Seek 2x tele doable? - Page 1
Forum section: electronics / general

author: pauledd
author_rank: Regular Contributor
timestamp: June 30, 2018, 06:38:52 am
content: HiI stumpled upon various posts in this forum of Uho's DIY lenses. He has a goodinfo pagefor that and I really would like to make such a magnifying lens too, BUT not for ~200€!So I just wonder if this could be done with this cheapo lenses, assuming that they are plano-convex, or meniscus at least:https://de.aliexpress.com/item/China-ZnSe-Co2-Laser-Focus-Lens-12mm-Diameter-FL38-1mm-1-5inches-For-CO2-Laser-Engraving/32812296054.htmlThen I just for fun put a d=20mm/f=76,2mm and a d=12/f=38,1mm lens in this simulation page.So the overall length of the "scope" would be ~10cm, I used a 5mm diameter for the Seek lens.Do you think this is doable? Of cause I would not expect super sharp images...And another question: To get proper focal length of the lenses that I draw on that page, I first set the refractive index of the lenses to 2.39 for ZNSE@~12µm, then I manipulated the bend-side of the lenses so that the beams from a light source meet at the focal length from the specs.The question is now, as others mentioned here, they would rather use a Germanium lens because of its higher (~4) refractive index to make the lens shorter... Butthats what I dont understand, if you use a GE lens the focal point would be closer to the lens... shure, but dont you choose the lens on its focal length? So should'nt make a 70mm GE lens no difference to a 70mm ZNSE lens with the only difference that the GE lens would have a much more "konvexetivity"

author: Uho
author_rank: Frequent Contributor
timestamp: June 30, 2018, 07:34:52 pm
content: Under such a scheme, you will receive a toy. It will be something that can be seen in the center and that's all. Great distortion will not allow to reduce the rays. This is very noticeable at low temperatures. I gave a link to a single non-commercial lens project. He is not perfect. I make my lenses out of three lenses. Two of germanium and one of zinc selenide. The third lens eliminates distortion. But this is a commercial project.

author: IwuzBornanerd
author_rank: Frequent Contributor
timestamp: June 30, 2018, 08:05:16 pm
content: If you don't mind popping the thing open, you can kluge in a direct replacement for the Seek lens. Getting a mere 2X might be difficult, though, as the lid might prevent you from getting it close enough to the sensor. A 20mm dia., 25.4mm FL ZnSe lens will get you about 4X over the Seek lens and about the same F-stop, and if the Pro has the same size mount as the XR you could use a common webcam lens barrel for your kluge like I did on my XR. I have not taken my Pro apart so I don't know if the lens mounts are the same size. This might still be a "toy", though. I posted some moon shots I got with a 100mm FL lens over on page 5 of the thermal imaging gallery; you can look at those to get an idea of the capability.

author: pauledd
author_rank: Regular Contributor
timestamp: July 01, 2018, 08:09:57 am
content: no, I am not willing to crack my seek open yet, just enjoing I fully working device, maybe in 2 years...

author: pauledd
author_rank: Regular Contributor
timestamp: July 01, 2018, 08:21:54 am
content: Quote from: IwuzBornanerd on June 30, 2018, 08:05:16 pmDid you remove the stock Seek lens?QuoteWell I cannot really judge your lens upon that images, for me they look like as taken with the wrong settings... the moon is not an ideal object for that, couldnt you have just use any urban area portait with greyscale pallette, your images suffer from the pallette and over-contast scene with plain sky and BÄÄÄÄÄM MOONIll maybe order thos two lenses I mentioned, as toy... if they really do not work well I can still use them apart as macro lens... I think

author: IwuzBornanerd
author_rank: Frequent Contributor
timestamp: July 01, 2018, 08:09:09 pm
content: Yes I removed the stock lens; It's sitting there next to the camera in that photo. And I understand your reluctance to open the camera. I had other reasons to open 2 & don't want to open the other 2. :~)I understand your point about the moon images; you need something that shows how clear the image is. I'll need subjects far away but not that far. I hope to post some images after I finish recovering the "good" software I lost when I broke the uSD card it was on (and had not been "backed-up" in 4 months!...for no reason). It will be a while yet.The cheap lenses should be good for macro; that's what other forum members use them for.

author: ikrase
author_rank: Regular Contributor
timestamp: July 11, 2018, 04:56:18 am
content: I wonder how a 2x or 3x reflecting telescope would do. Don't know much about optics but it seems like precision CNC machined mirrors made of hardened steel and gold-plated might work well.What sort of SD card / what device was it in -- a smartphone, or some kind of raspi/beaglebone / x86 tablet?

author: pauledd
author_rank: Regular Contributor
timestamp: July 11, 2018, 06:01:32 am
content: I have a 600mm F4 newton telescope and I will try the next weeks when I take it inside for cleaning to put my seek on it, but I somehow doubt that it will work, those mirrors are curved for light... I dont know how thermal rays? would differ in wavelength to normal light

author: ikrase
author_rank: Regular Contributor
timestamp: July 11, 2018, 07:35:24 am
content: Mirrors are the same for every wavelength! So no chromatic aberration! However, mirror coatings may matter -- gold is favored for IR if I am not mistaken.The other problem is the eyepiece. I *think* that typically a telescope without an eyepiece is used for a lensless focal plane array sensor and a telescope with an eyepiece -- i.e. at least one germanium or ZnSe lens -- is for a complete camera like a human eye or Seek. I've been trying to figure out if you can make a purely reflective eyepiece.

author: IwuzBornanerd
author_rank: Frequent Contributor
timestamp: July 11, 2018, 07:49:11 am
content: Quote from: ikrase on July 11, 2018, 04:56:18 amWhy do you ask/I'm developing code on a Raspberry Pi Zero. The micro SD card (uSD) protrudes from the end of the Pi so when you package the Pi in a tight case with the card inserted in a slot in the case & then yank the Pi out without removing the card first you end up with a 2-piece uSD card.This time around I'm typing & saving it on my laptop first...

author: Vipitis
author_rank: Frequent Contributor
timestamp: July 11, 2018, 09:42:39 am
content: You don't need an eyepiece if you build your telescope to be prime focus with the sensor. Given that you need to remove all refracting lenses.The issue you will face is the amount of light you get with an F4 or even F6 scope. Telescope mirrors are usually coated glass, but only aluminium which is 86% reflective to LWIR(this changes with other anti reflective coatings). Uncooled microbolometer need more light. Lenses are usually f/1.0 or f/1.2;You can buy precision mirrors with goal coating from Edmund or other optics suppliers - but they are expensive. Even a lower accuracy gold goated 50mm F2.0 mirror with 100mm folcal length is 59€ + shipping. And that is tiny. I am not sure if it is even possible to hook that up to a Newtonian design without obstruction of the secondary mirror to lose even more light. The goal was to watch the moon with a 80x60 Lepton - but since it's an afocal build I need to change my design again. I have yet to find a good optics simulator that I can use in Fusion360 and develop the 3D models I wanted to print.I have seen people hookup their thermal cameras to their Newtonian telescopes but the results were really demotivating.

author: pauledd
author_rank: Regular Contributor
timestamp: July 11, 2018, 02:14:46 pm
content: Quote from: Vipitis on July 11, 2018, 09:42:39 amWhats wrong with this chart? What ever protected/enhanced aluminium means...

author: ikrase
author_rank: Regular Contributor
timestamp: July 12, 2018, 02:35:17 am
content: They have coatings over the metal layer - either extra-reflective or physically protective.

author: pauledd
author_rank: Regular Contributor
timestamp: July 12, 2018, 05:31:02 am
content: Okay, thanks, I just saw that chart is from edmundoptics...

author: ikrase
author_rank: Regular Contributor
timestamp: July 12, 2018, 06:06:02 am
content: As to why I ask about the SD card -- I'm investigating the potential to build a self-contained scope out of a seek compact and a raspi / intel compute stick / who even knows and I'm interested in what kind of computers everyone is using.

author: IwuzBornanerd
author_rank: Frequent Contributor
timestamp: July 12, 2018, 08:49:40 am
content: Quote from: ikrase on July 12, 2018, 06:06:02 amSo maybe you are thinking of something like this; OR perhaps more of a monocular format? I set the thing up like this a few days ago thinking I could grab a few sample images with the 4x lens for @pauledd, but as if to prove my point about the software, I could not even do that.

author: ikrase
author_rank: Regular Contributor
timestamp: July 13, 2018, 07:13:30 am
content: I've been imagining something somewhat monocular format (probably using a removable display-loupe) and being able to accept a long-distance lens or use the native Seek lens.I've investigated using a tiny Android smartphone/tablet w/ native Seek app (hard to find tiny tablets, hard to control Seek any way other than touchscreen), using a Raspi (need an appropriate small display, unclear if appropriate software exists, maybe too low power), using an Intel Compute Stick or other tiny x86 computer (may use way too much power...)

author: IwuzBornanerd
author_rank: Frequent Contributor
timestamp: July 13, 2018, 08:02:04 am
content: Quote from: ikrase on July 13, 2018, 07:13:30 amMaybe I shouldn't continue off topic, but you might be interested to know that what is in the box pictured above is a Raspberry Pi Zero with a 3.5" touchscreen, 4 port USB hub, Real Time Clock & 4 AA Eneloop cells. It draws about 450mA while running the Seek. I have gone to extremes to get it to display 8fps out of the non-pro Seeks, so this is probably the minimum usable CPU. I use SDL2 for the graphics & found out too late that SDL2 does not run well on a Pi under X, so this runs under console login, no window system. The Pi2B does better, of course, with its 4 cores.It has been my intent to detail this project on the "Projects" section of this forum, once it is complete...

author: eKretz
author_rank: Frequent Contributor
timestamp: July 13, 2018, 06:29:45 pm
content: I have been looking into possibly making a tele lens for my cam also but from what I've been reading, it may be difficult to make something that doesn't have a pretty good amount of distortion around the edges. Most cameras these days are using aspheric lenses to correct that distortion, and those are not cheap and are often shaped specifically to the system at hand. If you use larger lenses so that all of the work is done in the center of the lens you may or may not get a good image. Expensive experiment though.

author: Bill W
author_rank: Super Contributor
timestamp: July 15, 2018, 11:12:28 am
content: Generally the longer focal lengths are 'easier' as the rays are not so convergent and a single spherical element will not suffer that much. It is short focal lengths and high angles that get difficult, especially if you need space for a shutter in there.Aspherics can also reduce the number of elements in the lens unit by combining the effects of several simple spherical surfaces that are often needed for a flat, evenly illuminated image plane and less distortion.Bill

author: eKretz
author_rank: Frequent Contributor
timestamp: July 15, 2018, 04:33:14 pm
content: Right. With most of this discussion being centered around a simple 2 element lens I figured that was relevant. There's a pdf floating around from a guy who made a 2 element germanium tele lens and the distortion is fairly visible.

author: ikrase
author_rank: Regular Contributor
timestamp: July 16, 2018, 05:13:15 am
content: Distortion is one thing. Aberration or coma is another. Is it hard to have a lens that distorts but doesn't do anything else bad?