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DSLR lens w PVS-14 : backspacing?


vineyard

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Hello,

In the spirit of constant tinkering, I'm trying to see if I can use an old prime lens on the front of my PVS-14.  I've mounted the lens on the front of an old one of these ZWO adapters and have an adapter from RAFCamera that converts the PVS-14 objective into a T2 female.  The RAF adapter has about 6mm optical train, and roughly measuring the distance to the front of the NV lens suggests about 6-8mm there - so a total of about 12-14mm: ie, within the 12.5mm-17.5mm optical length that these ZWO adapters assume on the back end.

But I couldn't find focus (trying a bunch of different spacers) - couldn't even see out of focus stars.  I'm probably doing something very silly, but not sure what?

(The logic I'm trying to use is the one described in this diagram from TV but taking the EP out: ie, get the DSLR lens to form the image focal plane on the NV objective.  I'm sure folks will have tried this?)

Thank you!

Vin

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Hi Vin — It sounds like you’re trying to use a camera lens afocally in front of the PVS-14 objective. Your PVS-14 needs parallel light beams hitting the objective (you can see this in the diagram you linked) to work afocally, but the camera lens is producing a light cone (like the telescope is in the diagram), so you won’t ever be able to reach focus the way you’ve been trying. Since you’re tinkering … if you could somehow add an eyepiece between the camera lens and the PVS-14 objective, this might work. Otherwise, you need a different night vision device, like a Mod-3, that has a removable objective lens. 

Steve

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@vineyard

1) Excellent re the tinkering. I think it’s very worthwhile since I read stuff like the 6-12 nm ha filters being best but after trying a 12,7,6,5 and 3nm filter it’s clear that for me the 3 is the best to bring out the most nebulosity with nv. So definitely keep on experimenting to work out what it best for your personal preferences.

2) here’s a cn link that may help you?

https://www.cloudynights.com/topic/730773-why-doesnt-a-camera-lens-work-a-focally/

3) Finally, (and probably least important), I’ve been able to try a camera lens and 75mm c mount lens in prime mode with my ovni-m. Both approaches disappointed me particularly on emission nebulae where with an ha filter both lens really struggle to show the nebulosity compared with my specialist 3x afocal nv lens. So I’ve stopped messing around with the camera lens as I’m happy with my afocal 3x lens setup. It perplexes me quite a bit about the positive comments made on cn re using camera lens/c mount lens with ha filters and nv as I just couldn’t get them to work at all well…

Edited by GavStar
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39 minutes ago, GavStar said:

I’ve been able to try a camera lens and 75mm c mount lens in prime mode with my ovni-m

Is it the computar f2.8 lens? If so, it's gathering about 1/4 the light intensity of a specialist 3x afocal lens (at f1.5), which might be why you're getting those results. 

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Thanks @stnagy I wouldn't have appreciated the (important) subtlety of parallel vs conical light beams (optics & physics being a long way in the past for me!).  Luckily I have a T2-1.25" adapter, so I can thread that in & put a TV40 in - will test that on the next semi-clear night (it seems to work in daytime).

Thanks for that link too @GavStar - a very interesting thread w other threads nested within it (finally getting round to understanding afocal speed maths).  chemisted in that set of threads seems to have had some success...I'll tinker a bit more w my old prime lenses & report back!

Cheers both

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48 minutes ago, stnagy said:

Is it the computar f2.8 lens? If so, it's gathering about 1/4 the light intensity of a specialist 3x afocal lens (at f1.5), which might be why you're getting those results. 

It’s the 75mm f1.8 fujinon c mount, so a bit slower than the f1.5 but not much. The difference was pretty embarrassing for the fujinon though…

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11 minutes ago, GavStar said:

It’s the 75mm f1.8 fujinon c mount, so a bit slower than the f1.5 but not much. The difference was pretty embarrassing for the fujinon though…

Interesting. I haven't tried the specialist 3x afocal lens. It sounds like it is worth a try. Do you mind me asking where did you get yours? How do you use it with a filter? 

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3 hours ago, stnagy said:

Interesting. I haven't tried the specialist 3x afocal lens. It sounds like it is worth a try. Do you mind me asking where did you get yours? How do you use it with a filter? 

Since I’m based in the UK I got from actinblack in Luxembourg. However if you are in the USA they are more freely available and there are multiple versions some of which are better then others.

I used this adapter to put the 1.25 filter between the pvs14 and 3x afocal lens. There is material vignetting due to the adapter etc but the centre 70 percent or so is excellent…

https://rafcamera.com/adapter-envis-3x-to-pvs-14?amp=1

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I just pop a 2” filter out the front and lose a tiny bit of aperture/speed. I don’t use such narrow filters so it’s not such a costly option. The 2x can be hard to find and supposedly there are a few variants, one of which is better… 

Peter

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@stnagy that trick worked.  The teleconverter didn't but putting an EP in did.  The image was however upside down which makes it a bit discombobulating.  Luckily the CZJ 135mm prime has a T2 style thread, so I could also attach it to a prism diagonal with short light path so that the image became right way up.  Have to test it out w stars to see what the FOV and viewing is like (this was just in a dark room).  If there's a way or re-inverting the image w/o a diagonal then this could be a handy straight through (a bit like an old nautical pocket telescope).

Cheers

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On 18/10/2021 at 12:32, vineyard said:

Hello,

In the spirit of constant tinkering, I'm trying to see if I can use an old prime lens on the front of my PVS-14.  I've mounted the lens on the front of an old one of these ZWO adapters and have an adapter from RAFCamera that converts the PVS-14 objective into a T2 female.  The RAF adapter has about 6mm optical train, and roughly measuring the distance to the front of the NV lens suggests about 6-8mm there - so a total of about 12-14mm: ie, within the 12.5mm-17.5mm optical length that these ZWO adapters assume on the back end.

But I couldn't find focus (trying a bunch of different spacers) - couldn't even see out of focus stars.  I'm probably doing something very silly, but not sure what?

(The logic I'm trying to use is the one described in this diagram from TV but taking the EP out: ie, get the DSLR lens to form the image focal plane on the NV objective.  I'm sure folks will have tried this?)

Thank you!

Vin

A NV eyepiece made for astronomy will work with SLR/Camera lens.

But your PVS-14 is made for terrestrial use, so you can't use it in prime and you can't add SLR/camera lens for handheld use.

Have a look to these reviews about NV binoviewer with SLR/Camera lens :

https://www.cloudynights.com/topic/789690-first-night-in-city-with-ovni-b-using-a-filter-wheel-in-all-modes/#entry11368888

https://www.cloudynights.com/topic/791613-ovni-b-with-more-camera-lenses-in-the-city/#entry11396988

Edited by joko
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On 18/10/2021 at 15:21, GavStar said:

3) Finally, (and probably least important), I’ve been able to try a camera lens and 75mm c mount lens in prime mode with my ovni-m. Both approaches disappointed me particularly on emission nebulae where with an ha filter both lens really struggle to show the nebulosity compared with my specialist 3x afocal nv lens. So I’ve stopped messing around with the camera lens as I’m happy with my afocal 3x lens setup. It perplexes me quite a bit about the positive comments made on cn re using camera lens/c mount lens with ha filters and nv as I just couldn’t get them to work at all well…

Fujinon is f1.8 while most OVNI-M users have Cosmicar 75mm f/1.4 and emission nebulae are amazing with h-alpha filter.

I never heard any negative feedback with the Cosmicar lens. All feedbacks are positive like those you read on CN.

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1 hour ago, joko said:

Fujinon is f1.8 while most OVNI-M users have Cosmicar 75mm f/1.4 and emission nebulae are amazing with h-alpha filter.

I never heard any negative feedback with the Cosmicar lens. All feedbacks are positive like those you read on CN.

Only about half an f stop difference between the Fujinon and the Cosmicar so wouldn’t be much of an impact. The 3x afocal lens is f1.5 and the difference I observed visually on emission nebulae with ha filter between the fujinon and afocal lens was more like 3-4 f stops rather than half, something else is making a bigger difference…

 

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10 hours ago, GavStar said:

Only about half an f stop difference between the Fujinon and the Cosmicar so wouldn’t be much of an impact. The 3x afocal lens is f1.5 and the difference I observed visually on emission nebulae with ha filter between the fujinon and afocal lens was more like 3-4 f stops rather than half, something else is making a bigger difference…

What do you mean by "something else is making a bigger difference…" Because there is something else you do not explain, the PVS-14 is just the housing, you have an OVNI Night Vision Astronomy grade tube designed for astronomy in your PVS-14.

And knowing you have an OVNI Night Vision Astronomy grade intensifier tube in your best PVS-14 housing, tube that i supplied to you, it means you have the same tube performance in your OVNI-M. And there are absolutely no other parts between the tubes and the SLR/Camera lens. So the only difference is this SLR/camera lens. Nothing else can explain the difference you get.

As you explain, there are a lot of positive comments on CN, (i never read any negative) so there are obviously something that makes the difference. For sure, it is the lens.

I already tried a lens at f/2 and the view was really bad, close from your Fujinon f/1.8. And it was incomparably better with the Cosmicar f/1.4 (close to your f/1.5 lens). Like most OVNI users have.

So the difference is due to the lens and nothing else.

 

Edited by joko
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2 hours ago, joko said:

What do you mean by "something else is making a bigger difference…" Because there is something else you do not explain, the PVS-14 is just the housing, you have an OVNI Night Vision Astronomy grade tube designed for astronomy in your PVS-14.

And knowing you have an OVNI Night Vision Astronomy grade intensifier tube in your best PVS-14 housing, tube that i supplied to you, it means you have the same tube performance in your OVNI-M. And there are absolutely no other parts between the tubes and the SLR/Camera lens. So the only difference is this SLR/camera lens. Nothing else can explain the difference you get.

As you explain, there are a lot of positive comments on CN, (i never read any negative) so there are obviously something that makes the difference. For sure, it is the lens.

I already tried a lens at f/2 and the view was really bad, close from your Fujinon f/1.8. And it was incomparably better with the Cosmicar f/1.4 (close to your f/1.5 lens). Like most OVNI users have.

So the difference is due to the lens and nothing else.

 

What I mean is that the difference in f ratio between the lens of f1.5 and f1.8 is not the key reason for the major differences I am seeing when observing nebulae. C mount lens like the fujinon and cosmicar are not designed for use with an nv monocular - it’s just that they have a c mount thread and so can be attached straightforwardly. The afocal 3x lens is specifically designed for use with a pvs14 - I think this a key reason why I am getting better results with it (using either my actinblack pvs14 or my Carson/ovni pvs14) than than ovni with fujinon lens.

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