33k3r]

18 minutes ago, angryowl said:

Ha! Having a closer look at the other lens, the one in the black casing in the pictures above, turns out it's a singlet when I ordered a cemented doublet in no casing. Have any of you ever heard of a achromatic singlet? I sure haven't.

Of course asked for refund for this as well, but at this point to tell the truth I am annoyed and frustrated that I now have to go somewhere and look for another source as I was sent the wrong item!

This is what I was supposed to receive!

Naaaah! i'm pretty sure you clicked on the rotten one full of dust motes and disgust ... surely this can't be right

[angryowl]

1 minute ago, souls33k3r said:

Naaaah! i'm pretty sure you clicked on the rotten one full of dust motes and disgust ... surely this can't be right

Yeah that must be it, thought to myself it adds value to the final image in the scope, sort of like a special effect type of thing!

[angryowl]

An update on this, Fred replied and confirmed that the lens I received in the black barrel is indeed a doublet, and that they were just using a generic photo on their website. The correct image is now up and looks exactly like the one I got and Fred assures me it's a doublet. Then this one's one me and it's perhaps my eyes that are failing then!

Anyway we've gone off topic with this issue with the provider.

A couple of updates on the actual progress of the project.

• Did a test with an LED light lighting some writing the right way up then started trying combinations of all lenses to see which produced the best result.
• Clear winner was the 10.9mm achromat as the eyepiece, the 9.90mm black barrel lens as the erecting lens and of course the Belseler objective.
• Tried the 4 element brass lenses both as eyepieces and erecting elements and both light transmission and quality of image were horrendous, though the field was indeed flat and colours were beautiful
• The winner combination does not have a perfectly flat filed and colour correction is good, not fantastic, but light transmission is fantastic so that comes in handy with such a small diameter objective.

Next step is some rolled paper tubes to simulate a fully working version of the monocular and test it properly on some distant objects.