Is this USB eyepiece camera a lemon?

[DaveC426913]

TL;DR Summary

Bought this item online. Does not give me an image. Don't know if it's me or if it's defective.

Looking for input on whether I've bought a lemon or if I just need some finesse.

For a lark, I bought this 1.25" eyepiece compatible webcam for my scope. I had low expectations but knew I could only find out by trying it.

https://www.amazon.com/gp/product/B08DP1YZP8/?tag=pfamazon01-20

First thing I notice is that there is no lens. I could reach in the pupil and touch the PCB.
I have no idea if that's normal or if I got a defective product.

I hooked it up to my computer (with a generic webcam driver I found online called Oasis.exe) and tried it out inside. It can detect light and dark (if I move it around), but is so far out of focus that I couldn't see a black barn in a snow field. It sure seems like it is missing a lens.

I tried it out on my 6" Newt and it's really little better.

I pointed it at a nearby streetlight to calibrate. In the diagram, you can see the streetlight in my finder (OK), in my 32mm eyepiece (OK) and in the webcam (not OK).

The webcam image is huge (at least, within the small 480x640 frame) but is so out of focus that it can't resolve anything. (I don't think *this* is because the streetlight is too close.) Also, the light is WAY blown out.

So I pointed it at a less bright subject (a lit window across the street) and could see nothing - completely black (with noise).

This makes little sense. It's blown out when pointed at a streetlamp but not sensitive enough to pick up a lit window - let alone Mars or a star.

And I don't understand why it's out of focus so badly. *Should* there be a lens in there?

 

[Drakkith]

With no lens, the imaging sensor should be placed at the focus of your telescope. This may or may not be possible depending on your scope. I would use an eyepiece and focus your scope on a distant target during the daytime and then replace your eyepiece with the imager. Move the focuser all the way in and then slowly bring it back out and see if your image gets better or worse.

 

[Keith_McClary]

focus of your telescope

So, for example, if he has a 30mm eyepiece the focal point is 30mm from the ocular (toward the scope and away from his eye).

 

[Drakkith]

So, for example, if he has a 30mm eyepiece the focal point is 30mm from the ocular (toward the scope and away from his eye).

For focusing on objects 'at infinity', yes. As objects move closer to the objective, the focus moves further back.

 

[davenn]

Summary:: Bought this item online. Does not give me an image. Don't know if it's me or if it's defective.

And I don't understand why it's out of focus so badly. *Should* there be a lens in there?

No, there shouldn't be a lens in there ... none of the astro-cameras have lenses
As Drakkith has said, this will be purely a focussing issue.
It's just necessary to experiment and find where that focussing point is.
It may be further out than an eyepiece or further in

It may be WAY further out and you need a short extension tube

 

[DaveC426913]

No, there shouldn't be a lens in there ... none of the astro-cameras have lenses
As Drakkith has said, this will be purely a focussing issue.

Good to know, thanks.

It's just necessary to experiment and find where that focussing point is.
It may be further out than an eyepiece or further in

It may be WAY further out and you need a short extension tube

Yeah, I tried that by hand. I'll try it again to confirm.

 

[DaveC426913]

One other question, while I'm experimenting:

Is a streetlight bright enough to burn out or at east damage the sensor?

Should I make an effort to find a dimmer target for my tests?

 

[russ_watters]

With no lens, the imaging sensor should be placed at the focus of your telescope. This may or may not be possible depending on your scope. I would use an eyepiece and focus your scope on a distant target during the daytime and then replace your eyepiece with the imager. Move the focuser all the way in and then slowly bring it back out and see if your image gets better or worse.

Yup. Focus and exposure are very tough to get right the first time (the focus point is not the same as your eyepiece -- it is probably "out" a little). If the image is too dim, you can't even see the image of what you are looking at out of focus. So you have to increase the exposure and then rack the focuser back and forth until you start seeing a giant blob, then reduce the exposure as you bring it into focus.

Dave; what are the specs on the telescope? Type, focal length and aperture?

 

[russ_watters]

Is a streetlight bright enough to burn out or at east damage the sensor?

Should I make an effort to find a dimmer target for my tests?

No. A streetlight is not very bright.

 

[DaveC426913]

Yup. Focus and exposure are very tough to get right the first time (the focus point is not the same as your eyepiece -- it is probably "out" a little). If the image is too dim, you can't even see the image of what you are looking at out of focus. So you have to increase the exposure and then rack the focuser back and forth until you start seeing a giant blob, then reduce the exposure as you bring it into focus.

Yeah, I'm pretty familiar with that. Now that I've eliminated some other possible problems, I'll be a lot more sure it's just a focusing problem.

Though it would not have occurred to me that an eyepiece would not come with its own barrel length built right in. But I guess that's what I get for spending $37 and buying no-name.

Maybe I can make one out of a toilet paper tube.
(Now I know what use a Barlow lens can be put to!)

Dave; what are the specs on the telescope? Type, focal length and aperture?

1000m Newt, 5.5" aperture on an equatorial mount. No training wheels (AKA electronic finder controller).

(A nice solid tripod with big fat legs (one of the reasons I bought this one).

But the gears have deteriorated. They're impossible to turn with the extension knobs - too much friction - I have to grab hold of the ... "knob nubs" directly. I've disassembled it and greased these parts but little joy.

And something has gone wrong with the Right Ascension coupling (the one with hours on it). It has become unseated. That's a bigger repair job.)

 

[chemisttree]

You can try to find the focal plane of the telescope with a sheet of paper. Aim at the streetlight with the focuser racked all the way in. Hold a sheet of paper over the eyepiece opening and move it back until the streetlight is in focus. That is the focal plane and the camera’s sensor needs to be right there. Might help to determine the right length of extension tube you need.

 

[DaveC426913]

Thanks.
Good idea. May be more convenient to move a piece of paper in and out than an eyepiece attached to my eyeball.

 

[glappkaeft]

I disagree that the camera focus should be further out than the eye piece focus. It will be further in and many Newton scopes (especially smaller ones) can't reach camera focus because often their focuser is optimised for visual use.

 

[DennisN]

Summary:: Bought this item online. Does not give me an image. Don't know if it's me or if it's defective.

Looking for input on whether I've bought a lemon or if I just need some finesse.

I hope you get it to work. I would like to hear a review of it.

 

[russ_watters]

Though it would not have occurred to me that an eyepiece would not come with its own barrel length built right in. But I guess that's what I get for spending $37 and buying no-name.

Maybe I can make one out of a toilet paper tube.
(Now I know what use a Barlow lens can be put to!)

No, cameras never come with extension tubes, because the focus location is always determined by the telescope. I have a a good refractor that came with removable extension tubes, a cheaper refractor that didn't, and a Cassegrain that doesn't need them because it has a lot of focus travel.

Newtonians are notorious for lack of focus travel though. It's probably because they want the focus to be close-in to keep the secondary mirror smaller. That means it sometimes happens that you can't get a camera close enough to achieve focus.

 

[russ_watters]

I disagree that the camera focus should be further out than the eye piece focus. It will be further in and many Newton scopes (especially smaller ones) can't reach camera focus because often their focuser is optimized for visual use.

Good catch. I've actually never paid close attention to whether it was in or out from an eyepiece because my scopes all need diagonals. So if I replace an eyepiece + diagonal I have to focus out to replace at least some of the extra focal length of the diagonal. But Newts are always straight out the side of the OTA.

...but if I add a focal reducer, it's definitely "in".

 

[DaveC426913]

No, cameras never come with extension tubes, because the focus location is always determined by the telescope.

I'm confused. All my eyepieces were used directly in the holder - they don't need any extension tube. And I've never seen or even heard of a scope needing an extension tube just to work with standard eyepieces.

So, if standard eyepieces work with all scopes, that would imply a standard extension tube should put a webcam within the scope's travel, regardless of the specifics of the scope.

 

[russ_watters]

I'm confused. All my eyepieces were used directly in the holder - they don't need any extension tube. And I've never seen or even heard of a scope needing an extension tube just to work with standard eyepieces.

Caveat first: @glappkaeft may be right that it is in-focus that is needed. If that's the issue, then it may not be solvable.

They don't - they need extension tubes (or more in-focus) for imaging. But whereas the manufacturer of your telescope knew you'd be using it for visual/with eyepieces, they didn't know you'd be taking pictures with it. Especially if it is an older or lower-end scope.

Newtonians are less forgiving than other types of scopes. For a refractor, they can just make the main telescope tube shorter, then add extension tubes on the back.

So, if standard eyepieces work with all scopes, that would imply a standard extension tube should put a webcam within the scope's travel, regardless of the specifics of the scope.

There's no "standard" for eyepieces. Here's a thread on another site discussing it, including a list of eyepieces a guy tested, with a total of 35mm difference in focus location:
https://www.cloudynights.com/topic/310666-master-eyepiece-focus-distance-chart/#entry3990093

A telescope manufacturer will know for sure that the eyepieces included in the kit will work. But different eyepieces have different focus points. And then adding a barlow or focal reducer changes it again. And cameras are different too. And then when you get seriously into astrophotography, you'll add a filter wheel... and maybe an off-axis guider...

 

[russ_watters]

Celestron's take:

Back focus is the distance from the end of your eyepiece drawtube to the focal plane of your telescope. It varies greatly depending on the type of telescope:

• Schmidt-Cassegrain telescopes (SCTs) typically have generous back focus distances of approximately 5 in. Similarly, Maksutov-Cassegrains (Maks) also have large back focus distances.
• Newtonian reflectors have much smaller back focus distances, sometimes as little as 1-2 in.
• Refractors usually have large back focus distances; their long drawtubes can travel well inside focus, too.

Back focus directly impacts your ability to use accessories with your telescope. With limited back focus, you may not be able to use Barlows, focal reducers, binoviewers, SLRs, and 2 in eyepieces. The design most heavily impacted is the Newtonian due to its short back focus; the only two possible fixes are to move the mirror and its cell up in the tube and/or get a low-profile eyepiece focuser.

Combining accessories can also cause back focus problems. Focal reducers also reduce back focus and, when used for prime-focus photography with an SLR, there may not be enough back focus left to accommodate the approximately 50mm needed for the camera body. This is true even with an SCT's long back focus distance. The M42 Spacer Kit can adjust back-focus between your camera and telescope for the best astroimaging results.
[continues]

https://www.celestron.com/blogs/kno...avily impacted,a low-profile eyepiece focuser.

 

[Keith_McClary]

I found:
Problems Focusing A Newtonian Telescope With a Camera

 

[DaveC426913]

Thanks everyone. This is a lot to chew on.

This is all good news because it means the problems I am having are due to inexperience with astrophotog (something that can be fixed!) and not crummy equipment (which can't).It wasn't so much the Jovian-Saturnian conjunction that was driving my timeline - it was actually Mars being high in the sky. So the fact that it looks like it's going to be clouded over tonight isn't really a tragedy.

 

[chemisttree]

And there won’t be any clouds between you and the streetlight. Check to find out what problem you have tonight, eh? Remember to rack the focuser all the way in before you start. If you can’t get a focused image on the paper by moving out the focuser or paper, you are out of luck unless you want to build a 1:1 relay lens to insert into the drawtube.

 

[collinsmark]

When debugging this issue, I suggest trying to focus on some distant, terrestrial target in the daytime. Try a distant treetop or a telephone pole. (Do not use the Sun, or anything near it, as the target.)

Once you have things set up and roughly pointed at the target (as best you can), adjust the camera gain and shutter speed (in whatever software program you are using to control the camera) such that image on the screen is brighter than completely black, yet darker than completely white.

The point of the above is to rule out problems with exposure. It could be that one of the reasons you weren't able to see anything is the exposure was too short. Adjusting the exposure for daytime, terrestrial objects is way, way easier than trying to get that figured out with celestial objects. (Of course you'll have to re-adjust that later for each and every celestial object; it's just way easier to do in the daytime, for preliminary focus debug.)

Once the exposure is somewhere in-between black and white, try to get the object in focus. (Now would be a good time to double check that the scope is pointed at an actual object and not an empty patch of sky.) Even if you can't achieve focus, you should at least be able to tell if the object's focus gets slightly better or slightly worse as you adjust focus.

If the ideal focus is farther out, you might be able to achieve focus by pulling the camera out of the eyepiece holder a little bit, and re-tightening the thumbscrew with the camera a little "out."

If the ideal focus is farther in, as in closer to being inside the telescope tube, things get more complicated. In that case, as previously mentioned, it might be possible to achieve focus raising up the primary mirror by adjusting all 3 collimation screws in the same direction, or by getting a lower-profile focuser.

As Russ and Drakkith mentioned, when focusing on infinity, you'll need a smidge more inward focus than you'll have when focusing on a terrestrial object. But this daytime procedure should at least get you in the ballpark.

 

[DaveC426913]

When debugging this issue, I suggest trying to focus on some distant, terrestrial target in the daytime. Try a distant treetop or a telephone pole. (Do not use the Sun, or anything near it, as the target.)

Yeh. that occurred to me.

Once you have things set up and roughly pointed at the target (as best you can), adjust the camera gain and shutter speed (in whatever software program you are using to control the camera)

Yeah. I was wondering about that. I'm just using a generic driver I downloaded called Oasis.exe and I looked for some sort of the 'gain' setting but no joy.

Next time I'm out, I'll do the checks mentioned.And while I'm at it, it's been a decade or two since I collimated my scope - long enough to lose my original collimator - so I bought a new one.

 

[sophiecentaur]

Newtonians are less forgiving than other types of scopes.

Newtonians all have a problem because of the secondary mirror. The secondary mirror will ideally have a diameter so that it intercepts a minimum of the light falling onto the primary reflector (i.e. the reflector needs to be small and in just the right position fore and aft). That means the overall focus has to be as close as possible to the barrel of the OTA. Until very recently, astrophotography was not the primary use of (amateur grade) scopes and the focuser tube would be of length appropriate for eyepieces. The primary image is formed in close and the film / sensor in a Mirrored SLR is embarrassingly far back. SLRs were never designed with this use in mind. It's a bit of a double whammy.

Afaik, the secondary reflector in most Newtonian is plane, which limits the possible focus range. If the secondary reflector is made (Edit concave convex)(expensive and probably 'tied' to the primary design) then the focus can be taken further out of the side tube. My two Newts (an 8 inch and an old 10 inch) both happen to allow my Pentax DSLRs to focus but other SW owners claim that theirs don't do it. I do remember removing a short length of extension tube that I found in the 8 inch Dob so perhaps other people never thought of doing this. (Automatic use of basic school optics helped me) Also, the focuser on the 10 inch is a replacement with more movement.

 

[chemisttree]

Did you ever get it to work?

 

[DaveC426913]

Haven't had the chance yet.